# Run central air on battery



## puttster

I would like to put the four ton A/C compressor on a timer or a meter of some kind and have it switch over to a battery for an hour or two per day. Just the A/C, so of there is a power issue it won't bring the whole house down. 

I am thinking about using a Tesla Powerwall but maybe regular batteries will do. The stats on the Tesla are 
•Inverter: Fully integrated
•Energy: 14 kWh
•Power: 5 kW continuous, 7 kW peak
•Round Trip Efficiency: 90%
•Price $5,500 
Initially I will fill the battery at night when the rate is low but eventually I'd like to fill it with solar. 

So my question is about the feasibility of a project like this and thoughts on the electrical hook up.


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## clarenceboddick

The electrical hookup isn't that big of a deal. You might have issues with local codes though. I can't see getting enough wattage easily, unless you use a lot of batteries. How many years of marginal utility rate savings will it take to offset the cost of the battery/inverter system? Batteries never seem to work as well in real life compared to on paper.

If this is a serious plan, I wonder if it would be a better idea to rewire the AC blower and compressor fans and compressor to DC? Not sure what voltage the sweet spot would be, if anything. Convert line AC to DC for the AC. Maybe use the heat from that to heat your water? Might help with the solar system.


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## Bret86844

Out of curiosity why are you doing this?


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## user_12345a

it's not practical at all to run such a large load off a battery. your 4 ton a/c if it's 13 seer will be burning up 4kwh/hr of run time or even more if it's less, so you're looking at displacing maybe 3 hours of run time?

and if the battery is totally discharged every hot day it won't last.

not sure if tesla power wall even puts out 240v, if not you're looking at a very expensive inverter.

it's a waste of money. 

if you want to do solar, charging a battery, only relying on the grid for backup you have to get your electrical use down to 5kwh per day or less, otherwise the cost of prohibitive. central air is out of the question.

off the gridders use hardly any electricity; most don't have a/c, a wood or propane or gas stove does the heating and gas is used for hot water and cooking as well.

off the grid houses are fossil fuel dependent for 90%+ of their energy, it's a myth that you can have the north american life-style without fossil fuels. (unless you live on a wood lot and harvest wood for heating, cooking, hot water yourself without any gasoline)

A much more practical approach now is to pre-cool when the rate is low and allowing it to warm up a bit during the day. you can run the fan during the day to keep the air circulating. A decent programming t-stat with programmable fan is all you need.

If you want you can add solar and do net metering, so the power produced by the panels when it's sunny offsets the a/c use. You would need 4 to 5kw of panels, at a very high cost. 



solar is stupid when you have the electricity grid, unless it's for emergency backup power to run some leds and small appliances. there's a reason it's not widely used.


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## Flannel Guy DIY

how much can you really save though? What is the payback time on this?


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## puttster

Here in Texas you can contract to track the wholesale price of power, which can run from 2¢/kwh at night to as high as the PUC price cap of $9.00/kwh on a hot July afternoon. To make some serious money back you just need to be able to get off the grid for a few hours a day, not all the way. Basically you can get maybe 75% of the savings with only 25% of the investment. 

I think the 100+ kwh batteries that come in an electric car will be able to fill the same or better role in a few years, so I'd like to get an early start on that concept while you can still get a 30%(?) tax credit for a 2017 setup.

Finally, I think solar and net metering and maybe a grid crisis will be in my future. This is a way of getting a favorable start on those things. 

I hope that answers everyone's questions. Now, about mine....


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## user_12345a

your area may have some program with integrated thermostat where they automatically raise the temperature when the rate is high.

do some research and see what's available in your area.

if you're worried about the grid going down, get a generator first, then a battery backup system and wire it to only run essentials.


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## Flannel Guy DIY

someday the cost of solar panels will drop. Then, the only issue will be inventing better batteries


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## user_12345a

they already have dropped. they've been working on batteries forever.

the trick is getting the energy use down to next to nothing, then solar becomes very viable. but the masses are never going to be running electric central heat or air off self contained systems.


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## puttster

Why is it when someone wants to drop an extra 50 grand on a BMW or wants to move into a 4,000 foot house people say "go for it, it's your money," but when someone wants to shell out five grand on a solar or other green deal people post that he's stupid, just pissing his money away?

Okay, any thoughts on the electrical hook up?


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## user_12345a

> but when someone wants to shell out five grand on a solar or other green deal people post that he's stupid[.quote]
> 
> Because a lot of these things are bad investments. if it's for the novelty or fun, like a crap mcmansion or gas guzzling car, or vacation yah go for it. I actually think those things are a colossal waste of money myself.
> 
> If you're trying to save natural resources or money, go with what gives the best return on investment.
> 
> LEDs have a fantastic return on investment and should be used.
> 
> If you're heating water with electricity, solar thermal is a good option to look at, would provide much more renewable energy at a lower cost than pv. (or just get a bigger electric tank and shift the use to off-peak with a timer)
> 
> 
> pv is very expensive and the money is better spent on other conservation/renewable energy projects.
> 
> If you could shift your a/c use off the peak periods with a $100 thermostat and pre-cool before hand, why spend thousands of dollars?
> (and get further savings doing low tech things like adding exterior window shading?)
> 
> Use the right equipment for the right application. PV is really good if it saves you from spending $10000+ to get electricity to your property in a rural application.
> 
> It's also good if you want a backup power system to run refrigeration and lighting, but not a central a/c. You only need like 5kwh per day or less to run the basics.
> 
> PV is not necessarily better for the environment or saves resources because of the toxic materials in the panels and batteries, but has it's place. The power output is so low that the real environmental savings only come from being forced to dramatically cut your energy use in the first place.


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## Oso954

> Here in Texas you can contract to track the wholesale price of power, which can run from 2¢/kwh at night to as high as the PUC price cap of $9.00/kwh on a hot July afternoon.


Those are spot prices, not long term contract prices.

The wholesale cost of power on the spot market is not directly connected to what you pay, even when on a time of use rate structure.

POCOs can pay big $$ to buy the last few mWh to meet peak demand. Averaged out over total generation and other purchases, it only has a slight impact on their average cost of power.The purchases are made to avoid brown outs, blackouts, and/or other power curtailments.

If you are basing your savings calcs on 2¢-$9 you are using the wrong numbers.


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## puttster

Oso954 said:


> The wholesale cost of power on the spot market is not directly connected to what you pay, even when on a time of use rate structure.



Maybe not in California. Texas is deregulated. My retailer sells me power at wholesale spot + 1.7¢/kwh + about 4¢ for the local distribution company. Spot prices are recalculated every 15 minutes by the Independent System Operator. 

My bill this winter has run 8.0¢ - 8.5¢ I expect it to be higher this summer and much, much higher in the afternoons. Like I said, one kw could get as high as $9.00/hr. That's what I'm trying to save with this plan.

Most people here though do go for long term contracts, which run around 12¢ or more, day or night, all year long. Probably more like in California. Buying power at night and storing for day use doesn't work for them.


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## user_12345a

> My bill this winter has run 8.0¢ - 8.5¢ I expect it to be higher this summer and much, much higher in the afternoons. Like I said, one kw could get as high as $9.00/hr. That's what I'm trying to save with this plan.


program your t-stat so that it doesn't run in the afternoon.

pre-cool when the rate is lower so it doesn't get too hot.

low tech solutions are best.


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## jeff00

puttster said:


> Maybe not in California. Texas is deregulated. My retailer sells me power at wholesale spot + 1.7¢/kwh + about 4¢ for the local distribution company. Spot prices are recalculated every 15 minutes by the Independent System Operator.
> 
> My bill this winter has run 8.0¢ - 8.5¢ I expect it to be higher this summer and much, much higher in the afternoons. Like I said, one kw could get as high as $9.00/hr. That's what I'm trying to save with this plan.
> 
> Most people here though do go for long term contracts, which run around 12¢ or more, day or night, all year long. Probably more like in California. Buying power at night and storing for day use doesn't work for them.



I understand what you're trying to accomplish here, but what you want to do is probably cost prohibitive. Even with the Musk Power wall, you would probably need two of them ( at $5000 each) to generate enough energy to power a 240v 12-15 amp central a/c. The batteries, cable and charge controllers would probably run you around $15000, not including labor


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## Red Squirrel

I've been toying with going solar for a while and the idea of running central A/C on solar is something I looked at myself, when you need it most, there just happens to be lot of sun out. There's various options such as only putting some stuff on solar, or whole house etc. They all have their pros and cons from complexity (splitting up circuits etc) to cost. For motor loads such as AC or even washing machine you need a very powerful inverter that can handle the startup load, and that will get very expensive. I'm sure it's doable though. 

Something like this could probably work:

http://outbackpower.com/outback-pro...ers/item/radian-series-gs8048?category_id=529

One MIGHT be enough but I'd probably put at least 2 in parallel. 

