Here’s the latest action we’re following on the GreenBeat today:

The Department of Defense must buy American-made solar panels — That’s according to a provision in an appropriations act signed into law this week, Greentech Media reports. It requires all photovoltaic devices purchased by the DoD to comply with the Buy American Act; that is, they must be purchased from U.S. manufacturers — but the provisions could potentially threaten the U.S.’s net exporter status in solar.

Mercedes-Benz runs hydrogen and electric car plays — The company plans to lease 200 of its F-Cell hydrogen cars (pictured) around the globe (customers began receiving them in December), which offer fast refueling times and longer driving ranges. It will also market its SLS AMG E-Cell in 2013, the all-electric version of its hot sports car that the company says will equal the original in distance, speed and performance.

Dupont bids $5.8 billion for Danisco — The chemicals giant is betting big on biofuels and food additives, Reuters writes. The two companies have a cellulosic ethanol joint venture.

Duke Energy to be largest utility in the US? — Duke offered $13.7 billion to buy out its rival, Progress Energy. Combined, the two would create the largest utility in the country. Duke has been experimenting with cleantech, with an energy efficiency pilot in Charlotte, N.C., wind farms and smart meters.

Green manufacturing stocks took a hit in 2010 — Some of the year’s biggest losers in renewable energy were manufacturers, including Q-Cells, A123, Broadwind Energy and Energy Conversion Devices, said an Earth2Tech article citing Bloomberg New Energy Finance. Energy efficiency companies did better, with the biggest movers including LED companies Universal Display, Zhejiang Yankon Group and motor company Baldor Electric.