Author Topic: cheapest way to heat with PV  (Read 7378 times)

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cardamon

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cheapest way to heat with PV
« on: September 10, 2014, 10:46:20 PM »
Say I have a bunch of real cheap PV, like .34 watt and all I want to do is heat water.  What is the cheapest way - and by cheapest I mean best compromise between cost and efficiency?  Maybe connecting directly to the right combination of series/parallel heating elements with a current sensor to switch the resistance between sunny and shade modes?

SparWeb

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Re: cheapest way to heat with PV
« Reply #1 on: September 10, 2014, 11:55:22 PM »
Um...  how about giving up on that plan altogether.  I'll even take those panels away for you.  What was the seller's phone number?


There will be a limit to the number of PV panels that can be hooked up to one water heater tank at a time, no matter how cheap they are.  The power rating of the heating element inside it can't be overloaded by the power provided by the panels.  Kind of stating the obvious, sorry.

Find a used electric home water heater that's still intact, check the resistance element still works, wire up the PV in strings that provide maximum voltage within the rating of the element.  Factor in cold temperatures and full sun when working out the max voltage.

Switching strings to boost the voltage only works if the sunny-day configuration has two parallel strings of panels.  Only then will there be any point to switching anything on a cloudy day.  In this case, double the voltage by switching the strings from parallel to series.  I wouldn't use a current sensor, but a voltage-sensitive circuit, to detect a cloudy-day situation like that.

I guess the number of panels in parallel is also limited by the current rating of the heating element, with respect to the short-circuit current of the panel.  Depends on how many PV panels you can get so cheap.

I've been assuming a direct connection so far.  For safety, a fuse or circuit breaker is essential.  Would you be planning any MPPT or regulation electronics?
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OperaHouse

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Re: cheapest way to heat with PV
« Reply #2 on: September 11, 2014, 12:52:41 PM »
I heat water with excess PV and it works great.  About 90% of may PV is excess capacity.  I use a $10 UNO to control everything and have two tanks, 10 and 20 gallon in series.  These have 120V heating elements (2000 & 1500W) and that is a decent match for 36V panels that run at a power point of about 52V.  YOU HAVE TO RUN AT POWER POINT, otherwise you will not even get half the power.  That is fairly simple to do with only a small capacitor storage bank and a FET.  Switching heating elements to match the panel just can not be done.  Computer controlled PWM is the only way to go.  Preferably it should be done with 48V panels.  In bright sun I go up to 56V wasting some power.  I was given these two office size tanks.  I heat the first use one to 45C and then switch heating to the second one.  Often I take a shower and when I finish the water is hotter than when I started.   I think this is the product of the future.  Direct heating is more efficient, but what a pain running plumbing up to the roof, having pumps and the worry of freezing.

analog man

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Re: cheapest way to heat with PV
« Reply #3 on: September 12, 2014, 02:03:23 AM »
It will work fine. Just select the right element for the panels voltage/wattage.
Been running 4 195 watt panels hooked in series. I bought a 3000 watt or maybe it was 3600,  220 or 240 volt element. Im going from memory but if I remember right I had 3 panels hooked up to this element at first, after a couple months I found I could be short on hot water sometimes, I added one more panel bringing me up to 780 watts, at 800 watts of panels I have free hot water I am never short. but I only use these panels from roughly  end of march to end of sept or mid Oct, as I heat with wood and my hot water tank is heated by the wood stove in the winter. Is it a waste to use panels only half a year...yes... do I care...no. Are there inefficiencies ...likely...do I care...no...Its free hot  water and I got the panels cheap enough. Just make sure your area gets lots of sun, mine does...nice long sunny summer days. just finished my second year of using them this way
I wont give you advice on how to hook it up as I am not quallified in anyway I will just say if its a typical hotwater tank (mines not) you may need some controls, talk with someone who can help you in that regard.

joestue

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Re: cheapest way to heat with PV
« Reply #4 on: September 12, 2014, 12:21:37 PM »
find a used dehumidifer on craigslist and run it from a VFD, wired up to your solar directly.

run the VFD from a 0-10 volt signal rather than a potentiomenter and wire up an arduino or something analog to regulate the speed to properly load the solar panels.
240vac VFDs will generally work from 270vdc to 370vdc.
120vac units will work on half that voltage.

