Community colleges in Hawaii expect to slash their energy use by nearly one-quarter and save a combined $58 million over the next 20 years due to conservation measures they are adopting.

University of Hawaii Community Colleges said Thursday it has signed a contract with Johnson Controls to reduce energy use at its various campuses.

Oahu campuses in the community college system will be installing solar water heaters, retrofitting lighting, and replacing ventilation and air conditioning systems. The steps are expected to cut electricity, water, sewage and gas use.

They’ll also get a full-time energy manager and electrical car charging stations.

The measures are forecast to cut power use by 6 million kilowatt hours each year, or by 23 percent.