# PV Solar electricity tied directly to a DC Water Heater



## JStofik

There are DC heater elements available for use in electric water heaters. Therefore, can PV Solar panel output (DC) be directly wired to a DC Water Heater of the matching voltage (assuming a thermal controller is installed to prevent over heating). Any ideas or brain storming?

Thanks,
Joe


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## Missouri Bound

Why not? What heats the water when it's cloudy?


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## JStofik

On cloudy days, the existing gas hot water heater will supply hot water. It will be plumbed so the DC electric is a feed tank to the existing gas water heater.


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## Missouri Bound

Got it!:thumbsup:


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## Thunder Chicken

You can do this, but energy-wise it is a waste of panel area. You would get more heat into the water using indirect solar thermal instead of PV. 

You generally only get about 10% of your incident solar into the form of electricity in PV. Solar thermal is far more efficient if your goal is to make hot water.


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## Solarboy

There are some situations where a PV to thermal might be considered...the collectors are lighter and easier to anchor. Wire is easier to run than pipe, especially if you have a long and complicated pipe run. PV system doesn't need freeze protection. There should be some efficiency gain without an inverter, and no batteries or grid tie is needed. 
But you are right, Thunder Chicken...last I checked, it took 5X's the money and 7X's the collector area for PV's to match thermal solar.


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## Oso954

> There should be some efficiency gain without an inverter, and no batteries or grid tie is needed.


Wiring PV directly to a heating element is not efficient. In fact, it may not work at all. The resistance of the heater will drive up the panel voltage. When you hit open circuit voltage, there will be no current flow.

You will need at minimum some type of heater controller, or a solar charge controller and a battery.


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## beenthere

Oso954 said:


> Wiring PV directly to a heating element is not efficient. In fact, it may not work at all. The resistance of the heater will drive up the panel voltage. When you hit open circuit voltage, there will be no current flow.
> 
> You will need at minimum some type of heater controller, or a solar charge controller and a battery.


So 1 ohm of resistance is too much?


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## Solarboy

While PV is not my field (thermal solar is my thing) my gut instinct says that PV panels producing DC, into DC heating elements...without an inverter should be more efficient overall. I don't know "what it would take", but the fewer conversions the better, as a general rule. A charge controller and battery? Ok....so the PV's charge the battery and the battery runs the heater?


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## ehoez

any links?


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## geno03245w

Testing shows that ordinary water heater AC elements work fine with DC,
... but ordinary water heater thermostats melt
Resistance can be varied by toggling between 1 or 2 elements... depending on intensity of solar.

Consider several diagrams posted on following link for making a DC water heater that is connected directly to solar panels.
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html#best-design


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## Oso954

Warnings from your posted link.

"This wiring violates water heater safety code and voids water heater warranty.
This wiring by-passes normal use of ECO thermal reset button located on upper thermostat.
This wiring is not guaranteed to work... it should work... but solid state relays are never completely OFF."


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## geno03245w

Thanks for rely...
Here's my take on it... please check errors in logic...

The water heater is ECO-protected in the usual manner... if water at top of tank exceeds ECO set point, the ECO trips and all power is cut to water heater.
This is particularly true since the specified DC-DC relay is Normally Open.

The TP valve would also function normally, and the power source coming from solar panels would have to be breaker-protected, and solar panels and water heater grounded per usual 

Violate code??
Commercial electric 3-phase water heaters have a box attached to water heater that contains 3-pole contactors? 
http://waterheatertimer.org/images/3-phase-balanced-converted-to-single-phase-400.jpg

There is not much difference between relay and contactor.
The DC solar water heater design seems electrically safe as long as functioning electrical parts are properly contained inside a box and all component parts are properly fused and grounded, with proper safety cut off.

Yes the water heater warranty is voided .,... the entire topic of connecting DC directly to a water heater voids product warranty

I think the DC water heater is a solid idea?
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html#best-idea


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## Oso954

The warnings were written by the owner of the webpage you linked to. If you want to argue them, argue with him.

It is one thing to experiment with something, another to suggest that you can safely install such experimental gear in a residence where people other than the experimenter reside. Or in many subdivisions, where people reside next door.



> There is not much difference between relay and contactor.


