The Sun4Schools project, funded by NorthWestern Energy's Universal System Benefits Charge, resulted in the installation of 2-kW photovoltaic (PV) systems at 27 schools within the NorthWestern Energy service territory between 2000 and 2003. The main objective of the project was to demonstrate the benefits of solar energy while providing a unique educational opportunity for students and their communities. (You can view the systems at the Sun4Schools photo album.)
In addition, the project is reaping other important benefits, including reducing the use of fossil fuels and resulting greenhouse gas emissions and thus helping to protect our environment, allowing the schools to save money by generating their own "clean" electricity from a renewable energy resource, providing experience with the net metering, and creating support for a Montana PV infrastructure.
To minimize cost and to simplify quality assurance of the systems, all installed systems are 2-kW peak capacity utility-intertie systems without battery storage. Of the roughly 3,000 kWh per year produced by each 2-kW system, about 1000 kWh will be provided to the utility grid and 2000 kWh will be used directly by the school. These systems can be expected to produce electricity at about $0.24 per kWh.
NCAT staff developed a solar energy curriculum unit for participating schools. This unit is an important component of the project because it brings solar energy education into the classrooms and thus allows students to use the installed PV systems as a learning tool, rather than simply viewing it as "hardware."
The curriculum provides teachers with materials they can use in their classrooms to teach students about solar energy and, specifically, the photovoltaic systems installed on their schools. The primary focus of the unit is solar energy, but it also provides information on other forms of renewable energy to give the students a well-rounded understanding of how solar energy fits into the overall energy picture. The unit contains nine hands-on lessons, as well as background information and resources for additional investigation.
The unit can be downloaded at the Montana Green Power website.
The systems installed under this program satisfy the following:
IEEE P929 interconnection standard defines the equipment and functions necessary to ensure compatibility between the PV system and the utility. UL 1741 inverter test standard deals with safety issues of grid-tied PV inverters, addressing electric shock hazard, fire hazard and utility compatibility. A utility-interactive inverter that passes UL 1741 will be a non-islanding inverter and satisfy the interconnection requirements of IEEE P929. The 1999 National Electrical Code requires all utility-interactive PV systems to use listed inverters that pass UL 1741. In effect, any small utility-interactive PV system in compliance with the 1999 NEC will automatically be in compliance with IEEE P929.
Solar Electric System Specifications
Each school is equipped with photovoltaic modules to make up an array with an output of approximately 2-kW (peak). The modules are framed and composed of flat-plate multicrystalline silicon cells. The modules have a UL 1703 listing and are warranted by the manufacturer to provide no less than 90 percent of rated power for 10 years, and 80 percent for 20 years.
The contractor provided all the materials for mounting the PV arrays. The mounting structure is capable, at a minimum, of withstanding winds of up to 90 mph, and is constructed of corrosion-resistant steel or aluminum. Both roof- and pole-mounted systems are mounted at a fixed 45-degree tilt facing south.
The contractor supplied and installed an inverter for each system to allow grid connection (120VAC, 60Hz). The inverter has a UL- or ETL-1741 listing, containing maximum power point tracking, islanding protection, over/under voltage disconnect, over/under frequency disconnect, automatic fault condition reset for loss of grid and voltage/frequency variations, GFI protection, AC and DC disconnect switches, communications adapter for PC connection/monitoring, as well as a five-year warranty.
The contractor provided a lockable AC disconnect switch located in an outdoor-rated enclosure mounted near the main electric meter for utility personnel use. The disconnect switch was mounted within 10 feet of the electric meter and labeled "Solar Electric Generator Disconnect Switch." In cases where the meter was far away from the PV system, the contractor labeled the meter base with "This net meter is connected to a solar electric generating system."
Participant Building Characteristics
All buildings in this project are located within the Montana Power Company electric service area. The buildings are connected to the utility's distribution system and have an MPC electric meter.
School officials were required to provide the building's electric bills for the previous 18 months or allow NCAT access to the bills (for a baseline determination). Each school also was required to sign a net metering agreement with MPC.
The participating schools share some basic site characteristics. For example, one of the building's roofs must be south-facing and have an area of at least 300 square feet. While PV arrays do not require guaranteed access to sunlight from sunrise to sunset, the installation sites are shaded as little as possible between 8:30 a.m. and 3:30 p.m. solar time, when nearly 90 percent of the sun's energy reaches the site. All of the PV systems (both roof- and pole-mounted) were installed with the south-facing arrays tilted at 45 degrees.
Sun4Schools is funded through NorthWestern Energy's Universal System Benefits (USB) fund, created by Montana's 1997 utility restructuring legislation. USB funds new and existing energy conservation activities, renewable resource projects and applications, and low-income energy assistance. For more information on Sun4Schools, contact Cathy Svejkovsky at the National Center for Appropriate Technology (1.800.275.6228).
A list of selected schools in Montana also is available.