State officials are directing more federal funds toward a rebate program for homeowners who purchase solar water heaters.

Hawaii’s energy office announced Friday additional money from U.S. Recovery Act would be allocated to rebates due to a large demand for the energy-efficient systems.

Hawaii Energy, which administers the program, first announced the rebate in March in order to lift sagging sales of the units.

The company says more than 600 households have purchased the systems and 220 customers are on a waiting list.

The state has authorized more applications for a $1,000 rebate on a first-come-first-serve basis. Officials did not say how much money was available for the program.

The systems are also eligible for a 35 percent and 30 percent tax credit on the state and federal level.