Hawaii’s solar energy boom has grown to the point where rooftop photo­voltaic panels are providing all of the electricity consumed during some daylight hours in about 13 percent of Oahu neighborhoods, the Hawaiian Electric Co. said.

The high level of PV penetration, far beyond what is occurring anywhere on the mainland, is the result of a doubling of solar power generating capacity in Hawaii nearly every year since 2005. The rapid growth has put Hawaii at the forefront of an evolving effort by utilities nationally to accept greater amounts of intermittent solar energy into their electrical grids.

While HECO is taking steps to integrate more solar energy, that could result in added costs for some new solar customers. If HECO determines improvements are needed in a certain area to accommodate additional amounts of solar energy, new solar customers may have to bear the cost.

This week HECO began contacting its Oahu customers planning on installing PV systems, as well as PV contractors, to make sure the customers are informed of any equipment upgrades they may have to pay for.

The upgrades to the Oahu grid are necessary, HECO says, because of the rapid growth in solar installations.

The latest numbers from HECO, unthinkable just a few years ago, show that solar energy provides all of the minimum daytime power needs for 54 circuits, or neighborhoods, out of the 416 circuits on Oahu. The threshold has been reached on 26 out of Maui’s 132 circuits and 17 of 143 circuits on Hawaii island.

"Those are impressive figures. Saturation on some of those circuits is higher than any other area in the country," said Tim Lindl, attorney for the nonprofit Interstate Renewable Energy Council based in Latham, N.Y.

Roughly 5 percent of HECO’s customers on Oahu and Maui, and 4 percent of its customers on Hawaii island, have installed PV systems, according to data from the utility. That compares with about 1.5 percent of the customers served by California’s two largest electric utilities, Pacific Gas and Electric Co. and Southern California Edison.

Engineers, who for years focused on managing the distribution of electricity produced by predictable, oil-fired generators, are now confronted with the challenging task of balancing the ebbs and flows of solar and wind energy to ensure the stability of the grid.

HECO may decide, for example, that it has to install equipment, such as a grounding transformer at a HECO substation. It will then recover the cost from customers adding new PV systems near that substation.

A grounding transformer typically costs about $10,000, according to HECO commercial customers who have had to install the devices. The cost to individual customers for any equipment upgrades will depend on how many customers in a certain area want to install PV. For example, a $10,000 grounding transformer spread across 20 customers would result in a $500 charge per customer.

HECO is asking customers who plan on installing PV systems to first contact the utility to check whether they may have to pay for a portion of equipment upgrades in their area.

Robert Harris, director of the Sierra Club in Hawaii, is concerned that adding another layer of bureaucracy for homeowners could slow down PV installations.

HECO already has similar "call before you install" systems in place for its customers in Maui and Hawaii counties.

In Maui County, homeowners who want to install a PV system must first get a letter from Maui Electric Co. stating the level of PV saturation on their circuit before that county will issue an electrical permit. HECO is negotiating a similar protocol with the Honolulu Department of Planning and Permitting, but no agreement has been reached.

On Hawaii island, the notification process required by the local electric utility has allowed PV customers to be better informed about the time and cost it will take to install a system, said Marco Mangelsdorf, president of Hilo-based ProVision Solar.

"Years ago the amount of PV power feeding into the grid was essentially inconsequential. That’s no longer the case," Mangelsdorf said. "Those of us in this business on the neighbor islands have had to play by similar rules for over a year and the world does not come to an end," he said.

The president of the Hawaii Solar Energy Association said HECO’s latest policy shift appeared to be a step in the right direction.

"Any proactive measure to help get distributed energy clients closer to being energy independent is an absolute plus for the industry and a plus for the state," said Andrew Yani, HSEA president and co-founder of Bonterra Solar. HSEA represents nearly 70 solar companies and other firms involved in the Hawaii energy sector.

HECO, and the Kauai Island Utility Cooperative, have both adopted policies in recent years to accommodate increasing amounts of renewable energy that were previously considered potentially detrimental to their grids.

"One of the biggest challenges is that we have had this growth in the photovoltaic sector that’s been so fast and so explosive," said Scott Seu, HECO vice president for energy resources and operations. "What we are looking at now is just trying to stay a step ahead," he said.

While adding the possibility of an additional fee for new solar customers, HECO is also decreasing the likelihood that residential solar customers would have to pay for a study to determine the impact of a PV system on the grid.

In the past, HECO has required some residential customers on Maui and the Big Island to pay for the so-called interconnection requirement study, or IRS, before installing a solar system.

Now HECO has increased the percentage of smaller PV systems that can be hooked into the utility’s electrical grids without conducting the study. Such studies cost about $3,000 on average for residential PV systems, according to industry participants. To date, HECO has required 83 residential customers in Maui County and five in Hawaii County to conduct such studies because they were on circuits with excessive PV penetration. No studies have been required for residential PV systems on Oahu.

Seu said HECO is extending the "no IRS" policy for all PV systems less than 10 kilowatts in size.

Seu said HECO made the decision based on a body of empirical data the utility’s engineers have compiled over several years. The comfort level of HECO engineers increased as they gained more experience with high penetrations of PV, Seu said.

"The issue with interconnection requirement studies is that they take time to do, and of course, they come at some cost," he said. "So as we’re looking at the current situation what we’re trying to do is say, ‘OK, can we learn from studies that we’ve already done? Can we apply the results of previous studies, or even just our own experience so that we don’t have to require new IRSs of customers especially as we see circuit penetration grow?’"