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Austin, Texas

A think tank tests the performance of west-facing photovoltaics

By David Sokol
March 2014
Photo © Pecan Street

The Mueller Community is a redevelopment of Austin’s former Robert Mueller Municipal Airport. The transit-oriented neighborhood, located three miles from downtown, thoughtfully mixes housing, open space, and commercial uses according to a green master plan that will surely be replicated by cities and towns across the U.S. But sustainability aficionados who visit the Mueller Community will notice that something feels slightly different from a best-practices model. For one, the place boasts a large concentration of Chevy Volts. For another, rooftop photovoltaics are not facing unanimously south, the installation convention for the Northern Hemisphere.

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Pecan Street is responsible for the anomaly. This University of Texas at Austin–based think tank promotes a smarter energy grid through two divisions: Its Pecan Street Research Institute analyzes utility system reliability, renewable energy integration, and especially customer resource-use behavior, while the Pike Powers Laboratory and Center for Commercialization incubates new companies pioneering smart-grid and other clean technologies.

Established in 2008 as a consortium of public and private partners, Pecan Street launched as a bona fide entity a year later. “Once we became an organization and focused on a demonstration project, we knew Mueller would be the best place to start,” says Colin Rowan, Pecan Street’s director of communications. The 700-acre community “was designed with heavy community involvement with green thinking in mind. The homes are efficient. The development is transit-friendly. The residents are eager early adopters. It’s the perfect place to demonstrate next-generation technology.”

One of the first subjects of Pecan Street’s research was the interaction between solar energy generation and energy use. Specifically, the group wanted to know more about the performance of photovoltaics that were installed as tools for reducing peak demand, instead of supplying the grid in general. That required mounting photovoltaics to produce maximum output during peak hours of usage—and hence face west.

Local utility Austin Energy incentivizes homeowners to invest in photovoltaics, and Pecan Street sweetened the pot for Mueller residents willing to break from south-facing convention. Rowan explains, “We wanted to test the impact of west-facing solar, so we added an additional incentive to west-facing solar to make up for the fact that over the course of the year, those panels would generate less power. In other words, we wanted there to be no financial difference for consumers of west- versus south-facing systems.”

West-facing photovoltaics generate less power on an annual basis, but during Pecan Street’s test of Mueller’s rooftop arrays—between June 1 and August 31, 2013—they outperformed their counterparts. Using a sample of 50 homes with a median photovoltaic area of approximately 6 kilowatts, west-facing PVs generated more electricity on the average day. Moreover, underscoring the study’s original hypothesis, west-facing PVs generated 49 percent more electricity during peak demand hours than south-facing systems, and experienced a higher percentage uptake within homes.

“We think that solar can play a significant role, particularly in this part of the country, in helping utilities that have to buy expensive excess power on the spot market to meet peak demand,” Rowan says, and Pecan Street’s research at the Mueller Community validated one means of peak-demand reduction. While the researchers acknowledge multiple variables affecting their outcome, such as whether residents work from home, their proprietary report released shortly after the summer test recommended that utility companies consider giving rebates for rooftop PV systems that face west. Perhaps even bigger rebates.

Concomitant to its study of PV mounting, Pecan Street was offering to match the $7,500 federal rebate incentive for Mueller homeowners who purchased or leased electric vehicles (EVs), in order to study these cars’ impact on the power grid. In another proprietary report published last fall, Pecan Street painted a finely grained picture of drivers’ charging patterns. The work effectively trounced the accepted idea that EV owners connect to their home charging stations during peak hours, an impression that spelled potential disruption to the grid.

Rowan says Pecan Street has many more queries to ask and apocryphal notions to upend, regarding EV charging, appliance performance, energy pricing, and more. To do so, moreover, its living laboratory now encompasses 1,100 homes that extend well beyond the original bounds of the Mueller Community. Overall, Rowan states, “Our purpose is to provide insight that will speed the innovation cycle for the energy industry. Our network has resulted in the first real-world, real-time database of energy use that can be used to test hardware, software, and analytical applications that relate to consumer electronic and consumer energy products.”



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