The inverter is probably going to be your biggest cost, you can choose batteries based on how long you want to be able to go for. Start with cheap Canadian Tire or equivalent batteries, and later on get better ones. Of course TOO big of a battery bank and your solar panels may not be able to charge it fully fast enough within the day. So need to size appropriately. Oversizing is never a bad thing if you can avoid discharging it fully though. Ex: if you only use 10% each day and it fully charges then those batteries are going to last very long. 

If your solar array can actually provide enough power to run the A/C + some left over power then you can probably get away with a smaller battery bank, as you can run off solar during the day when it's hottest and sun will be at it's peak. Then run a bit longer off the batteries then by then it will be "off peak" and you can switch back to commercial hydro. Could possibly automate that.


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## jeff00

any of this is doable. It boils down how much do you want to spend and what is his ROI. 

But i would submit, that *we* on the forum do not have the expertise to give sound financial advice on this matter. 

I will stick with my first assessment, Even living in sunny Texas, this would be cost prohibitive. His solar array would have to be fairly large and his Battery bank would therefore be fairly expensive. 

I would also strongly suggest he call these guys

https://www.wholesalesolar.com/

They can give you an accurate quote on the cost involved

p.s.: I have no affiliation with these guys and only suggest calling experts in this field


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## djlandkpl

Conceptually speaking. If you consider the Powerwall as a generator, use a transfer switch to change power sources. You need to isolate the battery from the grid to prevent backfeeding if there was a grid outage.


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## Flannel Guy DIY

I think there is a device that has not been invented yet. Something that produces more energy than the energy needed to power that device. An electronic version of a gear system. A small gear that uses little power but attached to a larger gear that is doing more work than the smaller gear.


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## jeff00

djlandkpl said:


> Conceptually speaking. If you consider the *Powerwall as a generator*, use a transfer switch to change power sources. You need to isolate the battery from the grid to prevent backfeeding if there was a grid outage.



thats is what a Power wall is (or battery bank), This "generator" has to be big enough to run whatever appliances you want without help from the grid.

The issue is replenishing the batteries.

In the Northeast you need enough battery to last 3 days without recharging. Or you need to be tied to the grid or you need a (fossil fuel) generator to charge the batteries if you don't have any sun for three days or more. Which up here is quite common. 

you have other considerations too. Your Inverter to the house must be "pure sine wave" type. Because almost everything nowadays has a computer. Computer do not like 'dirty electricity' they also don't like spikes. Pure Sine Wave Inverters are NOT cheap.

In Texas, it's probably not that big a deal as they get WAY more sun that we do in the Northeast.

If I lived in Texas, I would go completely off grid with a Wind/Solar Hybrid system. Generally speaking, if you don't have sun, you DO have wind.....generally speaking.:vs_cool:

Now some people maybe able to get away with a Forktruck battery. But their are issues. The first and most obvious, weight! These things weigh a ton ( or more) 

second, they are expensive but they have a ton capacity

Third, you're going to need a LOT of solar panels to charge the battery over the course of a day.

*The OP ( original poster) should call a solar professional, tell them what he wants to do and they can put a package together for him*

The rest of us are just guessing


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## puttster

Solar fill would be down the road. Here is a typical price curve to Houston, On that day in the hour of 4-5 PM I'd make $.70 x about 5 kwh. Then refill at night for $.02. 
Of course sometimes the high prices last longer and get up into the dollars range. If it hit $9.00 for two hours I'd make $90. More, if I could sell some extra back into the grid. Making a quick profit is not my primary goal, though. This is the Green Forum, after all, right? 

It'd be nice if my transfer switch could get real-time informed about prices!


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## jeff00

Im a little confused? what do you mean by "refill at night"


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## djlandkpl

Do you know how your utility's policy for net metering? I have grid-tie system and all that matters is the meter reading at the end of the month. If it's less than the start, they credit my account in dollars. If it's more I pay/deduct the credit. My rates are fixed regardless of time of day. Depending upon your utility's policy, you could use the grid as your battery.


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## puttster

The credit you get would be like 10¢/kwh, the average price for the month. I want the credit to be at the peak pricing, which is when I delivered the kw.


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## Bret86844

Deep thoughts - How many stages of cooling do you have? If by chance it's two stage, you could lock out the second stage for the price of a timer and some wiring. It would reduce your peak use and still provide some cooling.


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## puttster

jeff00 said:


> Im a little confused? what do you mean by "refill at night"


Refill the batteries from the grid for $.02.


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## jeff00

puttster said:


> Refill the batteries from the grid for $.02.


I think you're wasting your time and money. You need to go look up 2 volt solar batteries

The batteries alone are going to run you about $8000-$9000. A Trojan 2 volt deep cycle battery will run you about $350 EACH. and you're going to need a lot of them ( like 24 batteries) to have enough power to run a 4 ton a/c..

AND you're are going to want Flooded Lead acid batteries. NO ONE has come up with a better battery for off grid applications, not even the Musk Powerwall, which is about $5000 and you'll need two of those

You're going to want a 2v deep cycle for their storage and DOD (depth of discharge) 

you need to research 'solar batteries'

I understand you desire to "beat the system" but I think this maybe a waste of money.


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## jeff00

so after doing a bunch of looking around, I found THIS from wholesale solar:

https://www.wholesalesolar.com/1440...&product_id=&gclid=CP_tjLOI6tICFdmKswodmm8HHg

AND it puts out 240v......there ya go, Good luck :vs_cool:


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## beenthere

puttster said:


> I would like to put the four ton A/C compressor on a timer or a meter of some kind and have it switch over to a battery for an hour or two per day. Just the A/C, so of there is a power issue it won't bring the whole house down.
> 
> I am thinking about using a Tesla Powerwall but maybe regular batteries will do. The stats on the Tesla are
> •Inverter: Fully integrated
> •Energy: 14 kWh
> •Power: 5 kW continuous, 7 kW peak
> •Round Trip Efficiency: 90%
> •Price $5,500
> Initially I will fill the battery at night when the rate is low but eventually I'd like to fill it with solar.
> 
> So my question is about the feasibility of a project like this and thoughts on the electrical hook up.


I'm not sure a 7KW peak draw is enough to start the A/C condenser on a hot day. 

Condenser would need a hard start kit to get the compressor up to speed as quick as possible to get the KW draw down fast.

Does your A/C have a TXV or piston metering device. Easier to start against a piston than a TXV.


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## puttster

Thanks, Been, good info. I have a Lennox XC16 model 048 two stage scroll compressor that uses a TXV and the manual says a hard start kit is required where voltage is less than 230V. With all the neat stuff I read about those kits it seems like I should put one in there anyway to save compressor life. Might cut down on startup racket, too, the unit is just outside the bedroom window.


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## beenthere

It won't hurt it to have one.


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## puttster

djlandkpl said:


> Do you know how your utility's policy for net metering? I have grid-tie system and all that matters is the meter reading at the end of the month. If it's less than the start, they credit my account in dollars. If it's more I pay/deduct the credit. My rates are fixed regardless of time of day. Depending upon your utility's policy, you could use the grid as your battery.


In Texas everyone is required to use time-of-use "smart meters." These send your power use in 15-minute intervals to the power company's server, where it can be accessed by you or your retail electric company.

My company charges TOU. So if you use less when the wholesale rate is $0.70/kwh, you save the full $0.70/kwh, which could seriously lower your system payback. Most people don't use that TOU feature, they just pay at one fixed rate for their total monthly use, like you do. They can turn the A/C on full blast at 4PM and it only costs them ten cents, why not?


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## jeff00

puttster said:


> In Texas everyone is required to use time-of-use "smart meters." These send your power use in 15-minute intervals to the power company's server, where it can be accessed by you or your retail electric company.
> 
> My company charges TOU. So if you use less when the wholesale rate is $0.70/kwh, you save the full $0.70/kwh, which could seriously lower your system payback. Most people don't use that TOU feature, they just pay at one fixed rate for their total monthly use, like you do. They can turn the A/C on full blast at 4PM and it only costs them ten cents, why not?


you pay 70¢/Kwh, ??? or do you mean .07/Kwh....'cause 70¢/Kw is like the highest rate on the planet :surprise::biggrin2:


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## puttster

jeff00 said:


> I think you're wasting your time and money. .


Of course saving money today and in the long run are important. Thus my idea to buy power at night to use it in the afternoon when it costs way, way high. Some of my other goals would be to do something to lower emissions, cool the planet, reduce the need for new generators and those massive electric transmission lines, provide power to me and my neighbors in the event of a blackout, prepare for a solar future. 

If this was the screw everyone or the squeeze pennies forum, I would concede your point. But since this the Green forum I don't see your comment being particularly devastating, just somewhat misplaced. Thanks for contributing, though!


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## beenthere

The system you posted about in your opening post. Will give you just a tad over 3 hours if the A/C runs in second stage the whole time. Allowing for the high draw/drain of starting the A/C also. And should give a bit over 4 hours if it only runs in first stage the time. Time referring to the time its using the storage system. Not constant run time.

