Rising oil prices lift all alt-energy boats.

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For proof, look no further than the fat $130 million investment scooped up by eSolar, a company whose basic solar power strategy — using sunlight-reflecting mirrors to generate steam — was all but abandoned in the 1980s, and has recently recently caught investors' attention again.

The money, from Google's philanthropic arm, Google.org, and venture capital firms Idealab and Oak Investment Partners, will go towards the construction of eSolar's first functioning solar power plant.

"ESolar's long term is to become a viable replacement for all fossil fuel," said Robert Rogan, a Cal Tech Ph.D. and eSolar's executive vice president for corporate development. "The reason Google invested in us is that they saw the potential of this technology to beat the cost of using coal."

The company's core technology is an implementation of concentrating solar power, which uses mirrors to turn liquid into steam that drives standard electricity-generating turbines. CSP, also sometimes called solar thermal, is considered a promising replacement for fossil fuel power plants, particularly the coal plants that generate more than half of U.S. electricity. It's been around for decades, last seeing popularity in the early 1980s, when oil hit an inflation-adjusted price of $82 per barrel. Higher oil prices make fossil fuel plants more costly, making it easier for alternative technologies to compete. (Oil is currently trading for more than $115 a barrel, its highest level ever.)

Google's green-energy plan goes by the formula-like name RE<C, which sets out the goal of the company's operation — to find renewable energy sources that reliably generate electricity more cheaply than burning coal. In modern times, that's been impossible, with fossil fuel plants able to generate power for a few cents a kilowatt-hour while solar energy from photovoltaics has cost upwards of $0.25 per kwh.

But times are changing as coal and natural gas plants have gotten more expensive to build. That's happening for a variety of reasons: Banks are including the risks of climate change legislation in their pricing for power plant loans, the raw construction materials used in power plants have become more expensive, and natural gas and coal prices have gone up alongside the skyrocketing price of oil. Within this changing marketplace, wind power has been growing phenomenally fast, but is too intermittent to power the whole grid. As a result, many clean-energy advocates are turning to solar thermal power plants as the solution du jour.

"There's hope and optimism but a little bit of skepticism as well," said Ryan Wiser, a renewable energy analyst at Lawrence Berkeley Labs. "No one knows whether the technologies are really cost competitive with other energy alternatives."

That hasn't stopped Abu Dhabi's clean-tech fund, Masdar, from funding a $1.2 billion solar thermal company called Torresol. Another competitor in the market, Ausra, has received more than $40 million from blue-chip venture capitalists. Yet another player, Abengoa, recently signed a $4 billion deal with Arizona Public Utilities, and Brightsource recently landed a 900-megawatt deal with the California utility PG&E. Stirling Energy Systems, a company that has adapted the Stirling Engine, a 200-year-old invention, for concentrated solar power, even pulled in a $100 million investment.