So I ran across this idea while discussing solar thermal and solar air on the Masonry Heaters discussion, and thought I’d post it up for reference.
There are commonly three types of solar panels. Solar Thermal (water), which uses sunlight to heat a black box with water tubing, Solar Thermal (air) which does the same but to heat circulated air, and Solar Photovoltaic, which are the ones which produce electricity.
Add a fourth type, PV-T panels, or combined Photovoltaic-Thermal. This makes sense for several reasons:
High efficiency PV panels only convert around 22% of the energy into light. A bit is reflected, but around 70% of that is converted into heat. Panels can be around 30-40 F higher than ambient temps.
As PV panels get hot, they lose efficiency. For every degree Celsius above 25°C (77°F), a solar panel’s efficiency typically declines by 0.3% to 0.5%. On a hot 95 F degree day you may be losing 16% of the panel’s output.
Heat also shortens the lifespan of PV panels, and is a major factor in their 25 year lifespan. Cooled panels could possibly last twice as long, although this is hard to say given their already long life.
PV-T panels basically add a thermal capture device on the back of the panel, cooling it down and improving performance. The gathered heat can be either air or water, depending on panel design, and used accordingly. The air version looks very simple. The neat thing is, if you have solar panels anyway you really just need to build a box around behind them and blow air through it to cool it down. This looks very DIY friendly.
Here’s a video I found talking about it, haven’t dug much deeper than this.
This is all true. The cooler the cell is, the better the conversion efficiency. IF it is on your roof, the air gap, can actually be used to cool the roof as well since the panel catches the sun’s heat, then the air flow cools off the air before it gets to the actual roof and into the attic. And certainly if you have a use for the low temperature heat, it can be used the other way as well. You don’t even need the solar panel to get benefits from the airflow, but there is a cost vs benefit to this.
There was a group in I believe Utah University, that added thermo-electric to the back of panels. IIRC they gained 10% more output.They were most likely in the desert though.
Haha i was thinking only last summer i should make sure the junction boxes are water tight on the back of the panels seal the edges and fix a backing plate onto them and try filling with water to keep them cool with a small pump flowing from my water tank . might try that with just 1 panel this year .
you might be able to get away with a ‘convection water heater’. where the water moves up by convection, and thus eliminate the power sucking pump. The ones I have seen were strictly for hot water using plastic bottles to cover a hose running through them so I don’t know if the temp difference behind the panel will be enough for a good flow. Some people use the bottle method for pool heaters.
Not a bad plan if you are planning on putting them on a roof. If they are ground mounted better to take advantage of the new dual sided panels. They can gain an extra 10-20 percent production just from indirect light hitting the back of them …
While that is true, he might look more at agravoltiacs. Where you grow crops or graze around the array of panels. You supposedly can get better yields of certain crops that are grown under the panels because it keeps the plants cooler during the day, and warmer at night.
I communicated with an on-line fellow forum member in Maryland iirc quite a long time ago who was already then spraying water on the back of his panels and then collecting it at the bottom of the panels to pump back into his hot water tank in the house. He didn’t give details on the sealing around the wire connections but he must have I guess.