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Solar Water Heating
There are two types of solar water heating mechanism:
- Passive solar water heaters - Relies on the thermosiphon method of natural heat convection movement, whereby heated water rises above colder water due to gravity and buoyancy. Passive solar water heaters do not require pumps to transfer hot water to the storage tank. The storage tank s have to be positioned above the solar collectors.
- Active solar waters - Utilizes a small circulating pump to move water between solar collectors and storage tanks. An electronic controller works with aquastats/thermostats to control the operation of the pump to transfer hot water from the collectors to the tanks. Active solar water heating is more flexible in design and capacity of the water heating system.
- Flat plate collectors - durability and maximized collector area make this ideal in the Philippines for domestic water heating
- Evacuated tubes - higher efficiency but smaller collector area make this suitable for very high temperature industrial requirements. Evacuated tubes are also very fragile.
- Direct - Water directly heated by the sun is transferred to the tank for hot water use
- Indirect - A heat exchanger is utilized to transfer heat from the water or radiator fluid directly heated by the sun to the water for hot water use. This is a more expensive system recommended to prevent damage to the solar water heating system due to poor water quality. Indirect hot water tanks are available from A.O. Smith
Secondary Heating Method
In most cases, because solar water heaters rely on direct sunlight for heat, hot water produced by the solar water heaters may not be sufficient for the requirements of the household or commercial establishment. Hot water production is limited by the number of solar collectors and the volume capacity of the storage tanks. Thus, for large consumption of hot water, relying only on the sun for hot water may require a lot of rooftop space. Furthermore, if the tanks are placed on the roof, the storage capacity of the tanks are constrained by the structural capacity of the house or building roof.
Due to this, solar water heaters commonly employ a secondary "backup" heating method. Usually this just means a low-kilowatt electric heating element inside the storage heater. For more savings, gas-fired heaters and heat pump water heaters are also used as the backup component.