PV panel temps

System · June 2007

I've been wondering if anybody has ever attempted to cool their PV panels by heating H20. I camp a lot and frequently use solar showers. Mr roof is white but my windows are black. When I hang the solar shower, so it is leaning on the black window, not only does the Solar Shower heat up much faster, but the whole window itself(not just the shaded area) radiates much less heat to the interior of the van than the adjacent window, at least until the solar shower has a couple hours to heat up.

I'm thinking, say someone developed a system where cool water from a shaded tank were pumped up to the solar panel where an efficient heat exchange system bould both cool the solar panel, and heat the h20. If this could be accomplished efficiently, do you think that the cooler PV panels increased efficiency could overcome the increased load of the water pump.
Keep in mind that the water pump wouldn't neccessarily need a big gpm rating. Even less if the tank were higher than the PV's

If on the off chance that nobody has ever thought of this before, and a resounding "Eureka" ripples the solar world,
PATENT PENDING ,PATENT PENDING, PATENT PENDING!!!
LOL,
Geoff.

System2 · July 2007

Re: PV panel temps

eureka!

hey actually, ive noticed better output briefly when theyre cooled by a hose (or maybe its the reflective water, removed dirt, either way....). it would have to be something like a pvc pipe or hose, perforated along the top of the panels that would run down evenly, and it would have to run long enough to cool the glass first then the pv. it does sound feasible. im curious how much actually boost can be had from cooling, pumping water in small amounts is not very power intensive, but youd have water timing device drawing power too. and then theres the factor of how long between coolings, not long id guess to make a notable difference unless you had something super low power running all day.... options...

oh another factor: some pv's may vary in their response to heat and cold (some.., ie: my sanyos do better in the heat than shaps but certainly they both do better in cold than heat)

anybody have any numbers re: how much boost when you're cooling.

System2 · July 2007

Re: PV panel temps

Mattl,
I'm glad to get any response, I was starting to think all the experts were gonna leave this one alone. I happen to have family in the heat exchange business, and they found the idea intriguing and ran some numbers, and until I can say how much more efficient say a 15 degree drop over 6 hours is, the numbers can go no further. Something I never thought of is different brands of panels reacting different to heat.

I will say the idea I was thinking of is a closed system. Cool water would absorb heat from underneath the panel.
I was thinking that closed, the falling water would help to pull water up to the panel offsetting the size of the pump required. Maybee the surface misting/evaporating method could be used in combination. The number crunching determines that the pump would need significantly more flow than I'd originally thought.

Overall I'd say the idea is impractical for an already operating system, but if someone were setting up a fairly large system, and using the power therefrom to electrically heat water, than it could work. If a 15 degree drop in Pv temp is significant in terms of power output, maybee I'd invest more thought in it. I did read somewhere where something like 75% of a homes energy use goes into heating water. What a waste.

niel · July 2007

Re: PV panel temps

the subject has been brought up a few times here on the forum. you can look back to find the discussions, but briefly i'll say that you will gain a slight amount of power just by looking at the pdf specs for pvs by cooling a pv. the problem is that the power used to cool the pvs uses up far more than you've gained. direct utility water is also a problem if on a constant basis due to mineral buildups on the pvs and thus blocking vital solar energy. if you can figure out a way that won't use up the small gain and not be detrimental to the pv we'd like to hear about it. also, it shouldn't have a large pricetag or it'll be better to buy another pv to gain more power.

System2 · July 2007

Re: PV panel temps

Just a note, we've had a very late spring here, cool and wet, however, today bright sun.
Had a look at my panels, slight but quite visible coating of tree pollen on all of them.
Checked Morningstar TS60 in bulk mode, passing 29 amps to batteries. Ambient temp 20C, panels hot to touch. Garden hose, washed off pollen, cooling panels. Output went to 32 amps. Said OK, cooled panels and cleaned them, lets wait a few minutes. Panels hot again, output still 32 amps.
I know it wasn't a hot day, but the PV's were hot. I was expecting to see some relation. Perhaps they need to be super hot.
Wayne

Windsun · July 2007

Power drop with temperature is significant, but not as much as people tend to believe.

