San Diego’s one of the nation’s solar boom towns. The boom’s been most robust in northern communities away from the coast.

Data released by San Diego Gas & Electric shows the county’s top rooftop solar meccas are east of Interstate 5 and mostly represent people who own their homes instead of renting. Homeowners further from the coast often have higher energy bills that can make solar panels a more attractive investment. Hotspots include Poway, Scripps Ranch, Rancho Bernardo, Ramona and Lakeside.

The SDG&E data is based on the number of solar net energy metering connections – a state-mandated arrangement that allows solar customers to receive credit for energy their systems produce – per ZIP code.

This map shows net metering applications by ZIP code, plus the estimated kilowatts of power the area’s solar panels could produce.

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There are a handful of reasons some neighborhoods are more solar-powered than others.

Income and homeownership are particularly crucial.

Many of the early solar adopters in San Diego County own homes and had cash to throw at solar projects, even absent state incentive programs such as the California Solar Initiative.

“We really saw people installing solar who (had) higher incomes but at the same time (had) very big houses and very big electric bills. It made a ton of sense for these people,” said Benjamin Airth, senior manager of the nonprofit Center for Sustainable Energy’s renewable programs.

Those customers could afford to purchase the panels outright and immediately see substantial energy savings.

Airth said some East County and northern San Diego communities hit by the 2003 Cedar Fire – areas with lots of early solar growth – also benefited from another incentive program that handed residents rebuilding their homes up to $20,000 to install solar panels.

A decade later, an influx of solar companies, more diverse financing models and decreases in solar prices – plus increases in SDG&E energy rates – have helped make the technology more affordable for folks who use less electricity and have less money to invest upfront.

Many communities across San Diego County have seen significant upticks in net metering signups in the past three years.

Encanto and Normal Heights, for example, saw large spikes in 2014 and have already added almost the same number of solar systems in the first five months of 2015 than in all of 2013.

Some communities are still lagging behind.

Sometimes the reasons are obvious. Take East Village or Little Italy. You won’t find lots of single-family homes in either neighborhood.

In lower-income areas, there are other challenges.

Most low-income San Diegans are renters and those who are homeowners tend to live in older houses with roofs that don’t lend themselves to solar. That can mean increased costs.

“Their roofs may need structural reinforcement before the weight of solar can be added, which can add to the cost barrier to going solar,” said Kayla Race of the Environmental Health Coalition, a nonprofit environmental justice group.

Groups like the Environmental Health Coalition and the nonprofit Grid Alternatives, which installs solar panels on the homes of low-income families, are working to combat those roadblocks, which they collectively refer to as the green divide.

In San Diego County, Grid Alternatives has largely relied on funding from another California Solar Initiative program, the Single-family Affordable Solar Homes project, to help.

Paul Cleary, the group’s regional director, said the San Diego County organization has worked on many projects in City Heights, Barrio Logan and southeastern San Diego neighborhoods. (You can check out a map here.)

In recent years, Cleary said he’s noticed more solar companies pitching projects in some of the neighborhoods he’s focused on.

“People in those communities are interested,” Cleary said. “They just never thought they’d be able to take advantage of the technology.”

Correction: An earlier version of this post mischaracterized solar growth in North Park. A ZIP code that includes Normal Heights, University Heights and a portion of North Park added nearly as many solar panel systems in the first five months of 2015 as all of 2013.

This is part of our quest on whether solar will pay off for San Diego. Check out our previous post, SDG&E Wants Solar Customers to Pay Up, here.