 I will agree with that, IF they are both electrical mechanical. But, there is a big difference between an electrical mechanical relay and a solid state relay. The difference in their failure modes could have dire consequences in this application.

The last warning "This wiring is not guaranteed to work... it should work.." indicates to me that he probably never built the thing. That is a good enough reason not to offer the link as a possible solution.


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## geno03245w

What warning are you giving that is not already shown on the webpage?
The webpage does not tell folks to wire their homes with DC power. 

Objections might include what the code says about DC wiring.
Certainly there are facilities that are wired with DC power.
Certainly the discussion would benefit from knowing the code.

Singh writes in his power-generation book that long distance electric transmission is more efficient using DC... somebody invented that... somebody stepped forward with an idea.... sure folks need to be careful with any electric appliance, but I worked with electric water heaters for years and the DC water heater illustrations look good to me.

Illustrations at top of webpage look like valid DC water heaters.

You sorta cherry-picked objection from bottom of page... 
... where the webpage clearly says that the illustrations showing solid state relays appearing at bottom of page are experimental.... 
I assume the solid state relays are included because they are cheap to buy if somebody wants to 'experiment' with DC.
Your warning is the same one that shows on the webpage.

The illustrations at top of page look look good to me.
The top-page illustrations use expensive Omron DC-DC relay. The Omron spec sheet shows these relays are made for switching high-voltage high-amperage DC loads. They sell on the internet... Amazon sells them too.

The DC water heater webpage looks like a good invention... I'm sure if Rheem rolled it off the assembly line, they'd tell people to have qualified DC electrician install it.
The real problem is there are no qualified DC electricians...
Which is why I would appreciate input on the code that covers DC installation.

I worked with electric water heaters for years. The illustrations look good to me.
Look at it again carefully. What do you see that causes alarm?
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html#best-idea


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## Oso954

> Look at it again carefully. What do you see that causes alarm?


You should not have asked me to look again, closely.
I know see that you are affiliated with the site, if not the owner of it.

Not disclosing that fact, makes you dishonest and untrustworthy, IMO. 

Coupling your non-disclosure with all your "BUY links" to Amazon, is a 4 alarm reason to question everything on your site, and your "real purpose" here.


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## geno03245w

The purpose is to show a DC water heater.
Period.

It doesn't matter who invented something, it only matters if it works.
Does it work ?... yes !!

There is no copyright or sign-up-requirement or sleight of hand trying to remove money from somebody's pocket....
Instead the DC solar water heater is DIY build, using off the shelf parts that are clearly specified, that are available anywhere on the internet

The DC solar water heater illustrations are free to anyone ... to use any way they want ... and those illustration exist to assist the future inventor... and inspire the next generation of DIYers... 

So let's review the DC solar water heater
.... you found no electrical code violations
... you found no errors in wiring or incorrectly specified parts
.... you discovered the DC solar water heater design works
.... it works

Look at the illustrations again.
Please add what you know about DC electrical code to help the DIY community
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html


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## Oso954

> So let's review the DC solar water heater
> .... you found no electrical code violations


The first violation is the modifiation invalidates the NRTL listing. It cannot be installed.


> ... you found no errors in wiring or incorrectly specified parts


Why should I waste time, when I know it is against code to use it. I also pointed out that SSR failure mode increase the risks.


> .... you discovered the DC solar water heater design works


No I did not.


> .... it works


Really ? 
Take a 4500 watt 240V element, 12.8 Ohms.
How many watts are you pushing thru it at 24V ??
How much water are you going to heat with your answer ?


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## geno03245w

Well.
Thank you.
... please read the material, because younger more energetic people will absorb everything on this post

... DC will modify the water heater.
We know that.
The DC water heater can be wired safely... and the illustrations work.

... the DC water heater cannot be installed?
Which countries and regions are affected that ruling? Sudan, India, Greenland, Argentina, Australian outback?
Tent City? Rural Alaska? Off-grid Montana? Alberta? My garage?
Alexia shows demographic that includes viewer participation in India, Canada
http://www.alexa.com/siteinfo/http://www.diychatroom.com

... you mention solid state relays again... again??... absolutely we covered them previously as cheap experimental substitute for more expensive Omron relay. The spec sheets and exact information are posted on the webpage.

