Instructables
Some time ago I bought some PV cells (6"x3", from rebeccayi0904 on ebay, very nice seller!) with intention of building a PV panel (after reading a plaethora of instructables on solar panels here!).  While testing the individual cells out there in the sun I noticed that they got quite hot.  I then realized that PV panels convert to electricity only about 12% of the solar power that gets to them.  What about the rest?  It becomes heat (about 88%).  I figured that perhaps in the same surface one can harness both the electricity and the thermal energy of the panel....

 
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Step 1: Overall panel characteristics, items, etc.

I am not going to repeat all the details on how to build a solar panel, there are plenty of other instructables for this (search tool is your friend!).  I will give some basics, though... and then focus more on the "hybrid" nature of my panel (PV + thermal).

General characteristics:

- about 0.5 m^2 area, at a maximum of 1 kW/m^2 of irradiation and 12% efficiency this should produce UP TO 60 W of electrical power.  (at the same time this means that about 440 W of thermal power could potentially be harnessed!).

Materials:

- 36 cells, 3"x6".   Cost:  about $150 from rebeccayi0904 (ebay, nice seller!) for 80 cells (used 36 for this panel).
- aluminum backplate (26"x32", can't remember thickness):  about $10 in a sheetmetal store.
- small roll of Begquist sil-pad 400, cost about $50 from ebay (can't remember seller)
- glass front cover, about $15 at the hardware store
- aluminum rails for borders, about $12 at the hardware store
- about 25 feet of 1/4" copper pipe, about $20 at the hardware store
- some 2-3 tubs of silicone caulk
- aluminum flux paste from McMaster-Carr (about $30, but you can buy a smaller quantity, I only used about 1/20 of the tub)
- solder
- a 12 V water pump, search on ebay "12 V pump laser & cpu cooling", cost about $10.

Caution: Aluminum Flux Paste is a very nasty material.  It contains fluoride and if handled improperly it can cause serious harm to you.  Read all instructions and the material safety data sheet (MSDS), and if you are not 100% confident that you can work safely, do not.
shortw4 months ago

Would be a lot easier and cheaper to use black pvc tubing.

Very nice.
(1) Note that you REALLY don't want to use broken cells if only a few are nbroken as it affects the WHOLE panel output in proportion to the % area missing in the ONE cell. eg if a single cell has 10% area missing then the whole panel output will be 10% lower if all cells are otherwise the same. This is because current out is proportional to cell area while voltage is essentially nnaffected by area. So if you wire an -800- 800- 800- 600- 800- 800- mA cell string in series the 60- mA of the lowest cell "throttles the while string. In many cases if you have only one low output cell you may be better off shorting it out than leaving it in. eg if you have a 36 cell 18V nominal panel, if you short out one cell you get a 17.5V nominal panel. In practice it wioll usually be somewhat higher and in most cases when driving a 12V system with Vmax battery lead acid = 13.8V the 17.5V at full current is better than 18V at reduced current.
(2) The cooling water will add 5% to 10% to panel output on a hot day. I have tried running a very thin film of water over a panel surface with excellent results. Needs a continuous water supply or a pump :-).
robbytesla2 years ago
A very good instructable. Is it possible to double the copper tubing to increase the efficiency of your heat exchanger?, Like two staggered "U" configurations both interconnected? Also what about adding (radiator) coolant to increase the heat transfer and use that in conjuction with a secondary heat exchanger to heat water or preheat water for the house?I will follow your work , you are doing research in a field and opening doors to many of us neophites. Thank you again for your article.
servant742 years ago
Did you figure how much additional electricity you get from the PV with the 'cooled' vs 'not cooled' use?

Cooling the PV is supposed to allow them to be more efficient.

Thanks ... Jack
That thought came to mind as well but in a different manner. Solar hot water and PV may not be compatable. The water temperature that would be good for PV may not be satisfactory for domestic hot water and vice versa.
Respectfully aesthetics is a relative topic,relative to the individual. Personally I go for function first aesthetics last. All I can say is to look for collectors with the least amount of bulk & can be painted to match the surfaces the are mounted on. The frame and mounting hardware can be painted, not sure how to mask the actual collector while retaining the function. Was a time a TV antenna was a bit of a status symbol, but a lack of one indicated we can afford cable TV also a bit of status symbol :) Perhaps a good decorator could give advise how to mount a collector so it would blend in with other structural elements?
Yeah you can cover them in a thick coat of paint the same color as your roof.

Can you tell me what exactly is "dis"-pleasing about them? I really wish you could describe in detail what it is you object to about them because a local h.o.a. forbid its members to install them for the same reason (yet water panels, not PV were OK.. why?)...If we could understand this phobia of the looks of PV panels, maybe we could do something to make it less objectionable to those who find it revolting....

If it's the color, there isn't much that can be done about that without infringing on the panel's efficiency... They must admit all the blue light they can which means red to match roof tiles or green to match trees is out of the question. But purple or cyan might be possible..... :)

What's interesting is that the removal of heat from the thermal section should actually help act as an active cooler for the PV section, BOOSTing its efficiency!

:)
snotty mcarrell2 years ago
Environmental apocalypse is pretty ugly too.

Sometimes I wonder if we hesitate to be sustainable because changing our ways would mean we've doing something wrong. If we kill for oil in Iraq, perhaps subconsciously we must believe this was the correct thing to do; otherwise we would be accessory to murder. And that's an uncomfortable conclusion where cognitive dissonance kicks in. Thus we choose coal and nuclear over wind and solar. Which is ugly? Which is pretty?

