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Green companies to watch: Renewable energy

Can we electrify our way to a cleaner future? New companies commercializing old technologies are trying to make solar and wind more cost-effective.

Which are the companies to watch in clean tech? Most are definitely not household names but they are having an impact.

Below the photo is a list of some of the newsmakers in the renewable energy business, with a focus on start-ups. Along the way, you'll get a feel for the technology categories that define this corner of green tech.

A trial balloon or the face of solar power in the future? Cool Earth Solar

1. Ausra: Originally from Australia, Ausra is one of the movers and shakers in solar thermal, a technology that is already competitive with utility-scale fossil fuel power generation.

Mirrors reflect light onto a liquid that makes steam, which drives a traditional electricity turbine. Other companies have different designs including BrightSource Energy which recently signed a huge deal with Pacific Gas & Electric and eSolar, which is reported to have just raised $130 million. Honorable mention goes to Infinia, which uses a Stirling engine to make distributed solar electricity.

2. SolFocus: Another technology for utility-scale solar power is concentrating photovoltaics (CPV), where light is magnified onto high-efficiency solar cells. SolFocus, incubated at Xerox Palo Alto Research Center, is well funded and already has a few customers.

3. Southwest Wind Power. There are several companies taking different approaches to small wind turbines, designed for homes and buildings. Southwest Wind Power has turbines for remote off-grid locations but it now also has a ground-mounted one for homes. Another company to watch is Aerovironment which just had its small turbines installed at Logan Airport in Boston.

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4. First Solar. In the traditional solar photovoltaic market, First Solar the one to catch. The reason is simple: cost per watt. Its cadmium telluride-based panels take up more space than silicon cell panels, but its overall cost has set the mark in a highly competitive field. Hot in pursuit are other thin-film solar companies--Heliovolt, Global Solar Energy, and Nanosolar, which are making cells from yet another material, CIGS (copper indium gallium and diselenide).

5. Cool Earth Solar. Apart from the great name, this company is taking a potentially disruptive approach to solar electricity. Never mind expensive plants out in the desert. Why not just float reflective balloons in open fields?

Overall, you'll see that a lot of the action in renewable energy is not in the residential solar panel world, perhaps what most people would think.

Instead, most of the money is going to utility-scale power plants to make power at peak times of the day. And businesses, helped by favorable financing models, are the big buyers.

Expect it to stay that way in the coming years but not without some bumps. Lux Research predicts a shake-out among the larger companies because supply of polysilicon will overshoot demand in a few years, bringing prices--and a few solar vendors--down.

And will this influx of capital result in cheaper solar panels for average consumers? Yes, but government policies make a huge difference on the economic equation. What's also needed to make solar really widespread is more flexible financing to lower the hefty upfront cost.