... you suggest that 24 Volt DC is being pushed through the elements
... when the specs call for up to 240 volts DC, and the Omron relays are rated for 240 Volt DC 26 amp DC. The information, and resistance charts are posted on the webpage.

... maybe you want to limit thinking to what has been done in the past?
http://waterheatertimer.org/Add-another-thermostat-to-gas-or-electric-water-heater.html

Honestly, I am hoping you can help expand knowledge of DC power.
This is about the future.... 
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html


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## Oso954

I would suggest that you call your local building Dept and ask them if you can run a 240V DC branch circuit into a dwelling to a water heater.

I can tell you that if some one added batteries to the PV, you would be limited to 50V DC for branch circuits.


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## geno03245w

Thanks for not loading the cannon with glass and nails...

Partly the reason for DC water heater is to avoid the cost of batteries and related AC-DC conversion equipment.

And partly to create a new idea for others to consider... and possibly create new genre of cheap, DIY, off-grid products for the future.

And partly to offer alternative to the new DOE energy standards for water heaters due april 2015... that generally mandate expensive and complicated water heater designs that might not be DIY-friendly.

And partly to answer the question if a DC water heater can be made...

Of course anybody can connect solar panel to element that is attached to a plastic bucket, and heat some water. Drill 1" hole for element. Buy short element... usually rated for 120 Volt... and heat some water. No thermostat or ECO or safeguards... just hot water from the sun.

The DC water heater idea does not address the issue of powering a home with DC.
I don't know anything about that.
As I recall, Edison's DC voltage was 48V... and most off the shelf parts... such as golf cart, and electric vehicle relays etc are rated max 48 VDC and sometimes 96 VDC... with up to 250 amp rating.

They manufacture big DC switching relays for commercial solar arrays... to change the strings of panels so the electric output can be maximized as the sun changes during the day.

We've been working on the DC water heater design, and testing since December. It works, and we're trying to fine tune the array, and the photoeye design, and other tweaks ... to give enough hot water without overclocking the Omron relay or element.

Our research is not done... but primarily we want others to view the project with their solar expertise and build something else that's better.


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## Piedmont

As others have stated, a DC water heater is a poor idea compared to one that runs fluid. Sunlight does not convert to electricity very well, to the contrary it converts to heat well as I'm sure you've touched a tool sitting in the sun for a while. 

About 5 years ago I installed a 3 panel solar hot water heating system that runs glycol on the roof of my house after investigating a PV hot water heating system. After going to solar fests, doing the research, I was quoted $28,800 for a PV system that would heat my hot water in summer and be pretty useless in winter and this didn't include a tank. A flat panel hydronic solar company (the company I used is Radiantec http://www.radiantsolar.com/solar_packages_and_pricing.php) I did the 3 panel system with 120 gallon tank and after buying it got around $3,500 back from incentives. It takes seven 4x8 PV panels to heat as well as a single 4x8 hydronic panel... imagine my 3 panel FP system heats water as well as 21 4x8 PV panels... but cost around $3000 while a 21 panel 4x8 PV system would likely be about $50,000+. PV panels are around 11% efficient some can be up to 15%, and the hotter they get the worse their efficiency, and if you block one cell of them the efficiency of the entire panel typically drops 50% because the blocked cell becomes a resistor the others have to overcome (some have tech to avoid this). Whereas, a flat panel heating fluid is incredibly efficient heating water from 50F to 80F, very efficient from 80F to 110F, good to 130F, and then poor over that which is a good thing it prevents overheating and damage to your tank (my solar tank warns temps over 160F deteriorate the tank). 

I'll just leave it at that, if you have extra PV and don't know what to do with it that's fine. But if you want to buy this for heating your hot water you're going to likely pay 35x more and get 1/7th the result than a hydronic solar panel.


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## geno03245w

Not going to dispute your research or water heater decision... there is no perfect answer that fits everyone.

Among commercial water systems, glycol recirculation is probably considered most reliable, and aesthetically pleasing... and maybe most expensive compared to DIY solar water collectors.

For saving money... DIY solar might be best option
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
http://waterheatertimer.org/Review-solar-water-heater.html

****************
1) $28,000 for PV solar water heater? That's high.
I assume the price was not DIY?
... and price included batteries, inverter, everything normally associated with converting DC to AC.

