After five years of rapid growth in rooftop solar, Hawaiian Electric has had to slow down new installations amid worries that more solar will destabilize power delivery in some neighborhoods. It's a looming issue for other places where a high penetration of distributed solar brings new challenges to how the grid operates.
The company that represents three Hawaiian electric utilities last week said that last year it reached 300 megawatts worth of rooftop solar from more than 40,000 installations, or about 10 percent of its customers on the island of Oahu. That's a huge jump from 2008, when only 12 megawatts were connected to the grid. And during hours of full capacity, distributed solar is contributing as much as a medium-sized power plant.
But the high penetration of solar is creating concerns for Hawaiian Electric. In some neighborhoods, solar panels generate more than the utility's daytime minimum load, a situation that the current grid equipment wasn't designed to deal with. Solar generators increase the voltage on a power line and a high or varying voltage can cause problems with household electronics and the utility's equipment, says a representative from Hawaiian Electric.
"The excess energy from high amounts of PV on a neighborhood circuit can back-feed into the circuit, causing over-voltage and other power problems. This can be dangerous for utility crews and customers," said Peter Rosegg, a spokesman for Hawaiian Electric.
Fixes in the works
In September, the utility established polices to ensure additional solar won't destabilize the grid. And in the last quarter of 2013, the rate of new rooftop solar installations slowed down, the utility says.
"We are working to find ways to add more solar power, including on circuits that already have large amounts of PV installed," said Jim Alberts, Hawaiian Electric senior vice president for customer service, in a statement.
Hawaiian Electric now requires solar contractors to get approval before installing and interconnecting new PV systems in solar-heavy areas so that saftey studies can be done, says Rosegg.
"This is because even as we push out the thresholds for when a detailed study is needed, some circuits have very high amounts of solar above these thresholds," he said.
The utility is considering a variety of technical fixes to mitigate the issue and accommodate more solar. On the customer side, it's testing so-called smart inverters that are able to automatically adjust voltage so that it doesn't cause problems on the power distribution line. Hawaiian Electric is also exploring large batteries and other equipment to deal with high levels of distributed generation on a circuit.
Challenges and criticisms
Hawaiian Electric's decision to change its solar interconnection policy has brought criticism from customers who haven't been able to go solar and others who say the utility isn't doing enough to accommodate solar. "They're acknowledging that it's slowed. I'd say it's more than slowed, it's really hit a wall," Zach McNish of the Hawaii PV Coalition told Hawaii News Now. "I think people want a grid that will allow them to install solar."
Others contend that the utility is creating an artificial limit [PDF] on solar because consumers will be paying less to the utility. Hawaii generates much of its power from imported fuel, giving it the highest electricity rates in the U.S. and making solar PV an attractive way to cut monthy bills.
Hawaii is a particularly challenging environment because the island grids are small and remote, whereas grids with more customers have more flexibility to manage issues caused by distributed generation. But many people in the solar and utility industries say similar problems are bound to crop up elsewhere.
"I am from the future," Charles Wang from solar installer Hawaii Eco Project said at a solar conference last month. "The utility is a 800-pound gorilla. If you push it into the corner of the room, it's going to fight back. That's what's happening right now."
In parts of California and New Jersey, people in the solar and utility industries are already looking ahead at how to deal with voltage and other potential power problems on local grids.
"Often times you hear people say a utility is not letting people connect to the grid because they're afraid to lose money. You can see where there is an incentive for the utility to hide behind technical issues, but in theory, what they are saying is sound and there are technical issues that need to be dealt with," said MJ Shiao, solar analyst with GTM Research.
In some cases, one single large installation, such as a rooftop solar array at a retail store, will prompt utilities to ask installers to pay for grid upgrades. Often, the cost of those upgrades can make projects uneconomic, says Mark Goodreau, the director of sales at inverter maker Solectria Renewables. It's still not exactly clear how reliability issues from heavy clusters of solar will be addressed, but the issue is not going away.
"It does have to be resolved to allow PV to grow beyond the limits that are making utilities nervous,” Goodreau said.
Photo of sun in Hawaii by Vibrant Image Studio via Shutterstock