The answer depends on many factors -- the main ones being:
- The heat loss from your home -- that is, how well its insulated and how big it is.If you live in a cold climate with not much sun in the winter and have a large and poorly insulated home, you might have to cover half the county with collectors to get a high Solar Fraction. On the other hand, if you live in a in a good sun place (say Denver), and have a modest size and well insulated home, the collector area needed for a good Solar Fraction will be far far far less.
- Your local climate -- both how cold it is and how sunny it is.
- The percentage of solar heating you want to achieve -- the Solar Fraction.
Thanks to Andy Schroder's new simulation to estimate collector energy output combined with our Home Heat Loss calculator, there is now a fairly simple and fairly accurate way to answer this question for your house, your weather, and your collectors
The method basically uses Andy's simulation tool to estimate the heat output for the collector installation you are considering, and uses the Home Heat Loss Calculator to estimate how much heat your house is losing. Entering the results from the simulation and heat loss calculator into a small spreadsheet then gives you an idea of the fraction of your heat demand you can get from solar for the collector area you specify. The end result is a month by month estimate of 1) house heat demand, 2) solar heat output, 3) solar heating fraction, and 4) fuel dollars saved.
I think that the main value of the method is that it allows you figure out the best place to spend your money on energy saving projects. Are you better off to reduce your home heat loss with insulation and sealing projects, or would a solar heating system save you more, or is some combination of the two the best way to go?
All the gory details here...