The Senate tax-writing committee voted 23-3 today to give developers of wind, geothermal, biomass, landfill gas, incremental hydroelectric and ocean energy projects through December 2016 to start construction of new projects to qualify for federal tax credits.

The vote was on a tax extenders bill that would extend more than 50 expired or expiring tax benefits by another two years.

The bill will go next to the full Senate, although the timing and path forward are unclear.

The committee disappointed solar companies for now by failing to extend a 30% investment tax credit for new solar projects. Solar companies hoped the committee would turn a December 2016 deadline to complete solar projects to qualify for the 30% investment credit into a deadline merely to start construction. However, the committee chairman, Orrin Hatch (R-Utah), took the position that only tax benefits that already expired or will expire in the current year could be considered. (This was the same position that Ron Wyden (D-Oregon) took when he chaired the committee in 2014.) Solar companies will have another two chances to get into the Senate bill, first as part of a manager's amendment that is usually offered by the committee chairman when a bill reaches the full Senate or as an amendment offered by solar advocates on the Senate floor.

New wind, geothermal, biomass, landfill gas, incremental hydroelectric and ocean energy projects qualify currently for federal tax credits only if they were under construction by the end of last year. The IRS has issued four notices explaining what a developer had to do for his or her project to be considered under construction in time. The Senate committee bill would give developers another two years through December 2016 to start construction. It would preserve the option to claim production tax credits or a 30% investment tax credit on such projects.

Senators Pat Toomey (R-Pennsylvania) and Dan Coats (R-Indiana) urged the committee to strip or phase out the PTC extension, but withdrew their amendment.

The committee also voted to allow a 50% "depreciation bonus" on new equipment put in service by December 2016 or, in the case of transportation equipment and long-lived equipment like transmission lines, by December 2017.

A full description of the Senate committee bill can be found here.

Some changes that the committee chairman made to the bill immediately before the committee meeting can be found here.

Bills must pass both the House and Senate to become law.

The US constitution requires that tax legislation originate in the House.

The House tax committee is expected to take up tax extenders in September. House leaders have been calling to date for making a few of the expired or expiring tax benefits permanent and letting the rest expire.

This will come down ultimately to a negotiation between the two houses.

By Keith Martin, in Washington