Grants.gov is a great source for information about funding opportunities.  All agencies are supposed to post solicitations through the site, though it's always a good idea to check agency sites directly as well.  

 

Energy solicitations across all agencies are listed here.  Select the topic "energy" and which agencies you are interested in to see what funding is currently available.

 

 

Lots of opportunities are available to small businesses (fewer than 500 employees) through Small Business Innovation Research (SBIR) programs.  The following links will take you to various agencies that support clean energy research.  Phase I is typically $90-$150k over 6-9 months, followed by a Phase II of $500k-$1 million over two years.   

 

National Science Foundation (NSF) SBIR/STTR:  Search field for NSF funding opportunities is here.

 

Department of Energy (DOE) SBIR/STTR:  Current and future solicitations can be found here.

 

Department of Defense (DOD) SBIR/STTR:  The schedule of upcoming solicitation rounds is here. This link also includes Broad Agency Announcements or BAAs, which typically offer higher levels of funding for 2-5 years.