As the moon passes directly between the earth and the sun creating a total solar eclipse, it is expected that solar energy production will be interrupted for up to three hours in the path of the eclipse.

The Natural Resources Defense Council (NRDC) reports that the eclipse will reduce solar energy production in a broad swath, an impact that was not seen back in 1979 when the last eclipse occurred in the United States and solar energy was in its infancy. However, the NRDC states that most people will not notice any change in their electricity service due to preparations by the nation’s electric grid operators to ensure that the transmission system functions reliably.

Since 1979, the country’s energy system has significantly changed, with solar and wind energy becoming the fastest-growing sources of new electricity generation. At least seven million U.S. homes and businesses are directly powered by the sun, and the eclipse will interrupt solar power generation from their rooftops as well as from large utility solar farms.

Electricity generation for the entire country will be somewhat affected by the eclipse, but some states will see a larger drop in solar power than others, depending on how much of the sun is blocked by the moon in their specific location, reports the NRDC. However, there are many energy resources available to fill the gap (including wind, geothermal and hydropower), since electric grid operators have had years to prepare for this month’s celestial event.

Along the 70-mile-wide path of totality from Oregon to South Carolina, the moon will completely block the sun. The longest period of total darkening will be about two minutes and 40 seconds, according to NASA. However, the moon will block at least a portion of the sun nationwide, with the amount of obscurity varying by location. The longest period of partial darkness in any spot will last about three hours.

California and North Carolina may experience the biggest impacts from the eclipse because of the amount of solar produced in California and because of the timing in North Carolina as evening is approaching and customer electricity demand is beginning to peak.

Some states across the country are tying this unique event to energy usage. California recently launched a Do Your Thing for the Sun campaign that urges residents to reduce energy use during the eclipse so grid operators will have less need use less energy-efficient natural gas power plants, which also generate climate-warming carbon pollution. Homeowners, businesses, organizations and local governments are being encouraged to replace light bulbs with LED before the eclipse and turn off lights, unplug chargers and appliances that aren’t in use, and turn up thermostats during the eclipse.

Photo: An eclipse is reflected in computer-controlled mirrors at the National Solar Thermal Test Facility. By Randy Montoya/Sandia Labs, provided by NRDC