To select our products, we evaluated a large number of collectors, and selected the product from SolarPanels Plus.  We have tested a number of configurations for this product in the upper Midwest, and are very pleased with the heat energy collected, the design, and quality of construction.  Below, you will find a small fraction of the data we have collected for the SPP-30 product which we sell and install. 

The data in this section was collected using our model greenhouse located in Leonard Michigan. 

Heat collection rate on 11/06/2009 around 12 noon.  Our greenhouse has 2 SPP-30 panels mounted at a 42 degree angle pointed due south.  These panels are connected to a large heat reservoir using well insulated (R8) 3/4 inch copper pipe and a 80 watt Armstrong recirculating pump.  The collected data was used to determine the BTUs of heat collected per minute. 

Observation: 
Temperature of fluid entering collector cold side: 165 degrees F
Temperature of fluid leaving collector hot side: 196 degrees F
Flow rate 1.9 gallons per minute

Physical property data:
Water/Corn Glycol solution Specific Heat: ~ 0.85 BTUs/lb degree F
Water/Corn Glycol solution Density: ~ 1.046  or 8.368 lbs per gallon. 

Calculation:
BTUs per minute = temperature rise * weight per minute * specific heat
= 419 BTUs per minute = ~ 25135 BTUs per hour 

If we assume that we get 4 hours of Sun on a good day, this would be equivalent to over 100,000 BTU's.  One way to think about this energy, is to compare it to a gallon of propane.  A gallon of propane has between 88,000 and 91,000 BTUs depending on the information source.  Our two SPP-30 collectors are able to collect energy more than equivalent to a gallon of propane, on a good day. 

The night of November 5th in Leonard MI was a cold clear night with a low at our location of 24 degree F.  On the morning of November 6th, the collectors were covered with ice crystals.  A picture is shown below. 

The collectors were glittering in the sunlight.  Out of curiosity, we checked the collector temperature, expecting it to be quite low, and were surprised to see, that even when the collectors were covered in ice crystals, they were still generating heat, and at the time the picture was taken (~8:00 AM) the collector manifold had already heated up to 85 degrees.  We have measured the temperature of the collectors just before sun rise, and they are always near the air temperature.  We were fairly impressed that the collectors had heated up almost 60 degrees through the ice crystals in a short period of time. 

Shortly after we took this picture, the sun melted the frost off of the greenhouse windows and solar collectors.