Another 6 megawatts — enough for possibly 850 residential rooftop photovoltaic systems — will become available for hookup to the grid on Maui, according to Maui Electric Co.

In June, MECO had reached its 5-megawatt capacity limit for rooftop PV systems that connect to the grid and sell power to the utility under the “customer grid supply” program. That meant residents purchasing PV systems could no longer export their excess solar power but could set up battery storage, or “self-supply,” systems.

Solar industry groups asked the Public Utilities Commission, which regulates state utilities, to increase the capacity for PV hookups to the grid. The PUC denied the request but ordered Hawaiian Electric Cos., of which MECO is a subsidiary, to transfer capacity from rooftop PV systems that were approved but not completed to the cap under the customer grid supply terms.

Statewide, HECO said that amounted to 20 MW of power available on Oahu, Maui and the Big Island.

Shayna Decker, MECO director of communications, said last week that current estimates show at least 6 MW of customer grid supply available for Maui customers. The sizes of the PV systems vary with the applicant but the average size is 7 kW, which would be 857 systems for the 6 MW of availability.

If applicants for this new PV availability install “right-sized” systems calculated for actual energy use rather than systems designed mainly to sell power to the utility, more residents could take advantage of this extra space, she said.

Molokai and Lanai have already reached current capacity and do not have additional residential PV space on their grids, Decker said. MECO is currently working on pilot projects, such as E-Gear that incorporates energy storage technology, to utilize more “as-available renewable energy,” such as rooftop solar, on the smaller grids, she said.

The open space on the grid will be processed in the order received and only as capacity becomes available through Oct. 21, HECO said Wednesday. Customers interested in submitting an application should first review the HECO “Going Solar” webpage (www.hawaiianelectric.com/clean-energy-hawaii/going-solar) and check the online “Locational Value Maps” to determine if the circuit serving the neighborhood has room for more solar. If the circuit is saturated, installation of equipment may be required, potentially adding to the cost and time needed for approval.

In mid-December, MECO reported 973 approved customers who had not moved forward with PV installations on Maui. Approved customers under 10 kW have a year to install their systems, and those over 10 kW, 18 months, MECO said. Approved applicants may receive a one-time extension of 180 days if requested within two months of the deadline.

There has been an evolution in the acceptance of small-scale PV in Hawaii. The original “net metering” program allowed PV customers to sell their excess power to the utility at market rates while still drawing power from the grid at night. Those customers paid only an $18-per-month minimum fee to connect with the grid.

Concerns about PV capacity on the grid and the tilting of the cost of grid maintenance and fuel to those without PV systems were raised by HECO. The PUC approved the PV cap in October 2015 under the new customer grid supply program, locked in the PV crediting rate at 23.1 cents per kilowatt hour on Maui and raised the minimum monthly bill to $25, and created the “customer self-supply” option once the cap was reached.

Solar industry officials complained that the end of PV grid accessibility was a step toward shutting down the industry and reported reductions in the number of PV installation contracts.

Marco Mangelsdorf, owner of ProVision Solar based in Hilo, reported a near halving of the number of PV permits issued in Maui County in 2016 compared to the previous year. Using data from the county, he said there were 1,657 PV permits issued in 2016, compared to 3,153 in 2015.

* Lee Imada can be reached at leeimada@mauinews.com.