There is usually no problem using a 240v vfd to drive 120vac motors, but you have to set the volt/hz curve properly, also derate them
to drive a 1 hp dehumidifier you will need a 2 hp 240vfd for a number of reasons and you may want to throw more microfarads on the dc bus. (bypass the diode block, feed the vfd directly from solar)

building a heat exchanger without opening the refrigerant line isn't difficult either, just don't overheat the copper when soldering it with lead free plumbing solder to fabricate the heat exchanger. (don't use braze)
the aluminum fins can be cut off with a sharp knife, they are the easiest thing to remove.
the steel plates on both sides are the most difficult thing to remove.

the copper will probably still be soft so it is usually not very difficult to collapse the entire condenser into a 3" diameter bundle which can then be inserted into a pipe and closed off with some creative soldering and fitting up of copper plates to join to the refridgerant tubing.

of course some here will suggest you have an additional level of isolation.
so if you create a second loop you can use pvc or plastic and glue instead of soldering to the live refridgerant lines.
but then you need a second pump..


anyhow, if you can get a VFD for cheap and a dehumidifier for free.. then you can get a 2 or 3:1 coefficient of production which might equal you 500$ in solar panels.
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OperaHouse

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Re: cheapest way to heat with PV
« Reply #5 on: September 12, 2014, 12:48:13 PM »
"It will work fine. Just select the right element for the panels voltage/wattage."

That is just totally wrong.  It works but you will loooooooooooooose most of the power except at the peak hours of the day. 

Ebay has NYLE heat pump water heaters from a utility Hot Shot program if you want to run a VFD at $100 each. I bought two of them and  run one at my house. These were ones that died an early death from control board problems.  It was a moron programming job anyway and wish mine would die so I could replace it.  You will still need something to control the panels at power point.

analog man

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Re: cheapest way to heat with PV
« Reply #6 on: September 12, 2014, 11:35:25 PM »
"It will work fine. Just select the right element for the panels voltage/wattage."

That is just totally wrong.  It works but you will loooooooooooooose most of the power except at the peak hours of the day. 



You crack me up, yes it works thats the point...no fuss, simple, no pumps, motors, valves, etc.
How come you arent saying solar panels are all wrong because they dont work at night?
Yes, I am only hitting max power out roughly in the 12 to 3 period, but even in the shoulder hours whats produced adds up.  it adds up to give me what I want, and thats totally right.....
Free hot water for the rest of my life, how can that be wrong?
In the case of the OP he said he can get them for .34 cents a watt, thats incredible...good for him. I bet if he bought 1600 watts (twice what I have for water heating) he could have free hot water for 3 people for sure, and assuming good water conservation practices maybe 4 people, and all for a cost of 612.00..... Thats a home run hit if you ask me....Why arent more people doing it?

I have mine laying on a roof that extends out from the side of the house because the roof is close to the deck I built a frame for the panels thats raised off the roof and a screw type car jack that has a long handle welded on is used to tilt the panels east for the morning sun and west for the afternoon sun. I usually just leave them pointed flat and south, but if I am home I do step out on the deck and crank them for a little better performance. Anyway each to there own, it works for me, and will keep doing so for the rest off my life trouble free

OperaHouse

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Re: cheapest way to heat with PV
« Reply #7 on: September 13, 2014, 02:21:03 PM »
If you had access to a power point system, you would use it in an instant.   The OP says, "Maybe connecting directly to the right combination of series/parallel heating elements with a current sensor to switch the resistance between sunny and shade modes?"   If you are going to throw some electronics together, the cheapest way is with a UNO, a FET and some capacitors.  And if you want to use some water as early as you can, only a power point system can supply it.  Early morning off axis results are dramatic.  As far as low cost it was $10 for the UNO and free parts out of an old UPS.  You could have had the same results with two fewer panels.  How cheap is that.  Anyway, much of this discussion was for JohnWilliams who is interested in heating and appears to have the technical capability to construct it.  This discussion is in CONTROLS and directly connecting PV to a water heater isn't a control.
« Last Edit: September 13, 2014, 02:30:28 PM by OperaHouse »

