Goodfellow’s Solar Power System
The system as installed at Goodfellow Air Force Base features a metal roof retrofit system (metal over existing metal roof) that includes a laminated thin-film amorphous silicon PV system. The laminating was done in the field but can also be done in a factory, after which the laminated panels are shipped to the site.
The grid-tied balance of the system includes an inverter, array wiring, disconnects and other components required by code and good practice. The laminated thin-film PV system was installed over a building-integrated solar-thermal water-heating system also integrated into the retrofit roof assembly. The ability to harvest solar energy in the form of heat from the metal roof was important to the success of the retrofit. The project team wanted to transfer the heat build-up on the roof to glycol-protected heat transfer fluids, which, in turn, deliver the energy to space- and water-heating systems. Doing so not only doubles the total solar-energy harvest of the installation, but also improves the efficiency of the PV system by cooling the PV panel surface. This synergistic combination of thin-film PV with solar-thermal technology as part of the roof is called building-integrated PV-thermal, or BIPV-T. The two technologies, installed during new or retrofit roofing projects, work together to harvest the maximum amount of solar energy to generate power and heat water.
The performance data from the demonstration building being collected and authenticated by Oak Ridge, Tenn.-based Oak Ridge National Laboratory during a one-year period will be used to verify the predicted energy savings from the PV installation on the 11,900-square-foot roof. The PV system is projected to generate about 65,000 kilowatt hours of electricity and save the air force base approximately $5,200 annually on this building’s electric bill. Equally important to the base, the solar-power system brings it closer to meeting the federal mandate for the use of renewable-energy sources.
The Goodfellow AFB roof PV system has been in place since June 2012 and is already producing enough electricity to offset 37 percent of the building’s usage based on 2011 consumption levels. More importantly, 2011 was one of the hottest summers and achieved the highest usage rates in recent years in the San Angelo region. Goodfellow AFB has an electrical grid of its own within the base, so any excess electricity not consumed by the demonstration project building will be fed into the base’s internal grid and used downstream by the next base facility.
Bearing in mind that the goal is to provide a minimum of 25 percent of energy needs away from the grid, this performance exceeds the stated DoD goal. As an added bonus, the American Electric Power Texas North City Smart Program, which provides government institutions with cash incentives ($150 per kW) for reduced peak electric demand from renovation or new construction projects, gave Goodfellow AFB a onetime payment of $6,184 for this improvement. Ninety-six percent of this payment was credited to the PV system.
The base demonstration project is intended to verify the estimated kWh of electricity that can be generated for cooling/heating/operation of a building. In addition, the reduction in grid-required electricity will result in a significant reduction in carbon-dioxide emissions attributed to the building. The ESTCP project expects to generate data about energy and water reduction that can be used to model the performance of any building being retrofitted on any military base to meet its stated energy goals.