“You could call it the cleantech cliff,” writes the San Jose Mercury News:

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Global clean-technology venture investment plunged to $6.46 billion in 2012, down 33 percent from the $9.61 billion invested a year ago, according to San Francisco-based research and consulting firm Cleantech Group.

Why such a big drop-off?

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The low price of natural gas has made it harder for renewable energy to compete on cost. Venture capitalists are shying away from capital-intensive deals after seeing companies like Santa Clara-based Misasolé sold at fire sale prices. And global economic uncertainty took a toll: Several privately backed cleantech companies, including Oakland’s BrightSource Energy, were forced to shelve their IPO plans and raise additional funds from existing investors.

Political uncertainty contributed too, according to Sheeraz Haji, CEO of Cleantech Group. “That said, the entire venture capital industry contracted in 2012, so cleantech is not alone in experiencing this pullback,” he added.

The Mercury News reports that the “one bright spot belonged to SolarCity, a San Mateo-based solar financier and installer that had a successful IPO Dec. 13. SolarCity slashed its share price but ultimately raised $92 million.”

The cleantech sector is already looking brighter in 2013. Last week, a subsidiary of Berkshire Hathaway spent as much as $2.5 billion on a huge solar project, sending solar stocks soaring.

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But why leave cleantech investing to the big boys? If you live in California or New York, you can get into the game yourself via just-launched Solar Mosaic, a crowdfunding service for rooftop solar projects. Don’t let Warren Buffett have all the fun.