In my area, many many years ago. Off peak storage systems for heating were very common. The electric companies only charged about 20% of the peak rate when the systems recharged at night time, when electric demand was down. People were able to heat their homes fairly cheaply using these electric off peak storage systems. Until the electric companies did a way with the off peak rates. 

Now that more and more areas are going to TOU rates. Something like this may very well catch on, and become popular/common, in the not too distant future. Someone always has to be the first to try something new, or out of the box.


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## jeff00

puttster said:


> Of course saving money today and in the long run are important. Thus my idea to buy power at night to use it in the afternoon when it costs way, way high. Some of my other goals would be to do something to lower emissions, cool the planet, reduce the need for new generators and those massive electric transmission lines, provide power to me and my neighbors in the event of a blackout, prepare for a solar future.
> 
> If this was the screw everyone or the squeeze pennies forum, I would concede your point. But since this the Green forum I don't see your comment being particularly devastating, just somewhat misplaced. Thanks for contributing, though!


so how much do you expect to save compared to last years bills. also could you post the equipment and batteries you're going to install. I really would like to see how this is going to work


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## jeff00

beenthere said:


> The system you posted about in your opening post. Will give you just a tad over 3 hours if the A/C runs in second stage the whole time. Allowing for the high draw/drain of starting the A/C also. And should give a bit over 4 hours if it only runs in first stage the time. Time referring to the time its using the storage system. Not constant run time.
> 
> In my area, many many years ago. Off peak storage systems for heating were very common. The electric companies only charged about 20% of the peak rate when the systems recharged at night time, when electric demand was down. People were able to heat their homes fairly cheaply using these electric off peak storage systems. Until the electric companies did a way with the off peak rates.
> 
> Now that more and more areas are going to TOU rates. Something like this may very well catch on, and become popular/common, in the not too distant future. Someone always has to be the first to try something new, or out of the box.


so, if he comes home at 1pm and it's 100° outside and he wants it to be 78° inside. How long will the a/c run before it gets to 78°.....Im curious as to how long the batteries will hold out before the go dead.

I guess he could turn it on at night and never turn it off, that would help with mid-day start up's


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## beenthere

jeff00 said:


> so, if he comes home at 1pm and it's 100° outside and he wants it to be 78° inside. How long will the a/c run before it gets to 78°.....Im curious as to how long the batteries will hold out before the go dead.
> 
> Batteries(at least when new) a bit more then 3 hours running in second stage. How long to cool indoor temp to X degrees, of course depends on how warm the home was allowed to get before the A/C was turned on, or set to the lower temp.
> 
> I guess he could turn it on at night and never turn it off, that would help with mid-day start up's


Remember, while the system might only save him a low average or 3, to a high average of 5 dollars a day. In his area, that could be 270 days that it saves him that money, making it a $980.00 to $1350.00 a year savings. 

Even if its a wash, and it doesn't save him anything. It is a green system, since it reduces load on the grid during peak hours. 

Many of the first electric cars cost more to operate then a gas engine car did. And many/most still do. But they have been and still are slowly improving. puttster's idea is really no different then electric cars.

As to really finding out how a system like puttster's proposed system. Only when he, or someone else tries it. Will anyone know for sure. So hopefully, if he does this, he will let us know how this works out.


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## jeff00

beenthere said:


> As to really finding out how a system like puttster's proposed system. Only when he, or someone else tries it. Will anyone know for sure. So hopefully, if he does this, he will let us know how this works out.


I really would like to know the results.


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## beenthere

jeff00 said:


> I really would like to know the results.


I look forward to hearing from him as he progresses with this.


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## Bob Sanders

beenthere said:


> Remember, while the system might only save him a low average or 3, to a high average of 5 dollars a day. In his area, that could be 270 days that it saves him that money, making it a $980.00 to $1350.00 a year savings.


Well, you do have to factor in the price of the batteries, inverter... etc, as well as battery replacement.

It would be interesting to see if it flies though.


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## puttster

I mentioned that adding solar panels to charge the batteries would be something to be considered later. Then I read that they need to be part of the package to get the 30% federal credit. Anyone here able to verify that?


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## dmxtothemax

according to google a 4 ton ac compressor is 14KW.
so the reccommeded draw on power wall is 5kw 7kw peak
So you will need at least two of these.

So it is technically possible
but not easy or cheap

i wouldn't want to think about the cost of a 14KW invertor ?

i think the $$$ just don't stack up.

:glasses:


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## beenthere

dmxtothemax said:


> according to google a 4 ton ac compressor is 14KW.
> so the reccommeded draw on power wall is 5kw 7kw peak
> So you will need at least two of these.


Reread that article. No 4 ton A/C uses 14KWs an hour. 14KWs of electric consumption for 4 tons would be an EER of 3.42, instead of the 10 to 11 it should be for a 13 SEER A/C.

However, 4 tons of A/C is 14KWs of cooling(48000 divided 3.413=14.063KWS). But not a consumption of 14KWs.


Save​


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## jlhaslip

jeff00 said:


> so after doing a bunch of looking around, I found THIS from wholesale solar:
> 
> https://www.wholesalesolar.com/1440...&product_id=&gclid=CP_tjLOI6tICFdmKswodmm8HHg
> 
> AND it puts out 240v......there ya go, Good luck :vs_cool:


From that web page:



> Not appropriate for: Air-conditioning, heating or agricultural irrigation pumps.


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## jeff00

jlhaslip said:


> From that web page:


Love the quote about woodworking: :biggrin2:

and just because it says it's not appropriate for a/c....doesn't mean someone won't try it. :wink2:

I have been trying to find an article I read about families going off grid and they run their entire households off solar and batteries. There is a family in central NY that has done it and a Guy in Oregon.

Going completely off grid requires some "lifestyle changes"....

for example: its not advisable to have appliances with built in clocks or any other appliance that has a parasitic charge that is constantly "on" Modems and routers have to be turned off when not in use

you can't leave lites on all the time. Washing cloths and dishes is done during the daylight hours and you're going to have to buy either a gas fired refrigerator (Servel) or one that is specific to solar (and they are expensive) 

It would also help to live where you have cloudless skies 6+ hours a day

One more thing to keep in mind, the hotter a solar panel gets, the LESS EFFICIENT it becomes.

IMHO the best setup would be a wind/solar-battery system. Generally (around here) is you don't have sun, you do have wind. Even at night a wind generator could easily pick up the slack


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## djlandkpl

puttster said:


> I mentioned that adding solar panels to charge the batteries would be something to be considered later. Then I read that they need to be part of the package to get the 30% federal credit. Anyone here able to verify that?


The last sentence in my post is from the IRS and I don't understand it but the battery may be excluded. 

https://www.irs.gov/instructions/i5695/ch01.html#d0e53

It's under this heading: Residential Energy Efficient Property Credit (Part I)

You may be able to take a credit of 30% of your costs of qualified solar electric property, solar water heating property, small wind energy property, geothermal heat pump property, and fuel cell property. Include any labor costs properly allocable to the onsite preparation, assembly, or original installation of the residential energy efficient property and for piping or wiring to interconnect such property to the home. The credit amount for costs paid for qualified fuel cell property is limited to $500 for each one-half kilowatt of capacity of the property.









Costs allocable to a swimming pool, hot tub, or any other energy storage medium which has a function other than the function of such storage don't qualify for the residential energy efficiency credit.


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## puttster

Rats. Looks like I may have to install some token PV.


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## user_12345a

*Food for though, if convincing you that this is a crazy idea isn't a lost cause:*

Corporations that own buildings with several hundred ton chillers don't try to use batteries in their buildings to store electricity for day-time cooling in spite of paying wholesale prices. they don't use solar either.

it's uneconomic

And this is in spite of having flat roofs and a core mandate to deliver profit to their shareholders.

What is done is ice storage, they freeze water at night and melt the ice to provide cooling. a pound of ice needs 144 btu per pound to melt it.

read more here -> https://en.wikipedia.org/wiki/Ice_storage_air_conditioning

Now, you're not going to get a chiller and freeze water to use during the day.

But a far better idea than storing electricity would have a medium to sink heat into during the day so the a/c doesn't have to run.

Your house, with it's thermal mass is the medium and you could easily pre-cool the house 5F+ below your normal setting for a few hours before peak electricity costs are a factor. re-set to normal setpoint and the a/c won't come on during the hours with the highest costs.

When near zero energy houses are built, they usually use materials with a very high thermal mass so the house takes forever to warm up in hot weather. The cooling load becomes more consistent, the a/c if needed gets downsized and runs more consistently.

The thousands you want to spend on battery storage would be better spent increasing the thermal mass of the house; for example, there are flooring materials that have high heat specific capacity. (meaning they have to absorb a lot of BTUs to warm up)

Tiles, stone, etc. 