Just a theory.
However, if you paint the copper black you shouldn't have that problem, plus you'll have the added benefit of even more efficient heat transfer.
patenaude4 years ago
 It seems like mixing copper and aluminium is going to cause corrosion problems... probably on the aluminum. I would also assume that the aluminum backplane is electrically connected to one leg or the other of the cell, meaning you might be shorting all the cells together, wouldn't you?
Oops, I just spotted the sil-pad... so that's taken care of, but I'm still concerned about corrosion.


carlos1w (author)  patenaude4 years ago
Probably would be an issue in the long run (years?), but for a prototype it is probably OK (months...).  I guess it will be important to keep the whole thing dry (at least where Cu and Al are in contact).  Hopefully my liberal use of silicone caulk will take care of it! 

Does anyone know whether there is some kind of hollow aluminum panel of the right dimensions that could carry water inside?  Something with a profile like this:

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Why not use stainless steel scrap sheets? Better heat transmission capability. Even though greater weight, can be thinner as its a much stronger material.
aluminium or even better copper are much better heat conductors than SS..
In even slightly damp conditions, copper is very prone to corrosion, so aluminum or stainless is preferable.
Stainless is a horrible conductor of heat:

Thermal conductivity is measured by the formula BTU*ft/hr*ftE2*F

Copper: generally over 220
Aluminum 73 to135, depending on the alloy
SS 304 or 316 is 9.4

Data source: Materials Selector, 1993

Even the "worst" aluminum has 7 times the thermal conductivity of stainless.
However, if you paint the copper black you shouldn't have that problem, plus you'll have the added benefit of even more efficient heat transfer.
evad carlos1w2 years ago
Look into Bosch or 80/20 structural systems.
donde214472 years ago
See size does matter. In size of panel and flow of water or current thru size of cable.
Dr.Bill2 years ago
When the water heats up are the tubes on the back of the voltaic section hot as well?

If they are hot then where is the cooling advantage?

I just don't see it.
shastalore4 years ago
Great idea!

I've always noticed that those solar panels really heated up in the sun, but never considered harnessing that extra heat to produce hot water. Wow! It'll be fun to see how this bright idea develops and spreads.

One tip: With my trusty little HotPot solar cooker, I could sometimes force through 3 gallons of ambient temperature water, to boiling, on a given day. But the real challenge was keeping that hard-earned water hot.

And those commonly used stainless steel vacuum bottles just can't hold their heat for more than a couple of hours. You see, the neck of a stainless steel vacuum bottle is a serious design/materials flaw that allows heat to escape.

But glass-lined vacuum bottles, although fragile, can really hold their heat. For example, a typical 3 liter pump action airport pot, full of boiling hot water, will still be:
   - Scalding hot 24 hours later.
   - Hot 48 hours later.
   - Warm 72 hours later.

And several 3-liter glass-lined vacuum easy-to-use airport pots can be conveniently distributed to the kitchen, dining room, bathroom, and easily loaned out to a neighbor.

As boiling hot water has to usually be mixed with equal amounts of cold tap water, in most tasks, a 3-liter vacuum bottle goes a long way:  My wife washed and rinsed a large batch of dishes using only one 3-liter vacuum bottle of hot water -and the windows of the kitchen completely fogged up. That is testimony to the tremendous amount of energy stored in those bottles. And even unused warm water can be dumped back into the solar cooker, taking only half the time to bring back to boiling.
I'm fairly new at all this...no...I'm really new. Just one question. what is a 3 liter pump action airport pot and where do I find one? thanks.
Rather than trying to store the water, what my High School electronics teacher did with his solar heating panel was that he heated a reservoir, which was also sourced by his house's water heater. The solar heat reduced his water heater usage by doing a sizable part of the heating and was supplemented by the other heater when there was high use to keep the reservoir hot.

As an adaptation to your HotPot, you could try "recharging" you're already hot water since it would get up to temp faster than tap water. If you already have warm water from before, you shouldn't need as much newly heated water. Mixing leftover and tap would also speed up the heating process.

One draw back is that you then have to keep track of when the reheated water reaches the desired temperature to switch to the next batch.
mikesnyd3 years ago
You are right with the right solder you cna acomplish this but i think you would have been more successful with brazing the copper pipe to aluminum. Faster less fumes and no flux needed. Check this instructable out. http://www.instructables.com/id/Quick-and-easy-brazing-aluminum-copper-and-nonfer/
I really like your ideas so far. Nice instructable.
bahi3 years ago
This instructable shows the potential of solar based energy sources.
I wonder why there is no comercial product available using your dual
concept.
I tried to find something on the web, and this could interest you

http://www.websesame.co.uk/wp8.pdf

It's the DESIGN OF A DUAL FLOW PHOTOVOLTAIC/THERMAL COMBI PANEL.
You won't know for sure how a particular panel will perform until you build it and test it like this instructable shows .
By the way great instructable !!

IF a person had the regular type of flat plate solar collection system already then it is possible that the lower level heat coming from this type of panel could be used to preheat the coolant going to the flat plate collectors providing you built enough of these to get the coolant flow rates that you need for 2 arrays plumbed in series.
Run it through this type pf panel first then to the flat plate collectors.
You could even use the same pumps and not have to add any.

I just wonder though if a person would need more pump volume (i.e. a multiple speed pump) on a really good solar collection day to increase the flow a bit so as not to overheat any of the panels?

I guess I'll find out when I build it.

As long as the home built panels are to be used for things off-grid then there won't be any legal issues with certifications on the photovoltaic panels hooked to the power grid.
carlos1w (author)  Mechanic20113 years ago
Thank you for the comments (this and the earlier one, I am responding to both at once).

1) I used the thinner pipes because they were easier to bend and cheaper (I had already spent much more than I had planned, note: it is possible to use a cheaper insulator than the sil-pad if you are careful enough even tar paper will do). For this size panel I think that the 1/4" tubing is sufficient (I think it is hard to believe one will be able to collect more than 50% of the sun light). If anything, I would have liked to use a thicker aluminum backplate (wasn't patient enough to wait for one, and this is the thickest I could source locally). Another thing would be to place the pipes closer together.

