Solar panels size

Sizing Solar Water Heaters

Solar hot water systems are typically sized to fulfill 90% to 100% of the home's needs during the season or period of the year with the lowest consumption (the summer, in most cases). By doing so the solar water heater will not provide enough hot water in the coldest days and adverse periods, but that isn't the goal... Those extra-needs will be fulfilled by a backup gas or electric system, that is, this approach assumes a backup system...

Sizing the solar hot water system otherwise (to respond to 100% of the needs all over the year) would be too costly; it would involve an oversized system most of the year, and would not prevent water shortages in very adverse sunlight conditions or anomalous hot water demand peaks.

Solar Panels Size for solar water heating systems

There isn't an universal way to calculate the exact solar panel area for solar water heaters... Differences in the climate conditions and consumption render it impossible. Good solar calculators have it in account.

The best way to size a solar system is to discuss the issue with the installer, always paying attention to local solar resources and differences in the efficiency of solar panels.

Installers use spreadsheets and other software to calculate the size of solar systems. Some installers may also use some rules of thumb, but the quick technological evolution and differences in the efficiency of panels may render older ones ineffective. An example of a rough guideline used to size a flat solar panel area:

Around 20 sq. feet (1,85 m2) of solar collector area for the first and second family members; and... around 8 square feet (0.7 m2) in sunny locations for each additional family member; or... around 12–14 square feet (1.1 – 1.3m2) in cloudy sites, for each additional family member.

See also: Solar calculators

Solar storage tanks

Installers may also use some broad rules to calculate the storage tanks size. Something like:

- 50-60 gallon (190-230 liter) storage tanks for 1-2 people households;
- 80 gallon (300 liter) storage tanks for 3-4 people households;
- 100-120 gallon (380-450 liter) storage tanks for 4-6 people households.

Anyway, the solar storage tank depends also on the type of solar design. Systems with pumps demand an higher tank storage: typically 1.5 gallons per sq. foot of solar panel in cold and moderate climates, or 2 gallons of storage per square foot of panel area in very hot and sunny climates. That, to avoid overheating problems.

Sizing a solar swimming pool heating system

Sizing a solar swimming pool system depends on its configuration, patterns of use and climate zones. See, for details: Solar swimming pools sizing

solar Panels Size in air/Space Heating

Sizing a solar space heating system is not so crucial as sizing a solar water heater system - assuming that it is used as an auxiliary heating system. In such cases you may use a simple rule of thumb... Something like: 4x8 foot solar panel provides 25-50% of the energy needed to heat a 400-900 sq. foot space...

See, for more information on these systems: Solar Space Heating

Sizing solar PV system (Solar electricity)

The area of solar panels for photovoltaic stand-alone systems depends on how much power you need and on sunlight resources. For details, see: Solar PV Size.