Friday, April 30, 2010

How much solar collector area do I need to heat my home?

I get asked this question a lot.  Its a good question, but the problem is that its tough to give a good answer. 
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.
- 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.
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.

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...



  1. Assuming a fixed setup, they always seem to be aligned for maximum efficiency in summer. In August, the water coming out of my panels is 210 degrees. Instead of having (for example) 100% efficiency in Summer and 30% in Winter, wouldn't it be better to have 60% efficiency all year?

  2. Hi,
    I did mine with a steep tilt for more efficient collection in the winter, and for less efficiency in the summer. I think its a good way to go, but you do have to install somewhat more collector area than a system that has the tilt optimized for spring/summer/fall.

    I'd guess that on commercially done systems with collectors costing $30 a square foot that they feel its better to put in just enough collector area for the system to work well in 3 seasons with and to let the system performance fall in the winter.
    If you are doing the system yourself at $5 a sqft for collectors, it seems to me it make sense to add the extra collector and make the tilt more optimal for winter.


    It realy depends on where you live and what you're using the hot water for. For DHW the best tilt angle is your latitude. BUT if you're collecting heat for both DHW and home heating you should go for a steeper angle. Don't even try to collect heat in December. Overheating is sometimes a problem in the summer so I optomize my tilt angle for mid February

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