2) For larger panels you may want to have larger water flow to avoid the chance of it heating too much (at which point your heat capture would drop drastically). If you have several panels, I would probably connect the pipes in parallel rather than series, again because once the water becomes too hot your heat capture will be reduced.

3) Please check my comment on "May 14, 2010. 7:31 PM" about aluminum extruded panels. I think these are used for the side walls of 18-wheeler trucks and maybe are not too expensive if you can source them (I couldn't). This will be the best option (no soldering, best water flow, best thermal connection, probably quite good rigidity).

4) Also, please check my comment on "Nov 14, 2010. 3:01 PM" about aluminum and copper brazing without flux. I bought some of these products on ebay and they work great (and no nasty fumes, or at least not that I could tell). Note that you do need to get the materials quite hot for this technique to work (hotter than tin soldering).

5) Please give me an update (even better, post an instructable and put the link here) when you build your system!!!

Wow this is a great instructable !!
Thank you for posting it .
I have been looking for for one like this .
I want to build from scratch a whole array of these types of panels.
If you have a good thermal conversion/extraction from this panel , you might be able to get around 800 BTU per day/square foot of collector.

I have one question the though , wouldn't it be better to use 3/8" copper tubing ?
From 1/4" to 3/8" tubing would increase your flow of coolant 2.25 times.

I realize the coolant will have to flow through it slowly to pick up the heat but if I have a whole bunch of these on an array together then the flow becomes an issue.
What do you think ?
Foxtrot703 years ago
Love the Instructable, a friend of mine is overhauling the tracking system on his photovoltaics I suggested this Instructable to him. With the back panels as you show the tubing, better heat transfer can be accomplished by brazing the tubing to the aluminum. Another method of heat transfer would be to use a series of aluminum angles brased to the back side, this would give more surface area for air to pass and improve cooling.
MacOSJoey3 years ago
Great instructable! One idea: Run the pipes inside of the panel instead of behind it. I know you don't really have a lot of room on this panel, but if you made more room and had the pipes run alongside the cells (assuming you don't have any leaks), you should be fine and have hotter water.
dimovi4 years ago
I don't know how useful that heat is, however the solar panel is going to be more efficient the colder it runs. So, you should see if the heat you remove from the panel improves your efficiency enough to justify a water pump.
carlos1w (author)  dimovi4 years ago
The pump is not solely to cool the cells, it is to extract heat for heating water for household use. 
Of course, if you put the storage tank HIGHER than the top of the absorption system it will self-circulate, ( simple convection) and automatically stop circulation when the sun goes down, and the collector is the coldest part...this leaves the opportunity to harvest the hot water (take a shower). No need to process the power/energy any further. Hot water is a pretty expensive commodity, energy-intensive (carbon-polluting!) and it's by far the best way to harvest solar energy. Twin-walled polycarbonate roofing is a much larger and more durable example of the soft real-estate sign material. It should only be sealed using a neutral-curing silicone. I used Polyurethane (Sika-Flex) on a project, and it caused bad cracking of the Polycarbonate. Also, I'd check possible leaching of nasties from the polycarbonate, and any other plastics in the system.
Using a convection circulation, you would need to use considerably larger pipes.
carlos1w (author)  devonfletch3 years ago
Thank you for your comment! Convection would work, though with such thin pipes I am not sure it would be fast enough, and sometimes forcing the circulation with a pump (in this case solar powered too!) would be more convenient. Regarding polycarbonate: I have read that it may leech some chemicals into the water, so perhaps it would then need to operate with a separate circuit, and not circulate the water to be used. Then again, this is perhaps advisable for other reasons: (i) use of anti-freeze for safety, (ii) elimination of build-up problems in pipes (calcium, etc) sicne we would use a closed-system.
With sizeable enough system you could also recirculate it through an under floor network of tubing to provide radiant heat as well as just warm water for consuming.
bethehammer3 years ago
nice... solar power and heat exchanger... the water is not only heated but carries heat away from the solar cells, theoretically making them more efficient. this is a great start however you may want to put more "loops" of copper... perhaps using fittings rather than bending, or utilizing the pre-moulded panels used for solar water systems..
vontzy3 years ago
Carlos1w, there is another Instructable entitled "Solar-Thermal-Water-Heater-For-Less-Than-Five-Dollars" that might offer a less expensive way to collect the Heat from your PV array. Instead of getting the heat from the Sun the $5 Collector could absorb the heat from the PV array. The Copper Pipe alone, in your parts list, is $20. Love your instructable and hope merging the two ideas coulds save some bucks.
carlos1w (author)  vontzy3 years ago
Thank you for the reply. For anyone interested, the instructable is http://www.instructables.com/id/Solar-Thermal-Water-Heater-For-Less-Than-Five-Doll. Note that the above mentioned instructable makes it chep because they get the heat exchanger from the dumpster. This is obviously excellent (I love recycling!). I have thought about using a refrigerator coil instead of the copper pipe too but could not find one. I am also not sure how easy it will be to bond the coil to the back of the solar panel. Perhaps some glue instead of solder? (for the skeptics: you do not NEED a very high heat conducting material because the power per unit area is actually not that big, though obviously it is better to use something that is highly conductive)
carlos1w (author) 3 years ago
Please see this other instructable (http://www.instructables.com/id/Quick-and-easy-brazing-aluminum-copper-and-nonfer/) for a likely better way of bonding the Al and Cu without the nasty flux.
Skyriam3 years ago
Great idea and concept, congratulations!! One question: How exactly do you harness the heat of the water? You could also use peltier plates, although they are quite expensive for large builds like this. Thanks!
carlos1w (author)  Skyriam3 years ago
Hi Kal00! Thank you for your comment. The *idea* would be to use this to heat water for household use. It seems the conditions are ideal (heat water to 40-50 C, perfect for dishwashing, bathing, etc) and the cost would be quite low. The temperature differences involved are not so great to make for an efficient thermal->electric conversion (the PV conversion is more efficient) but the direct use of the heat is very efficient.

