Cooling Solar Panels for Improved Power Output (clipped from thread)

solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
newenergy wrote: »
It says Phoenix in the PVWatts page.

The PVPowered string sizer doesn't like strings of 9. It predicts 25.6V x 9 = 230V on the warmest days, which is below the DC voltage operating range.

(from what I can figure it looks like their sizer is allowing for much hotter cell temperatures than ambient temp)

So, above 105f or something like that your inverters may not work properly. That would be fine where I am, but in Phoenix it sounds like an average summer day.

Yeah I was guessing that was the case, The 3 strings of 10 seemed to work last summer but I had no data acquisition on the system then but knowing more now the numbers for generation in June July & August look pretty low but it is unclear how the utility calculates that. i.e. must be the amount of time/watts it spun the meter in the reverse direction.

In Phoenix 115 ambient is not out of the question and 30f is really a cold day here, and is very rare.

I saw some program on TV a while back that showed a water cooled backer for the panels, anyone have any info on that possibility to hold panel temps down?

Comments

  • newenergynewenergy Solar Expert Posts: 291 ✭✭✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    I saw something like the water cooling system at a trade show. I'd be a little skeptical about whether that's worth it on a new system where you are using the heated water for something (pool or preheat domestic water). But, in a retrofit I'd think it would be much better to just put any added modules on a new inverter or even micro-inverters if you have to.

    If I were in your spot anyway, I'd at least see what's happening this summer before doing anything that requires removing the existing system. I definitely wouldn't change to strings of 9.
  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    OK so here is the new caveat, I am not sure what model panels are actually up there, Ningbo shows 2 different models of panels @175Watts, here is the sizing on the "other model"

    Guess I need to get up there and take a look before I beat up my installer to much.
  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area
    newenergy wrote: »
    I saw something like the water cooling system at a trade show. I'd be a little skeptical about whether that's worth it on a new system where you are using the heated water for something (pool or preheat domestic water). But, in a retrofit I'd think it would be much better to just put any added modules on a new inverter or even micro-inverters if you have to.

    If I were in your spot anyway, I'd at least see what's happening this summer before doing anything that requires removing the existing system. I definitely wouldn't change to strings of 9.

    Found one:
    http://sundrumsolar.com/index.php/products/34-all/51-sdm100
    sent off e-mail to them waiting to hear more about it.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    Seems to catch whatever sunlight goes through the PV panel?

    Sounds a bit like having your cake and eating it too - which normally means you end up with less.

    How much sun (watts/m2) actually penetrates a PV panel?
  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area
    russ wrote: »
    Seems to catch whatever sunlight goes through the PV panel?

    Sounds a bit like having your cake and eating it too - which normally means you end up with less.

    How much sun (watts/m2) actually penetrates a PV panel?

    No No it is strictly a thermal sink for the panels.

    Say here in PHX a 115 F day your panels could be as high as 145-150 F sapping there effectiveness. suck off some of that heat and the efficency goes back up.
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    With no direct contact (doesn't seem you want your panels sitting in water) heat transfer will be very poor.

    There would be no comparison to what a solar thermal panel would do though İ understand that is not the object but panel cooling is.
  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    There have been many threads on this forum on this subject and a simple search reveals this:
    http://forum.solar-electric.com/showthread.php?t=5185&highlight=sundrum+solar

    Tony
  • solarvicsolarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area
    solar_dave wrote: »
    OK so here is the new caveat, I am not sure what model panels are actually up there, Ningbo shows 2 different models of panels @175Watts, here is the sizing on the "other model"

    Guess I need to get up there and take a look before I beat up my installer to much.
    Yes you need to check the model of your panels. I like this setup for your temperature. You should get a nice improvement on your output. S:Dlarvic
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    Neils reply on the forum referred to:

    yes a pv would benefit by being cooler, but you won't gain very much in power. the voltage rises, but the current falls too and it just doesn't quite equalize so there is a slight gain in power when cooling.
    great, now we've established a slight gain, but how do you get it? water? ok, so does the water just sit there behind the pv? no, it has to move and that takes power. you might say, "but so what we've gained solar heat". have you? the pv is cooled and the water temperature recovered is on the low side as it was on;y used to keep a pv lower in temp and so the water just slightly raised its temp to cool the pv. this is not real usable heat. so how do you gain from doing this?
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    any effort to gain will result in expending more power than that which is retrieved. why go through hoops to gain a watt, maybe 2 depending on the efforts done and the pv in question? the best one can do is allow allot of air to be able to pass over and under the pvs and using at least a 6in space underneath will help that tremendously.
  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area
    solarvic wrote: »
    Yes you need to check the model of your panels. I like this setup for your temperature. You should get a nice improvement on your output. S:Dlarvic

    Thanks solarvic

    Yeah spoke to the installer and the panels I have are the ones that will work in a 8 X 9 string setup with 2 PVP5200. I expect a pretty nice bump in output to a mid day peak this time of year to about 10,000+ watts. My peak day average hour was yesterday with 8396 watts with a peak minute of 8531.

