What is the annual operating cost of a solar water heating system?
To calculate the operating costs, determine the system’s solar energy factor (SEF), the fuel type of your auxiliary tank (gas, electric, oil) and local utility costs. With a gas auxiliary tank system: You need to know the unit cost of fuel by Btu (British thermal unit) or therm. (1 therm = 100,000 Btu) 365 × 41,045/SEF × Fuel Cost (Btu) = estimated annual cost of operation OR 365 × 0.4105/SEF × Fuel Cost (therm) = estimated annual operating cost Example: If the SEF is 1.1 and the gas costs $1.10/therm 365 × 0.4105/1.1 × $1.10 = $149.83 With an electric auxiliary tank system: Convert the unit cost of electricity by kilowatt-hour (kWh).