BTW: currently I use the panel to recharge some car batteries someone gave me and power a LED light system for my deck. Unfortunately I am not using the hot water part of the system now (too complicated for such a small system, but it would be feasible for a larger installation).
evad4 years ago
While I know aluminum is cheaper than copper sheet,  you might end up (after a number of years?) with the aluminum being eaten away by being in contact with the copper.  On the galvanic scale, copper is up near the top, one of the most  "noble" metals.  Aluminum is way low on the scale, (ignoble?) down below steel.  With condensation as an electrolite, or even humidity, a potential (voltage) is set up between the two metals, and eventually, the aluminum will begin to disappear via galvanic corrosion- basically, all three make a (weak) battery. 

I'd be curious to know if there is a voltage present:  put your voltmeter on the millivolt DC scale, one probe on the copper and one on the aluminum, and see what voltage you get out.
carlos1w (author)  evad4 years ago
I put my voltmeter with one terminal on the copper tubing and the other on the aluminum plate and the voltage measured is 0.0 mV (that is as low as it goes).  Would this mean that corrosion will be minimal?
Late to reply, I know.... Galvanic corrosion will occur even in the uV (microvolt) range... BUT, in practice, you needn't be worried. Something else will likely fail first ;) A pertinent example of dissimilar metal contact is the cheaply made mini fridge... If you were to take one apart (which I DO NOT recommend - you must destroy it due to the assembly process used) - you'll find copper tubing being used as the condenser in contact with the sheet metal (low grade steel) enclosure. Now if you were using a steel bolt in an aluminum fixture that needed to be taken apart frequently - then yes, it's something to consider ;)
evad carlos1w4 years ago
I'd say it's not happening...  As I said, you need three elements- the two dissimilar metals, and an electrolite like rain, or humidity.  I  should  qualify my statement by saying it would be more prone to happening if the unit was constantly outside. But, you seem to have it covered up pretty good.

I live near the ocean, and have a steel boat trailer... About 6 years ago, I repainted it,.  I used some stainless steel hardware here and there, and where the screw heads touch the steel, the steel is rusting around the head- not bad, but, I will replace them with steel this summer.

And I forgot to say- Nice project!
kmpres4 years ago
Interesting project, and well documented. Your attention to detail is just what I need to help me decide if I want to go ahead with a similar project. I have often thought of combining heat and PV in the same panel but have been discouraged by the fragility of the cells. The last thing I would want to have to do is to take down the panels from my roof (a very difficult task in my case) because of a leak or rain water got in and corrupted or shorted the cells. The panels should be rigid enough to eliminate the effects of thermal expansion and parts degradation and sealed enough to prevent water infestation. Commercial solar panels are usually maintenance free for 20 years or more but they're still too inefficient (12% isn't breaking any records these days) and still too expensive, so, I will wait for the efficiency to approach the cells used on satellites (about 35%) and the prices to drop. Also, .2mm is indeed thin, about the thinness of two sheets of printer paper. A good substrate is imperative for such a panel to last 20 years or more. You've a good start. I look forward to reading about improvements to your design.
danbenedix4 years ago
 Why not take the heat you are moving and run it across some peltier (thermoelectric) coolers.  These are the modules used in those iceless coolers.  This is my recollection of how they work.

When current is applied one side gets and one side gets cold to change the hot and cold side just swap the polarity.

Here is the neat part.  If heat or cold is applied they will generate current.
So since you are already capturing the heat and have a system setup to flow electricity why not tie the peltiers back to the inverter?
chamb4 years ago
Cool project:  I like the idea of using both the electric and the thermal power in the same surface!  Plus the flowing water keeps the PV cells cooler which improves their efficiency!!!  Construction seems well done and the photos are well taken and the explanations are good.  I particularly like the results you show on the last page.  GOOD!!!
RedMeanie4 years ago
I am just about to start building my panels. I bought from Rebecca_k too. Im going too add this to them, but my design for my panels is a little more strange! Not the typical rectangle or square. Mine will be designed to track the sun with a circuit Ive designed based on Redrocks circuit. I will post this with my panel build. They will also roll upside down at night and during bad weather and hurricanes. And now you have given me an idea, so back to the drawing board! LOL
All you should add is a solar tracker, they are easy to get the plans for just go to redrock dot com. I think he even has them assembled too and kits. These are so cool, they are very, very accurate.
Other than that, Bravo! Very good idea and Instructable!
carlos1w (author)  RedMeanie4 years ago
Thank you for the comments.  If you build a hybrid like mine (hopefully a much improved version!), please let me know.  What I think would be an ideal material for the backplate would be a "corrugated plastic" like the ones sometimes are used for storage boxes, etc.  They are essentially composed of a lot of small channels and water could go through them (the trick may be how to make a good link between these channels and the external pipes).
coro9.jpg
For my setup I will be using either 4" pvc cut in hlf in 8' lengths with the cells running the length of the pipe. The location Im going to be mounting mine is ideal for running a passive solar water heater through the back behind the cells. Im going to be mounting these vertically on the roof of my garden house. This way the Hot water will naturally rise to the top and I should be able to get the natural flow to work without having to use a pump.
Now I just need to figure out if I can get it sealed water tight behind the cells and what material to use. Also if I can find someway to mount the cells directly onto the back plate to get the best contact area for heat transfer. Im thinking to do this I need to either insulate all the solder points and contact strips or I need to find a Back plate that is not a conductor but has good heat transfer capabilities? Any advise? Im still gathering materials for this project so please ANYONE with advise, please give it. Of course you will be given credit in my Instructable once complete. 
carlos1w (author)  RedMeanie4 years ago
At least with the PV cells I got, the ENTIRE backside of the cells is conductive.  The soldering pads are merely places that are made for easier soldering.  Perhaps it may be sufficient to use some lacquer or paint to cover the back side of the PV's?  Take one PV cell and give it a try! (and please report your results).
Kralc carlos1w4 years ago
Carlos1w,
You should consider using aluminum tubing. Here's a link.
http://andersonmetalscorpinc.thomasnet.com/viewitems/assorted-products-tubing/aluminum-tubing

