To generate a lot of energy from rooftop solar panels, you need two things – a lot of sunshine and a lot of roof space.

Orange County, it turns out, has both, making it one of the most solar-ready regions in the country, according to a report from the National Renewable Energy Laboratory.

Mission Viejo topped a list of 47 cities studied, with rooftops capable of generating 88 percent of the city’s electricity consumption. Since apartments make up just 15 percent of the city’s housing, roughly half the state average, Mission Viejo has a very high proportion of rooftop per resident, and a lot of space for solar panels, according to the report.

But Mission Viejo isn’t unique in Orange County. It was just the local city that researchers happened to study. Researchers said the characteristics that make Mission Viejo a potential solar hub are found throughout the county.

“You guys have a fantastic place for solar – there’s no question about that,” said Pieter Gagnon, the report’s lead author who is based in Golden, Colo.

California, overall, fared well in the rooftop survey. The state could generate 74 percent of its 2013 electricity demand using rooftop solar panels – the highest percentage in the nation, according to the report. And a typical roof of a small building in the Los Angeles County/Orange County region has enough space for solar panels to generate more electricity than the building consumes, the report said.

The local solar market is strong for a couple of key reasons:

• Buildings here generally are more energy-efficient than buildings nationally.

• Also, compared with many other regions, there are fewer trees or other high objects that can block sunlight from solar panels.

The potential for solar energy already is translating into real-life production.

Southern California Edison, which provides electricity to most of Orange County, connected more solar panels to the grid last year than any utility in the country – 1,258 megawatts, roughly enough power for 943,000 households. San Diego Gas & Electric, which delivers energy to south Orange County, came in fourth, with 441 megawatts, or about 308,000 homes.

In all, about a quarter of the energy sold by Southern California Edison and more than one-third of the energy sold by San Diego Gas & Electric came from renewables, figures that don’t include residential rooftop solar, indicating the real percentage of renewables is higher. By 2030, half of the electricity sold by California utilities must come from renewable sources, such as solar, according to a state mandate.

To sort out which roofs have the most potential for solar production, researchers used three-dimensional city maps created by the Department of Homeland Security. The security agency had used airplane-mounted lasers to collect data on urban areas, and the energy researchers built on that by measuring how much sun would hit roofs in each community during different seasons and times of day.

The report excluded small roofs and roofs that tilt north because they aren’t suitable. And researchers examined only existing roof space, though they said that adding solar panels to carports, the sides of buildings and unusable plots of land could generate even more energy.

Gagnon, the report’s author, noted another big opportunity: Though most solar technology is installed on residential roofs, commercial rooftops ultimately could generate even more electricity; panels on office buildings could take advantage of energy generated at midday, when most people are at work and houses are empty.

Commercial solar is challenging, however, because office rooftops come in many shapes and often require unique panel designs. Also, the people who pay for solar installation on commercial properties, building owners, sometimes don’t get direct benefits from cheaper energy bills.

In the short term, solar energy is likely to keep coming from two sources – residential rooftops and huge solar power plants that use mirrors to direct intense amounts of sunlight at molten salt and other materials, which stay hot late into the night and can be used to generate electricity.

But to really boost solar power, Gagnon said lawmakers and regulators will need to craft policies that foster the technology and industry.

“With solar, it’s probably going to be mostly dependent on policies going forward,” Gagnon said.

Two cases in point: Last year, Nevada changed its solar rules to make residential solar rooftops less attractive, while still allowing growth for big, utility-size solar production. California, meanwhile, ruled that utilities must continue to compensate homeowners for solar energy at a rate close to what they currently pay, a decision viewed as a win by the solar industry and clean-energy advocates.

Another key to solar’s future is the development of batteries that can store solar-generated electricity, said Micah Fromkin, director of Southern California operations for Sunrun, a solar installer.

Such batteries are important because they can help solve a basic problem of solar energy, keeping energy flowing at night and during cloudy days, when there isn’t enough solar production to meet demand. Fromkin said batteries could dramatically boost solar power production if they follow the model of other technologies, becoming cheaper for consumers even as they become more efficient.

“That’s the next big step forward.”

Contact the writer: aorlowski@ocregister.com. Twitter: @aaronorlowski