But that show you get more from cleaning your panels than from cooling them

icarus · July 2007

Re: PV panel temps

You gotta live where I live. (Far northern Ontario, Canada) My panels in the summer put out 16 amps, but come winter, -35c the same panels put out 30 amps. The combination of super cold and major reflection off the snow. Of course the batteries suffer, but even if thier capacity is reduced, thier longevity is increased.

Icarus

System2 · July 2007

Re: PV panel temps

Yeah, I've seen major increases with winter reflection off the ice and snow covered lake. The panels are mounted on the north shore. Works great.
One other thought about running water over the PVs to keep them cool. Perhaps any one considering this route, should use steam distilled water, otherwise, in short order you could have major mineral buildup from evaporation, starting around the outer edges of the frame and working in from there. Now that would do a job on the output. But don't worry, it can be cleaned off with a strong solution of Hydrochloric Acid. Hahaha

crewzer · July 2007

Re: PV panel temps

You gotta live where I live. (Far northern Ontario, Canada) My panels in the summer put out 16 amps, but come winter, -35c the same panels put out 30 amps. The combination of super cold and major reflection off the snow.

Something’s not quite right here. While reflection from snow and ice will indeed increase panel current output, temperature will not. Is that increase in current output from your panels directly or via an MPPT controller?

Regards,
Jim / crewzer

SolarJohn · July 2007

Re: PV panel temps

Quote from icarus: You gotta live where I live. (Far northern Ontario, Canada) My panels in the summer put out 16 amps, but come winter, -35c the same panels put out 30 amps. The combination of super cold and major reflection off the snow.

Quote from Crewzer: Something’s not quite right here. While reflection from snow and ice will indeed increase panel current output, temperature will not. Is that increase in current output from your panels directly or via an MPPT controller?

Crewzer, I don't understand your response. I've always heard that panel efficiency decreases as temperature increases. This, of course, means that current will increase as temperature decreases.

John

BB. · July 2007

Re: PV panel temps

I think that what Jim is saying is that (more or less) panel voltage is inversely proportional to temperature and that current is proportional to the amount of solar energy received by the panel.

So his question is where was the doubling of current measured? Was it from the solar panels themselves (which would require 2x solar radiation--refection from snow) or the output of the solar controller.

And, was the charge controller a PWM or MPPT type--either controller will directly pass a current increase from the panels due to refection (and clear air), but only the MPPT controller can increase current--total power (from increases in panel voltage because of the low temperatures). A PWM controller would not be able to increase current/total power because of higher panel voltages.

-Bill

crewzer · July 2007

Re: PV panel temps

I've always heard that panel efficiency decreases as temperature increases. This, of course, means that current will increase as temperature decreases.

Bill's on the right track:

PV module power efficiency increases/decreases as cell temperature decreases/increases.
PV module voltage increases/decreases as cell temperature decreases/increases.
PV module current actually decreases/increases as cell temperature decreases/increases, but the % of change is relatively small compared to the % change in voltage.

For example, take a look at the specs for the Kyocera KC85T. The Voc temperature coefficient is negative, but, though small, the Isc temperature coefficient is positive.

HTH,
Jim / crewzer

niel · July 2007

Re: PV panel temps

jim,
did you mean to duplicate this post? i'll let you handle it being it's your post.

crewzer · July 2007

Re: PV panel temps

niel,

Thanks... slow network response during East Coast lunch hour = duplicate post... :grr

Regards,
Jim / crewzer

niel · July 2007

Re: PV panel temps

**it happens. lol hmm this requirement of 18 characters is annoying me now.

icarus · July 2007

Re: PV panel temps

Since I seemed to start a bit of a bruhaha here I will explain as best I can. I was always led to believe that the output of the panels DECREASES with temp, and ergo INCREASES with lower temp. What I don't know is if the voltage increases or the current (amperage) increases with the cold. What I do know is that at the battery/meter shunt the number reads about 14+-vdc 14-15amp on a good noon in the summer. +25c (80f)

At -35c (-30f) on a good solar noon I get the same basic voltage, but can approach 29-30 amps of charge. I have never tested the open circuit voltage/amperage of the panels. I should also note that in the summer the panels are adjusted for summer elevation. (My useage in the summer is very limited since it isn't dark until 11:00pm and light again at 4:00.
As noted, the panels are mounted on the northshore of the lake, and they get a HUGE amount of reflection especialy in the winter. I don't know how much of my increase is due to the temp, and how much from the added insolation. My hunch is that it is more relfection than cold. Having said that I do notice an output difference between 0c (32f) and -35c.

