Sunpower for School Kids
A PV system can supply some of the energy your school needs, but may be even better as a teacher of physics, energy, and sustainability concepts.
Continuing Education
Use the following learning objectives to focus your study while reading this month’s Continuing Education article.
Learning Objectives - After reading this article, you will be able to:
- Explain how photovoltaics produce electricity.
- Describe a typical photovoltaic application.
- Describe how schools are teaching photovoltaics to students.
Every day, the sun bathes the earth with enormous amounts of free energy-enough in one minute to meet the world's current energy needs for an entire year! Schools are beginning to harness this limitless natural resource as a way to meet their energy needs-and provide educational opportunities for their students in the process.
Photovoltaics are one solution. PV systems convert sunlight into electricity-one of the most elegant and environmentally benign ways to produce power. This article explores how teachers, administrators and facility managers are beginning to look for ways to produce their own power.
What are Photovoltaics?
In 1839, French scientist Edmund Becquerel observed the photoelectric effect-when a current could be measured across an electrode suspended in a solution exposed to light. And, in 1921, Albert Einstein won the Nobel Prize for his theories explaining the photoelectric effect. The photoelectric effect was not put to work until 1954, when Bell Laboratories created the silicon photovoltaic cell-the first cell able to convert enough of the sun's energy to power electrical equipment. Given a large boost by the space program, development of PV cells has proceeded uninterrupted since they were first manufactured, with conversion efficiencies (how much solar energy is converted to electrical energy) increasing from 4 percent for Bell Labs' first prototype to more than 50 percent for the specialized prototypes of today. More common for building applications are overall PV system efficiencies of 12 to 17 percent depending on the type of solar cells and system technology used.
How Does PV Work?
When sunlight strikes a PV cell, electrons are dislodged and gathered by wires attached to the cell to form an electric current. This basic action-simple, quiet, non-polluting, and requiring no moving parts-is at the core of every PV system. Cells may be more effective in areas like the Southwest, with a lot of clear, sunny days, but they will still provide substantial amounts of power in areas like the Northwest, with more overcast days.
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Since most cells are relatively small, typically from 1/2-inch to 4 inches on a side. They produce very little power, and need to be electrically connected to other cells to increase energy output to levels appropriate for building applications. These collections of PV cells, referred to as "modules," are what we typically see on the roofs of buildings. They are typically 2-to-4 feet by 4-to-6 feet in size. Modules are typically connected to each other to form PV "arrays," which can range in size from one or two modules to several thousand, depending on the power output desired. School projects in the U.S. have used various sizes, from small arrays-from 1 or 2 modules for demonstration purposes-up to the array on the three buildings that make up a high school in Bayonne, New Jersey that has more than 5,000 modules and supplies a substantial portion of the school's electricity.
A functioning PV system also needs an inverter to convert the direct-current (DC) power generated by the modules into alternating current (AC) that can be used in the school. Wiring is needed to connect everything together; and some form of mounting system is necessary to attach the array to the roof, wall, or grounds of the school. The mounting system can be fixed at a set angle, or track the sun throughout the day. This can substantially increasing the energy output of the array, but at a considerable cost.
Where Does the Energy Go?
PV systems are either stand-alone or grid-connected. The electricity from a stand-alone system is either used as it is produced or stored in batteries. In grid-connected systems, power generated by the array is used to supplement power supplied by the electric utility. When the modules don't provide enough electricity, the utility supplements the array. When the modules provide more than is needed, the excess is fed back into the power grid and the school's electric meter runs backwards. In these situations-in the 35 states that allow it-the school sells electricity back to the utility. This can be particularly important during "peak" periods of energy demand, when the utilities charge higher rates. These periods often coincide with times when the output from the PV array is also at its highest. If the school is getting maximum energy from its array at these times, it is buying less of the expensive "peak" energy from the utility. For most schools, a grid-connected system makes the most sense, especially (as is usually the case) when the PV array is not large enough to meet all the electricity needs of the facility. In special circumstances-for example, when a school is a designated place of refuge during emergencies-batteries can be added to a grid-connected system to store electricity when the utility grid is down.
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PV on-and in-the Architecture
The most common application of photovoltaic systems in buildings is the one we're most familiar with: an array mounted on the roof of a facility, facing south and tilted to take maximum advantage of the sun. Because schools typically have large expanses of roof area, such systems make a lot of sense for both new and existing construction, especially for larger arrays.
To mount PV arrays on schools, a number of different approaches can be used. In facilities with sloped roofs that face south (or slightly east or west of south), modules can be attached directly to the sloped roof with rails or some other form of bracket system. In schools with flat roofs, some form of frame system is typically used to hold the modules at the correct angle to maximize sun exposure. Ballasted systems are relatively new. They allow a PV array to simply lie down on the flat roof without the need for mechanical fasteners between the roof and the ballasted modules. This makes installation much simpler and avoids the multiple roof penetrations of a frame system.