Bruce S

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Re: cheapest way to heat with PV
« Reply #8 on: September 17, 2014, 10:04:37 AM »
analog man;
We the GMs and Mods really would like NOT to interject in posts. However we do at times jump in to keep things calm.
Couple things you might remember when posting.
Try to stay on track of what the OP is asking for. Sure even the GMs and MODs will get off track, but we generally try to stay nice  >:( .
Try NOT to slam fellow posters, especially one who has stood the test of time such as Operhouse who lives by the systems he's built.
IF you feel the NEED to slam someone, type it up, go take a moment to think about it, then come back re-read what you type up, then post if you're sure that is the route you want to go.
IF you mean it as a joke , remember to insert smiley faces.
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dnix71

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Re: cheapest way to heat with PV
« Reply #9 on: September 17, 2014, 09:13:17 PM »
I think you all are missing the obvious here. If you have lots a panels the cheapest way to heat water would be to put some thermal solar collector pipes under the panels and use the solar PV to pump the coolant to a heat exchanger in your water tank. All you would need is a thermostat and switch to regulate the pump. Cooler panels produce more electricity and you want the hot water.

Solar thermal direct is the cheapest way to heat water. The solar PV is just a substitute for grid power to pump coolant.

DamonHD

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Re: cheapest way to heat with PV
« Reply #10 on: September 18, 2014, 01:41:09 AM »
Given how PV prices have fallen, and the fact that PV doesn't need some elements such as anti-freeze or drainback or stagnation protection, and that PV can continue to work when it's too cold for thermal, eg in UK winter, I no longer expect thermal to be cheaper than thermal.

Also it is possible to buy PV/T panels already containing the pipework suitable for water or refrigerant (heat-pump) use, from which you can get several units of heat for each unit of electricity.

I very much dislike the waste of exergy implied by electric resistance heating, but sometimes it may be the right thing to do.

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OperaHouse

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Re: cheapest way to heat with PV
« Reply #11 on: September 19, 2014, 12:19:47 PM »
I am envious of your situation.  Sometimes more panels are not an option.  Technically, all my working panels are not even on my property.  I don't have permission but that is not likely a problem. Just purchased another 100W panel so I can have a matched string when I go to 48V next year. The replaced 90W will go with some other near dead panels on the roof but they get less than two hours a day. No net AH gain is expected. There is no suitable location on my property to place any more panels that would produce useful output.  These panels have to supply all power plus hot water.  Efficiency counts.

A Solar Divide is approaching.  A majority of people will not have significant access to solar because of where they live.  Someone will  have an active solar array and a neighbor will add a second story or plant a tree.   Who owns the sun will be the question of the future.   Case law is just starting on this.

cardamon

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Re: cheapest way to heat with PV
« Reply #12 on: October 04, 2014, 10:13:55 PM »
Sorry for the long delay in replying, IVe been busy,  Thanks for the replies and ideas.  sparweb, you are welcome to the panels, go to sunelec.com.  Toying with the idea of grabbing several KW just for water heating.  At that price, one has to really thing about how much money in controls it is worth putting in :)

gww

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Re: cheapest way to heat with PV
« Reply #13 on: October 04, 2014, 11:52:08 PM »
Are the panels at sunelec the flexible 250 watt no frame panels for 49 cents a watt.  That may insue other issues.
gww

OperaHouse

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Re: cheapest way to heat with PV
« Reply #14 on: October 07, 2014, 11:08:02 AM »
I think they have been selling those 49 cent panels longer than the $300 Jeep in a crate. :)

Moderators, I have added the smiley face as per a previous comment in case I may have violated the Pink Unicorn Rule.

