Overall, solar power still isn't a big part of America's energy landscape. The most it contributes is about 2% of supply in big solar states like California. But solar has been growing very rapidly. By early 2014, there were more than 480,000 solar power systems in the U.S., delivering enough energy for 2.4 million homes. Between 2010 and 2013, the number of installations had jumped almost 500%.
For a readable account of solar's progress, take a look at this new report from the Union of Concerned Scientists. It sizes up the boom, looks at what's driving it, and explores what needs to happen for it to continue. Below are a few key points; the key graphics are in the slideshow above.
Between 2010 and 2013, the price of a typical home PV system fell by almost 30%, while the capacity of the average system tripled. A standard 5
megawatt kilowatt installation now costs $23,000 to install, before tax credits and other incentives. The federal solar investment tax credit delivers 30 percent back, while local rebates and support frequently get the consumer price under $10,000.
Most households actually pay nothing up front: With the solar leases and power purchase agreements, they pay off the cost of the unit over time. Where America falls down is in "soft costs," including permitting, inspection, connection to the grid, and the margin enjoyed by installers. For the average home, these account for half of all costs; in Germany, another solar superpower, it's only a fifth.
Large-scale installations accounted for about half the growth in solar capacity between 2010 and 2013. These are sites with thousands or even millions of panels packed together, like 290 megawatt Agua Caliente project in Yuma County, Arizona, which has 4.9 million panels. The cost of electricity from such systems has fallen 50 percent since 2010. It's now 60 percent lower than residential solar power, even including the heavy upfront cost of setting up the plants.
The U.S. has also pioneered the use of solar thermal power (CSP)—where water is boiled to produce steam that drives a turbine. But these projects haven't fallen in cost so quickly. "The main components of CSP projects—steel and mirrors—have not experienced the dramatic cost declines that solar panels have," the report explains.
While critics of solar complain about "intermittency" issues (that you can't generate power when the sun doesn't shine), fewer acknowledged is solar power's benefit to grid stability. "In many regions, demands on the electricity system peak in the afternoon on hot, sunny days, when air conditioning demands are high and when rooftop solar is performing strongly," the report explains. "Such systems therefore help utilities meet peak demand without firing up seldom-used but expensive and more-polluting power plants fueled by oil or natural gas." It is also more efficient to produce power where it's consumed, rather than passing it over distribution infrastructure.
The problem is the grid isn't always set up to take back power in the opposite direction. In neighborhoods where lots of homes have installed panels, "feeder" lines are now reaching capacity, making additional installations more difficult. Utilities also have to cope with increased variability of supply, though forecasting the sun's output on any given day has become more sophisticated. We can now predict how much power solar will provide.
Though the most (and biggest) installations are in California and the Southwest, the report stresses that solar is viable everywhere. A typical 5
megawatt kilowatt rooftop system in Phoenix generates between 7,000 and 8,000 kilowatt-hours per year—enough energy to power a home.
The equivalent installation in Portland, Maine, achieves 85 percent of that, and 95 percent of the same system in Miami. Across the U.S., from the sunniest to the least sunny state, sunlight availability varies by a maximum of 30 percent, the report says.
By 2017, half the states could have rooftop solar that's as cheap as grid power. By 2020, between 900,000 and 3.8 million homes could have panels, projections show. But not without state help. The Union of Concerned Scientists wants Congress to continue with the federal investment tax credit (which falls from 30 percent to 10 percent in 2016), and for governments to consider ideas like "value-of-solar tariffs," which reward homeowners not only for delivering electricity to the grid, but also for environmental benefits and grid stability. The city of Austin, Texas, pioneered the idea in 2012.
"Solar is a broadly accessible, low-emissions energy choice for America," the report concludes. "Forward-looking policies and investment decisions by government, industry, and individuals will continue to be crucial for driving solar’s impressive development."