Whenever you install a new system or appliance in your home, efficiency is an important factor. Different systems and appliances measure their efficiency in various units. For a solar hot water system, efficiency refers to one of two things: the thermal energy output or the amount of energy the system offsets from a conventional gas or electric system. The units used to determine the efficiency of solar hot water systems are ones you may be unfamiliar with, so let’s take a look at each.
Solar Energy Factor (SEF)
Energy delivered by the system / conventional energy input = SEF
Solar Energy Factor values range from 1 to 11, and most residential solar hot water systems have a water heater rating of 2 to 3. The higher the number, less conventional energy is being used to heat water.
Solar Fraction (SF)
The solar fraction refers to the amount of the total hot water heating load which was produced by solar energy. A higher solar factor means more solar energy has contributed to heating the household’s water. Solar factor values range from 0 to 1, and most residential solar thermal systems have solar factors between 0.5 to 0.75.
Btu/(ft²day) indicates how much thermal energy is produces per square foot of collector space each day. Btu is the abbreviation for British thermal units, a measurement of thermal energy needed for water heating. Higher Btu/(ft²day) measurements mean fewer square feet of space in the collector are needed to heat the same amount of water. This rating is used for most models of solar collectors.
If you have any questions about determining the efficiency of your solar hot water system, give us a call. Smith Sustainable Design’s team of solar hot water systems contractors are happy to discuss solar options for your New Jersey or Pennsylvania home.