I should caution that the winter numbers are from memory since it is now July!. The true reality may not be a dramatic as stated but dramatic non the less.

My point was more humorous than detailed. It is illustrative of the effect of temp/reflection.

I will log it this winter and report back sometime.

Icarus

icarus · July 2007

Re: PV panel temps

Ps to the above,,,it wouldn't let me edit for some reason,

PS As Wayne from NS notes, the clear air might have a signifcant effect as well. While we don't suffer from huge humidity in the summer, it it very dry and very clear in the winter (when it is clear!) As a guess I could account for a 5-10% increase due to the clearer air. Also the panels tend to be cleaner in the winter, as they are not subjected to to pollen drop, tree sap, errant leaves and needles, etc.

If I had know this was a forum with so many technical people (and very helpful by the way) perhaps I would have thought more about such a flippant posting! lol.

nigtomdaw · July 2007

Re: PV panel temps

Has anybody consider passive cooling from the other side of the panel. I gave thought to bonding on allumininium foil cake dishes 2 inch dia to the rear of the panels to help with cooling the panel, also could you use the rear of the panels as a hot water solar collector ?. Didnt bother with the bonding of foil dishes as might prove problematic with warranty claims!

System2 · July 2007

Re: PV panel temps

icarus wrote: »

If I had know this was a forum with so many technical people (and very helpful by the way) perhaps I would have thought more about such a flippant posting! lol.

Not to worry, we're all human here. Life is a learning experience for all of us.
Welcome to the form. It would be great to hear of your PV experiences both good and bad, using them that far North. A glimpse of a different world for most of us.
All the best.
Wayne

crewzer · July 2007

Re: PV panel temps

We live with 150 watts of panel, 750amphours of battery, a xantrex tc 20 charger, morningstar 300 sw inverter, Honda eu1000 generator, tri-metric meter. We use about 25amp/hours/day, the system charges at about 10-12 amps average.

Icarus,

What make and model PV module(s) and solar charge controller are you using?

More later,
Jim / crewzer

icarus · July 2007

Re: PV panel temps

It is a little complicated, for reasons that I won't go into. I think the panels are BP solar 55watt+- and Siemans 63watt+-. I have them cobbed together with two seperate controllers, SCI Mark 22(s). The reason I do this is because there are times when I charge a seperate battery bank with seperate loads. The batteries are similar to the trojan L16, 4 of them.

I am currently building a new building and will do a proper single installation in the new building.

Icarus

crewzer · July 2007

Re: PV panel temps

...I think the panels are BP solar 55watt+- and Siemans 63watt+-...

One of each? Two of each? Or...?

Thx,
Jim / crewzer

icarus · July 2007

Re: PV panel temps

2 55 watt, 1 63 watt if memory serves.
Icarus

RCinFLA · July 2007

Re: PV panel temps

Silicon temp coefficient is -2.5 mV/degC. Polycrystaline panels are not perfect to this number as the monocrystaline are but it will be close.

For a 32 v panel with 72 cells in series that would amount to 0.17 vdc/degC or an increase of 2.7 vdc for a 15 degC cooling. That's about 17 % more power. But cooling 15 degC is pretty big.

There are several companies working on similar idea using a freznel lens focusing about 3-5x sun intensity on a smaller cell that is cooled. Object is plastic lens is cheaper then silicon cell area.

landyacht.318 · July 2007

Re: PV panel temps

Thank you for the Numbers! Although I have since lost the incentive to heat my shower water when camping by running some elaborate closed circulating water heat exchanging system. It's good to know a 15 deg c drop yields about 17 percent more power.

Now I'm kind of thinking of ways to increase the Airflow around/under my panel, only when keeping it flat , slightly above the roofline of my RV. I've come to realize that my 130 watt panel will not power my 2.7 amp fridge with the surplus I originally thought I'd have before I started reading this forum. I'm trying to figure out ways to reduce the duty cycle of said fridge.
Does anybody know if the internal temperature sensor is located on or very nearby the cooling tray on a Norcold DE 0040? My thinking is that if I'm not using the full interior capacity of the fridge I could block off areas on the bottom I'm not using, decreasing the amount of space the condensor has to cool, reducing the duty cycle. I've posed this question on some RV forums and have come to the conclusion that a majority of people are practicing politicians: They ramble on endlessly without addressing the question.
Am I being slightly hypocritical?:D

BB. · July 2007

Re: PV panel temps

Generally, it is not the space that is being "cooled"--it is the heat coming in through the exterior insulation that is being removed by the refrigeration unit.

