Sizing of Solar System

Just as you have to choose a 30, 40, or 50-gallon (114-, 151-, or 189-liter) conventional water heater, you need to determine the right size solar water heater to install.Sizing a solar water heater involves determining the total collector area and the storage volume required to provide 100% of your household’s hot water during the winter and summer.

Solar storage tanks are usually 50, 60,80, or 120-gallon (189, 227, 303, or 454-liter) capacity. A small (50 to 60 gallon) system is sufficient for 1 to 3 people, a medium (80-gallon) system is adequate for a 3- or 4-person household, and a large (120-gallon) system is appropriate for 4 to 6 people.

A rule of thumb for sizing collectors: allow about 20 square feet (about 2 square meters) of collector area for each of the first two family members and 8 square feet (0.7 square meter) for each additional family member if you live in the Sun Belt.

A ratio of at least 1.5 gallons (5.7 liters) of storage capacity to 1 square foot (0.1 square meter) of collector area prevents the system from overheating when the demand for hot water is low. In very warm, sunny climates, experts suggest that the ratio should be at least 2 gallons (7.6 liters) of storage to 1 square foot (0.1 square meter) of collector area. For example, a family of four  would need between 64 and 68 square feet (5.9 and 6.3 square meters) of collector area and a 96- to 102-gallon (363- to 386-liter) storage tank. (This assumes 20 square feet of collector area for the first person, 20 for the second person,