    They are having local code issues, the code department doesn't seem to understand this is just a panel add. Those guys were a PITA before as well.

    Keep spinning the meter in the right direction!
  • jeffkrusejeffkruse Solar Expert Posts: 205 ✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    Please move the cooling of panels to it's own thread.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    Good suggestion Jeff...

    I think I got all of the relevant posted moved here from:

    Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    You know, this comes up over and over again and not just on this forum. It seems like such an obvious win-win situation; cool down the panels and get hot water.

    Let me point out two things which should make the reasons why it doesn't work obvious:

    1). Photovoltaic panels would like to operate at 70F or less.
    2). The most desirable temperature for hot water is 140F.

    That's quite a discrepancy. Maybe someone should consider using air to cool them, after all 70F is a good temp for heating your house, right?

    But who wants to heat their house in August which is when the panels need cooling?

    Never mind the technical problems/losses with engineering such a system; the thermal difference alone makes it impractical.
  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    Well if your primary goal was to cool the panels to improve the output and any heat you gained was just sinked off into say a swimming pool, and thermal gain would be usable.

    Granted if you were trying to achieve domestic hot water I think it would be futile.

    I will let you know in July how bad I am impacted.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area
    russ wrote: »
    Neils reply on the forum referred to:

    yes a pv would benefit by being cooler, but you won't gain very much in power. the voltage rises, but the current falls too and it just doesn't quite equalize so there is a slight gain in power when cooling.
    I don't know that cooling PV panels is a feasible idea, all things considered, but the effect of temperature on voltage is quite a bit larger than its effect on current with crystalline silicon modules. I'm looking at a cut sheet for a particular module, and the voltage temperature coefficient is -0.33%/degree C, while the current temperature coefficient is only +0.05%/degree C.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Illustration of 8 KW (DC) GT Solar PV System Install for Residence in Urban Area
    ggunn wrote: »
    I don't know that cooling PV panels is a feasible idea, all things considered, but the effect of temperature on voltage is quite a bit larger than its effect on current with crystalline silicon modules. I'm looking at a cut sheet for a particular module, and the voltage temperature coefficient is -0.33%/degree C, while the current temperature coefficient is only +0.05%/degree C.

    Yes indeed. And if you take that increase in Voltage and feed it through an MPPT controller you get an increase in current.

    Which is why 'balancing' a system up in the frozen North gets tricky; -40 in Winter, +40 in Summer!
  • solar_davesolar_dave Solar Expert Posts: 2,389 ✭✭✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    Ah I did mean to get back here, The panel cooling idea is very expensive, $700 per panel installed. While it sounds, nice you would be better off just adding to the PV system size to compensate.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)
    solar_dave wrote: »
    Ah I did mean to get back here, The panel cooling idea is very expensive, $700 per panel installed.
    Yikes! I agree; just add more PV instead.
  • solarixsolarix Solar Expert Posts: 713 ✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    An easy (wasteful) solution would be set up a mister on the modules and spray the water on them. (What were you going to do with the warm water from a rear cooler anyway)

    Another good example of Newton's law paraphrased:
    1) you can't break even
    2) you won't even come close

    People don't understand that efficiency brings with it complexity and expense.
    I worked on an avionics program one time that tried to save fuel on airliners. A real sophisticated cruise control system. We learned that it is very difficult to be successful in business by being a little bit more efficient than the competitor. Success really requires a serious advantage. Like being able to sell sugar water to the masses with a big profit margin, or play rigged card games like in a casino, or punch out some nicely curved sheet metal with some glossy paint and call it car, or burn some crap you dig out of the ground and turn it into electricity. Incremental efficiency improvements usually cost way more than they are worth. Simple, wasteful solutions are what works for most of humanity.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)
    solarix wrote: »
    An easy (wasteful) solution would be set up a mister on the modules and spray the water on them. (What were you going to do with the warm water from a rear cooler anyway)

    Another good example of Newton's law paraphrased:
    1) you can't break even
    2) you won't even come close

    I believe you are talking about the Second and Third Laws of Thermodynamics, and Newton didn't come up with them although his work contributed to their later development.

    TD #2 - the best you can do is break even.
    TD #3 - you can't break even.

