Wednesday, March 27, 2013

Solar water heaters facts

Solar water heaters are devices and systems which use solar energy to heat water. Solar water heating or solar hot water systems comprise several innovations and many mature renewable energy technologies that have been well established for many years.

Solar water heating (SWH) systems include storage tanks and solar collectors in which water is heated. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which do not have pumps. Passive solar water heating systems are typically less expensive than active systems, but they're usually not as efficient. However, passive systems can be more reliable and may last longer.

Solar water heating systems are designed to deliver hot water for most of the year. However, in winter there sometimes may not be sufficient solar heat gain to deliver sufficient hot water. On cloudy days, if it is for a day or two, one still get warm water as water gets heated due to diffused radiation available in the atmosphere. The system, however, is either connected to an electric geyser in the house or an electric al backup is provided in the storage tank of the system which is switched on when water is not sufficiently hot.

SWH systems reduce energy spending: sunlight is free, so once system is paid for the initial installation hot water costs will be reduced. Also, this system will reduce carbon footprint: solar hot water is a green, renewable heating system and will reduce carbon dioxide emissions when installed.

Maintenance costs for solar water heating systems are generally very low. Most solar water heating systems come with a five-year or ten-year warranty and require little maintenance. In a well maintained system, pumps can last for more than ten years.

In order to heat water using solar energy, a collector, often fastened to a roof or a wall facing the sun, heats working fluid that is either pumped (active system) or driven by natural convection (passive system) through it. The collector could be made of a simple glass-topped insulated box with a flat solar absorber made of sheet metal, attached to copper heat exchanger pipes and dark-colored, or a set of metal tubes surrounded by an evacuated (near vacuum) glass cylinder.

There are records of solar collectors in the United States dating back to before 1900, comprising a black-painted tank mounted on a roof. In 1896 Clarence Kemp of Baltimore, USA enclosed a tank in a wooden box, thus creating the first 'batch water heater' as they are known today.

When designing solar water heaters two big issues must be addressed: freeze protection and overheat protection. Freeze protection measures prevent damage to the system due to the expansion of freezing transfer fluid. Drainback systems drain the transfer fluid from the system when the pump stops. Many indirect systems use antifreeze in the heat transfer fluid. When no hot water has been used for a day or two, the fluid in the collectors and storage can reach very high temperatures in all systems except for those of the drainback variety.

Home solar water heating systems cost an affordable $1,500 to $3,500, and pay for themselves in four to eight years. This can be very good investment in current climate of rising energy prices.

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