Hawaiian Electric Co. said Tuesday that Oahu’s first “self-supply” rooftop solar system was recently turned on at a home in Honolulu.

Unlike the most common rooftop solar systems, self-supply systems connect to batteries and do not send excess power to the grid. Homeowners with self-supply systems can draw power from the grid when needed but get no credit for any excess power generated.

Self-supply avoids the problem of solar systems sending too much power onto the grid, according to HECO.

Last fall the state Public Utilities Commission replaced a popular solar incentive, known as net energy metering, with a new “grid supply” system, which allows customers to send solar power to the grid for a reduced credit. The state put a 35-megawatt cap on the grid-supply program. Maui has already reached the limit. Oahu and Hawaii island are at about 70 percent capacity.

HECO wants customers to know that there is still an option for installing solar power even after the grid-supply systems are maxed out. That option is self-supply.

HECO said in a news release that it has been working with SolarCity, Sunrun, Vivint Solar and RevoluSun on developing self-supply systems.

“Generating electricity, storing it, and using the energy on-site is the new normal. This product (self-supply) will help make the grid stronger and more reliable,” said Jon Yoshimura, director of policy and electricity markets for SolarCity, in the HECO news release. SolarCity recently installed a self-supply system with batteries at a home in Manoa.

HECO is also suggesting customers limit the size of their solar systems to just the power their home needs.

“Hawaiian Electric recommends a ‘right-sized’ system calculated for the household’s actual energy use rather than an oversized system designed mainly to sell electricity to the grid,” the news release said. “Oversized systems cost more and can potentially export more electricity than the homeowner will receive credit for on their electric bill, since credits expire at the end of each month. Also, the more large systems that are installed on each island, the less room that will be left on the grid for customers who may want to install solar in the future.”

“It’s been five years since rooftop solar really took off in Hawai‘i, and more than 77,000 customers have made the choice to use it,” said Jim Alberts, senior vice president of customer service at Hawaiian Electric. “The shift to self-supply is an important evolutionary step to ensure that the rooftop solar option remains sustainable, cost-effective and available to some of the 85 percent of customers who don’t have it.”

For more information, including how to gauge the correct size of a system, go to hawaiianelectric.com/clean-energy-hawaii/going-solar.