Solar thermal Power

Solar thermal heating harnesses solar energy to heat a home by distributing heat via an electric fan or pump. Using air or liquid as a medium, heat is transferred directly to the living space. Solar thermal cooling requires a thermally activated cooling system to manufacture and distribute the cooled air into living spaces. Solar thermal cooling is more common in commercial settings because of the large size and initial costs of the thermally activated cooling system.

There are two types of solar thermal cooling systems: desiccant and absorption. Solar absorption systems work essentially like a refrigerator. They use thermal energy harnessed by a solar collector to separate a mixture containing an absorbent and a refrigerant liquid. The refrigerant is then condensed and evaporated to produce a cooling effect throughout the building. The evaporated refrigerant is then reabsorbed to continue the cycle. There are single, double, triple effect systems which use the solar produced heat once, twice, or three times respectively. The efficiency of the system increases the more times the heat is reused.

The downfall of solar absorption systems is that they require a high temperature to operate. A temperature high enough that it is difficult to maintain using just solar panels and no auxiliary power supply.

Solar desiccant systems use solar thermal energy collected to regenerate desiccants that dry ambient (fresh) air. The system then uses that dry air in evaporative stages to provide cooled air. Solar heat is used to regenerate the desiccants and effectively drive off absorbed water and, subsequently, heat. Desiccant systems can work at relatively low temperatures which gives them an advantage over absorption systems.

Because of the initial expense of thermally activated cooling systems, solar cooling is not often utilized, especially in a residential setting. However, like all other renewable energy technologies, study and research is ongoing to find even more efficient, low-cost ways to use solar power to cool homes and offices.

April 22nd in Going Solar by Dan

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