An unavoidable aspect of photovoltaic (PV) solar panels is that they become less efficient when they warm up. [Tech Ingredients] explains in a new video the basic reason for this, which involves the input of thermal energy affecting the semiconductor material. In the subsequent experiment, it is demonstrated how cooling the backside of the panel affects the panel’s power output.
There are commercial solutions that use water cooling on the back of panels to draw heat away from panels, but this still leaves the issues of maintenance (including winter-proofing) and dumping the heat somewhere. One conceivable solution for the latter is to use this heat for a household’s hot water needs. In the demonstrated system a heatsink is installed on the back of the panel, with fans passing cool air over the heatsink fins.
On a 100 Watt PV panel, 10 W was lost from the panel heating up in the sun. After turning on the fans, the panel dropped over 10 °C in temperature, while regaining 5.5 W. Since the installed fans consumed about 3 W, this means that the fans cost no extra power but resulted in increased production. Not only that, but the lower temperatures will in theory extend the panel’s lifetime. Though even with active cooling, even the best of PV panels will need to be replaced after a couple decades.
Thanks to [Stephen Walters] for the tip!
Nice experiment. I would have gone for two panels, so you could test them simultaneously. The reference panel wouldn’t have te construction on the back, because that will influence the temperature to i guess.
A friend of mine with PV on his roof found spraying the hose over the panels made a very noticeable boost on hot days. (He didn’t do it normally, just as a test to see how temperature affected them).
Overall production could be higher on bright but overcast/cool days than on the super sunny days.
This is not correct. Overcast is 95% cloud coverage and therefore production will be very low. Solar panels need direct sunlight to produce the most except for maybe some specific instantaneous special situations. They do love a cold and sunny spring day though.
This is a cool overcast day(66 F 10 hr 6 min):
https://pvoutput.org/intraday.jsp?id=90740&sid=80341&dt=20230112
This is a cool sunny spring day(59 F 13 hr 9 min):
https://pvoutput.org/intraday.jsp?id=90740&sid=80341&dt=20220419
This is a hot sunny summer day(86 F 14 hr 22 min):
https://pvoutput.org/intraday.jsp?id=90740&sid=80341&dt=20220620
Everyone should have at least a single panel system and a weather station. It is a great way to learn about solar and the movement of the earth around the sun.
Poor practice. Thermal shock can cause panel glass to shatter. Minerals in the water will leave a residue that will decrease the panels efficiency over time, eliminating the accumulated gains
But cleaning them is recommended to remove dust so your argument us voided
If the glass is of such poor quality that it can be cracked by hosing it on a hot day, it shouldn’t be used to protect solar panels. Think about car windows and pyrex for baking pies.
Every type of glass has a maximum cooling and heating rates. If you hit hot pyrex with ice water, it can shatter.
Borosolicate glass Pyrex will tolerate that sort of 100-150°C thermal shock. American ‘Pyrex’ will not, as that is tempered soda-lime glass.
Borosilicate glass takes about 180 C thermal shock. If you take a dish out of a hot oven and dunk it in cold water in the sink, it too will explode.
As it can rain while the sun is out, I would offer that that’s poor specification, let alone build quality.
I’d previously thought of creating a box stand for a solar array that would cool the panels and lead the “waste” heat to an air source heat pump – the idea being that during the winter (and summer) it would improve the efficiency of both.
In the winter alllthough waste heat would benefit a heat pump, it would not be necessary for the PV pannels because they are cool from the environment (assuming cold weather and therefore heating requiremnt). In the summer the waste heat would not benefit a heat pump if it was operating in cooling mode. If you live far north and heating is required in the summer as well then your PV pannels would most probably not require cooling anyway.
I had a similar thought, but using water cooling and doing a liquid to liquid hot water tank heat pump
Having airflow beneath the panels can be quite a simple way to improve efficiency a bit.
Forced air is an improvement, especially with a bit of heat sinks.
Water cooling is interesting.
For winterization one can add antifreeze to the water. A 60% glycol in water mix doesn’t freeze until about -50 C, and few places on Earth gets that cold.
However, how to watercool the panel is debatable. I have seen some use corrugated plastic pressed up against the back of the panel. With milled out openings in the corrugation and glued on plastic cover plates for the fittings and water distribution into the corrugation. Seems a bit “cheap” in my opinion, especially since plastic isn’t that good of a thermal conductor.
Personally think just gluing on a second backing would be simpler. Effectively forming an aquarium between the back and this extra sheet. Where the water then has direct contact to the backside of the panel.
Or you could just drain it in the fall
Glycol also helps reduce corrosion and biological growth. So it isn’t just about not freezing to be fair.
There are bacteria that eat glycol.
This concept is facinating to me. I’m an HVAC contractor specializing in whole home electrification projects in MA. We see cold winters and hot summers here. We often install air to water heat pumps with radiant floor heating systems. It seems to me like the extruded aluminum plates used for staple up radiany systems could be installed on the underside of the panels and then pex could be run just like we do in staple up radiant applications. We use variable speed delta tee circulators that draw anywhere from 9 to 57 watts. This water could be run through the coil of an indirect water heater to preheat or potentially provide full heating for the domestic water. It seems as though if gaining 5 watts per panel anything after 10 panels is a gain and that assuming a really hot day with heavy demand on the pump AND it discounts the free domestic hot water.
