## Step 9: Conclusions

Overall I am quite pleased with the results, but I did spend a lot more \$\$ than I had anticipated!!!  Whether this can be a cost-effective solution for people's homes remains to be seen.  I like the idea of using as much solar power as possible, and it makes for a most complete utilization of the surface area (e.g., a home's roof).  One extra advantage:  the water keeps the temperature of the PV cells lower, increasing their efficiency (or so I hope).

If you find this instructable interesting please comment.  If you have suggestions please comment.  What other types of heat exchangers could be used?  I still have enough PV cells to make a second panel, but I would like a cheaper and simpler way to harness the thermal energy.  Any suggestions are welcome.

Please enjoy and if you decide to make a panel like this let me know. THANK YOU.

Carlos Wexler
(carlos1w@yahoo.com)

Note (added May/13/2010):  a google search reveals that there is apparently some commercial systems that use the same concepts (using both the electricity and the heat in a single package).  Please see, for example:  http://solarwall.com/en/products/solarwall-pvt.php, where they use air convection on the backside of the panels (instead of water).
Very nice. <br>(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 &quot;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. <br>(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 :-). <br>
A very good instructable. Is it possible to double the copper tubing to increase the efficiency of your heat exchanger?, Like two staggered &quot;U&quot; 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.
Did you figure how much additional electricity you get from the PV with the 'cooled' vs 'not cooled' use?<br><br>Cooling the PV is supposed to allow them to be more efficient.<br><br>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.
&nbsp;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.<br /> <br /> <br />
Probably would be an issue in the long run (years?), but for a prototype it is probably OK (months...).&nbsp; I&nbsp;guess it will be important to keep the whole thing dry (at least where Cu and Al are in contact).&nbsp; Hopefully my liberal use of silicone caulk will take care of it!&nbsp; <br /> <br /> Does anyone know whether there is some kind of hollow aluminum panel of the right dimensions that could carry water inside?&nbsp; Something with a profile like this:<br /> <br /> ---------------------------------------<br /> |&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; |<br /> ---------------------------------------<br />
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: <br> <br>Thermal conductivity is measured by the formula BTU*ft/hr*ftE2*F <br> <br>Copper: generally over 220 <br>Aluminum 73 to135, depending on the alloy <br>SS 304 or 316 is 9.4 <br> <br>Data source: Materials Selector, 1993 <br> <br>Even the &quot;worst&quot; aluminum has 7 times the thermal conductivity of stainless. <br>
However, if you paint the copper black you shouldn't have that problem, plus you'll have the added benefit of even <em>more</em> efficient heat transfer.
Look into Bosch or 80/20 structural systems.
See size does matter. In size of panel and flow of water or current thru size of cable.
When the water heats up are the tubes on the back of the voltaic section hot as well?<br><br>If they are hot then where is the cooling advantage?<br><br>I just don't see it.
Great idea!<br> <br> 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.<br> <br> 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.<br> <br> 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.<br> <br> 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:<br> &nbsp;&nbsp; - Scalding hot 24 hours later.<br> &nbsp;&nbsp; - Hot 48 hours later.<br> &nbsp;&nbsp; - Warm 72 hours later.<br> <br> 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.<br> <br> 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:&nbsp; 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.<br><br>As an adaptation to your HotPot, you could try &quot;recharging&quot; 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.<br><br>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.
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. https://www.instructables.com/id/Quick-and-easy-brazing-aluminum-copper-and-nonfer/<br> I really like your ideas so far. Nice instructable.
This instructable shows the potential of solar based energy sources.<br>I wonder why there is no comercial product available using your dual <br>concept.<br>I tried to find something on the web, and this could interest you<br><br>http://www.websesame.co.uk/wp8.pdf<br><br>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 .<br>By the way great instructable !!<br><br>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.<br>Run it through this type pf panel first then to the flat plate collectors.<br>You could even use the same pumps and not have to add any.<br><br>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?<br><br>I guess I'll find out when I build it.<br><br>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.<br>