Remember when soldering or welding aluminum you must completely remove the oxide or you will burn through. Also allow enough loose ends to allow for expansion of the tube
Aluminum does corrode, a silicon oil, Therminol or mineral oil will reduce this a lot. Using water is not recomended, but if you use an automotive anti freeze, make sure it is aluminum compatable.

If you live in a colder climate you might want a temp sensor with a drain down valve with an air break. Pretty simple to add on.


With my design, Im thinking since my panels will be long and skinny, that I will be running my copper between the pads length wise.  You know how the pads have the about 3 inch gap between them with the 6 inch side horizontal. This should allow me to run the copper right up against the cells. The one concern is the absolute fragility of the cells. I sneezed yesterday while holding one and quite literally a sneeze can break these things! And to anyone not familiar with just how fragile these are, the next time you scramble or fry an egg and there is that little bit that got away and stuck to the side of the pan, pick that up and hold it in your hand without breaking it. That's how fragile they are! I guarantee you break the first one you take out of the box if you have never handled them. :) Unless you remember this warning!
carlos1w (author)  RedMeanie4 years ago
LOL!  Yes, these cells are VERY FRAGILE (see one of the photos in Step 4, this was not my only mishap!).  As for tips soldering:  use flux, put some tin into the pads and tin the tabs, and them bring them togethet and heat until melting, then keep them in place somehow until it freezes again.  Make sure you do not overheat.  I had success with a 700 F tip, and ruined a couple of cells using an 800 F tip.  Try to operate quickly.
Pvc will not handle the temperature. CPVC Might but I doubt it. The temperature may reach boiling point if circulation is stopped . In fact I have developed high temperature steam Only not enough to run`a turbine
The water will be ran inside Copper, Then Insulated completely on the backside with Styrofoam. The PVC is strictly going to be the casing for the panel.
a metal one would be better as metal, has better heat transfer, maybe sandwiching some strips of metal between to sheets to form the channels. almost like a computer water block. quick 3d model attached
waterblock.jpg
carlos1w (author)  grimgroper4 years ago
Looks like a neat idea, indeed.  Please note, however, that at 1 kW/m2, the heat that needs to be transfered is not so big and it is likely that plastic would work decently. 
 would also solve the connection issue 
Got my 150 panels today, but they didn't send the wiring components. But I have had time to over design my panels. :) I will post when I'm finished and post here also. If I run into any difficulties Ill be sure to ask. Any tips on soldering these things? or anything else?
carlos1w (author)  carlos1w4 years ago
I just found a perfect instructable:  linking http://www.instructables.com/id/Build-your-own-flat-panel-solar-thermal-collector/ and my own should be my next project!
lloydrmc4 years ago
Some years ago, when solar cells weren't nearly as efficient, ARCO made a panel that featured individual cells centered in small parabolic reflectors, with the whole lot cooled by water.  Nothing new under the sun, eh? (pun intended)

Still, just because it's been done before doesn't mean it wasn't a very creative idea on your part - clearly you came up with it independently

I've been toying with the same idea myself, though I haven't yet worked out the details to my satisfaction.  I might post it if I ever come up with something.  Thanks for posting your project, as it is inspirational.
patenaude4 years ago
I really like this project, but I see some problems and possible improvements.

The first problem is the corrosion/electrolysis caused by using differing metals that I mentioned a few pages back. And the second is how you use the hot water.

While you might be able to fix the electrolysis by using a copper backplane rather than aluminum, that would either be very expensive to be structurally rigid enough for the PV cells.  A way to handle that is to solder the copper pipe to a very think copper backplane, and make it rigid by attaching the pipes to sheetrock or plywood. Alternatively just build a form and pour a thin layer of mortar around the pipes.  You'd need to experiment to see what will be would be rigid enough to keep the PV cells from cracking, and also if it expanded or contracted too much with the temperature.

Even better, you might be able to get rid of conductive pipes altogether.  While not as good as copper, you could use the same plastic tubing used in floor heating systems attached to some plywood, covering the tubing with a layer of mortar as in those systems.  You could attach the PV cells to the mortar, which acts as a small thermal sink while the water carries the excess heat away. This would allow you to get rid of the silicone insulation barrier altogether, and reduce potential problems with corrosion or shorts.  While thermal transmission isn't quite a good, it would probably reach equilibrium with the PV cells getting only a few degrees hotter.

Lastly, if this were being used in my house, I think I might use this in a closed loop filled with mineral oil rather than water (to protect the system from freezing.)  This loop would heat the tank of a standard hot-water heater (most are 40-50 gallons~150-180 liters/Kg.)  I would either use or replace my existing hot water heater, and have that feed a tankless, on-demand style water heater. Since the tankless system is getting preheated water, it will use less gas/electricity.  (If you can get the large tank to 126F, then that's close to the temp. that domestic hot water should be anyway, and further heating mostly unnecessary.)

