What is the energy efficiency of a solar water heating system?
To calculate the energy efficiency of a solar water heater, you need the solar energy factor (SEF) and solar fraction (SF). The solar energy factor is the system’s energy output divided by the electrical or gas energy input. The higher the resulting number, the greater the energy efficiency. Solar energy factors range from 1.0 to 11, with a common result of 2 or 3. The solar fraction is the portion of the total conventional hot water heating load (delivered energy and tank standby losses). The higher the solar fraction, the greater the solar heating source, which reduces the energy demand from the backup water heater. The solar fraction varies from 0 to 1.0 with typical solar factors running 0.5–0.75.
