Hill Library recommends:
Use the Database of State Incentives for Renewables & Efficiency (DSIRE) to identify state, local, utility, and federal incentives and policies that promote renewable energy and energy efficiency. DSIRE is actually two databases - one on renewable energy and one on energy efficiency - that you can search individually or simultaneously. There's also a section with information on federal incentives.
You can find incentives using an interactive map, or use DSIRE's summary maps or summary tables. Summary maps include grant programs for renewables, loan programs for renewables, rebate programs for renewables, PACE financing, and more. Summary tables include financial incentives for renewable energy, financial incentives for energy efficiency, and rules, regulations and policies for both.
There is also a library of reports, technical papers, and articles authored by DSIRE staff.