2) After incentives, can I ask what was final cost for your glycol system 5 years ago.
I assume the installation was not DIY?

3) Are the glycol incentives are still in effect? 
Or have incentives changed along with the new water heater standards April 2015?

4) Approximately what area of world do you live?
Warm climates favor water circulation collectors.
While cold climates favor PV energy collection
Windy location favors PV because it cools panels, while windy location is not best for water collector because it cools panels.

5) An important price consideration is durability...
Glycol systems last about 12-14 years? And that lifespan includes collection panels and storage tank... the entire thing.
PV panels last about 25 years? But that doesn't calculate replacement of storage tank, batteries, etc for converting to DC to AC.

I would estimate the cost comparison between glycol and PV is about 1:1.6. So if glycol system lasted 1 year... the PV system would last 1.6 years. Total cost comparison should consider this. 

6) Glycol system generally must be located near to water heater, for example on rooftop.
PV panels are more numerous and can be located farther away... on the ground... but greater distances causes more power loss... and PV panels consume a lot of space if located on the ground.

7) PV systems must accommodate resistance changes as solar output changes... as you noted... while glycol systems just heat or don't heat depending on solar output.

8) The DC solar water heater has different price structure because of simplicity..... no batteries or conversion from DC to AC.
My estimate to set up DIY:
$3000-3500 for 10-12 panels that last 25 years.
$400-600 for ordinary water heater (buy 2 before prices go up)
$600-800 for converting tank to DC and connecting to panels
Total $4000-5000. Or $200 per year.... which is expensive, when you can just put an old tank out in the sun and heat water.... except in north latitudes where PV can draw more power out of sun
Maintenance, and part replacement costs estimated $40-60 per year over 25 years. 
Includes new tank after 12 years in event the anode rod is not changed out each 2-3 years. Replace anode each 3 years, and cost could drop $15 per year. Today's prices.
http://waterheatertimer.org/Convert-AC-water-heater-to-DC-water-heater.html


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## Piedmont

geno03245w said:


