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Local rooftops could provide 28 percent of Austin’s current power needs

Monday, August 31, 2009 by Bill McCann

A new study commissioned by Austin Energy shows that if solar electric panels were installed on all viable rooftop space in the area, the panels could supply 84 percent of the utility’s existing generating capacity and almost 28 percent of the power produced yearly to meet customer needs. Time of day and season determine the availability of solar power and account for the difference between generating capacity and power sold to customers.

The top 10 areas with the most available rooftop space for solar photovoltaic (PV) equipment, or solar cells, are scattered throughout the city. The rooftops include residential, commercial, industrial and public buildings.

The two ZIP Codes with the most potential are in North Austin, the study shows. They are 78758 (north of Highway 183 and west of I-35), with 13 million square feet of rooftop space; and 78759 (Highway 183 area west of Mopac Expressway), 11.2 million square feet. Both areas have extensive residential, including single and multi-family, as well as commercial buildings. ZIP Code 78758 also has considerable industrial operations.

Other top areas include ZIP Code 78746 (west of Austin, including West Lake Hills), 10.2 million square feet; 78745 (South Austin, south of Ben White Boulevard), 10.1 million square feet; 78753 (I-35 corridor north of Highway 183), 9.1 million square feet; 78704 (South-Central Austin), 9 million square feet; 78744 (Southeast Austin), 8.9 million square feet; 78731 (Northwest Austin), 7.1 million square feet; 78727 (far North Austin), 6.5 million square feet; and 78741 (East Austin/Pleasant Valley Road area), 6.2 million square feet.

The study is a useful planning tool for the utility, which advocates the installation of solar electric panels to help meet the city’s goal of reducing greenhouse gases from its operations, said Roger Duncan, Austin Energy’s general manager.

About 900 solar electric systems currently are installed on Austin-area rooftops as a result of the utility’s solar rebate program, compared to 16 in 2003, said Duncan, who believes one day Austin will have tens of thousands of solar-equipped buildings. 

“There has been a lot of speculation about what was technically possible, but we really did not know the rooftop potential (of solar power) before this study,” Duncan said. “Now that we know the potential, we need a long-term plan to begin to develop that potential. It is not going to happen in the next 10 years. But it will happen and the tipping point will be as the cost of solar goes down and competes head-on with other alternatives.”

With $53,500 from the U.S. Department of Energy, Austin Energy hired Austin-based Clean Energy Associates last year to determine the potential rooftop space suitable for solar electric systems in the utility service area, and to determine the potential power- generating capacity and energy production from these systems.

Using data from the Travis and Williamson County appraisal districts and the City of Austin Geographic Information System, researchers estimated the gross available rooftop space in Austin Energy’s service area to be 536 million square feet. After subtracting structurally unsound roofs, roofs improperly oriented to the sun, shaded roofs, and roofs with other impediments, the researchers calculated the total potentially viable roof space for solar photovoltaic development at 142 million square feet.

With currently available photovoltaic technology, the researchers estimated that, if fully developed, the potential rooftop solar electric capacity would total 2,324 megawatts, about 84 percent of the utility’s current generating capacity. These solar units could produce about 3.3 million megawatt-hours of energy yearly, or nearly 28 percent of the current annual energy generated. Austin Energy currently gets about 10 percent of its energy from renewables, (mostly wind), 26 percent from natural gas, 27 percent from nuclear power, and 32 percent from coal, according to the study.

The study showed that residential rooftops make up almost half of the total solar power potential. Commercial buildings make up almost 30 percent. 

The final report, entitled, “Assessment of Rooftop Area in Austin Energy’s Service Territory Suitable for PV Development,” was submitted to Austin Energy in July.

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