Read up on passive solar design. I know about it just from having had to take courses in school.

Green building is 99% design of the envelope, 1% high technology.

People have been building super energy efficient homes which need minimal active heating and cooling for several decades long before pv technology got better or we had condensing furnaces or heatpumps.

It's a myth that technology makes things "greener", in fact a lot of the time it drives higher consumption.

incandecent light bulbs are far more energy efficient than candles. 

Candles run at under 1 lumen per watt, incandecents 5 to 20.

When the incandescent lamp became common, energy consumption for lighting didn't drop, it sky-rocketed.

The governments with their silly green tax credits and subsidies to install solar and distorting the market, causing people to do things that make zero sense.



The government money isn't free so if they give out lots of tax credits, they either have to raise taxes, mostly on the poor. or they have to borrow money and the next generation has to pay for our crappy do nothing solar panels and tesla batteries. 

where i am they heavily subsidized solar and wind (wind mills and solar panels are just toys for rich people payed for by the poor!) and the price of electricity skyrocketed as a result.


----------



## beenthere

user_12345a said:


> *Food for though, if convincing you that this is a crazy idea isn't a lost cause:*
> 
> Corporations that own buildings with several hundred ton chillers don't try to use batteries in their buildings to store electricity for day-time cooling in spite of paying wholesale prices. they don't use solar either.
> 
> it's uneconomic
> 
> A lot of commercial down here use solar to power their lighting loads.
> 
> And this is in spite of having flat roofs and a core mandate to deliver profit to their shareholders.
> 
> The amount of battery storage they would need makes it uneconomical. First, they would need to provide the space to have the battery bank, then that area would also need to be cooled, or have a fresh air system.
> 
> What is done is ice storage, they freeze water at night and melt the ice to provide cooling. a pound of ice needs 144 btu per pound to melt it.
> 
> read more here -> https://en.wikipedia.org/wiki/Ice_storage_air_conditioning
> 
> Down here, most commercial buildings are on demand meters. Highest 15 minute demand is the rate they are billed for. So ice storage only makes real sense on systems using more then 100 tons of cooling.
> 
> Its also not a green technology, since it takes more energy to freeze the water, then it does to cool the air. The only reason it saves a company money, is because of the large discount they receive on the electric used at night time.
> 
> Now, you're not going to get a chiller and freeze water to use during the day.
> 
> But a far better idea than storing electricity would have a medium to sink heat into during the day so the a/c doesn't have to run.
> 
> Your house, with it's thermal mass is the medium and you could easily pre-cool the house 5F+ below your normal setting for a few hours before peak electricity costs are a factor. re-set to normal setpoint and the a/c won't come on during the hours with the highest costs.
> 
> Over cooling the house by 5 degrees in the morning until peak rate starts is also not green. Plus, on days when the outdoor temp is at design, the A/C most likely won't be able to over cool the house.
> 
> When near zero energy houses are built, they usually use materials with a very high thermal mass so the house takes forever to warm up in hot weather. The cooling load becomes more consistent, the a/c if needed gets downsized and runs more consistently.
> 
> The thousands you want to spend on battery storage would be better spent increasing the thermal mass of the house; for example, there are flooring materials that have high heat specific capacity. (meaning they have to absorb a lot of BTUs to warm up)
> 
> Which also means they can present problems during the heating season, when you want the home to be warm, and not use a large amount of energy to heat those materials.
> 
> Tiles, stone, etc.
> 
> Read up on passive solar design. I know about it just from having had to take courses in school.
> 
> Green building is 99% design of the envelope, 1% high technology.
> 
> People have been building super energy efficient homes which need minimal active heating and cooling for several decades long before pv technology got better or we had condensing furnaces or heatpumps.
> 
> I doubt the OP wants to rebuild his house to obtain super energy efficiency, which would have no pay back in his lifetime.
> 
> It's a myth that technology makes things "greener", in fact a lot of the time it drives higher consumption.
> 
> incandecent light bulbs are far more energy efficient than candles.
> 
> Candles run at under 1 lumen per watt, incandecents 5 to 20.
> 
> When the incandescent lamp became common, energy consumption for lighting didn't drop, it sky-rocketed.
> 
> Because electricity was extremely cheap when incandescent bulbs where first invented.
> 
> The governments with their silly green tax credits and subsidies to install solar and distorting the market, causing people to do things that make zero sense.
> 
> Finding new ways, or improve on old ways to lessen peak demand on the grid makes ton of sense.
> 
> The government money isn't free so if they give out lots of tax credits, they either have to raise taxes, mostly on the poor. or they have to borrow money and the next generation has to pay for our crappy do nothing solar panels and tesla batteries.
> 
> Those panels, and batteries will improve in efficiency over time. Whether that is 30 years, or 50 years from now. It will happen.
> 
> where i am they heavily subsidized solar and wind (wind mills and solar panels are just toys for rich people payed for by the poor!) and the price of electricity skyrocketed as a result.


Keep in mind, that hydro is not actually a green method of producing electric. When they build a damn, they also flood whatever is upstream. Changing what nature has done/created.


----------



## beenthere

puttster said:


> Rats. Looks like I may have to install some token PV.


Find out the min you need to install, to get the best bang on return/tax credit.


----------



## user_12345a

green energy is a myth. Hydro isn't good for the environment, neither are solar panels because of the materials and energy needed to make them.

Hydro is good though because while construction is very environmentally destructive, a dam will provide 100 years of electricity without having to mine anything or produce emissions. 

It's the only source of base load power we have that doesn't require a fuel input once it comes on line.


meaning if the concern is either being dependent on dwindling resources or putting pollution into the atmosphere, hydro is better than all the other alternatives.


----------
I wasn't suggesting that it makes sense to rebuild a house, just that some principles be applied.

Using the existing thermal mass just with a programmable thermostat and even looking at exterior window shades would yield similar savings to a battery at a lower expense with less complexity.


----------



## beenthere

user_12345a said:


> green energy is a myth. Hydro isn't good for the environment, neither are solar panels because of the materials and energy needed to make them.
> 
> Hydro is good though because while construction is very environmentally destructive, a dam will provide 100 years of electricity without having to mine anything or produce emissions.
> 
> The repair and maintenance of the generators does require emissions to make the parts needed.
> 
> It's the only source of base load power we have that doesn't require a fuel input once it comes on line.
> 
> Many small ones actually use electric at night time from other fuel burning plants to pump water back up into the damn while electric demand is low.
> 
> meaning if the concern is either being dependent on dwindling resources or putting pollution into the atmosphere, hydro is better than all the other alternatives.
> 
> 
> Keep in mind, the Three Gorges Damn has actually altered our rotation.
> 
> ----------
> I wasn't suggesting that it makes sense to rebuild a house, just that some principles be applied.
> 
> Using the existing thermal mass just with a programmable thermostat and even looking at exterior window shades would yield similar savings to a battery at a lower expense with less complexity.
> 
> Over cooling the thermal mass in the morning uses more electric, and won't prevent the A/C from coming on during peak billing hours.
> 
> Yes, setting the thermostat higher during peak billing hours will reduce the amount of electric used. His area is already experiencing temps in the 80s. He may also live in a high humidity area. How uncomfortable do you suggest that he becomes?


Exterior window shades may or may not help. Don't know how much exposure he has. But he would still be using electric for the A/C during peak billing hours. 

Remember, just because you wouldn't do, or spend the money on this project. Doesn't mean someone else shouldn't. There are a lot of things other people get, that you don't like. What is right for them to do, probably isn't right for you to do.


----------



## jeff00

Here ya go. A mini-split that runs on 900 watts ~~~ supposedly this is a 65 SEER Heat pump 

http://www.hotspotenergy.com/solar-air-conditioner/HotSpot-ACDC12b.pdf


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## beenthere

jeff00 said:


> Here ya go. A mini-split that runs on 900 watts ~~~ supposedly this is a 65 SEER Heat pump
> 
> http://www.hotspotenergy.com/solar-air-conditioner/HotSpot-ACDC12b.pdf



It doesn't run on only 900 watts. With 900 watts of solar panels. The panels will provide 720 watts of power to offset the electric that would normally be used from the grid.


----------



## jeff00

> Your air conditioner needs the most power when the sun is shining, a coincidence you can take advantage of with our
> ACDC12B solar air conditioner.
> 
> It can keep an indoor area cool during the day for pennies. Literally, pennies, operating above SEER 35 with only two 230w solar panels connected, and above SEER 65 with three 300w panels. Use this system to cool a
> small area or to augment a larger system.
> The unit uses solar energy up to 720w (up to 900w of solar panels), and adds in utility power, with no need for batteries. Even
> when the sun is not shining at all, this ultra high-efficiency (SEER 21 without solar) heat pump will keep you comfortable and
> save you money using far less electricity than a normal AC or heat pump unit of the same capacity.


the point is, at 900 watts you don't use the grid during peak operation....isn't that the whole point of this conversation


----------



## beenthere

jeff00 said:


> the point is, at 900 watts you don't use the grid during peak operation....isn't that the whole point of this conversation


First, it doesn't use the whole 900 watts of the panels, it only uses 720 watts. Next, he also wants to use the stored electric if the grid power goes out for a while.