Wow this is a great instructable !!<br>Thank you for posting it .<br>I have been looking for for one like this .<br>I want to build from scratch a whole array of these types of panels.<br>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.<br><br>I have one question the though , wouldn't it be better to use 3/8&quot; copper tubing ?<br>From 1/4&quot; to 3/8&quot; tubing would increase your flow of coolant 2.25 times.<br><br>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.<br>What do you think ?<br>
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.
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.
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.<br />
The pump is not solely to cool the cells, it is to extract heat for heating water for household use.&nbsp; <br />
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.<br>Using a convection circulation, you would need to use considerably larger pipes.
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. <br>
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 &quot;loops&quot; of copper... perhaps using fittings rather than bending, or utilizing the pre-moulded panels used for solar water systems..
Carlos1w, there is another Instructable entitled &quot;Solar-Thermal-Water-Heater-For-Less-Than-Five-Dollars&quot; 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.
Thank you for the reply. For anyone interested, the instructable is https://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)
Please see this other instructable (https://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.
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!
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-&gt;electric conversion (the PV conversion is more efficient) but the direct use of the heat is very efficient.<br><br>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).
While I know aluminum is cheaper than copper sheet,&nbsp; you might end up (after a number of years?) with the aluminum being eaten away by being in contact with the copper.&nbsp; On the galvanic scale, copper is up near the top, one of the most&nbsp; &quot;noble&quot; metals.&nbsp; Aluminum is way low on the scale, (ignoble?) down below steel.&nbsp; 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.&nbsp;<br /> <br /> I'd be curious to know if there is a voltage present:&nbsp; 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.<br />
I&nbsp;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).&nbsp; Would this mean that corrosion will be minimal?<br />
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 ;)
I'd say it's not happening...&nbsp; As I said, you need three elements- the two dissimilar metals, and an electrolite like rain, or humidity.&nbsp; I&nbsp; should&nbsp; 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.<br /> <br /> I live near the ocean, and have a steel boat trailer... About 6 years ago, I repainted it,.&nbsp; 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.<br /> <br /> And I forgot to say- Nice project!<br />
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.
&nbsp;Why not take the heat you are moving and run it across some peltier (thermoelectric) coolers. &nbsp;These are the modules used in those iceless coolers. &nbsp;This is my recollection of how they work.<br /> <br /> When current is applied one side gets and one side gets cold to change the hot and cold side just swap the polarity.<br /> <br /> Here is the neat part. &nbsp;If heat or cold is applied they will generate current.<br /> 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?<br />
Cool project:&nbsp; I&nbsp;like the idea of using both the electric and the thermal power in the same surface!&nbsp; Plus the flowing water keeps the PV cells cooler which improves their efficiency!!!&nbsp; Construction seems well done and the photos are well taken and the explanations are good.&nbsp; I&nbsp;particularly like the results you show on the last page.&nbsp; GOOD!!!<br />
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 <br /> 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. <br /> Other than that, Bravo! Very good idea and Instructable!<br />
Thank you for the comments.&nbsp; If you build a hybrid like mine (hopefully a much improved version!), please let me know.&nbsp; What I&nbsp;think would be an ideal material for the backplate would be a &quot;corrugated plastic&quot; like the ones sometimes are used for storage boxes, etc.&nbsp; 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).<br />
For my setup I will be using either 4&quot; 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. <br /> 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.&nbsp; <br />
At least with the PV&nbsp;cells I&nbsp;got, the ENTIRE&nbsp;backside of the cells is conductive.&nbsp; The soldering pads are merely places that are made for easier soldering.&nbsp; Perhaps it may be sufficient to use some lacquer or paint to cover the back side of the PV's?&nbsp; Take one PV&nbsp;cell and give it a try! (and please report your results).<br />
Carlos1w,<br /> You should consider using aluminum tubing. Here's a link.<br /> http://andersonmetalscorpinc.thomasnet.com/viewitems/assorted-products-tubing/aluminum-tubing<br /> <br /> 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<br /> 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.<br /> <br /> 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.<br /> <br /> <br />
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.&nbsp; 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!<br />