Sizing a Solar Water and Space System

Sizing Solar Water Heaters

When sizing a solar heating system the rule is to size the collectors area and the storage tanks to meet 90%–100% of the household's needs during the season with the lowest consume (the summer in cold and temperate climates)

Why that rule? Such a sizing procedure will mean that the installed system will not provide enough hot water in the coldest days or other adverse periods, but it is not practical to size a solar powered system otherwise. The system would be too costly, and oversized for most of the seasons and days. It’s preferable to have an auxiliary gas or electric system, to compensate the solar system insufficiencies during the non-favorable periods.

Collectors Area for solar water heating systems

In the case of solar water heating systems, contractors follow some rough guidelines to size the collectors area:

Around 20 square feet (2 m2) of solar collector area for the first and second family members.

For additional family members contractors use to add:

Around 8 square feet (0.7 m2) in sunny locations;
Around 12–14 square feet (1.1 – 1.3m2) in cloudy sites.

solar water systems: Storage Capacity

Storage tanks are commonly sized to around 1.5 gallons/5.6 liters storage per square foot (0,092 m2) of collector area. In very warm and sunny climates the value are sometimes increased to around 2 gallons/7.5 liters storage per square foot.

For simpler solar systems, it’s common to use a 50 to 60-gallon tank for households with 1-2 people, a medium 80-gallon storage tank for households with 3-4 people, and proportionately larger ones for households with a larger number of members.

Sizing a solar swimming pool heating system

The solar collectors area of a solar swimming pool system varies with the intended uses and climate: see, for details: Solar swimming pools sizing

Sizing a solar space heating system

Space heating systems based on direct pumping of heated air, may use an unglazed panel of around 12–14 square feet. The goal of such a panel is merely to complement another conventional heating system in favorable weather. See, for more information on these systems: Solar Air Heating Solutions

Sizing solar Powered Hydronic Systems

Other solar powered systems, involving radiators or radiant floor, demand a much larger collector area, very dependent on local climate conditions.

See, for more information: Solar Radiant Heating and Solar Space Heating with baseboards and radiators.

Sizing a solar electric system

The number of solar modules depends, first of all, on how much power you need for your home – something you may see in your electric utility bill (through your average monthly kilowatt-hours).

Sunlight resources is another element to consider: if you live in a sunny (non-cloudy) location your needs will be lower…

For details on these issues, see: PV sizing: the number of modules