Your still using grid electric. It only reduces the amount of grid usage by 720 watts according to the link.

Key phrase is "and adds in utility power". So it only reduces the A/C grid electric usage by 720 watts. 

Listed as 11,500 BTUs of cooling. 
It list its COP as 3.81 
So 720x3.413=2457.36 
2457.36x3.81=9362.54 BTUs of cooling. 
To get the other 2137.46 BTUs, it uses grid electric. So that would be 164.37 watts of grid power.

The OP is operating a 4 ton A/C. So he would need 4 of these to come close to his current capacity. And still be using 657 watts from the grid, at a guess of up to 4 hours( 2.628 KWHs) a day, at as high as 9 bucks a KWH.

Plus, the OP said he also wants to be able to use the stored electric when the power goes off. He couldn't use these for that.

Yes, he could only cool 1 or 2 areas of his house using these. Reducing his grid usage. But probably for the cost of 2 of these. He would be half way or better to the cost of the set up he wants to put in.


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## puttster

beenthere said:


> Find out the min you need to install, to get the best bang on return/tax credit.


It would take a lot of solar panels to fill a 14kw battery. You are going to lose 50% of the design wattage due to sun angle, clouds and heat, plus another 10% on the round trip through the electronics. So even operating 6-8 hours a day I'd need 4-5kw on the roof. That's why I'm thinking: just get by with the minimum panels to get the 30% tax credit on the system, save the rest of the panels for another day. 

So your question is a good one. Seems like you could build a story around 1kw of panels for 8 hours, planning to cycle the battery down only 50%....

Edit: looks like in 2012 the tax credit for the battery would need to be proportional to the share of recharging coming from the roof. http://www.renewableenergyworld.com...nergy-tax-credit-but-imposes-limitations.html Not sure how one could know what that proportion is, though. I like what these guys say, https://www.wholesalesolar.com/solar-information/federal-tax-credit , full credit for the battery as long as just one panel is connected??


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## beenthere

Full credit if it doesn't get any charge from the grid. If it gets 90% of its charge from solar, and 10% from grid, then only 27% of the battery system cost is credited.


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## djlandkpl

The 30% credit makes the investment so much more palatable. Without it, it may not be worth the investment. If I didn't get the tax credits and ongoing energy credits, I wouldn't have installed a system as there would have been no payback. 

Check out this site, http://pvwatts.nrel.gov/ You enter your address and enter a few parameters for a system. The neat part is you draw on a map where your system would be and it calculates your solar production by hour and day of the year. 

Depending upon your system's relationship to the sun, you might not need as many panels. I'm in MA. On a clear June/July day, my 7.7 Kwh system will generate 60 Kwh.


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## anony

The battery will last 10 years. It will last significantly less in Texas hot garage, you'll want to locate the battery inside conditioned space.


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## puttster

It does seem like a Powerwall wired for backup only and filled over a period of a couple of weeks with a small, maybe 100w, panel might qualify for the full tax credit.


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## beenthere

Taking a couple weeks to charge it, then renders its useless for your original purpose.


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## puttster

Yes, but after a while, not sure how long, I could rewire so the battery can be filled nightly from the grid and used daily to run the air conditioner.


----------



## Red Squirrel

Yeah should keep battery at 25C or below. 20-25C is kinda optimal for performance, but if you go lower it's life is increased. 

This got me wondering, if they make DC powered compressors. Would be simpler as you can just use a huge capacitor bank to handle the startup load. A bit harder to do this with an inverter, I guess you can still do it on the DC side, but the inverting side has to be able to handle the load. 

Either way the biggest challenge here is the inverter. Whether you go with lead acid batteries, or powerwall etc you still need an inverter that can handle the startup and continuous load. Probably want to check what the stall draw is as well, as you want your inverter to not blow up if the compressor does stall. Idealy you'd have a slow reaction time fuse or breaker that would eventually blow/trip.


----------



## user_12345a

puttster said:


> It does seem like a Powerwall wired for backup only and filled over a period of a couple of weeks with a small, maybe 100w, panel might qualify for the full tax credit.


Yah, game the system when it's not even for 100% renewable energy so there's less money for roads, schools and social security.


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## beenthere

puttster said:


> Yes, but after a while, not sure how long, I could rewire so the battery can be filled nightly from the grid and used daily to run the air conditioner.


I believe the wait would be 5 years.


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## beenthere

user_12345a said:


> Yah, game the system when it's not even for 100% renewable energy so there's less money for roads, schools and social security.


No such thing as 100% renewable energy.


----------



## user_12345a

If this renewable energy tax credit is helping him buy a battery primarily used for shifting to off peak rather than storing power produced by panels, and a 100w panel is being added just to get a credit, that's called gaming the system.

It's bordering on fraud.


----------



## jeff00

user_12345a said:


> If this renewable energy tax credit is helping him buy a battery primarily used for shifting to off peak rather than storing power produced by panels, and a 100w panel is being added just to get a credit, that's called gaming the system.
> 
> It's bordering on fraud.


ya, it's like filing a 1040 ~~~~ everyone bends the rules


----------



## beenthere

user_12345a said:


> If this renewable energy tax credit is helping him buy a battery primarily used for shifting to off peak rather than storing power produced by panels, and a 100w panel is being added just to get a credit, that's called gaming the system.
> 
> It's bordering on fraud.


He already said he can leave the panels charge the battery for a week, and not use grid power to charge it for how ever long he has to. That is not fraud, or bordering on fraud. Rather, it is following the IRS rules.


----------



## jeff00

I honestly don't see the point of this---still! 

you still end up using the power company to charge your batteries and when you do run the a/c off the batteries it's only for a few hours of the day, like three or four hours, then you are right back on the power company to charge your batteries to full charge. even if you wait til night to charge the batteries at 2¢/Kw, how long will it take to bring the batteries back to full charge and at what amperage? so you use the batteries for 5 hours a day, the rest of the time you're charging them, 19 hours a day

On top of that, when he does run the a/c off the batteries what is his DOD (Depth of Discharge) of the batteries

A completely charged battery will be at 12.7 volts.....50% discharged is 12.5 volts....completely depleted 12.3 volts. Not to mention the CONSTANT maintenance of checking the specific gravity of the battery acid and refilling them. Vented lead acid batteries are about the only thing you could use here. You could try AGM and/or sealed batteries, but neither one will last as long as a Lead acid. ALSO, you will need a "equalization cycle" every 90 to 120 hours. 

If he cycles the batteries to 12.3 volts everyday (or lower) , he will be buying new batteries every two or three years at $5K to $7K...even if he could manage to get them to 5 years, he's still going to need new batteries more often than necessary

The smarter thing to do here is what most grid tie people do *with solar panels.* Run your high amperage appliances off the batteries during a bright sunny day. Pull power from the batteries AS THE PANELS are being pounded by bright sunlight and the batteries with high a amperage charge. That way you get the full benefit of being off grid, you save money AND you can go back on the grid at night and run the a/c for virtually nothing.

This idea of charging batteries off peak is a noble one, however I see it as a complete waste of time and money. The batteries are the key here and_ I don't think most of you understand what you're asking of the batteries. _

What some people do, is go get a couple 12v forktruck batteries. But those batteries take a very high amperage to charge them up and they literally weigh a ton.....so that maybe a wash.


----------



## puttster

All these questions have been answered already. Some of them several times. Well, maybe not your suggestion that the peak A/C power (about 5 kW) is best provided using lead acid batteries instead of Lithium, as in a Tesla Powetwall.

This has been a good thread. Thx, all.

OP


----------



## user_12345a

Grid-interactive solar does make sense and mostly to be able to run essentials if the grid goes down.

Run the essentials like a fridge, lights, electronics, furnace fan off of battery charged by solar, and when the solar isn't enough charge the batteries with the grid. Could even to a small window a/c.

if the grid is down charge them with a generator.

The large optional loads get run off the grid.

*As a cash generator or saver, renewable energy or storage* makes no sense and isn't viable without subsidies.

*If you're trying to save the environment or resources, it would make more sense* to actually do solar thermal, domestic hot water.

i wouldn't be surprised if a $5000 domestic hot water system collected 10 to 15kwh per day of energy.

To do that with pv and have a battery storage arrangement, you would have to spend several times as much money to get the same amount of renewable energy.


[qoute]He already said he can leave the panels charge the battery for a week, and not use grid power to charge it for how ever long he has to. That is not fraud, or bordering on fraud. Rather, it is following the IRS rules.[/quote]

getting a tax credit for a super expensive battery, only to get 100w of solar -> very low electricity production. they're trying to encourage people to use renewable energy and the subsidies are for generation.

it may not be against the rules with loop holes on paper, but it's not proper. it's gaming the system.


