For as good as solar panels are at converting sunlight directly into usable electricity, especially for how cheap they’re becoming, they can still only gather around 20-30% of the energy that hits them. That’s fine if you have a large roof or a huge tract of land, but if you have limited space and need to do something like heat a home, there are better options available to capture more of that energy. [Greenhill Forge] has built five solar air heating panels to test this concept, and do it much more inexpensively than commercial options.
These solar heaters use sunlight to heat a fluid, in this case air, and move that heated fluid to another space. Each panel is about two square meters, insulated on all sides except the top, and configured in a way that air can flow past something that the sun has heated. The first panel, a control, does not use a glazing to help trap this heat, but the rest all have a polycarbonate window to increase the greenhouse effect of the panels. The four remaining all experiment with the way air flows around a black corrugated steel sheet to gather more of the heat, with the fifth panel using a set of black screen instead.
With the panels all set out in the sun, [Greenhill Forge] is using a set of thermocouples from a previous project to measure the efficiency of each panel. Surprisingly, he found that the panel using the layers of screen was the best at gathering energy, although he notes several times that these types of panels are extremely sensitive to changes in physical configuration, so this is not the most definitive test possible. However, at only around $100 per panel it’s quite a deal if the goal is a usable space heater that doesn’t use any fuel or grid electricity.


???
I’m kinda confused, why wouldn’t you rather use a solar water heater and then use radiators to get the heat out? Air is terrible at carrying any significant amount of heat.
I might be missing something. But it’s definitely not the fact that it’s an experimental DIY system.
Air is easier to pump around, and doesn’t freeze in the winter.
air isnt really easier to pump around than liquids are. And there are plenty of fluids that do not freeze at the temperatures of earth winters.
I think it is. Air is everywhere, so you don’t have to mind small leaks and your pump doesn’t need to be perfectly sealed or have very fine tolerances to keep pressure.
yeah the not freezing in the winter is huge. having to add antifreeze to my solar hot water system is the biggest pain about it.
since the antifreeze makes the water non-potable it also has to be kept separate from any useful water you are trying to heat — and that requires a heat exchanger. to simplify things, i am considering a system that automatically shuts off and drains when air temperature drops to 35 degrees, but you really can’t have your microcontroller flake out on you in a system like that
Also, if you have an efficient insulated collector, it can also boil the water into steam and build up pressure until something breaks.
If your ventilation fan stops, the collector might get hot but nothing dramatic will happen.
Warping if it gets too hot.
Me, in the Uk, wondering why on earth you’d want to heat your house when it’s 35C…
I’d keep the separate system with antifreeze. My grandma had solar water heating and it was very effective even in the winter, dropped her gas usage significantly.
He says it in the video, you can use the air directly for drying grain, or for air heating with out adding complexity of heat exchangers. If you want hot air this is easier and more effecient. He is working on a similar video for solar water heating, he also has a crew videos about making super efficient wood fueled water heaters
This is cool, well rather warm, but the solar heaters he built are only useful when the sun is up, and useless at night when temperatures drop.
I really like the idea of parabolic solar troughs with heat transfer fluid storage. That way you have stored heat to use when you really need it.
There are also evacuated tube solar water heaters. They take a lot less space and work fairly well even in cloudy winters.
I have them on my roof and they make our water heating bill zero. Always put a sediment filter though in their inlet thought, it’s a pain to clean individual tube otherwise.
It’s not very difficult to pile up a stack of bricks and blow the hot air through that first. At night, you simply bypass the collector and keep getting hot air from the pile of bricks.
Exactly this.
You’re not real smart are you. I live in Hawaii where everybody has solar water heaters. We have this because every type of fuel is super expensive here. Electricity super expensive fuel oils and gases have to be shipped in so they’re super expensive.
Your water heater tank stays hot for a very long time. You obviously don’t really know what you’re talking about. So maybe think about the things we may not know before we speak about them. If we haven’t tested them or experience them, we maybe not. Should speak about them.
If you need hot water, you would obviously heat water.
If you need hot air, you would obviously heat air.
Heating water to heat air, or heating air to heat water, would obviously add unnecessary complications unless there’s a proper reason to do that.
Alright: 22% efficiency* for the PV panels vs. 70-80% efficiency* for solar thermal panels sounds good. But it’s leaving out the whole chain beyond it. Heat transfer losses may amount to way more than your electrical losses if your heat source isn’t exactly where you need the heat. And if you have a need for heat in the warmer months you can use a heat pump which runs at about 500% that season of the year which will almost certainly get you more yield than the solar thermal approach. I get that this is cheap, simple, DIY and all. But the framing is missing the whole system aspect and quite frankly sounds quite ridiculous.
Long gone are the days when one would just build the thing for fun and tinker with it (which I think this video should’ve been). Now, (and I get it) in order to soothe the YouTube algorithmic overlords, everything has to be framed in such a ridiculous way.
The panels are all neat. But if your system delivers depends on all components and how they interact. I guess for your Jalapeño greenhouse this is great and that’s what the framing should’ve been.
*) And for the “efficiency” bit: That’s conversion efficiency from free sunlight. So it’s more of a yield than an efficiency in the classical sense.
How about replacing the black corrugated sheet with a solar panel, making a system that collects thermal and ev energy?
And exactly this.
Solar panels like to be cool. If the temperature goes up to 50-60 C the panel becomes less efficient and degrades faster.
Example:
https://www.semanticscholar.org/paper/The-Effect-of-Temperature-on-Photovoltaic-Cell-Fesharaki-Dehghani/4eb139ee8e2cc5d722b14ced834f35a8183b1188
go big or go home? https://en.wikipedia.org/wiki/Crescent_Dunes_Solar_Energy_Project
‘filed for bankruptcy twice’ that figures. Started construction in 2011 and by 2026 had their lunch eaten by cheap solar panels and cheap batteries. Maybe we shouldn’t go big, maybe we should go medium sized and numerous to minimise risk.
I wonder if you could get the benefits of the peak heat provided by the bug screen transpire one but also make it less sensitive to cloud passover by adding the sheet metal for some thermal mass.
Instead of painting the insulation black as he did with the bug screen one, lay a piece of the painted sheet metal down and put the vent through it as with the front pass one. Basically adding the two layers of bug screen for the transpire effect on top of the front pass design.
I just saw “Huge tracts of land” and stared snickering
https://www.youtube.com/watch?v=GPX-mW4l1rU
I wonder if that was an intentional reference?
Can the heat in summer be used to heat something else (soil ?) to be used for winter ?
no.
your asking waaay too much.
Storing heat for months is beyond reason.
It has been done, and it works well.
https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community
Couldnt work that well given that
“In 2024, a decommissioning process for the Drake Landing Solar Community began, where the majority of the 52 homes were converted to natural gas-fired furnaces”
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