Solar Hot Water Numbers in for March 2011

Now that we have a solar hot water system, I've been computing the contribution to the water heating load. My house is at 42.5 degrees latitude in eastern Massachusetts. My solar panels are tilted at 45 degrees and the roof azimuth is 250 degrees (south is 180 degrees, southwest is 225 degrees, west is 270 degrees). I have three Schuco Slimline panels.

• In January, the panels were buried in snow. The solar contribution was 0.0%. 
• In February they were in snow for 6 days. The contribution was 7.6%. 
• In March, the contribution was 19.5%. 

On the best day, the system captured over 18,000 BTUs (British Thermal Unit). A BTU - raises one pound of water one degree Fahrenheit. My tank is ~120 gallons or about 1,000 pounds of water. Therefore, if we didn't use any hot water on that day, my tank temperature would have gone up about 18 degrees.

Priceless!