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## beenthere

Takes about 13 hours to completely recharge a 120 AH battery at a 13 amp charging rate.


----------



## jeff00

beenthere said:


> Takes about 13 hours to completely recharge a 120 AH battery at a 13 amp charging rate.


from what state of charge? completely discharged? I have four 6v 215 aH batteries, but mine never go below 12.5 volts. Mine will recover within 4 or 5 hours on a bright sunny day, 6 or 7 hours on a cloudy day. Mine even charge the batteries on a rainy day, although the batteries only get charged at 2 or 3 amps. This is my Morningstar 45amp charge controller on a sunny day


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## beenthere

Completely discharged.


----------



## user_12345a

what size is your system and how many kwh per day does it produce?

do you feel it's worth it?


----------



## jeff00

lets go back to some quick math:

if the 4T condenser draws 40 amps @ 240v that = 9600 watts

If the 4T condenser draws 30 amps @ 240v that = 7200 watts

the largest Pure sine wave inverter I could find was Magnum Energy 4400watt. 120/240 output at $2255.00 with a 48v input, you could go with a 24v input too?.....you're going to to need a 'few' batteries 

and you're going to need TWO inverters 

so before you even get started, the inverters are going to cost you $4400, now add $10K worth of batteries and/or powerwall.

to me, this is not a viable ROI (Return on Investment)

BTW: none of those figures above, include the indoor blower motor...????? 

Knockyourselfout if you think you can make this work, I would really like to see your ROI, I would LOVE to see your setup---> Battery bank, inverter and transfer switch gear.


----------



## user_12345a

depends on the efficiency.

if it's 13+ seer it's not going to draw close to even 6kw running. 

but then again the inverter has to be able to supply starting amps.

honestly, shut off the central a/c during peak hours and use window or mini-split unit to condition only the room that's occupied if it warms up.


----------



## beenthere

4 ton 13 SEER is around 4KWHs an hour.

Its about a 12 grand up front cost set up using 2 inverter/chargers, 8-200AH 12 volt batteries(500 bucks a pop), and a few other accessories for switch over.


----------



## anony

21 SEER AC only costs like $3000.


----------



## beenthere

anony said:


> 21 SEER AC only costs like $3000.


And will use around 3.2KWHs an hour of run time during peak rates, of up to 9 bucks a KWH. So as high as $28.20 an hour of run time during those peak rate times.


----------



## anony

beenthere said:


> And will use around 3.2KWHs an hour of run time during peak rates, of up to 9 bucks a KWH. So as high as $28.20 an hour of run time during those peak rate times.


Depends on the ton I guess, over here electricity is like 5c per kwh, solar just does not make sense.


----------



## beenthere

anony said:


> Depends on the ton I guess, over here electricity is like 5c per kwh, solar just does not make sense.


If you read what the OP posted, he has very high peak electric rates. And he has a 4 ton A/C.


----------



## user_12345a

anony said:


> Depends on the ton I guess, over here electricity is like 5c per kwh, solar just does not make sense.


you're lucky - either you have lots of hydro, coal or both.

What the politically correct green jurisdictions do is jack up the cost of electricity by replacing coal with gas, putting carbon taxes, doing feed in tariff porgrams that pay in insane amount per kwh per producers.

people are forced to cut back (not a bad thing, but for the wrong reasons) and put on useless grid tied solar to offset the increases.

california and ontario are leading the way in making life more difficult and unaffordable to score climate change brownie-points - and doing nothing to make the electricity grid less reliant on fossil fuels or reliable.

At 5 cents per kwh 10 seer is good enough.

at 15 to 25 like the green states/provinces are paying, even 15 seer is lots of $$$$ to operate. 

it used to be 10 cents all inclusive.

and a/c is not even a giant polluter/fossil fuel consumer if commissioned right and used wisely - heating and transportation use far more. a modern a/c is giving 3 to 4 units of cooling for every unit of energy consumed.


----------



## LawnGuyLandSparky

beenthere said:


> If you read what the OP posted, he has very high peak electric rates. And he has a 4 ton A/C.


Well not exactly, he doesn't have high peak rates yet, he would switch to a plan that would change a constant Kwh rate to time of use - trading very high peak rates for very low off peak rates - then recharge the batteries during the off peak time only.


----------



## beenthere

LawnGuyLandSparky said:


> Well not exactly, he doesn't have high peak rates yet, he would switch to a plan that would change a constant Kwh rate to time of use - trading very high peak rates for very low off peak rates - then recharge the batteries during the off peak time only.


Until the solar part came into discussion. That is what was being planned by him all along. Charge the batteries during the off peak times. And use the batteries to run the A/C during those peak rate hours.


----------



## puttster

beenthere said:


> If you read what the OP posted, he has very high peak electric rates. And he has a 4 ton A/C.


The Texas PUC maximum legal wholesale rate is $9/kwh. In the 2011 drought, rates hit the max for 20 hours, so if you has a rate schedule that tracked wholesale rates (which I have now) and a 4 kwh air conditioner you could potentially save $720. Of course that year there were many more hot hours at like $8/kwh, more at $7, more at $6, etc, I don't know how many hours were sold at over a dollar a kwh but there were lots. 

Most of the peaks occurred at 3-5 PM, I would guess. We have had some hot years since but not like that. Maybe this year! Being able to supply yourself on those peak hours from a battery that only cost $5,500 and could be recharged every night for maybe 8 cents/kwh would be a great investment. Even better, imagine if you could also tie your 70 kwh electric vehicle battery into the grid, and sell that power. It will happen one day. Get ready for it.


----------



## beenthere

puttster said:


> The Texas PUC maximum legal wholesale rate is $9/kwh. In the 2011 drought, rates hit the max for 20 hours, so if you has a rate schedule that tracked wholesale rates (which I have now) and a 4 kwh air conditioner you could potentially save $720. Of course that year there were many more hot hours at like $8/kwh, more at $7, more at $6, etc, I don't know how many hours were sold at over a dollar a kwh but there were lots.
> 
> Most of the peaks occurred at 3-5 PM, I would guess. We have had some hot years since but not like that. Maybe this year! Being able to supply yourself on those peak hours from a battery that only cost $5,500 and could be recharged every night for maybe 8 cents/kwh would be a great investment. Even better, imagine if you could also tie your 70 kwh electric vehicle battery into the grid, and sell that power. It will happen one day. Get ready for it.


I don't doubt it.


----------



## Red Squirrel

Only way this would really be cost effective is if you can build your own inverter. I would start with a H bridge configuration using IGBT bricks. Some of those can handle like 200 amps with adequate cooling. I don't know enough about that to know how big you'd need to make the inductors and transformers but I imagine they would be fairly big and a good chunk of the cost. 

You could also build several smaller inverters and sync them, but if something goes wrong with the syncing process you're going to have a very bad day. I'd personally go for one beefy inverter that can handle the whole load. Though in an off grid application I would do multiple for redundancy but ensure that if one fails the other can handle the load. 

I've been wanting to get more into power electronics myself as I kinda want to do the same where I charge batteries off peak and discharge on peak. But I'd also inject solar into the mix. The electronics is what really drives the price high once you get into the multi kw levels of AC power. Batteries are a big cost too, but that is one of those things where you can always cheap out at first and see how long you get by, then pay for better ones down the road.


----------



## anony

Wasn't OP in Texas?

See the free market rates!
http://www.powertochoose.org/


----------



## jeff00

Red Squirrel said:


> Only way this would really be cost effective is if you can build your own inverter. I would start with a H bridge configuration using IGBT bricks. Some of those can handle like 200 amps with adequate cooling. I don't know enough about that to know how big you'd need to make the inductors and transformers but I imagine they would be fairly big and a good chunk of the cost.
> 
> You could also build several smaller inverters and sync them, but if something goes wrong with the syncing process you're going to have a very bad day. I'd personally go for one beefy inverter that can handle the whole load. Though in an off grid application I would do multiple for redundancy but ensure that if one fails the other can handle the load.
> 
> I've been wanting to get more into power electronics myself as I kinda want to do the same where I charge batteries off peak and discharge on peak. But I'd also inject solar into the mix. The electronics is what really drives the price high once you get into the multi kw levels of AC power. Batteries are a big cost too, but that is one of those things where you can always cheap out at first and see how long you get by, then pay for better ones down the road.


it would NOT be cost effective to make your own inverter. How would you make it a Pure sine wave without a lot of Transducers, and bridge rectifiers.
and, the largest inverter I could find is 4400 watts, he would need two of them and if one went down, he better have the other protected?


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## Red Squirrel

jeff00 said:


> it would NOT be cost effective to make your own inverter. How would you make it a Pure sine wave without a lot of Transducers, and bridge rectifiers.
> and, the largest inverter I could find is 4400 watts, he would need two of them and if one went down, he better have the other protected?