I'd also probably build a simple circuit that checks to see if the system temp was higher than the tank temp before turning on the oil circulating pump. That's maybe $20 in electronics parts.. a simple comparator or microcontroller feeding a relay to control the pump.  The microcontroller would also allow you to track and publish the data back to your home computer, and you can make plots of hours of operation along with system and tank temperature.
carlos1w (author)  patenaude4 years ago
Thank you for your comments.  All of your comments are quite valid and would certainly make a lot of sense for a permanent installation (please bear in mind that this was merely a proof-of-concept device, and I really wanted portability and to reduce issues with possible spills-hence the use of pure water).  There are quite a few alternatives that can be used instead of the Cu/Al mix and all have positive and negative aspects: a) all Cu (good but too soft and expensive), b) all Al: I would think that it could be possible to have an extruded form like mentioned below, I think this would work best; c) polypropylene "corrugated plastic", and others.
carlos1w (author)  carlos1w4 years ago
Here is what I think should work well: an extruded aluminum pane like shown in one of these figures:
Screen shot 2010-05-14 at May 14,  9.28.59 pm.png
You dont need such a complex Aluminum form, even a single celled structure would work.

If you want to get more efficient and loose the pump look into heat pipes, in particular pulsating (or oscillating)  heat pipes. You can use the heat to transfer it's self to the store water and get to use all of the solar power.
Foaly74 years ago
You could even make a tribrid wind turbine with these style panels as the blades (for those of you wondering, my comment is just a spin-off idea of a wind turbine in the fourth Artemis Fowl book).
LadamaB4 years ago
Why dont you use the copper to conduct the electricity and the H2O
seems it would cool more efficiently
carlos1w (author)  LadamaB4 years ago
Because nobody wants a panel that produces 0.5V and 133 A, most of us would prefer 18 V and 3.7 A instead even if this is still 66 W.
efootprint4 years ago
Is it possible to just get an old coil from the back of an old refrigerator and use it?
 possibly... but dont release the refrigerant gass!!! 
rothm4 years ago
Really a nice and efficient design -- I like it. Wonderful utilization of space and resources. It would be good to see how much of the system you culd make from purely recycled goods. Maybe someday places like Panera will be using these practically!
sum4all4 years ago
how many volt and watts are your cells? thanks for the instructable. Will you eventually put a charge regulator on this and maybe add a battery?
carlos1w (author)  sum4all4 years ago
Cell Specifications:
Average Power (Watts): 1.75 Wp
Average Current (Amps): 3.5 Imax
Average Voltage (Volts): 0.5 Vmax
Thickness 200 ìm = 0.2 mm
Exact dimension: 3 1/4 inches x 6 inches, or 80 mm by 150 mm

Weight: Just above 6 grams, or 0.2 oz.

As for the regulator:  precisely!  I made the whole panel generate 18 V which would be perfect for charging a 12 V battery (once the voltage drop at the regulator is taken into account, and the fact that batteries are charged at close to 14 V).
Here's a link to rebeccayi0904's eBay page if you're looking for those deals:

http://shop.ebay.co.uk/rebeccayi0904/m.html?_nkw=&_armrs=1&_from=&_ipg=
AT4 years ago
Interesting idea.  I like it.  Another use would be to produce Hydrogen!  Use the electricity of from the PV cells to pump the water around and also do some electrolysis on the water.  My understanding is that the warm water will use less energy to break into its base components H2O.

Then mount this on top of your Hydrogen powered car and you have a car that runs on water!  ;-)  Well, water and sun.
tuckersaspy AT4 years ago
 that sounds amazing but i doubt itd be a practical amount of H2 to run a vehicle on
den316a4 years ago
why not just raise the water tank above the panel add a angle and allow convention currents to move the water and allow reheating  to a usable temp
Shiftlock4 years ago
Perhaps you should have traced the pipe's shape onto the Al sheet, brushed the flux onto the path, then pre-melted the solder along the path.  Then you could have tinned the entire copper pipe and simply joined them together with the heat of a propane torch.  I think that would have created a continuous contact point, and made it a lot neater.  It probably would have been quicker and easier than soldering a bunch of contact points as well.
carlos1w (author)  Shiftlock4 years ago
Good idea, this is one of the neat things about instructables:  you always learn something new from your "readers".  Next time I will try it the way you suggested.
ieso534 years ago
Original and excellent idea. Congratulations.
carlos1w (author)  ieso534 years ago
Thank you for your comment!
fasinating thankyou for sharing this.
excellent craftsmanship.
i would very much like to see if there is a difference with and without the pump on say 30 gal of water 
carlos1w (author)  manleyjames624 years ago
Thank you for your comment!

Well, it would take some time (with this 0.5 m^2 panel) to get 30 gal up to 52 C (several hours).  If you think about it, it is not so bad.  In 1 day you get enough hot water for a shower.  Alternatively, one should get a bigger panel!
achituv4 years ago
Why pump the water? simply place the 'cooler' in a place that is higher than the panel and use thermodynamics.
yes. Thermosiphon. no pumps needed just checkvalves. lowers cost of system.
carlos1w (author)  unclejoe4 years ago
The pump was only $10.  Considering the rest of the cost of the system, I did not mind having a more controlled convection.
I like the concept, but was mislead by the title into thinking you were converting heat into electricity as well.  I suppose the idea is to provide off-grid power as well as hot water?  Maybe by using a black barrel to hold the water (and the heat) you could replace your water heater?  Those things suck resources (mine uses electricity, gas, and city water..I want to use the sun and water filtered from the creek that runs through my property to replace it.  Thanks for the inspiration...I'd like to see what you do with it with regards to practical application!

Instead a barrel, why not feed the heated water from something like this into your existing hot water heater?  It already exists and is tied into your plumbing, it's made to hold water, and it's insulated.  That way, the hot water heater would use less power to reach the temperature you set it at.
Could you run your water pipe past the heat source (PV panel) to heat it? Should the water sit there for a time? Trying to think of the most efficient/easy way this could work.
I don't think letting the water sit in the PV panel would do much good, since the volume of water that the pipe holds is rather small, and you want it to continuously draw the heat away from the heat source the way a liquid-based CPU cooler or a car radiator works.  The water should keep recirculating through the panel, using your hot water heater as the holding tank.  I think the pump should return the water to the top of the tank, and draw it from the bottom of the tank.  That way it will re-heat the water as it cools and falls to the bottom.

