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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Signing UpStep 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.
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.
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Fact: It will take you more than 10 years to pay back
Solution: Using Surplus Solar Cells You can get pay back in 1-2 years
There is an Engineer from Chicago his name is John Sommer
He explain it All in his <a href="http://topdiysolarpanels.com">DIY Solar Panels</a> Blog Search for him using Google
Type "top diy solar panels" Open the first Result.
Note: Ignore the adds at the top.
(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 :-).
Cooling the PV is supposed to allow them to be more efficient.
Thanks ... Jack
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!
:)
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.
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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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.
If they are hot then where is the cooling advantage?
I just don't see it.
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.
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.
I really like your ideas so far. Nice instructable.
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.
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.
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!!!
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 ?
Using a convection circulation, you would need to use considerably larger pipes.
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).
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.
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!
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?
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.
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.
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.
seems it would cool more efficiently
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!
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.
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.
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).
http://shop.ebay.co.uk/rebeccayi0904/m.html?_nkw=&_armrs=1&_from=&_ipg=
Then mount this on top of your Hydrogen powered car and you have a car that runs on water! ;-) Well, water and sun.
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
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!
Someone correct me if I'm wrong.
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.
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!
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.
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.
you'd need a heat exchanger to draw heat into a water system though.
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.
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.
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
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.