Due to the regulatory environment PVT panels are quite common in France and there are a dozen of manufacturers that offer PV panels with water heat exchangers on the back. The water is not to warm, but can be usable for heating if you have floor heating and a heat pump.
The keyword for effective googling is “PVT panel”.
Really? Consult you power bill and find how much you pay for 1 kWh. And how much time to wait until the fans are pay with the watt difference. Lol.
Do the math. He recovers more than 5% of the rated power and extends the panel lifetime. It’s not nothing, and as he explains, it’s not even fully tuned for best efficiency. A tuned solution could potentially approach 10%.
yes, but no costs for the extra hardware is given, and fans running outdoors are likely to need to be replaced multiple times over the years. More data is needed including lie costs to determine if this is useful.
I lived in the Middle East – next to Abu Dhabi’s Masdar area where they do a lot of solar research. At the time the panels did perform like crap so 300w panel would give maybe 170 watt output – and cable loss was very high as well. Then add dust from the Desert and you went to maybe 100 watt out per 300w panel during summer.
Masdar claims now to have solved some of the issues with heat so loss is about 30’ish % less. But still high.
I had a few panels running with sea water cooling at my home – and that increased efficiency quite a bit – but in the summer the sea-water is up to 35c – so it took a lot of flow to cool the panels – eliminating most of the gains. And you had to deal with lots of rust as the water there is very salty. (Salty, both due to evaporation and many ME countries dumping their brine from sweet water reverse osmosis plants back into the sea)
Yeah when I was over there I was amazed at the amount of work needed to make a city habitable. Reminds me a little of Dune
I believe at Masdar City, their solar panels were net negative. The way they were mounted increased internal building temperatures enough that more energy was spent running air conditioning than they produced.
He greatly exaggerates the impact of heat on panel life. The LONGi LR4-72HBD panels on my roof are warrantied for <=0.45%/yr degradation. Actual degradation in temperate climates is around 0.1%/yr. The top 2 failure modes for PV panels are backsheet failures (cracking or delamination) and blown bypass diodes. I prefer bifacial panels because the dual glass eliminates backsheet failures.
I have sprayed panels with water, and it does cool them down and increase output. A garden soaker hose laid on the roof above the array may be worth trying for evaporative cooling.
Just don’t try in an area that has water restrictions.
I would be concerned about alga and moss growth if one continuously wets the surface. Since these will quickly block the sun’s rays.
And some mosses and algae grow really fast.
However, growing algae can be an energy source in itself. But I doubt that is economical nor practical at a small scale.
So put some of those MicroDrip (or what they are called) watering systems in the space under the panels and spray them from the back side. This eliminates problems with residues on the glass after evaporating as well. Turn on when the panel temperature gets too high and blow the remaining water out before winter time. It may suffice to put out short water blasts every now and then, evaporating carries away quite a lot of heat. [Testing needed]
That can indeed be another solution.
However, the connection box underneath each panel might likely complain about water spray. But it is a difference between a water mist and a pressure washer. So this is likely not a major concern.
Good point: the test setup should consider the effect of hot spots (more precise: not cooled spots) on the panel, where something on the back side blocks the water, be it connection or mechanical support structures, or just uneven water distribution. On the other side, series connected single cells should be less affected by this than by shadow, since the temperature changes the operating voltage, while the current depends on light intensity. Mechanical stresses by too much or too suddenly applied water should be monitored in a test setup, but I would guess a solar panel rated for outdoor use in wind and hail storms can handle this sufficiently well.
One definately should avoid pressure washing the connection box with the cooling water, but a plant watering system should already avoid pressure washing the soil, so… :o)
nope – while outside temperatures in the UAE are around 50+c in the summer – the black solar modules are > 95c in the sun – (95-125c observed over a day) that is a decrease of panel efficiency by about 30-45% (theoretical temperature coefficients) – excluding cable loss and charger loss at high temperature.
Charger loss could be as much as 30% at 50c ambient dependent on charger placement. Battery loss gets high as well as batteries slow down absorption when they are hot. Btw It is very hard to find “constant” cool shade in the ME.
Some modern panels are better spec wise – but still about 25% loss at > 95c – and then there are ALL the panels with spec sheets that are very “optimistic…”
That’s a great test to show the effects of forced air cooling on the panels. Fans have a limited run life, can get jammed with objects, waterproof ones are expensive, etc. etc. Probably better off making heatsink fins or something similar on the back of the panels as it would be more reliable for a maintenance free setup.
It might be interesting for a roof mounted setup to assist with hot water heating. There are solar (non pv) panels that are designed for this already (to heat swimming pools, etc.) I’m curious if there a hybrid setup already exists out there, one where part of the system is PV to generate electricity and some other attachment to also heat hot water or radiant floor heating.
