Natural Bridges National Monument Solar Power System is an experimental electrical power plant at the Natural Bridges National Monument in the southeastern portion of the U.S. state of Utah. It consists of 256,812 solar cells arranged in 12 rows, each measuring long. Direct current energy from the array is converted to alternating current at an equipment building, then supplied to the park's staff buildings and visitor center. Excess energy is stored in a bank of batteries that is used on cloudy days. The system is controlled by computers and creates fewer emissions than the diesel generators that it replaced.
When it was dedicated in June 1980 by the Utah Governor, it was the world's largest solar plant at 100 kW. The solar power station was later downsized to 50 kW and supplemented with a diesel generator backup system which allowed the solar array to operate more efficiently.
History
The electrical power plant, located in Natural Bridges National Monument, is a joint experimental venture between the Massachusetts Institute of Technology's Lincoln Laboratory and the United States National Park System and Department of Energy. It was initiated in 1979 and when dedicated in June 1980 by the Utah Governor, it was the world's first solar-power generating system. It is above sea level and located in a desert in the southeast corner of the U.S. state of Utah. An array of solar panels are set up and located on adjacent to the park's visitor center. The visitor center has an observation platform nearby overlooking the solar cells and recorded narration explaining the function of the facility. Natural Bridges receives sunlight year-round and is far from other commercial power sources, making it an ideal site for an experimental solar cell power system.
The 1980 project cost $15 million ($ in 2022 dollars) and a power plant 30 years later would cost about $1.5 million ($ in 2022 dollars) because of technical advances in solar cell production. The power plant operated for 10 years before it was shut down for overhaul and upgrading. The plant was downsized from 100 kW to 50 kW and supplemented with a diesel generator backup system which allowed the solar array to operate more efficiently. At this time the modernization involved adding 18 kW of new state-of-the-art solar modules, replacing the battery bank and upgrading the wiring to a higher gauge. The electric power system was again renovated in 2003 with new 319 kilowatt lead-acid rechargeable batteries and 100 kilowatt electronic DC to AC inverters.
Characteristics
The photovoltaic system (PV) plant is from the nearest power line. It originally consisted of 256,812 individual solar cells with diameters of and , arranged in 12 rows; these were originally capable of 100 kW at noon with full sunlight. The direct current (DC) power generated by the solar cells is converted to alternating current (AC) power. AC electricity is used for the visitors' center, six staff residences, maintenance facilities, and the local water sanitation system. The system is protected with lightning rods.
When the array started operating, it contained 39 rechargeable lead-acid batteries, each weighing , with a combined capacity of . This provides enough power for the park to operate for two cloudy days, when it typically uses . There are two diesel generators as well. When the batteries are nearly fully charged, the array's control system can disconnect some of the 48 array stations.
The PV system saves $30,000 annually compared to diesel generators that provide the same amount of energy; in addition, the arrays are quieter and produce less air pollution than diesel generators. Furthermore, the PV plant reduces annual emissions by of sulfur oxides, of nitrogen oxides, of carbon dioxide, and of carbon monoxide.
Photovoltaic equipment
The array consisted of 12 rows of panels. Each row is approximately long and has 48 solar cells. The 576 solar panels have a total area of . They replaced a set of 40-kilowatt diesel generators, which used of diesel fuel each month. The costly diesel fuel had to be trucked to the Park facilities and came from to away. The network of rows of panels required 288 piers to support them. Each pier is in diameter and ranged in depth from to depending on the engineer's assessment of the load and the depth of the subsurface rock. The surveying for the location of each of the piers began August 1, 1979.