Windows and fenestrated facades affect significantly the energy needs of buildings. In the US, windows are responsible for 12% of the total energy consumed by the existing US residential and commercial buildings due mostly to uncontrolled solar heat gains. External shading devices are commonly used features to control solar radiation as well as natural lighting through fenestrated facades to reduce both heating and cooling thermal loads and ultimately improve the energy performance of buildings. At the same time PV cells and modules have been widely integrated and attached to building envelope including roofs, facades, and windows. Driven by advances in solar cell efficiencies and materials, substantial reduction in installation costs of PV systems, availability of detailed design analysis tools, and growing desire or requirement of designing net-zero energy buildings, the interest in building integrated PV systems has grown noticeably in the last decade.
Researchers at the University of Colorado have developed PV arrays with sliding overhangs to both generate electricity and reduce heating and cooling thermal loads for US residential buildings. Basic control to operate the sliding overhangs are considered to minimize annual net energy demands with and without the integrated PV arrays. A series of sensitivity analyses is performed to assess the impact of design and operating conditions on the energy performance of the sliding overhangs. The analysis results clearly indicate that when integrated with PV modules, sliding overhangs can significantly reduce the energy demand for US housing units especially when they are set at the optimal angles specific to the building location to maximize their electricity generation and solar shading effects. Specifically, it is found that sliding overhangs can not only reduce energy demand but also can achieve net-zero energy conditions for US houses with large windows and located in mild climates even when monthly adjustments are applied to operate the shading systems. To minimize design and operation complexities, it is recommended to consider sliding-only overhangs set at the latitude of the location to reduce both heating and cooling demand as well as increase PV array output.
Available for licensing.