Oh you'd definitely have to know what you're doing, and I won't pretend to be an expert myself but been looking into it and reading a lot on SMPS. Basically you PWM the sine wave and smooth it out. You can think of it as acting like a variable DC power supply, except it's constantly changing the voltage up and down to create the 60hz wave form. The PWM frequency would be in the 100 of khz range but the output after filtering would be a 60hz sine wave (or whatever you program it to do.) Basically how a VFD works I believe.


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## jeff00

Red Squirrel said:


> Oh you'd definitely have to know what you're doing, and I won't pretend to be an expert myself but been looking into it and reading a lot on SMPS. Basically you PWM the sine wave and smooth it out. You can think of it as acting like a variable DC power supply, except it's constantly changing the voltage up and down to create the 60hz wave form. The PWM frequency would be in the 100 of khz range but the output after filtering would be a 60hz sine wave (or whatever you program it to do.) Basically how a VFD works I believe.


well you're way ahead of me on the tech curve. You start in with PNP/NPN transistors, bridge rectifiers and buck/boost transformers and Im hitting the Capt'n and Coke :biggrin2:besides, I don't have the money for a Oscilloscope and all the other crap thats goes with that. 

Id rather just buy a good Pure Sine Wave inverter with a nice warranty :vs_cool:


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## Red Squirrel

This might be able to do it then, and it's on sale! Yeah it's going to cost more than the air conditioner itself.  

https://www.solarwholesaler.ca/product/outback-gs8048-radian-8000-watt-48-vdc-invertercharger/

Though if you get two, you could just do the whole house and call it a day. 

I've kinda looked into it myself just more money that I'd want to spend. Though my new electronics hobby is probably going to cost me about that if I don't stop buying stuff.


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## beenthere

Red Squirrel said:


> This might be able to do it then, and it's on sale! Yeah it's going to cost more than the air conditioner itself.
> 
> https://www.solarwholesaler.ca/product/outback-gs8048-radian-8000-watt-48-vdc-invertercharger/
> 
> Though if you get two, you could just do the whole house and call it a day.
> 
> I've kinda looked into it myself just more money that I'd want to spend. Though my new electronics hobby is probably going to cost me about that if I don't stop buying stuff.


Could get 5 of these https://jet.com/product/detail/0178...978929_pla-293279044778:na:na:na:2&code=PLA15 for the cost of 1 of those.


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## jeff00

ok kids, I have found the solution to a perceived problem

Taa-daaa

solar air conditioning


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## beenthere

While it does run the compressor 100% off of the solar panels on sunny days. It still doesn't run the entire A/C from solar. It requires either a UPS, or grid electric to run the indoor unit. 

Does seem to come in a 2 ton size, so the OP would only need 2 of them. And then would have to hope the Chinese designed and built it right.

Of course, it still doesn't provide the home with back up power as the OP said he wanted, nor the ability to sell electric back to the POCO like the OP said he wanted to be able to do.


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## jeff00

beenthere said:


> While it does run the compressor 100% off of the solar panels on sunny days. It still doesn't run the entire A/C from solar. It requires either a UPS, or grid electric to run the indoor unit.
> 
> Does seem to come in a 2 ton size, so the OP would only need 2 of them. And then would have to hope the Chinese designed and built it right.
> 
> Of course, it still doesn't provide the home with back up power as the OP said he wanted, nor the ability to sell electric back to the POCO like the OP said he wanted to be able to do.


it does have a battery backup, so this will get the OP halfway to his goal


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## beenthere

jeff00 said:


> it does have a battery backup, so this will get the OP halfway to his goal


Unfortunately, its not enough battery back up to do squat as far as selling some back, and still running the A/C.


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## KPDMinc

red squirrel said:


> this might be able to do it then, and it's on sale! Yeah it's going to cost more than the air conditioner itself.
> 
> https://www.solarwholesaler.ca/product/outback-gs8048-radian-8000-watt-48-vdc-invertercharger/
> 
> though if you get two, you could just do the whole house and call it a day. :d
> 
> i've kinda looked into it myself just more money that i'd want to spend. Though my new electronics hobby is probably going to cost me about that if i don't stop buying stuff.



buying electricity from a utility in turn will also out-cost the ac itself, as with all appliances...


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## jeff00

AFA I'm concerned, the only way to make this worthwhile is to go completely off grid. 

*But thats just me*. AND it requires a lifestyle change. People are addicted to electricity. 

we just had a major windstorm that knocked power out for 6 or 7 days for some people (I never lost power and I loaned my generator out to some friends that weren't so lucky) you should have heard to outrage form people. 

Folks with natural gas backup generators didn't bat-an-eye. But people with no power were scrambling to find a generator to power their frig, freezers and furnace.


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## beenthere

jeff00 said:


> AFA I'm concerned, the only way to make this worthwhile is to go completely off grid.
> 
> *But thats just me*. AND it requires a lifestyle change. People are addicted to electricity.
> 
> we just had a major windstorm that knocked power out for 6 or 7 days for some people (I never lost power and I loaned my generator out to some friends that weren't so lucky) you should have heard to outrage form people.
> 
> Folks with natural gas backup generators didn't bat-an-eye. But people with no power were scrambling to find a generator to power their frig, freezers and furnace.


Whats your electric rate?


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## jeff00

beenthere said:


> Whats your electric rate?


I really don't know. No one can figure out the bill......here, knockyourselfout

if you can figure it out, I know about 3 million other people that would like an explanation


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## Red Squirrel

Lol reminds me of Hydro One. So many BS charges. Except double or even triple those numbers.


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## beenthere

jeff00 said:


> I really don't know. No one can figure out the bill......here, knockyourselfout
> 
> if you can figure it out, I know about 3 million other people that would like an explanation


Your actual electric rate is very cheap, just $0.0234 a KWH.
The other charges is what brings up the bill. At a rate of $0.0462 KWH. 
But your still paying a very cheap total rate, of just $0.0696 a KWH. 

Now imagine what your bill would be like if you had to pay $7.25 a KWH for 112 KWHs out of the total KWHs you used in that bill. It shouldn't be hard to see how the OPs idea could save him a lot.

When those of us only looking at our electric bill, its easy to forget what its like for people that pay $0.35 per KWH or more, plus all the other charges. And only think of how something might have to be done in our area to work.


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## jeff00

beenthere said:


> Your actual electric rate is very cheap, just $0.0234 a KWH.
> The other charges is what brings up the bill. At a rate of $0.0462 KWH.
> But your still paying a very cheap total rate, of just $0.0696 a KWH.
> 
> Now imagine what your bill would be like if you had to pay $7.25 a KWH for 112 KWHs out of the total KWHs you used in that bill. It shouldn't be hard to see how the OPs idea could save him a lot.
> 
> When those of us only looking at our electric bill, its easy to forget what its like for people that pay $0.35 per KWH or more, plus all the other charges. And only think of how something might have to be done in our area to work.


there is no way I would put up with a $7+ per Kw rate. I would spend every last penny to get off the grid. at that rate, a solar/wind hybrid system would pay for itself with in 10 years. I mean seriously, you go from $7+ to less than a couple dollars why wouldn't you????


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## user_12345a

> Now imagine what your bill would be like if you had to pay $7.25 a KWH for 112 KWHs out of the total KWHs you used in that bill. It shouldn't be hard to see how the OPs idea could save him a lot.


if i had a rate like that, i would do everything to shift usage and not run heavy appliances during that time.

any electric ac, water heater, heater, stove/oven, dryer would be off during that time.

just run some led lamps, electronics.

means sacraficing comfort and convenience, but worth it.

as is, already have expensive electricity:

http://www.ontarioenergyboard.ca/oeb/Consumers/Electricity/Electricity Prices

5 to 6 cents get added to that for other charges, plus $20 a month for the grid connection.

back b4 government started meddling with the grid and subsidizing solar it was 8 to 10 cents all inclusive, no time of use rates.


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## beenthere

jeff00 said:


> there is no way I would put up with a $7+ per Kw rate. I would spend every last penny to get off the grid. at that rate, a solar/wind hybrid system would pay for itself with in 10 years. I mean seriously, you go from $7+ to less than a couple dollars why wouldn't you????


Solar and wind off grid require a good amount of life style change.

What you or I would do isn't of real importance. Its what the OP wants to do, that is, and is what he should receive help with.


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## jeff00

beenthere said:


> Solar and wind off grid require a good amount of life style change.
> 
> What you or I would do isn't of real importance. Its what the OP wants to do, that is, and is what he should receive help with.


although I agree with you, what the OP is asking is not workable in a economic way, in my opinion. 

He's not going to solve his problem and still have a ROI. He has been given MANY solutions to his issue. Not many of them are workable.

Half of us here have suggested a workable solution, the other half is saying you can 'do this' but it will cost you...$XXXXX.xx and your ROI will be 20+ years...blah blah blah. 

