Solar Power
NCAT
Hooks Up to Solar Power
Photovoltaics fill
some of the power needs at the headquarters of the National Center for Appropriate
Technology in Butte. The PV system installed on NCAT's roof in May by
Solar Plexus of Missoula consists of 60 Siemens SP75 modules. Each module
is rated at 75 watts and is flush-mounted on the south-facing, third-floor roof;
total module area is about 480 square feet. Peak electrical output of the system
is 4.5 kilowatts.
Thirty modules make
up each of the east and west arrays. Each array is electrically connected to produce
direct current (DC) at 48 volts. The output from each array can be disconnected
for comparison purposes. The system's DC electrical output is connected to a Trace
SW4048UPV utility intertie inverter.
The inverter, connected
to the utility grid, senses the utility's voltage and frequency and produces alternating
electricity at the utility's voltage and frequency. The inverter is designed to
operate only when utility electricity is available. Whenever the utility goes
down, the inverter shuts down and will only turn back on when the utility line
comes back on.
The system will provide approximately 13 percent of the NCAT building's electrical
consumption. It is assumed that the annual kWh use of the building will be 50,416
and the PV system will provide 6,750 kWh. Helena solar data was used for the performance
calculation.
NCAT
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