    But your point is valid nonetheless. Sorry for the nitpicking, but I am an engineer and cannot help myself. :p
  • System2System2 Posts: 6,290 admin
    Re: SIMPLE....Cooling Solar Panels for Improved Power Output (clipped from thread)

    Why not paint the backside mat-black? This is the color that radiates heat the best.

    That is what I did to my panels -it is so very cheap. I never did any measuring to check the improvements though.

    Christian
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    Why not paint the backside mat-black? This is the color that radiates heat the best.

    That is what I did to my panels -it is so very cheap. I never did any measuring to check the improvements though.


    Painting the backside black would make zero difference. Black is not used because it radiates heat but because it absorbs radiation best. The top side of any solar thermal collector will be black or near black for that reason.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)
    russ wrote: »
    Why not paint the backside mat-black? This is the color that radiates heat the best.

    That is what I did to my panels -it is so very cheap. I never did any measuring to check the improvements though.


    Painting the backside black would make zero difference. Black is not used because it radiates heat but because it absorbs radiation best. The top side of any solar thermal collector will be black or near black for that reason.

    russ,
    sorry, but i have to correct you on this as black makes a great radiator too. usually the better it can absorb the better it can radiate and visa-versa.

    i don't know what difference it might have made on the back of a pv though without more controlled experimentation as the paint itself could insulate or interfere with some of the natural radiation.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    Niel is correct... Generally what radiates heat well also absorbs heat well.

    I remember years ago that NASA spent a bunch of time and money trying to find the right "paint" that would reflect heat from the sun well and radiate heat to space well... If I recall correctly, the best material was not much better than any of the other options.

    In the case of solar panels, I am not sure that it would make any difference at all... You have a slight insulation effect (paint is not a good conductor of heat, plus the back of the panels are plastic--also not a good heat conductor). And, you may end up with warranty problems--paints have solvents and additives which could attack the membrane materials on the back of the panels.

    If you want to keep your panels cool--ensure there is at least 5-6 inches of airspace behind/under the panels and a way for air to circulate.

    Ah--found one NASA report from 1983 (PDF file)... Has a whole bunch of information about colors/materials and their absorption and emission of heat. Hmm, looking at the results--I would probably be more tempted to paint the back of the panels white than black... Very similar emission results, and much less absorption with white.

    But of so much variability (materials, coating thicknesses, the way it is applied, mounting differences, etc.)--You would really have to do A/B testing of your specific panels and coatings.

    Don't think it is worth doing it...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    It could just be that colour has no effect on radiating heat as opposed to absorbing energy, including that within the visible spectrum which then becomes heat.

    So why do they paint wood burning stoves black, then?
    Because "lamp black" was made from charcoal and was a cheap thing to coat the iron with to keep it from rusting. Likewise, black paint is cheap, always matches, and black goes with anything! Right fashionistas? :p

    I apologize in advance for the argument this will no doubt start.
  • BB.BB. Super Moderators, Administrators Posts: 32,608 admin
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    And why did farmers paint their barns red? (at least a popular theory):
    Ferric oxide (rust), a primary component of red paint, is inexpensive and this appealed to the thrifty farmers of New England and New York State

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • russruss Solar Expert Posts: 593 ✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)

    If I read the NASA document correctly color, can make a difference in absorptance but not in emissivity.

    I always loved the IR guns (thermometers) guys from the office would use at site. As you have to know the emissivity of the object in the temperature range you are working in there is a lot of reading between the lines normally done. Any change in surface texture, color, temperature could significantly change the emissivity setting.

    The office guys almost always got the answer they wanted and when they left İ would have people go along behind them to replicate the checks - try to figure out how the fudged the numbers.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Cooling Solar Panels for Improved Power Output (clipped from thread)
    BB. wrote: »
    And why did farmers paint their barns red? (at least a popular theory):



    -Bill

    Actually, I hail from that region originally and that answer is about 80% correct. It was not just that iron-oxide based paint was cheap to obtain, however, but that it was durable. When you're painting something as large as a barn you don't want to have to do it every year. That Barn Red would be there for a long, long time. Maybe faded, but still protecting the wood from New England winters.

    Whitewash, on the other hand, is basically dissolved lime. It is not durable at all, and was initially used inside dairy barns because of its bacteria-inhibiting properties. The white may have looked nice, but that wasn't the primary reason to use it - except on fences. Remember Tom Sawyer? :p

    Does anyone else remember when painters mixed paint on-site? I don't mean stirred it; I mean put the linseed oil and turpentine together with the pigment(s) - which included lead oxide. Now where have we heard about that before? Yes: batteries! :D
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