Several tax credits that support the development of renewable energy sources expired at the end of 2013. One of the largest was a tax credit to encourage wind energy development, but also eliminated were credits for solar heating, combined heat and power installations, and advanced energy manufacturing. Not affected was an investment tax credit for solar installations, which runs through 2016. In a letter to Senate Finance Committee Chairman Max Baucus (D-Mont.), 24 senators cited 10 expiring credits and urged that the committee quickly extend them. The wind energy credit alone, they said, has driven some $25 billion in private investments. The Senate committee, however, is expected this year to consider a draft proposal by Baucus to overhaul the entire system of federal energy-related tax breaks. The proposal notes the weakness inherent in short-term tax stimulus. But action is likely to be slow because Baucus, who has been recommended to be the next ambassador to China, has said that he will retire from the Senate at the end of the year.