> Not going to dispute your research or water heater decision... there is no perfect answer that fits everyone.
> 
> Among commercial water systems, glycol recirculation is probably considered most reliable, and aesthetically pleasing... and maybe most expensive compared to DIY solar water collectors.
> 
> For saving money... DIY solar might be best option
> http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm
> http://waterheatertimer.org/Review-solar-water-heater.html
> 
> ****************
> 1) $28,000 for PV solar water heater? That's high.
> I assume the price was not DIY?
> ... and price included batteries, inverter, everything normally associated with converting DC to AC. It was for an installed package that didn't include batteries. The government tested the FP panels I got independently for SRCC rating and from their rating mine produce 21,450kW per day after inefficiencies which should translate into a 6700 watt PV hot water system. There seems to be something low about your pricing, or it's not apples-apples. Per the government most PV systems people install are 4kWh with an average price of $32,500 per install. My coworker has a 16kWh system he did and it was $86,000. My other coworker is getting a PV system over $40,000 on his house. Spreading like crazy here because they don't pay for a dime of it the state incentives + the installing company sells the excess leaves the homeowner paying for nothing in the end. My state I think is going to go bankrupt if they keep this up.
> 
> 
> 2) After incentives, can I ask what was final cost for your glycol system 5 years ago.
> I assume the installation was not DIY? It's a DIY kit, has everything needed to DIY except pipe (pick up at local store), fittings, and insulation. Total cost after incentives was just under $3,000 for everything and I mean everything. But, $1000 of it was for electrician and a corrupt plumber because in my state you have to be licensed to do any electrical or attach to drinking water. The electrician charged $325 and spent a good portion of the day, the plumber charged me $785 for 40 minutes to install the tank. Told you the plumber was corrupt, he even used my scrap pipe from my solar and installed it where a previous tank was. I couldn't believe after about 8 solders and 40 minutes he leaves and mails me a bill for $785.
> 
> 
> 3) Are the glycol incentives are still in effect?
> Or have incentives changed along with the new water heater standards April 2015? When I did it it was no sales tax on anything solar, 30% back on entire project, 15% back from Federal, no increase in property tax. Now instead of a flat 30% back on entire project you get $ back per panel based on the kW rating. Since hydronic FP's have such a high kW output per cost ratio they actually cost around -$300 here after incentives now. Install 8 panels and the state will pay for them in credits AND give you a check for $2,400 beyond. Install 10 and they'll pay for them all and you'll additionally get $3000 (or whatever the max is).
> 
> 4) Approximately what area of world do you live?
> Warm climates favor water circulation collectors.
> While cold climates favor PV energy collection
> Windy location favors PV because it cools panels, while windy location is not best for water collector because it cools panels. I live in the cold parts of Massachusetts (far away from Boston). Cold doesn't affect solar much, just wind. It can be -5F and sunny and my solar will have the bottom of my tank over 120F. If 20F and very windy I can expect around 90-100F. Even so that's the very bottom of my 120 gallon tank. My solar is designed since we have 2-3 days of clouds/rain a week typically one day of sun and my solar turbo heats enough water for 2-3 days of coasting. Mine is not meant for day after day of sun, though it includes overheat protection.
> 
> 5) An important price consideration is durability...
> Glycol systems last about 12-14 years? And that lifespan includes collection panels and storage tank... the entire thing.
> PV panels last about 25 years? But that doesn't calculate replacement of storage tank, batteries, etc for converting to DC to AC. There's 2 kinds of Glycol systems I suspect you're thinking of the evacuated tube kind. Flat Panels are strictly made of glass, copper, and aluminum and the lamination technology binds the coating to the aluminum so it can't delaminate. If you saw todays Flat Panels you'd have a hard time finding any thing that can fail before 40 years, just the fluid running in the pipe over decades causes the pipe to get thinner and thinner and eventually it will fail. My house has original copper pipes and is 1962 and they're still going should be more than 50 years.
> 
> I would estimate the cost comparison between glycol and PV is about 1:1.6. So if glycol system lasted 1 year... the PV system would last 1.6 years. Total cost comparison should consider this. As mentioned I see no reason why a glycol FP system would fail within 40 years. The reason I chose FP's was because my in-laws have a solar house from 1983 with factory made FP's (not home made of wood, screws, see-through fiberglass, etc.). So far in 32 years they have had to replace a pump which was easy enough, otherwise their solar FP's are still going strong heating their house and hot water.
> 
> 6) Glycol system generally must be located near to water heater, for example on rooftop. All the solar installs here the water heater is in the basement and we run glycol pipes up to the roof through the panels and back into the basement. Attics here are ventilated to prevent ice dams so attics are typically the same temp as outside which can get below 0F... terrible place for a water tank  Everyone puts them in the basement and pipes the glycol up through the panels on the roof.
> 
> PV panels are more numerous and can be located farther away... on the ground... but greater distances causes more power loss... and PV panels consume a lot of space if located on the ground. You can put hydronic anywhere as well it's just pipe (though must be copper). PV system does take up a lot of room I calculated one would need a 24 panel (420 sq ft system) to heat as well as my 3 panel (96 sq ft).
> 
> 7) PV systems must accommodate resistance changes as solar output changes... as you noted... while glycol systems just heat or don't heat depending on solar output.
> 
> In short you can do it, not saying it won't work just that it's almost certain you'll end up with a lot more parts, complexity, price, space, and failures sooner than the alternative.
> 
> To see if there's solar incentives for your state (Federal should be 15% on entire project) you can check out http://www.dsireusa.org/


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## geno03245w

Thanks for your time.
Your answers are very useful for many folks who will see this post in the future.

Can I ask a couple follow-ups...

1) You say it was a DIY package.
Did you buy directly from manufacturer such as AO Smith or Rheem or Bradford White? ... or from another source?

2) Can you give general idea of the sellers or brand... or source people might be able to locate same-similar product on the internet?

3) Where did you get instructions?
Did instruction come from seller?
Are the instruction available online?


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## geno03245w

Want to add another question or two...
I shared your information with a PV guy. 
He has been studying both glycol and solar from a scientific point of view.

He pointed out some obvious things I overlooked ...
First of all PV is for the whole house, while glycol is for water heating only.
Also that PV panels have dropped in price from $5 per watt to $1 per watt in year 2015.