Someone correct me if I'm wrong.
Raid the junkyard for an old refrigerator and you have ready made water heat transfer pipe.Just be careful not to collapse the pipe when you cut off each end and use plenty silicone around the rubber hose connectors.
johnj_074 years ago
Ok I will ask so one of you guys with a handy dandy fancy calculator can do the work im too lazy to google how to do...What is the feasibility of running a few of these from/into my pool. Using the pool as the source and the discharge for the water so in the winter I have some degree of heating? I live in Arizona btw so by winter I mean no less than 50° F during the day and tons of sunlight. Think I could maintain 70° if I started running it in the summer when the water was still hot?
 Okay, going to go ahead and judge you for having an outdoor pool in Arizona. That's not a luxury item though, is it.
I'd say it is a luxury item as much as I'm paying for it lol, but what's wrong with an outdoor pool here, you lost me on that part?

Pazzerz4 years ago
You might try square aluminum tubing, arranged side by side, and connected so that the water flow is zig-zagged through the entire backside of the solar panel.  It would cover 100% of the photovoltaic panels and cool them much more efficiently.  The tubing, when soldered or welded together, would provide the necessary stiff framing for your panels.  A thin sheet of black plastic between the cells and the aluminum will electrically insulate it and allow more heat absorption.  You can even heat the plastic up enough to bind to the aluminum tubes.
carlos1w (author)  Pazzerz4 years ago
Thank you for your comment.  I like your approach.  This would be ideal.  Note:  it is not really necessary to zig-zag, parallel motion along the tubes would actually work better since the temperature gradient will be more uniform.  My only concern is whether the aluminum tubes (square) would be too expensive.  I think that given the small amount of heat power per unit area even a plastic material would conduct enough heat without a major performance hit, e.g. using a corrugated plastic like the picture in some comment below shows.
rhotaling14 years ago
OK I am now replying. If you tin and heat the substrate to solder the tubes the substrate will warp. I have a metal roof of 1800 sq. ft with 6000 lin ft of 3/8 copper tube. I use 2 5000 gallon reservoirs and circulate water for heating and air using water source heat punps to heat and cool my house in Atlanta. PV would work on top of the piping and cool the PV. I used silicone caulk to glue the pipe to the roof. It has worked fine for 25 years. I circulate 15 gal/ minute to get 15 degree temp difference..
carlos1w (author)  rhotaling14 years ago
Very interesting.  Perhaps you should post an instructable!!!
Great Idea! 
Looking at your graphs, I noticed that if you hooked your heat exchanger up to a closed loop preheat domestic water or for radiant heating, the water would spend more time in its peak linear phase due to having more mass to heat.  It would also keep your panels more cool - obviously, that depends on rate of flow through the preheat-tank/heating system and total number of panels, but it does offer a nice opening for optimization.
carlos1w (author)  linesofflight4 years ago
Indeed, every time the reservoir temperature drops it automatically increases the heat transfer.  In fact, most solar water heaters have two thermometers and the water pump is only activated if the temperature difference is bigger than some threshold.  One thing I have still to test is how the efficiency of the PV panels would decrease if the water pump is off (since the back is insulated and there is a layer of air in the front, I presume they will get really hot!).
dddddd carlos1w4 years ago
It sounds liike you already know that efficiency plummets as cell temperature increases.
A cell at 105 degrees produces only 90 percent of the power of a cell at 77 degrees.
At 122 degrees it produces only 85 percent of the power of a cell of a cell at 77 degrees.
On the other hand, if you could limit your cell temperature to 105 degrees during the day, it would probably be cooler than an equivalent air-cooled cell would be at the same time under the same sunlight.

I didn't know you could solder aluminum to copper, using the right flux. Thanks!

rhotaling14 years ago
chrwei4 years ago
what about using a thermal epoxy instead?  might cost more, but it would be a lot easier to control and cover the full contact point of the pipe to the sheet
carlos1w (author)  chrwei4 years ago
I think that epoxy would have worked pretty well (even non-thermal epoxy) given the small energy/surface area ratio.  
grimgroper4 years ago
 you could mount your cells to some thermoelectric coolers,  then on the other side some sort of passive heatsink. that way they well also generate a small amount of electricity.. they are not very efficient but they will generate some
NightLord4 years ago
Hmm, these hybrid panels may have an extra advantage... in the winter water can circulate hot water through them and the snow (or ice) on them will melt.

Since this requires quite some energy to do that (possibly even more than you gain), this is only practical if heat would be oterwise wasted... e.g. heat from greywater - it  has still got > 15°C, more than enough to melt the ice.
Woodenbikes4 years ago
Nice Instructable!  I'm glad you put in the graphs of test results.  It seems you are able to get 3-6 times as much energy (electricity and thermal) from the combined panel as from a solo electric panel.  Good idea for taking advantage of small sunny portions of roofs. 

Perhaps an easy low cost method would be to start with plastic or metal solar swimming pool panels and then apply a flexible adhesive backed thin film solar PV panel.  Then you have an unglazed low temperature solar panel.  You could put it in a glazed box if you wanted to boost the thermal production at the expense of some of the electric production (losses from glass reflectance and absorbency as well as PV efficiency loss as cell temperature rises.) 