*BTW: I did a search for electric rates throughout America. the OP mis printed his electric rate:*



> Here in Texas you can contract to track the wholesale price of power, which can run from* 2¢/kwh* at night to as high as the PUC price cap of* $9.00/kwh *on a hot July afternoon.


I think he meant to say 9¢/kilowatt. why would anyone pay 2¢ at night and NINE FREAKING DOLLARS during the day?? According to the U.S. Energy Information Administration, the most anyone pays in Texas is 10¢/per Kwh

https://www.eia.gov/electricity/monthly/epm_table_grapher.cfm?t=epmt_5_6_a


New Yorkistan is at 17¢/Kwh (Thats why I said no one can figure out the bill, it appears to look like 4¢, but with all the added surcharges and crap it's much higher) 

so at this time it appears the OP is wasting his time and money. For him, it would not be advisable to change anything as he would never see a ROI.

_edit: the OP'r should post the name of the power company so anyone here can confirm or deny the $9/Kwh claim. _


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## puttster

Texas is not run like New York https://www.greentechmedia.com/arti...e-Texas-System-Wide-Offer-Cap-to-9000-in-2015. The cap is $9/kWh.


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## jeff00

puttster said:


> Texas is not run like New York https://www.greentechmedia.com/arti...e-Texas-System-Wide-Offer-Cap-to-9000-in-2015. The cap is $9/kWh.


so your electric bill for 500Kwh/month is $4500 per month? 

I don't know what the problem is here, but the math is messed up. 3rd world countries don't pay that much. 

Later today or tomorrow, I'll be calling the Texas Public utilities for a explanation

I don't have the time right now


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## anony

Nobody pays $9.00/kwh in Texas, are you guys retarded? Texas rate is around 5c to 10c per kwh.


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## jeff00

> The Electricity Reliability Council of Texas (ERCOT), which manages Texas’s grid, will raise the system-wide offer cap (SWOC) to *$9,000 per megawatt-hour in 2015*





you're posting the market cap as claimed by the Green Market Media. 

and if my math isn't off, that translates into 90¢ /KwH..... or about $1.00

thats $9000 per million watt hours.....is my math off or what? 

I want to know the name of the power company the OP'r buys his electricity from so we can call and confirm the pricing? 

This a ludicrous price even at 90¢...

something is seriously wrong with the OP'r numbers


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## KPDMinc

jeff00 said:


> [/U][/B][/U]
> 
> 
> you're posting the market cap as claimed by the Green Market Media.
> 
> and if my math isn't off, that translates into 90¢ /KwH..... or about $1.00
> 
> thats $9000 per million watt hours.....is my math off or what?
> 
> I want to know the name of the power company the OP'r buys his electricity from so we can call and confirm the pricing?
> 
> This a ludicrous price even at 90¢...
> 
> something is seriously wrong with the OP'r numbers


even in its highest tier, we dont pay that much in California...


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## beenthere

jeff00 said:


> although I agree with you, what the OP is asking is not workable in a economic way, in my opinion.


Again, we can only have an opinion, and voice. 

But, it doesn't matter. Sometimes, some people want to do something, and see if they can make it viable.

Not really our place to keep on telling him to do something different.


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## beenthere

jeff00 said:


> [/U][/B][/U]
> 
> 
> you're posting the market cap as claimed by the Green Market Media.
> 
> and if my math isn't off, that translates into 90¢ /KwH..... or about $1.00
> 
> thats $9000 per million watt hours.....is my math off or what?
> 
> I want to know the name of the power company the OP'r buys his electricity from so we can call and confirm the pricing?
> 
> This a ludicrous price even at 90¢...
> 
> something is seriously wrong with the OP'r numbers


1 megawatt is 1,000 KWs. 9000/1000=9. So its a $9.00 KWH cap.


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## jeff00

beenthere said:


> 1 megawatt is 1,000 KWs. 9000/1000=9. So its a $9.00 KWH cap.


look where that information comes from. 

it's unrealistic to believe he actually pays $9/Kwh. No one on earth pays that


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## beenthere

jeff00 said:


> look where that information comes from.
> 
> it's unrealistic to believe he actually pays $9/Kwh. No one on earth pays that


I was mainly correcting your math.

Doesn't matter if anyone pays it or not. Its still an interesting idea/project.

Constant nay saying, simply robs us of ever finding out how it worked, or how it didn't work.

Good thing Ford, Hershey, and Disney didn't listen to the nay sayers.


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## jeff00

beenthere said:


> I was mainly correcting your math.
> 
> Doesn't matter if anyone pays it or not. Its still an interesting idea/project.
> 
> Constant nay saying, simply robs us of ever finding out how it worked, or how it didn't work.
> 
> Good thing Ford, Hershey, and Disney didn't listen to the nay sayers.


LOL, Dude, the guy asked if his "project would work" I think, we as professionals gave a resounding NO! 

we then offered, not only reasonable but workable solutions to his problem. 

on top of that the OP'r gave us faulty numbers, it's ludicrous to think anyone in America pays $9/kw for electricity ..... lets just imagine what that monthly electric bill would look like. 

I want....I demand to know what power company in America charges $9/kwh. 

*PRODUCE THE NAME OF THE POWER COMPANY THAT CHARGES THAT MUCH. come up with that, PROVE to the class this is an actual number and I will happily apologize to the OP'r *


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## beenthere

jeff00 said:


> LOL, Dude, the guy asked if his "project would work" I think, we as professionals gave a resounding NO!
> 
> we then offered, not only reasonable but workable solutions to his problem.
> 
> Reasonable by opinion only.
> 
> on top of that the OP'r gave us faulty numbers, it's ludicrous to think anyone in America pays $9/kw for electricity ..... lets just imagine what that monthly electric bill would look like.
> 
> He never said he has had to pay that at any time yet, let alone for a whole month. And he did say this was a plan for getting a head start on things.
> 
> I want....I demand to know what power company in America charges $9/kwh.
> 
> Not required to be posted.
> 
> *PRODUCE THE NAME OF THE POWER COMPANY THAT CHARGES THAT MUCH. come up with that, PROVE to the class this is an actual number and I will happily apologize to the OP'r *


Not required.


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## jeff00

beenthere said:


> Not required.


Im done! :vs_worry:


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## puttster

At the risk of repeating myself, here is a chart I found showing the wholesale price of electricity in houston in 15-min intervals one day a few years ago. It will give you an idea of what I am trying to do. In this instance the peak price was just $.70/kwh but of course on many days it is much higher. I think the mean summer peak-hour price was something like $2.00. The cap permitted by the PUC is $9.00/kwh. 

My retailer charges me by the 15-minute interval (which is what he pays), not the monthly average. If I cut back when the spot price is $.70 /kwh, $5.00/kwh, that is how much I save. It is a pretty sophisticated system.

So my thought is to load the battery at night for next to nothing and then unload it when the price peaks. Later, I can load the battery with solar in the AM and then unload when it hits the peak price around 4 PM. 

My question was really about how to do this, in particular the wiring. Did not expect to be challenged (by someone from out of state) on how the Texas grid system works. To those of you who contributed, and those who search and find this thread, I apologize for the distraction.


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## jeff00

this thread is BS. 

there are over 60 different electric plans to choose from in the Houston area

you can choose a rate that suites your electric usage....nowhere in the Houston area is the rate over 12¢

https://www.saveonenergy.com/texas/houston/

so help me understand where you're getting these ridiculous electric rates

and......your chart is from 3 years ago.


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## Red Squirrel

Wow did not realize some places actually had tiers that were that granular. I thought here it ws bad lol, but at least it's rather set amounts, low peak, mid peak and peak. There's a winter and summer version but that's it. Always the same rate at the same times. Here where they get you is all the add-on fees. You can use zero electricity and still pay about $100.

As for the answer I'd say that YES it's possible, but as I mentioned, the inverter is where it's going to get crazy expensive.


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## beenthere

Red Squirrel said:


> Wow did not realize some places actually had tiers that were that granular. I thought here it ws bad lol, but at least it's rather set amounts, low peak, mid peak and peak. There's a winter and summer version but that's it. Always the same rate at the same times. Here where they get you is all the add-on fees. You can use zero electricity and still pay about $100.
> 
> As for the answer I'd say that YES it's possible, but as I mentioned, the inverter is where it's going to get crazy expensive.


By not tying himself in to one of the contract plans. The OP can control how much his electric bill is, and possibly make a few bucks by selling back electric. Whether profitable or not, depends on the weather they have in the summer.


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## puttster

jeff00 said:


> and......your chart is from 3 years ago.


Here's one from yesterday. It is priced in MWH. Yesterday was beautiful, I teed off at 2:00, just as pricing hit a peak for the day of 44¢/kwh. Still, I might have made 3-4 bucks if I could have run my A/C off a battery for a few hours. 

Might be ten times that this summer.


----------

