Prior to the installation of the PV system in May 1980, the Monument relied on diesel
generators, operated continuously. The Monument consumed up to 200,000 kilowatt hours
of electricity annually, and the noise and pollution was incompatible with Natural Bridges'
pristine desert setting. With installation of the PV system (in 1980 it was the world's
largest PV array) and the implementation of energy-efficient measures, the Monument now
consumes about 70,000 kWh annually with over 90 percent of that coming from the sun.
Most heating and cooking needs continue to be met by liquefied petroleum gas.
System components are PV (original Block III) modules nominally rated at 100 kW, inverter
(50 kW), 39 deep cycle batteries (600 kWh), and diesel generator (40 kW) - all original
components have been mostly replaced in he 1990's). Maximum draw down of the batteries
is 450 kWh, enough for two days of operation. The automatic control allows the PV system
to operate for extended periods without human intervention. Near full charge, the
controller will disconnect (shed) one or more of the 48 array stations to prevent
overcharging the batteries. It also starts the backup diesel generator automatically when
the battery state-of-charge (SOC) falls below 20 percent.
The original batteries provided excellent service for 10 years. Then for two years the
system was not operational. In 1992, the system was refitted with new batteries and the
PV array was downsized to 50 kilowatts. By the late 1990s, the original PV modules were
replaced with Block V modules working with a diesel generator to charge a battery bank.
This is the oldest continuously operating renewable energy hybrid system in the world
(since 1980).