Hawaiian Electric Co. and its subsidiaries have issued new specifications for the installation of rooftop solar photovoltaic systems that the utility says will allow more homeowners to put up PV panels in neighborhoods with high levels of solar power generation.

The new technical standards specify the speed at which a PV system needs to be able to disconnect from the circuit in the event of a voltage spike, according to information HECO sent to PV installers Wednesday.

The HECO companies developed the new guidelines in consultation with the local PV industry in response to the utility’s concern that excessive amounts of solar energy being generated by rooftop systems could have adverse effects on the utility’s electric grid. The guidelines apply only to smaller PV systems with a generating capacity of 10 kilowatts or less.

HECO officials are most concerned with distribution circuits where the amount of electricity being generated by PV panels is 100 percent or more of the electricity being consumed in a particular neighborhood at certain times during daylight hours. HECO refers to that threshold as 100 percent of daytime minimum load.

HECO previously said that customers who wanted to install PV systems on circuits at or above the 100 percent threshold could be required to pay for an interconnection study or install protective equipment such as a grounding transformer. Those guidelines, put in place in September, caused many PV projects to be put on hold.

The new standards allow customers to connect their PV systems where solar energy accounts for up to 120 percent of daytime minimum load as long as the PV systems meet the new requirements.

The specifications address a problem called "transient over-voltage," or TOV. The problem occurs when two conditions occur simultaneously: The amount of solar generation exceeds the load on a given circuit, and there is no place for the excess power to go.

"Under these circumstances more power is being generated than can be absorbed by loads on that circuit, causing voltage to rise rapidly," according to information sent out by HECO.

HECO has identified two "mitigation options" that will allow the interconnection of PV systems on circuits at the 120 percent threshold. The first option for customers is to use a PV power inverter that has the ability to stop exporting power when a certain high level is reached. In cases where an inverter does not have that functionality, customers can opt to install a "fast-acting automatic transfer switch" that meets the same standard as the inverters.

With either solution the equipment needs to be able to trip off within one-sixtieth of a second when it senses voltage above 120 percent of normal, according to HECO.

Solar industry leaders said the new specifications are expected to help ease some of the backlog of PV installations.

"This is a meaningful step in the right direction. It’s a recognition of the principles the people in distributed generation have been advocating for some time," said Mark Duda, president of the Hawaii PV Coalition. "We’re pleased, but there is more that needs to be done. We look forward to working together to take the next step."

Leslie Cole-Brooks, executive director of the Hawaii Solar Energy Association, also welcomed HECO’s announcement.

"This is a good thing that will allow more customers to go online with their PV systems," she said. "It’s one step in what we know is a series of technical solutions that show we can accommodate more distributed generation. And distributed generation is part of the solution to get Hawaii off of imported oil."

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Star-Advertiser news services contributed to this report.