GM buys another stake in the development cellulosic ethanol ; Sony shows-off a new, hand-sized fuel cell; and eight things which might cloud the future of solar energy. Welcome to the weekend — and your Saturday edition of the Daily Five.

GM and Mascoma Partner in the Race to Commercialize Cellulosic Ethanol: So you’re a major automobile manufacturer, and you’ve dropped a ton of cash to make sure your fleet will run on E85 ethanol-additive gasoline by 2012. It makes sense, then, that you’d invest in ethanol production. That’s what General Motors has done, inking a deal to develop cellulosic ethanol technology with Mascoma Corporation. Mascoma uses a process called Consolidated Bioprocessing to reduce biomass (such as switchgrass and wood mulch) to ethanol using bacterial and enzymes. (Clean Edge)

What’s better for heating a mug of water: The stove or the microwave?: Here at EcoTech Daily, we’ve always considered the microwave oven to be the champion of energy-efficient food preparation. But now the folks at Cognitive Daily have actually constructed a scientific shootout between the stovetop and microwave. Which will boil water for afternoon tea most effectively? We’d love to see them add an electric kettle to the experiment next time. (Cognitive Daily)

US Car Sales in April Outpace Trucks for Second Month in a Row: It looks like U.S. car buyers may finally be getting the message. Sales of passenger cars outpaced those of light trucks for the second straight month in April. Not coincidentally, General Motors has just announced they’re scaling back truck and SUV production, citing rising fuel prices and a softening economy. (Green Car Congress)

Sony Unveils Ultrasmall Hybrid Fuel Cell: Sony took advantage of the Small Fuel Cells 2008 conference in Atlanta — which ended yesterday — to show off a new, hand-sized fuel cell. The device is expected to find its way into mobile consumer electronics, and contains a backup lithium polymer battery. Sony’s pint-sized fuel cell is said to provide 14 hours of continuous movie playback on a cellphone screen using only 10 milliliters of methanol. (Tech-On!)

8 Offbeat Hurdles for Solar Power Plants: These are exciting times for solar power advocates. But Earth2Tech’s Katie Fehrenbacher points out a few things which could still cloud solar’s future, ranging from the practical (steam turbine hardware is in short supply) to the bizarre (ecoterrorist “monkeywrenchers”). While each of these are interesting food for thought, none seems likely to derail the Solar Century. (Earth2Tech)

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