Philadelphia will provide rebates to residential and commercial property owners who install solar systems under a new law signed Wednesday by Mayor James Kenney. But the money will be available next year only on a first-come, first-served basis.

The program, approved June 20 by City Council, will provide a pool of up to $500,000 from the general fund for rebates to property owners who install systems after July 1, 2019.

Applications will be taken starting Jan. 1.

The city will provide residential buyers of solar systems 20 cents for every watt of solar installed, so a typical 5-kilowatt rooftop photovoltaic system would receive a $1,000 residential rebate. Rebates for commercial buyers are set at 10 cents per watt, or $500 for a 5 kW system.

A 5 kW system with an installed price of $3 a watt would cost about $15,000.

Solar installers are planning to step up marketing this year with the aim of consuming the entire pool of money available for rebates, providing a signal to City Council to increase grant funds, said Christine Knapp, the city’s director of sustainability.

The Office of Sustainability and the Philadelphia Energy Authority will work together to develop an application process for the program.

The city incentives would supplement 30% federal investment tax credits available for solar installations through the end of 2019, when the tax credit is scheduled to decline to 26% next year and then step down to zero by 2022.

Kenney signed the bill as part of the city’s Solar Week activities to promote renewable energy; the city has pledged to transition to 100 percent clean energy as part of a goal to reduce citywide carbon emissions 80% by 2050.

The solar rebate bill was introduced by Councilwoman Blondell Reynolds Brown.