Free heat

For those of you looking to reduce your heating bill without converting to another fossil fuel or buying a wood stove, this might just be the ticket. Convection Solar space heating. How is this different than a PV solar panel? Well first of all, it' not Photovoltaic,or PV, so it does not generate electricity. In fact, trying to heat your house with electricity produced by your own PV panels is like trying to power your car with rubber bands. Yes it can be done, you just need a lot of rubber bands. On the other hand, if you use all the power from the sun, not just 13% which is what PV panels capture, then you are in for a surprise as to how much heat you can produce and how much money you can save!





This type of solar panel heats air which is then allowed to enter the house therefore reducing the load on the main heating system during sunlight hours. There are many companies making these convection solar space heaters that work just great, but of course, there is a cost; somewhere around $2700. Not cheap considering the output of a single unit.

But if you have a little time on your hands and if you are handy and want to venture into making one of these yourself, the good news is, you CAN! In fact, some units are made exactly of that! CANS. Yes recycled pop cans that have had the top and bottoms removed, painted black, and glued together under a sheet of glass or plastic. Of course, there are different ways of putting one of these things together. You can use any highly conductive material ie. aluminum, under glass or plastic, so as not to loose the heat gain, then vents in and out of the unit from the house as depicted in photo.

Here is a little math for those who want to build one.
We know the sun delivers slightly more than 1000watts per square meter and we know that there are losses in the area of 30% to 40% because of heat dissipation, reflection, inefficient heat transfer etc. I assume 40% so as not to over estimate. This leaves us with 600watts per square meter.

A sheet of plywood is 4'x8' or 32 square feet, just over 3 square meters. It can therefore absorb the equivalent of 1800 watts or just over 6100 BTU. (just over 2000 btu per square meter), or 56.25 watts per square foot. All calculations are based on a "per hour" basis.

Now calculate the size of the available wall (south facing of course and no obstructions!) and determine the amount of heat you would like to produce. You will probably run out of wall!

In winter, the sun does not shine all day long. To be realistic and not to over estimate, the actual average sun light based on the worst month of the year is 2.5 peak sunlight hours per day. Of course it's more than that overall, but not peak.

Lets say you have 24 feet of wall, 8 feet high, you could potentially produce 27000 watts per day, or 92000 btu. The amount of heat an average furnace produces in one hour of non-stop operation.

Now consider the savings. At $0.10 per Kwh, you are saving $2.70 per day for the worst month. Of course the other months get better so the saving is actually higher. $2.70 x 31 days is $83.70 savings per month based on electric heat. Not bad for free heat!

Now go get that tape measure and start figuring!