Comments on: Build Your Own Solar Window Heater for $10 – Save $45 a Month

By: Scott

Scott — Fri, 05 Nov 2010 04:43:30 +0000

Use black felt – thick enough that you can’t see light through it while still allowing for good air penetration. This increases the solar energy capturing surface by magnitudes –

http://www.builditsolar.com/Projects/SpaceHeating/Kreamer%20Air%20Collector.pdf

By: jim spagnola

jim spagnola — Tue, 14 Sep 2010 19:17:57 +0000

Here at our huge sustainability project we have several solar heat applications. I was looking to hear an elevator control room, roughly 600 cubic feet. I would have to agree that the surface area of the solar collector has to be greater than the window itself. A widow by itself is a solar heater, it just comes over a larger area. I can see how a commercial solar window heater may give the illusion of producing more heat by concentrating it via fans through a small area. This application may be great for better spot distribution of heat, but as others have said, unless you increase the solar energy capturing surface, there is no greater energy yielded by an interior mounted solar capturing device.

By: Ben

Ben — Tue, 11 May 2010 21:29:58 +0000

Sorry Dudes – my PHD in physics brain calculates the value to be nearly zero – once the sun goes in the window, you already have most of it making heat. Unless you put something on the house siding to INCREASE the effective window surface that catches sun then you get no gain. Try another clear layer on front and hook it so air flows in and out through a window and you may have something! Best to use some insulating board to make the sides and back too.

Biggest thing is – gotta mount it outdoors to increase the heat into the house!

By: css1971

css1971 — Fri, 25 Dec 2009 16:30:51 +0000

It works because black substances absorb all (most) light and convert it to heat. Most rooms are light specifically to reflect as much light as possible. For the sceptical engineers and physicists, go look up emissivity and/or albedo.

However…

1. The max you’ll get is about 800-900 Watts per square meter of collector. That’s just the limit of what the sun can provide. So you’ll probably need several of these things. Making them into internal shutters on all south facing windows might be worth it. A single device, it’d have to be a small room with a lot of sun.

Curtains are usually designed to restrict air flow. They insulate windows, so even black curtains will be less efficient due to lack of air flow.

2. Insulation is way more important. If you have single glazing you might as well not bother, the heat will just go right back out the window. Take a look at the thermal conductivity of glass between 5 Celcius (winter outside) and 20 Celcius. It’s huge, kiloWatts in most windows. Adding a sheet of Plexiglass/Perspex/acrylic to the window with a 2cm air gap can cut that to a tiny fraction.

By: Jennifer

Jennifer — Thu, 17 Dec 2009 05:46:05 +0000

I tried this thing at home.While the air inside the box did indeed get quite warm-up to 120 deg F, it did not warm the room, nor did it give out any heat at all. Perhaps a slow-moving fan would help it circulate.I made the box out of insulation board, painted black, with a glass cover and a hole at the top and bottom.I had such high hopes for this simple device. Oh well…

By: karen

karen — Mon, 14 Dec 2009 14:44:09 +0000

Would this work with lowE newer windows? We are getting them, and wondered, as the sun heat doesn’t come through them much as traditional windows.

By: chasd60

chasd60 — Wed, 25 Feb 2009 02:16:00 +0000

It works because it is changing light energy into heat energy.

Paint one white and one black and you will see the difference. The white will reflect the light energy and the black will absorb the IR spectrum and convert it to heat.

The downfall to this concept is that you give up X amount of window space for X amount of heat. A better idea would be something like the sungrabber shown here http://campfire.theoildrum.com/node/5095

By: Shadowtek

Shadowtek — Thu, 02 Oct 2008 18:06:05 +0000

The box works by channeling solar radiation into a usable form, such as heat. Thats why you need a conductive source, as in copper.

SIDE NOTE

“By the way – I believe it is illegal to damage United States Currency in that fashion.”

Btw, I pay taxes, those pennies are mine to do with what I please.

By: YouDumbAsses

YouDumbAsses — Mon, 21 Jul 2008 21:25:44 +0000

you’ve all been had…

By: heatmiser

heatmiser — Thu, 01 May 2008 20:09:32 +0000

I may not be a professor, but I did go to engineering school where they drummed into our heads the concept of conservation of energy. Mike and Joan.of.the.arch are correct. That cardboard box with pennies in it is not going to make more energy come into the window than was coming into it before. Whether the sun is heating your hardwood floor or those pennies makes no difference. The box is probably just collecting heat that would normally have just radiated away into the house. There is only so much sunlight that is going to fit in that window.

By the way – I believe it is illegal to damage United States Currency in that fashion.