Solar Energy Technology: Photovoltaic Systems

• By Terry Liette, Ian Hadden
• 12/01/09

As more school districts across the nation embrace renewable energy technologies, many are now considering the merits of photovoltaic systems. This technology is a form of solar energy that converts sunlight to electricity through the use of photovoltaic cells.

Photovoltaic cells — often referred to as PV cells or solar cells — are devices made of semiconductor materials, such as silicon. When sunlight hits a cell, the light causes the movement of electrons, which is then captured by wires attached to the cell to form a direct electric current. The direct current is converted to alternating current through electrical inverters, and is then available for building use. Several PV cells form a module, and photovoltaic arrays or panels, as might typically be found on a rooftop, consist of several modules.

Like other forms of renewable energy, photovoltaic technology holds much promise for energy-savings while also reflecting a district’s commitment to sustainability and the protection of natural resources. When considering such a step, schools should look first to be sure that a building is as energy-efficient in design and operations as possible. This may include conducting an energy audit and reviewing all of the building systems and equipment.

Next, explore options to help fund renewable energy options, including photovoltaics, such as subsidies, grants and rebates — particularly at the state level. Many states have adopted incentive structures such as Renewable Portfolio Standards and Feed-in Tariffs. Feed-in tariffs require that utilities pay a higher-than-market rate for energy supplied through renewable sources.

School districts may also consider a lease-back arrangement, through which third parties lease roof space to install, operate and maintain photovoltaic panels and enable the district to lock in a utility rate. These agreements are often called Power Purchase Agreements or PPAs. All of these options can help offset system first cost and will likely expand as more states adopt Renewable Portfolio Standards. For information on state, local, utility and federal incentives and policies, visit the Database of State Incentives for Renewables & Efficiency.

Schools are good candidates for the benefits of photovoltaic technology for a number of reasons. The energy demand within schools is highest during the day, when there is the most gain available from solar energy. School buildings generally feature expansive rooftops that will easily accommodate a photovoltaic array. The technology is in keeping with the increasing focus on environmental stewardship and sustainability that our nation’s schools now readily embrace, and many schools are finding that the systems can be used successfully as a hands-on teaching tool. Information on incorporating energy-related resources and activities into a curriculum is available through the National Energy Education Development Project.

Most systems are roof-mounted and require southern exposure with no obstruction from trees or other buildings. Schools will typically have “net-metered” systems that are connected to the utility grid. This allows for use of the utility when solar energy is not available, and for potentially returning power to the grid when the amount of solar energy exceeds building demand. Schools in particular may be able to bank excess power with the utility during weekends and the summer, when building use may be lower, as credit against future energy demand.

One school that has successfully implemented photovoltaic technology is the newly reopened Phelps Architecture, Engineering and Construction High School in Washington, D.C. Phelps, a historic school property that was recently modernized after standing vacant for several years, now features four rooftop photovoltaic arrays. The system allows for peak shaving, which reduces the building’s peak electrical demand and is monitored regularly by students as part of the school’s curriculum.

Terry Liette is a principal and the executive director of engineering with Fanning/Howey Associates, Inc.
Ian Hadden is client liaison for engineering and sustainable design for the firm.