Concept

Solar heat collectors are the focus of this discussion. Collecting solar energy for electricity (PV) is the focus of the next section.

Insolation is the amount of solar radiation received on a surface at a particular location. This can be expressed as BTUs/square foot. At any point in time, insolation is maximized when the surface is facing directly toward the sun. Thus, the conceptual answer to energy maximization is to have a tracking array with the panels always pointing directly toward the sun; this would require the tracking mechanism to move east to west during each day and the angle relative to the horizon would change through the seasons as the sun passed higher or lower in the sky. So while tracking can provide significant gains, it is a bit impractical for PV in our climate and most dubious for 10 panels filled with water and connected to copper pipes.

Micro climates can affect insolation during a day. If you typically have clouds or fog in the morning, the moving your orientation towards the west will increase insolation. I don’t have that problem on a regular basis, so due south is still best for us.

The main question that remains is, "At what angle should the collectors be set?" to maximize solar heat.

Application

I approached this with a little common sense rather than a lot of modeling or analysis. First, I decided to have two sets of collectors that could function independently. This allows me to shut down one set during the warmer part of the year and then just collect heat for domestic hot water.

I set both arrays at 63 degrees. At this angle the collector is perpendicular to the sun at noon on the coldest day of the year, January 21st. While this won’t maximize annual or even winter BTUs, it will maximize BTUs around when I need them most, December 21st through February 21st.

The only question that remains for my house is, "How many panels in each array?" I decided on four smaller panels (approximately 3x10’) for year round operation. This should be more than enough for domestic hot water during the warmer months.

The larger array, which primarily delivers heat during the winter, is six panels (approximately 4x10’).

One of the interesting questions that remains is, "Do I have the right number of panels?" What is nice about both the number of heat panels is that it is easily adjusted. Heat collectors are not like PV, where each string needs to be balanced. It is unlikely that I will need more heat collecting panels, but if I do, I can just add one.

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