Technology
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Solar Domestic Hot Water systems (SDHW) are a mature technology that first became commercially available in the late 1800s. Over the years, significant research, development and experimentation has lead to a highly developed and market ready technology. Globally, over 125 million square meters (about 46 million homes or 88 Gigawatts Thermal (GWth) are installed. The top 5 leading countries in SDHW installations are China, Turkey, Japan, Germany and Israel. SDHW installations have been growing at a rate of about 15% or higher for the past 6 years. (www.ren21.org). In some jurisdictions around the world, such as Israel and more recently Spain, Solar Hot Water systems are required on most buildings. Today, SDHW is a mature technology with high quality standards and equipment to suit cold and warm climates and a wide variety of uses.
Solar Hot Water collectors can be mounted on roofs, walls or the ground. The collectors absorb heat energy from the sun and transfer that heat to a storage tank, usually with a heat exchanger. Two SDHW systems appropriate for climates that experience freezing are Closed Loop Drain Back systems or Closed Loop Anti-Freeze liquid (usually propylene glycol) systems with heat exchanger systems.
The most common type of solar collectors for domestic use are Glazed Flat Plate collectors. Another type available for SDHW systems are Vacuum Tube collectors. The collectors have different characteristics and the choice of collector will depend on temperature, seasonal hot water needs and other design requirements. For example, Glazed Flat Plate collectors are used when temperature requirements are below 60°C whereas vacuum tube collectors can be used to meet hot water needs above 80°C. (Typical domestic hot water temperature range is 50-60°C). Appropriate sites for SDHW systems have a clear southern exposure on the roof or close to the house or building free from shading from about 10 AM to 3 PM or longer. The size of the collectors and storage tank will depend on factors such as the climate, solar exposure and amount of hot water required.
Components of a SDHW system, in addition to solar collectors, heat exchanger and storage tank(s), can include tank and pipe insulation, a circulation pump (AC or DC), PV panel (to run DC circulation pump), water reservoir (for drain back systems), thermostatic controls, timers, connecting pipes, collector mounting structure, filters, heat and flow meters, and pressure gauges.
Modified: 02-13-2008
