Solar Collectors and the Greenhouse Effect


Before examining SOLAR COLLECTOR PLANS you should clearly understand the difference between solar collectors and solar panels. Solar collectors harvest solar energy in the form of heat while solar panels harvest solar energy in the form of electricity. Solar collectors make use of the greenhouse effect while solar panels convert radiant energy into electricity and  are today only cost effective in remote off grid areas with a price of about $5/watt. A typical residential photovoltaic system has a price tag of $40,000 with a payback of about 50 years. A complete cold climate residential solar hot water system can be installed for less than $10,000 with a payback of less than 12 years. If you build your own solar hot water system for  $1500 the payback period should be less than three years. After that Mr. Sun will be paying your hot water bill. If $1500 is too much to invest you could always throw a few hundred feet of garden hose on your roof to impress your neighbors with your enthusiasm for solar energy application. 

Solar collectors harvest heat by using the greenhouse effect  heat trapping system. Two basic types of collectors are the flat plate collector and the parabolic trough concentrating collector. My plans call for cold climate, flat plate, serpentine collectors. Most commercial flat plate collectors are assembled with a parallel pipes as demonstrated below.



Notice how fluid levels are higher at the end pipes, this is because fluid pressure tends to be higher at the beginning and end of the connection junctions. This is an unfortunate occurrence since it would be better for flow rate to be at a maximum for the central riser pipes where most of the solar energy is concentrated. To moderate this problem connecting pipes are made larger than the vertical riser pipes. This  lowers the pressure demands on the circulator system and improves flow rate uniformity within the riser pipes.
On a commercial level this parallel pipe system may be practical, however on a do it yourself level it is impractical due to the dozens of T fittings and myriad of sweat joints to worry about. A more practical design simply employs one continuous coil of 3/8 flexible copper tubing.


One serpentine collector would be impractical due to the 3/8" tube restriction stress, however if four or more of these collectors are connected in parallel fluid pressure drops and circulator efficiency increases. To learn more click on the banner or visit other areas of interest. Thank you for visiting this site. 


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