This definitely works. As a laboratory experiment, it’s pretty cool. But the cost and hassle of adding an aluminum plate and fans to a solar panel far exceeds the ~10% power gain. It would be less costly to just add 10% more panels.
There are lots of things you can do to improve performance of a system, but you have look at the options.
For a more passive evaporative cooling approach there are the agrivoltaics options …
Maybe some ionocaloric cooling?
https://www.sciencealert.com/scientists-just-invented-an-entirely-new-way-to-refrigerate-things
We, in South Africa recommend and have installations of FLOPPY Sprinklers which are overhead sprinklers delivering 750l/hr@2bar spaced at 12x12m intervals spread over and in between the panel array. These sprinklers use water from ambient temp supplies, which distributes it over and above panels which then simulates rain with 3.7mm dropplets. Short bursts of 5 minutes at regular intervals, which can be automated, then instantaneously cools the panels as well cleaning them from dust, debris and bird droppings. From data gathered, it is apparent that when applying the water, an immediate positive result is measured on the delivery. The installation is very easy at low capital cost with enormous long term returns. Large and small array’s can be equipped during installation or on existing applications.
Is the water deionized?
Rotating and moving up and down to peak the panel output, Plus a passive heat sync is more efficient than putting fans on the back. Most Solar panels are not even pointed directly at the sun for any meaningful amount of time. So, they never see peak efficiency… but for a couple of minutes a day.
Dual-axis tracker mounted panels?
Yes… that would be great.
Sun-tracking solar panels is a well-known idea. It significantly increases the electric energy output.
Also well-known is that the electro-mechanical system require to move the panels is problematic, and it is cheaper and more reliable to just put up more fixed panels. That’s why tracking is rarely done.
100w Photovoltaics with a 3watt fan cooling them gain 10w greater power, it seems possible that air moving piezoelectric crystals on pv panels vibrating at well known 1-11 mhz cycles per second, or levered, overlapping mhz piezoelectrics could vibrate a billion times per second, motionizing many orders of magnitude more air than a fan, causing even greater cooling and energy gain, with, possibly, or possibly not, the ability to make the piezoelectric on the wafer during the ic fab like process, another cooling of photovoltaics technology is to use 2 nm resolution published silicone mold printing to print nanopillars on the back of the wafer, or emboss very soft electroplated metals, or vapor deposited metals that are as hyperaffordable as aluminized candy wrappers and aluminized mylar balloons that already have semitransparent metal thickness, these could work on 300-800 suns concentrator photovoltaics as well.
Um the fan will croak long before the solar cell will. Fans are the Achilles heel of electronics. You can get a nice notebook with an SSD and you think good, I am done with moving parts but you still have the fan that will craok in a year. Urg..
Fans are available with all sorts of lifespan ratings.
Why not put shade cloth in front of the panels to stop them heating up?
Sure, you could even fit flexible panels on the shade to multiply the gain.
more seriously, my brother installed some west-facing shade cloth over the large inverters of his solar farm, and saw some nontrivial improvements in efficiency.
they’ve got fans for active cooling, but just keeping the direct sun off shaved 10C or so (if i recall correctly) from their daily peak temperature.
As with the various ideas often thrown around for getting rid of dust on Martian surface probe solar panels (from brushes to air-dusters to shaking panels to electrostatic dust repellers, etc), it is very likely that whatever cost an efficiency improvement system has could be better spent on growing the solar array for the same or better power gain without introducing a new failure mode.
loss of the active cooling doesn’t produce a failure in this case, just a slight reduction in efficiency. (not that i’d personally bother with this except in some remote energy harvesting application.)
They could possibly cheaply laser engrave, or even chemically etch micrometer or nanometer sized depthy microtexturing on the back of the photovoltaic wafer slice, at an egg crate 3D depthy parabolic pattern 1/2 to 1/4 mm deep, and tapering from 499 micrometers of diameter at the back of the wafer surface to 4-8 nanometers of diameter at the deepest area that’s a bunch more warmth radiative surface
We conducted a test of active watercooling on a 25MW floating pv-plant.
There were noticeable improvements in efficiency and thun increased yield.
However, the gains were outweighed by the power consumtion of the pumps and the cost of maintaining the cooling system.
Has anyone considered passive cooling? I used to work on lighting control systems and they often put off a lot of heat. The design of the casing can be done two ways. Forced air with fans and filters, or with passive, chimney style design. These can be used for north of 10 years with minimal dust buildup and can dissipate quite a bit of heat with no maintenance.
Beware of using the cheapest method of hosing panels. It is quite correct that you can get accumulated lime or other minerals which can cause “hot spots” on the back and dead spots on the front.
The use of a copper finned rear cooling system has been proven effective. My friend has used it in Hawaii since the 1980s and has ELIMINATED the need for his electric hot water from the output of the fins into a reservoir in his attic.
At the time of installation, there was no backend allowed to the power company so he has an LED lighting system around his whole house and an inverter for the important appliances.
It has proven very cost effective.