I don't know if you benefit from selling glycol systems... we all come from somewhere.. you obviously seem genuine. Do you benefit from selling glycol systems?

the more I think about it, I am skeptical that glycol panels last 50 years as a general rule.
I want to add caveat that some areas of the world get less solar intensity than other areas... and as you said, your system is not made for several consecutive days of sunshine which matches your relatively cloudy environment and possible longevity of panels ... while areas like Texas get a solar whooping nearly every day of the summer.
So the solar panel would probably last longer in cloudy Mass than sunbeat Texas.

Also it seem improbable that a solar indirect tank would last 50 years even with the cleanest water. If bottom of tank is 120F, then top must be 140F? Chemicals percolate out of water at 140F.
Do you have to drain and clean the tank each 6 months?
Do you change the anode rod every 3 years? Around this area of Texas, our well water causes a lot of odor problems.
And the hard water scale cannot be cleaned out of a tank completely...

Certainly the glycol systems deteriorate over time because it is constantly expanding and contracting.
Of course we all know copper pipe lasts many decades... but the solder joints do not always have same lifespan... we used to remove rooftop systems occasionally after the panels developed leaks... but this was years ago. The solder joints gave out... maybe because the panels flexed in the sun.

Also, the government charts show comparable 12-14 year lifespan for solar glycol units.
Of course you mentioned different panels, implying that some panels last longer than others.

Your price showing $6800 before incentive seems about right for DIY.
But also out of reach for many folks who want hot water without paying thousands up front for a promised benefit later.... which of course is same problem with DC water heater costing $4000-5000 up front, with average hot water cost $260 per year spread over 25 years.

You did not mention how much additional electric power you used to heat water in your area.
Can you give some insight how much electric power is consumed to heat your water.
I realize most people don't put electric meter on their water heaters, but you probably have before and after electric bills that give approximation.

You insight is valuable for all concerned folks


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## Piedmont

Sorry for the long email... I'm not sure I can keep this up there's a lot of heavy questions asked  


If I worked for a solar company I would have more than just solar hot water heating I would imagine. I like probably most, was curious why I was quoted $28,000+ for PV solar that would only supply enough heat energy in summer vs. $5,000 for a system that was able to heat all year long. Finding out PV's are 11-15% efficient, comparatively complex, and expensive while FP's are 60-85% efficient, simple, and inexpensive there isn't really much more that needs to be said which should be used for heating purposes.

Did they take the link away from where I got my solar? I posted it prior... it's http://www.radiantsolar.com/solar_packages_and_pricing.php as they say _"Installation packages__ are "do it yourself friendly"". _The one I got is the 3 panel and 120 gallon tank package. The comment solar isn't likely good in Texas because it's too sunny is like saying you shouldn't put windmills where it's windy. If it's constantly sunny the size can be much smaller, installation less costly, and payback much sooner. I calculated one 4x10 FP panel should equate to a 3000 watt PV system for heating hot water in TX though it depends looking at Texas state incentives. They are usually only if you live in certain cities. Some are very strict like, it has to be a system that can heat enough hot water for 5-6 people, the tank 80 gallon minimum used strictly for solar in a pre-heat design (meaning one tank is preheated by solar which feeds another tank that you draw from), and glycol based. That's a pretty robust system I think for Texas, even my system doesn't meet it!

Because of all the people making FP's in their garages in the 80's out of wood, glue, and tape the government created the SRCC, a rating authority for solar heating. An SRCC rated Flat panel has been tested, rated, performance posted, and gone through a rigorous stagnation test to ensure it can withstand extended times of a pump failure (or power outtage) and extreme temps without damage to the panels. No worry TX is too sunny.

I did state PV for heating makes sense if you have PV already and just looking for someplace to put the excess. If installing a PV system strictly for heating, all I'm saying is it's not the right tool. 

