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What is Solar Fraction? On this page, we'll examine the solar fraction for typical residential installations in the continental U.S. The solar fraction of a single 4'*10' Solene Aurora panel will be examined in detail. Data comes from www.solar-rating.org, the SRCC OG-100 section of that website. Properly sized solar thermal systems can easily produce 70-80% of the hot water needs of a typical family. In other words, most residences can achieve a 70-80% solar fraction. Achieving this level of solar fraction is a function of geographic location, collector type, size, orientation and shading. Some form of back-up hot water should always be available to provide energy during cloudy and cold days. Below is the btu output for a single 4' by 10' Solene Aurora collector (40 s.f.) given a Kansas City, MO location. The light blue bars represent the monthly BTU's necessary to produce 80 gallons of 120 degree (F) water given an average cold water tap temperature of 60 degress (F). The estimate of required BTU's is approximatel 1.1 million btu. The dark blue bars represent the monthly output of the single collector. The collector overproduces in summer months, and underproduces in the winter. The need for seasonal backup system is illustrated.
Next, we examine the solar fraction provided by two 4' by 8' Solene Aurora collectors (64 s.f.) The addition of 24 s.f. of panel (64 s.f. for two collectors verses 40 s.f. for a single collector) is graphically presented. Oversizing the collector array does expand production.
Please note the consistency month to month of the two systems. Many months, the solar system will overproduce. By the same token, that same solar system will underproduce in winter months. In no month will there be more than 100% solar fraction. During winter months, the system will produce a small solar fraction. Backup hot water will be required. This pattern of supply is consistent across the U.S. Attached as a link is a Single vs. Two Collector BTU Output in 5 Cities comparison (.docx format). Comparison of single vs. two collector systems is shown for Kansas City MO, Sacramento CA, Philadelphia PA, Charelston SC, and Ausin TX. Next, we examine solar fraction for a single 4' by 10' collector by the numbers, given Kansas City, MO. Again, data is curtesy of the SRCC OG-100 ratings. A single 4' by 10' collector will provide approximately 65% solar fraction given 80 gallons per day need. Next, we examine the solar production given two 4' by 8' collectors, a 64 s.f. array, again in Kansas City. The two panel system produces an estimated solar fraction of 74%.
Summer Months: Solar systems produce an abundance of hot water. *The above BTU/Day calculations are estimates and are bases on low wind conditions and historical averages of daytime air temperature and solar insolation levels for Kansas City, MO..
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