Bruce S

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Re: cheapest way to heat with PV
« Reply #15 on: October 07, 2014, 05:22:42 PM »
Operhouse

A kind word often goes unsaid BUT never goes unheard

cardamon

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Re: cheapest way to heat with PV
« Reply #16 on: October 08, 2014, 11:38:06 PM »
Are the panels at sunelec the flexible 250 watt no frame panels for 49 cents a watt.  That may insue other issues.
gww

No these were mounted in rigid frames, sharp, .34 per watt.  This was a month ago so those specific ones might not be available, I havent checked........

analog man

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Re: cheapest way to heat with PV
« Reply #17 on: October 08, 2014, 11:56:21 PM »
analog man;
We the GMs and Mods really would like NOT to interject in posts. However we do at times jump in to keep things calm.
Couple things you might remember when posting.
Try to stay on track of what the OP is asking for. Sure even the GMs and MODs will get off track, but we generally try to stay nice  >:( .
Try NOT to slam fellow posters, especially one who has stood the test of time such as Operhouse who lives by the systems he's built.
IF you feel the NEED to slam someone, type it up, go take a moment to think about it, then come back re-read what you type up, then post if you're sure that is the route you want to go.
IF you mean it as a joke , remember to insert smiley faces.

First Bruce, I missed your post, I dont think I have been back here since maybe after operhouse posted and I thought to myself what a lass.

What were you going on about? keeping things calm? who wasnt calm? what wasnt calm? I was in stitches, I thought it funny as hell, someone not liking the way I was doing something, but admitting it would work, which it does.

Slam posters?.....What? I didnt even dissagree with his suggestions to the op... I assume what he suggests will work fine, I only offered a alternative suggestion, in case you didnt notice the slam was the other way around, but you didnt hear me complain about it. I have big shoulders.

"Lives by his systems"  interesting.. you assume I dont? I dont talk out of my ass..if I suggest something you can bet I have done it, am doing it or set up others who are doing it.

Bruce, what you and maybe other are unhappy with is I havnt toed the line...you know the mppt line, your sponsers product.. not that I dont think its a good one, just that there is never one way to do anything, other considerations, other circumstances, other preferences..lots of other ways and reasons to do something whether you agree with them or not. There was a time you could come on this board and explore options, weigh alternative ways to get the job done...frankly its been years since thats so..may as well just have canned answers now... and the same dozen guys  patting each other on the back and repeating the same mantra.. Let me hand you back your membership right now, delete me, I wont be back.

For anyone else who was interested in water heating with panels, and if this post isnt deleted I can tell you direct water heating with panels works fine, more and more people are doing it, My cousin just set himsellf up using his electric hot water tank. Picked up a 240 volt element from canadian tire, He told me the resistance is 12.5 ohms.screwed it into his tank, hooked 4 250 watt Canadian Solar panels in series. I think these are 8.5amps at 29.5 volts or so. The resistance goes up a little when warm...maybe as much as a ohm, so 118 volts/ 13.5 ohms= 8.7 amps  very near a perfect match. Its just been since spring but he tells me its made all the hot water his wife and him use, dont know about into october as I suspect it might be coming up short now, but free hot water spring summer and fall sounds good to me....he did add a relay and thermal for high limit protection . The relay is a potter and brumfield PRD-11AJO-120 20amp at 125vdc though I have used this relay up to 200 volts dc and 35- 40 amps no problem at all, it has mag blow out, and is good for billions of cycles. he tells me he does not think its been needed as the hot water used has been roughly whats produced,but the wife likes the peace of mind of it for safety.

When you find yourself on any board anywhere where there is only one way to do anything....then its time to tell them to pound sand....See you  on the flip side....over
     





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analog man

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Re: cheapest way to heat with PV
« Reply #18 on: October 09, 2014, 12:46:11 AM »
Hmmmm. I just checked and I cant delete my account, or maybe I have missed where to do this but I dont think so......so Bruce get operahouse to roll off you and  ;D delete my account or I will come back and post a pic of my rooster or something and force you to...I dont bluff...ever ...I wont tell you twice ;D

Bruce S

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Re: cheapest way to heat with PV
« Reply #19 on: October 09, 2014, 09:44:20 AM »
Dude ;
I don't EVER EVER threat ! and I'm not smart enough to be afraid of any human .
I have no problem locking your account forever.
Deleting ? NOPE not gonna just because I don't have to  :-*
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This site is held up by bailing wire and gum.
Another GM may move this part of the post, but ,,,

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