You can read up on the solar panels I got they're AE-32 and can be read at http://www.aetsolar.com/literature/AE_Collector_Brochure.pdf notice the fins have a 30 year written warranty and the panels are designed for 30-50 years of service. If you do a search for "how long does copper piping last" the answer is 70-100 years and includes the fittings. With copper it's not the fittings that fail (well just thought of compression fittings  I'm not sure you can use them in heating). Okay, barring compression fittings a soldered fitting slides over the copper pipe and is the thickest part. For it to fail you have to go through the pipe, solder, and fitting which you won't because the actual pipe next to the fitting will fail beforehand it's weaker. The copper pipes I've seen fail is where the person attached a different metal to the copper (direct steel to copper for example) as different metals in direct contact with each other with a fluid joining them forms an acid which eats the lesser of the 2 metals. Or, they ran the copper through cement, or pressure treated wood, something that causes 2 dissimilar metals to come in contact with a fluid joining them. The other is where a copper pipe freezes, it will split but I've not seen it happen at a fitting. So the copper piping should last around 70 years, the glass & aluminum over 300 years, leaving the connection between the alunimum fins and copper pipe the most likely point of failure and it has a 30 year warranty against failing, which is worst case. 50 years is reasonable. 

Heating/contraction doesn't affect longevity actually. Best explained by baseboard forced hot water heating which is probably the most common form of heating in New England. How it works is, houses have copper heating pipes running in the ceiling of the basement and these pipes are typically uninsulated. Any heat lost to the basement is gained in the floor above so it's not really considered a loss. Unfinished basements here are typically 45-55F so that's the temp of the water in our heating pipes the boiler is 160F to 180F. When your house calls for heat, you send 160-180F water through pipes that are 45-55F and you can hear them clicking and popping as the extreme water cycles through the baseboards. These houses have been doing that since before the 60's on original copper. Solar is far more gentle, my system turns the pump on low speed when the temperature of panels reaches 6F higher than the temperature at the bottom of my tank, medium speed when it reaches 10F difference, and high at 16F. The cold glycol coming in is slowly heated through 3 panels before it cycles down to my tank.

I'm not sure what you're considering a failure, I'm getting the sense you're trying to say the system should be avoided because in 15 years you may need to replace a simple expansion tank, if that happens that's the end of its life throw the system out and bring it to the dump. Like saying don't buy a car because the headlights on it will only last 10 years and when one goes out, you'll be calling the tow truck and having your car brought to the dump. The panels and plumbing won't be failing, any part that can fail is all in one spot called the plumbing mechanical package. There's nothing stopping you from say, every 15 years replacing the entire plumbing mechanical package if you want. You are supposed to check the glycol PH every year and there's a "spigot" for doing that.

Okay... next thing is temperature. Since I have a high quality solar tank it can go up to 160F after that wear is rapid. Here's the benefit of FP's... their efficiency is directly proportional to the temperature difference. For example, to heat water from the 50F ground temperature to 100F the efficiency of my panels is ginormous something like 2x more efficient vs. heating from 100 to 140F. Going from 140F+ the efficiency drops to probably 1/4 normal. The only times I've been able to get my solar to heat the water in my tank over 160F was when I went on vacation the week of July 4th, each day was 90-100F+ and sunny. When I got home, my tank was 172F. However, the kit I have comes with a solenoid that opens the hot water in your house which you can set to go at whatever temp you want. So if you go on vacation you can set it to open anytime the water tank gets over 160F. When it does, it will dump hot water down the drain cooling the tank down. Second you can also set your solar controller to always run when the tank temp is above 100F so while on vacation at night it will continue to run when the sun isn't out and cool your tank down. 

Electricity... I went from an oil boiler to a solar tank. My oil boiler heated my house and hot water, and was constantly idling to keep the temps 160-180F. My solar tank has an upper heating element, if my solar can't keep up the upper heating element kicks on and heats the top of the tank to 120F, the bottom is heated by the solar. If it heats the bottom to say 100F in winter then my upper element only needs to heat the water 20F. If it heats over 120F then it's heating the entire tank strictly by solar. In February I shut off the heating element breakers to the tank so our house is strictly solar hot water only (no electric or oil backup) and I turn it back on in late November. Maybe twice during those 10 months I'll turn the breaker on if we have say a week of rain. For electricity from Feb - Nov it should be $3-$4/month and December & January it's hard because we have the Christmas lights. I really don't know what to tell ya since we only have the electric heating element on in our tank for 2 months, and even so the solar on sunny days will heat the tank, otherwise it's just boosting. I did get an electric meter that goes on the breaker panel so I can monitor my electricity just arrived. When I turn on the breaker to the water tank in December I'll be able to measure. 

Phew... :laughing:


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