You could try "insulating" the side/bottom/door (where the cooling plate/coils are not)... Placing insulation on the outside of the unit is generally not a great idea. Typically, water condenses between the wall and the new insulation, causing corrosion and mold in the puddles.

Otherwise, if it is available, I would just place block ice in the areas where you have "extra" space in the fridge. It could last for days and reduce the cycling (a bit) of the cooling unit.

-Bill

landyacht.318 · July 2007

Re: PV panel temps

Bill,

It is not a top loading fridge, so a block of ice would wind up puddling on my yet to be installed hardwood floors.Waterproof plastic bags rarely stay that way. And a plastic container wastes so much space, not to mention the inconsistency with block sizes. I frequently camp for extended stays deep in Baja, far from any stores. If and when I aquired Block Ice down there, it seemed not to last as long as the blocks I'd buy north of the border.
Once I built a superinsulated container inwhich to place my 5 day cooler, and could squeak out 10 days of cold beer in 90 degree heat, but after that it was hot beer, canned food and fish that wouldn't keep past the next meal.

The fridge is designed to be installed into a tight fitting cabinet, and I'm hoping that 1/2 inch plywood on both sides, will help insulate it somewhat. I plan on polyurethaning the adjacent wood and using some extra hardwood floor undlerlayment/moisture barrier foam between fridge and plywood. I have a large louvered vent behind the compressor and cooling fins.

I realize a top loading fridge would be more efficient, especially with continous door openings, but went with the front door for convienence/interior design. It's only a 1.7 cubic foot fridge, but I figure after 2 or 3 weeks or without a resupply run, the only thing I'm gonna need to keep cold, is any fish I catch and some condiments, and maybee some cheese. I was thinking if I effectively blocked off the unused portion of the fridge's interior with some thick high R value foam tight fitting foam. The duty cycle would drop accordingly.Especially in 90+ degree daytime heat.

I guess the only way to find out is to try. However if the internal temperature sensor is not located up top, by the freezer compartment, then there is no point.

Right now The AC/DC fridge is in an 86 + degree windless laundry room, and when I chose to run it in these conditions (on AC) ,I estimate it ran 40 minutes out of 60. The door, sides, and bottom were cool to the touch.

16 hours x 2.7 amps = 43.2 amp hour daily in 85 + degree heat. I'll have 210 or 220 amp hours of deep cycle house batteries, and only a 130 watt panel.

You can see why I'm stressing the duty cycle.

BB. · July 2007

Re: PV panel temps

If you don't need the freezer section of your "fridge"... Take a look at this thread "Chest Freezer as Refrigerator".

Jay has a standard 120 VAC 60Hz 7 cuft freezer (running as a fridge) using about 1/2 the energy as your 1.7 cuft dedicated unit.

I am not sure that this meets your overall needs (in an RV?), but may be worth thinking about using a generic energy star approved fridge vs a dedicated DC unit (other thread here and information there about how inefficient some of the off-grid appliances really are).

-Bill

crewzer · July 2007

Re: PV panel temps

We live with 150 watts of panel, 750amphours of battery, a xantrex tc 20 charger, morningstar 300 sw inverter, Honda eu1000 generator, tri-metric meter…. We use about 25amp/hours/day, the system charges at about 10-12 amps average

You gotta live where I live. (Far northern Ontario, Canada) My panels in the summer put out 16 amps, but come winter, -35c the same panels put out 30 amps. The combination of super cold and major reflection off the snow.

What I do know is that at the battery/meter shunt the number reads about 14+-vdc 14-15amp on a good noon in the summer. +25c (80f)

At -35c (-30f) on a good solar noon I get the same basic voltage, but can approach 29-30 amps of charge…. As noted, the panels are mounted on the northshore of the lake, and they get a HUGE amount of reflection especialy in the winter. I don't know how much of my increase is due to the temp, and how much from the added insolation. My hunch is that it is more relfection than cold. Having said that I do notice an output difference between 0c (32f) and -35c.

