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.
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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.
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
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.
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.