Low-Temperature Solar Thermal Systems: An Untapped Energy Resource in the United States

Abstract

The number of buildings appropriate for solar depends in part on population density and climate. The actual market penetration depends on many factors, including among others first and lifecycle cost, availability, customer preference, and local building and plumbing codes and standards. For the sake of argument, assume a market penetration of 50% of current electric water heaters and 20% of gas water heaters optimistic but achievable goals. A reasonable estimate of the average solar fraction of these systems the fraction of the energy provided by solar with the remainder supplied by the current energy source is 0.5. With this assumed scenario, solar water heaters would displace about 88 billion kWh 0.3 quadrillion BTU of the primary electricity and natural gas in residential buildings. The consequent reduction in greenhouse emissions would be 6.7 million metric tons of carbon 6. If commercial water heating is treated in the same manner, an additional 50 billion kWh 0.17 quadrillion BTU of primary energy consumption could be avoided with a carbon reduction of 2.7 million metric tons. The total projected carbon savings is equivalent to removing 7 million passenger cars from the road 7. Note