I should caution that the winter numbers are from memory since it is now July!. The true reality may not be a dramatic as stated but dramatic non the less.

the panels are BP solar 55watt+- and Siemans 63watt+-. I have them cobbed together with two seperate controllers, SCI Mark 22(s).

2 55 watt, 1 63 watt

Icarus,

Thanks for all of the additional info. You’ve no need to explain your system configuration; it is what it is. I remain a bit corn-fuzed by the system specs and performance data you’ve posted.

Due to your location and its wide range of environmental conditions, you should indeed see a corresponding range of output current values from your system. However, because your controllers are PWM type and not MPPT, temperature will have little effect on your PV array’s performance.

I can’t find specs on a Siemens 63 W PV module. But, let’s assume that’s what you have, and, along with the two BP 55 W modules, that you have an array rated at ~173 W STC. The Imp spec for each BP module is 3.33 A. Assuming ~3.75 A from the “63 W” module, that all adds up to 10.4 A. Allowing for a summer array tilt angle local environmental conditions, readings in the 10 A to 12 A range make sense.

Frankly, I’m having trouble with the summer 16 A figure. The reflection of sunlight from water in the summer is quite low (due to low albedo associated with high angle of incidence of sunlight striking the water), and a summer tile angle (~34 degrees?) is not geometrically conducive to surface reflections. But, exceptionally clear air and/or high altitude and/or an edge of cloud event would lead to an increase in output current. So, brief excursions up to 14 A, 15 A, and even 16 A are possible, but, based on what you’ve described, a sustained output in the 10 A to 12 A range is what makes sense to me.

Winter performance in your location should indeed be something else. Reflection from fresh snow is in the 80% - 90% range, and reflection from the Sun at very low angles on water is >90%. So, assuming a winter tilt angle for your array (64 degrees or more?) output current could easily be doubled to 20 A to 24 A. Again, 29 A to 30 A would be possible, but I’d be surprised to see it as a sustained value.

But, I haven’t seen it all, so who knows?

Finally, let me make a pitch for spending some of your money for you. Considering your location’s cold and exceptionally bright winters, an MPPT controller should be of great use to you. Dropping from 25 C to -25 C ambient should see an array MPP voltage increase of ~25%, and an MPPT controller would convert most of that “extra” voltage into additional charging current. :cool:

HTH,
Jim / crewzer

icarus · July 2007

Re: PV panel temps

Jim,

You've got it just about right. When I started this thread it was only to show by anicdote the effect of cold. I make no claim that I can get 15-30 amps "normally". My point was that I "have" seen these numbers when conditions are perfect.

For the purpose of calculation, i use 10 amps as an average output and that seems to work. As to your suggestion about the controller, I do understand. This system has evolved over the years. (And I'm cheap!) I know i could get more output from the system by employing a number of methods, but the fact is, I almost can't use all the energy that the system produces on a daily/weekly basis if the weather is good.

I think that the trap that most people who have come from grid power fall into is not looking at the load side very carefully. With the advances in cfl/led lighting, as well as inverter technology, we get by with a very small average amp hour draw. (there is a nice selection of 5-7watt, glass globe cfs out there) With a bit of planning, with everything running in the evening including the radio (.6amp) satellite modem (1.4amps) 2 small fans (.25+-amps each) plus a slew of cfs we tend to burn less than 4amps/hour. We are good at turning things off when we don't need them, but we keep enough lights on to be comfortable. (I grew up on kerosene lamps, so having 24/7 ac lights is really nice!) So in round numbers 7 hours @ 4 amps=28a/h. My panels average 10 amps for about 6 hours=60a/h. Toss in 10-20a/h for charging things like the phone and the laptop during the sunny part of the day.

As I have said earlier, the "needs" grow as the technology improoves. We started this system to run the circuit board on the propane fridge. Then "Oh, how 'bout a night light, a radio, and so on. I have tripled the panels in 14 years and quadripled the batterys. I'm sure there will come a time when I "need" more,,,but.

I love this stuff and wish I could afford all the toys.

Icarus

PS. Once again, don't quote me on the above calcs, they are from memory and serve only to illustrate the point.

crewzer · July 2007

Re: PV panel temps

Ah... much clearer!

Thanks,
Jim / crewzer

PV panel temps

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