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Advancement of residential solar water heaters

About 35 percent of natural gas used in California homes is used to heat water. To reduce the use of natural gas the California Energy Commission has funded research to increase the effectiveness of residential solar water heating systems and reduce the price tag.

Researchers at the University California, Merced are developing an aluminum solar mini-channel collector that is showing promise. Now the UC Merced campus is interested in installing these collectors as it pursues the goal of zero-net-energy by 2020.

The “channels” found in mini-channel solar water heating panels have a much smaller “hydraulic diameter” (the area that water flows through in a pipe) than the copper tubes found in traditional solar water heating panels. This smaller diameter allows for a much greater number of tubes or “channels” to be fitted on to a similar sized solar panel. The increased number of channels translates to an increase in the surface area that can absorb solar energy and result in an increase in the amount of solar energy that can be absorbed by water or other fluids. Because of the significant increase in solar energy absorbed, researchers were able to use aluminum (a metal much less expensive than the copper used in traditional solar water heating panels) as the material to build the solar panels.

The price of a traditional solar water heating system is significantly more than the typical natural gas water heating system. Solar water heating can cost about $6,700 for a typical California home. Natural gas systems are typically at prices of about $1,000. Yet the operating cost of solar systems can be less than natural gas systems. It is estimated that if only 20 percent of potential solar water heating savings were realized, California homeowners would save nearly $200 million a year. Experts consider home solar water heating systems as the home feature with the highest potential to reduce the use of natural gas.

Mini-channel technology has been successfully utilized in the automotive, air conditioning, and electronics cooling industries due to improved performance and compact size compared to round-tube heat exchangers. The transition to mini-channel technology, however, has not taken place yet in the solar industry.


For more information about this project and other innovations funded by the Energy Commission please see the recently released Natural Gas Research and Development 2014 Annual Report.

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Research & Development

California Energy Commission

The California Energy Commission is the state's primary energy policy and planning agency created by the Legislature in 1974.
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