According to the US Department of Energy, enough sunlight strikes the Earth every hour and a half to power the entire world for a year.
Of course, not all of Earth's surface is covered with solar panels, and running a solar-only grid would be a huge challenge. But solar energy generates carbon-free electricity and is a valuable source of clean energy.
“Renewable energy is a safe household resource that conserves water, reduces emissions and reduces costs,” said Michael Weber, professor of energy resources at the University of Texas at Austin.
As Texas rapidly expands its solar power capacity, here are five things you should know.
When sunlight hits solar panels, it is not fully converted into electricity.
Most major brands of rooftop solar panels have an efficiency of around 20%. This means that only 20% of the total solar energy that reaches the solar panels is converted into usable energy. The remaining 80% is lost as heat.
This is a significant loss, but it is close to the upper limit of efficiency (about 29% efficiency) possible with typical silicon solar panels.
Silicon is a semiconductor, which means it is sandwiched between a conductor (such as copper wire) and an insulator (such as rubber). Thanks to its semiconductor properties, it extracts energy from sunlight and converts it into electricity.
To get around the 29% limit, silicon can be combined with perovskite, another semiconductor. Two articles published in July showed that with these combination panels it is possible to obtain returns of about 30 cents.
Sometimes the sun produces a lot of electricity.
Even with limited efficiency, the sun can sometimes be very productive. At noon, when the solar panels receive the most sunlight, they can produce enough electricity to meet demand.
ERCOT and other power grids are constantly trying to balance energy supply and demand. On a sunny day when the solar energy supply is high, ERCOT can instruct solar energy systems to intentionally reduce the amount of electricity produced to avoid overloading the grid.
Overproduction can also be a problem when power lines are unable to move electricity efficiently from where it is generated to where it is needed.
There are also concerns that too much solar will affect energy savings and force electricity prices to follow the sun's cycle.
"When it's hot and the solar is on, it's very valuable right now," said Jan Klisel, an engineer at the University of California, San Diego. "But if you have a lot of solar energy, then ... it's not helpful at all."
Giant batteries can harness solar energy at dusk.
To address overproduction, several new projects plan to store excess solar energy generated during the day in large batteries.
William Shavarman, director of the University of Delaware Solar Energy Research Center, explained that electricity demand peaks between 5 and 8 p.m., when people get home from work. This does not match peak solar energy production, i.e. before that.
"By shifting that peak from mid-afternoon to mid-afternoon... you can get more out of your solar system," Schaffarman said.
Batteries enable solar power producers to make this change and are becoming an increasingly popular part of solar power plants. “Batteries can outpace solar power…,” said UT-Austin's Webber.
Of major solar projects in Texas through the end of 2022, data from Lawrence Berkeley National Laboratory shows that 37% involve battery storage.
Hotter is not better.
As counterintuitive as it may seem, solar panels are most productive in cold weather. At temperatures above 100 degrees, the average rooftop solar panel produces 5% less energy than at 77 degrees.
"Solar panels work best on a sunny northern winter day, when there is bright light but cooler temperatures," Schafarmman said.
Clouds affect solar energy, but not as much as you might think.
Solar energy is really simple because more solar means more energy. However, on cloudy days, solar systems can generate electricity. Rooftop solar panel manufacturers report that performance typically decreases by 10-25% on clear, cloudy days.
Kleissl is working on tools to make accurate predictions of when clouds will be over a solar panel. He says ERCOT and other facilities usually look for accurate forecasts that forecast clouds for the day at five- to 10-minute intervals.
With advance warning, the power grid can prepare to accommodate other types of power plants as solar production declines. "The sooner you can do it, the cheaper it will be," Klessel said.
Researchers estimate that accurate predictions could save the New England grid tens of millions of dollars annually.
Laila Levinson reports on the science for the Dallas Morning News in a fellowship with the American Association for the Advancement of Science.