Maybe even better would be the unglazed pool panel type of system (with PV film layered on it) with a heat pump extracting heat from warm fluid coming off the panels to make sub cooled fluid returning to the panel at or below ambient temperature for zero heat loss. 
Tinker834 years ago
well... you could always flood the chamber with white oil (the stuff used to cool transformers and flood overclocked computer cases), and circulate heat directly from the cells. i don't know what the oil would do re: electrical efficiency, but a direct cooling might offset that.
you'd need a heat exchanger to draw heat into a water system though.
carlos1w (author)  Tinker834 years ago
Mmm, that is interesting.  Perhaps the cells can be attached to the front glass, and a narrow gap can be at the back and oil circulated there.  Perhaps that would work better in a more industrial setting, but for a home made device I think that water is better (no messy spill if you have a leak!).
actually the cells would be in the oil, fully submerged. transformer oil is non conductive, so placing the cells in the oil gives you a direct heat transfer.
karossii4 years ago
Another method of harnessing the solar heat would be to use a Seebeck unit (almost the same as a Peltier, but using heat variance to generate electricity instead of vice versa)...

Look into TEGs (ThermoElectric Generators) - not super efficient, but if combined with a PV setup, could add a bit of electricity to the mix, if you're not in need of heated water.
(removed by author or community request)
Absolutely, which is why I said 'if you're not in need of heated water'...

I'm looking into getting a MicroCHP setup which uses natural gas (same kind used by many hot water heaters, furnaces, cook tops, etc.) to power a generator, which generates electricity for the home; and uses the waste heat to heat either air (replacing a furnace) or water (replacing a water heater)...

So in my case, converting it to the electricity would be more desirable. And I am sure there are others who, for similar or dissimilar reasons, are in more need of electricity than heat.
I'm not sure how well this would work, but you can have the PVs on top, the Seebeck cells under it, and the water pipes under those.  The Seebeck cells would generate electricity with more efficiency with the water pipes under it, and you can still get heated water, but probably not as much.
I would also like to add, that if you venture into an industrial arena, there is quite a bit of 'wasted' heat.  Take a steel mill for example (I used to work at one) there it a large amount of wasted heat, that is just flowing out the rafters.  As thermal-voltaics get more efficient, it would be an ideal situation for some industries to recapture some lost energy.
tweeterorhs4 years ago
I do not understand exactly what the output of the thermal portion is. Hot water? If not what and where did you link the two systems (PV and thermal) to produce energy?
kazael4 years ago
You should do some testing to see how much the cooling improves the efficiency of the panels. For example a few hours with the water flowing, then flush the water out and another few hours with no cooling.
carlos1w (author)  kazael4 years ago
That is a good idea.  I was also thinking of measuring the temperature of the cells, perhaps by using a non-contact thermometer (through black-body radiation).  Well, when I have time to do this and test I will post a new section to the instructable.  
would a self-assembled solar panel be more efficient than a single panel of the same size? Or just cheaper?
jekkian4 years ago
 Have you considered adding salt to the water to decrease the rate at which the water cools off?
carlos1w (author)  jekkian4 years ago
I am afraid salt could cause corrosion in the water pump.  Perhaps I could add anti-freeze (also lowers the vapor pressure), but at the moment I want to keep the system as simple as possible. If I use salt or anti-freeze or oit, then I need to use a closed-loop system, and clean-up of spills will be harder (at the moment the setup can be disassembled simply by removing the nipples off the copper tubes and some water is spilled).
kikiclint4 years ago
 If anything, by cooling the cells, solar cells run more efficiently at lower temperatures, therefore increasing the output at full sun.  Now you just need to find a good purpose for warm water whenever it is sunny.  I have heard of heating the dirt under your house for heat storage for winter.  You could also run warm water through pipes in your floor for heating, with a diverter to the dirt heating for the summer months. In the winter heat the water from the dirt and run it through the floor tubing.
RedMeanie4 years ago
Ok, sorry I forgot to ask this, would copper be a better material for the back sheet? Also Why not just use some Pipe straps to hold the copper tube to the back sheet instead of welding? Im just curious because allot of our people on here can't weld. (Me) LOL. Also I see areas of your tubing that is not in contact with the Back plate. Im thinking that is cutting down efficiency. Maybe Im wrong, Im no expert on this and I want my panels to be as close to perfect as I can get. 
carlos1w (author)  RedMeanie4 years ago
Copper is much more expensive then aluminum.  Pipe straps would work, and probably some epoxy too.  The gaps are not ideal, but considering the relatively small amount of power per surface area (at most 1 kW/m^2, translates to 0.1 W/cm^2) probably almost any thing would work OK, perhaps even plastics!  Note that in heat sinks for electronic equipment it is normal to have several W/cm^2, e.g. in a modern CPU you can have 85W in a surface area close to 2 cm^2, the situation is quite different there.
mtchastain4 years ago
Nice job!

Have you thought of possibly trying a thermosiphon and see what kind of flow you can get? You could save power by not using a pump if it can provide enough volume.

Thermosiphon - Wikipedia Link
carlos1w (author)  mtchastain4 years ago
That would work too, but the power used by the pump is really minimal at this point and probably increases the uptake efficiency. 
Truehart4 years ago
I'm still a little confused as to how you're using the thermal heat.  But if all you're trying to do is keep your cells cool there are a number of different ways to do it.  One, you could add a fan to your cooler to blow air across the water.  You could also put copper (or another conductive material) panels in your cooler with strategically placed holes to allow the "hot" water to pass through while touching as much of each panel as possible and orient your fan to blow parallel to the panels. 

Another thing is to get heat sinks from old electronic equip. (i.e. computers, stereoes, etc.)  and put those on the back of your panel. 

These are just ways to keep the cells cool.  Neither suggestion really presents a way of harnessing the thermal energy in a useful manner, but at least they're some options.
carlos1w (author)  Truehart4 years ago
The heat is used to heat the water in the cooler, the idea would be to use it to eventually heat water in a tank for household use.
tim_n4 years ago
SinAmos4 years ago
I appreciate the way you think. 
Great idea! This should improve the efficiency of your solar panels slightly by cooling them.