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In new construction, photovoltaic systems can actually be incorporated as substitutes for other building systems, such as roofs, atriums, canopies. Such an approach-referred to as "building integrated photovoltaics" (BIPV)- can result in first-cost savings, since the PV system isn't being added to an existing building component but is simply replacing it. The system can also be financed as part of the entire building, rather than as an "add-on."
While this sounds good in principle, BIPV systems are still relatively rare, especially in the schools market, and high-profile examples like the atrium glazing for the Tiger Woods Learning Center are exceptional.
The Upsides of PV in Schools
There are three types of benefits to incorporating some form of PV into a school facility: environmental, educational, and economic.
By using the sun's energy to create electricity, PV systems offset the need for-and the pollution and CO2 created by the burning of fossil fuels to create electricity. As one of the most benign forms of energy production available, PV provides clear and compelling environmental benefits. From an educational perspective, the photoelectric effect is an elegant and scientifically compelling phenomenon. It is intriguing to children and adults alike and lends itself easily to being used as a teaching tool. It is for this reason that several states and/or local utilities have initiated demonstration programs to install small PV arrays on schools, primarily for educational purposes.
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Madison Gas and Electric in Madison, Wisconsin, for example, has funded PV arrays on 10 high schools as part of its "Solar in Schools" program. The arrays are modestly sized-roughly eight modules each, producing 2400 watts of peak power, and are designed primarily as teaching tools. The utility installed monitoring equipment in each school so that students can keep track of the output, and it developed a comprehensive "solar curriculum" that students and teachers can use to optimize the learning experience offered by the system. Similar programs, such as New York State's "School Power Naturally" and Pacific Gas and Electric's "Solar Schools" program, have been or are being implemented across the country. Clearly, the educational benefits-scientific, environmental, and social-of PV systems are a compelling justification for incorporating them into schools.
Economic Benefits
The economics of PV are a little more complex. PV power is still not cheap, especially relative to other sources of electricity in the U.S. Even though costs have come way down-from $80 per watt in 1973 to as low as $3 per watt today-amortized over a 20 year period, the cost of generating one kilowatt hour of power from photovoltaics is still as much as four times greater in some parts of the country than the cost of buying that kilowatt hour from the local utility. And while the price per watt for PV is expected to continue its downward trend, the fact remains that it is difficult to justify the cost of PV in schools based on energy economics alone. However, there are a variety of federal, state, and local incentive/rebate programs across the country that are helping to "buy down" the costs of PV installations for schools. Some of these are demonstration programs, such as the Wisconsin "Solar in Schools" initiative, that fund very modest PV arrays primarily for educational purposes. Others, like New York's Energy $mart program or the California Solar Initiative, are more substantial and can help defray the costs of installing much larger systems. While the school district still needs to provide some of the funding through combinations of rebates and other incentives, they can often cover substantial portions of the upfront investment-as much as 70 percent in New York's case.
All the energy savings go to the school, and it can really add up over the minimum 25-year life of a PV system. As a consequence, it definitely pays to check out any and all locally available incentive programs that could help defray the cost of a PV installation. In addition to rebates, some states are exploring innovative ways of financing PV installations. New Jersey, for example, is looking at Solar Renewable Energy Certificates (SRECs) as an alternative to rebates. SRECs would be issued to PV system owners, such as school districts, for every kilowatt hour produced by one of their PV systems. The SRECs that a district or individual school receives can be sold to utilities, who are required by state regulations to either produce or purchase a specified amount of electricity from renewable sources each year. Usually a utility commission or similar body sets the prices and maintains the stability of the market. The revenue generated by the SREC sales can then be used to pay off the cost of the installation.
While new and still evolving, the SREC approach allows a school district to finance the entire cost of a PV system out of projected savings, rather than receive a rebate for only a portion of the system. This can be the difference between a go and a no-go decision on PV and is definitely worth investigating in jurisdictions that support SRECs. Third party financing may also be available.
The Bottom Line
The bottom line on PV in schools is that where jurisdictions support demonstration programs, putting it in is a no-brainer. The installation won't meet much of the school's electrical load, but it will be a great-and inspirational-teaching tool. In jurisdictions that provide some form of subsidy for larger installations-those intended to significantly reduce energy use in the school-it will depend on the economics of the situation: the level and type of support provided, the amount of investment (if any) that the school is expected to provide, any regulatory restrictions that may apply, etc. In some areas, substantial PV arrays make a great deal of sense: The program in New Jersey, for example, is currently oversubscribed with a substantial waiting list. In others, even when the incentives are reasonably high, the installation may simply not "pencil out." In areas without any subsidy, the argument for PV is much harder to make. To the extent possible, a school should try to incorporate a demonstration scale array (2 KW or so) as a teaching tool, but from what school officials across the country seem to be saying, even this is an expensive "extra" to add to a school budget-for either modernization or new construction.
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The best advice? If at all possible, go for it, at least at the demonstration scale. If some form of rebate, incentive, or financing is available, install the largest array you can afford-it will continue to provide energy and education benefits for a long time to come. In any case, don't think of PV as a substitute for good, basic, energy-efficient design and construction. Energy conservation should always precede on-site, renewable energy production.