e-News
Issue 79 March 2011
Solar Thermal: n Introduction n Typical Applications n Pool Heating n Domestic Water Heating n Thermal Power n System Performance n Cost Effectiveness n Innovative Technologies n Related Resources n Training Highlights n About e-News
The Sun is at Your Service Introduction
S
olar thermal systems have been used for decades for domestic water heating and space heating. They provide a cost-effective alternative for water heating, a major component of residential building energy use. Solar thermal systems are also very effective at pool heating. Newer technologies are available that combine photovoltaic (PV) panels with solar water heating or space heating. Another emerging technology is solar-assisted absorption cooling. Solar thermal collectors can also be used to concentrate the sun’s energy and produce power in large-scale installations. Solar thermal energy can be used in a variety of applications, from residential systems to commercial systems to power plants.
Typical Applications Pool Heating Perhaps the simplest use of solar thermal energy is solar pool heating. Unglazed solar collectors heat water to 10-15°F above the ambient temperature. The heated water can then heat the pool water indirectly, through the use of a heat exchanger. Depending upon solar availability and project requirements, the collector area needed for pool heating is roughly 75% of the area of the pool. The first efficiency step for pools should always be a pool cover. For outdoor pools, approximately 70% of the heat loss is due to evaporation. Wind screens can also be effective at reducing the convective heat loss from the pool’s surface.
Domestic Water Heating For domestic water heating, a typical solar domestic hot water system consists of the solar collectors, a solar storage tank and heat exchanger, and controls. The medium-temperature collectors used are either flat-panel collectors, or evacuated tube collectors. Evacuated tube collectors produce higher temperature water (180-200°F), but are considerably more expensive. The controller typically turns the pump on when the return temperature from the collectors exceeds the temperature at the bottom of the storage tank by 10°F. For Figure 1 - Solar Thermal Installation water heating, there are four basic system designs: direct The installation of solar thermal panels is shown and indirect, active and passive. Direct systems heat above. These panels supply a solar domestic hot the domestic water without the use of a heat exchanger. water system with a 120 gallon storage. These are only suitable for climates where freezing is not a concern (southern Florida). (Note that water can freeze Courtesy DOE/NREL, Industrial Solar Technology Corporation
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Energy Design Resources
e-News March 2011