Solar Water Systems

Solar water systems use solar energy to pump water. The water can be used for domestic consumption, watering livestock, or irrigating crops. The pump is usually connected directly to the array, although domestic battery systems often use the already existing battery to power the pump. For pump information see the section on water pumps.

For domestic systems, the water is usually stored in a water tank, located higher than the house to provide adequate water pressure. The water tank is sized to provide water for a number of days (usually 15 days or more), plus a reserve for emergencies like fighting fire. The pump and array are sized to refill the tank in the available days of sunshine. For instance, if the design calls for 10 days to fill the tank and 15 days supply, this assumes that it is sunny 40% of the time (10 / (10 + 15) = 40%). When it is sunny, the pump and array must fill the tank and supply the water used.

If the pump is run from a battery, a pressure pump and pressure tank can be used to supply the normal water pressure. The pressure tank uses compressed air to supply the water while the pump is off. This keeps the number of on-off cycles of the pump to a minimum, which extends the life of the pump and control circuits.

Livestock watering systems are similar. The trough can function as the storage tank or a separate storage tank can be used. The source of water can be a fenced-off stream to prevent the livestock from contaminating it.

Crop irrigation is normally accomplished without storage, pumping from a shallow well or surface water source. The irrigation is done when the sun shines.

The SolarSizer program, supplied with the Solar Design book, includes provision for sizing the water tank, pump, and array.