Israeli solar-thermal manufacturer Solel said Monday it snagged a whopping $105 million from London-based investment firm Ecofin.

The funding will no doubt help Solel move forward with such projects as a 553-megawatt plant in the California part of the Mojave Desert.

In July, the company signed an agreement with Pacific Gas & Electric to supply the utility company with electricity from a large-scale plant. Solel is also in the process of building 150 megawatts worth of solar-thermal plants in Spain.

But the funding will only get Solel so far. That's because the company's technology, which uses the sun's heat instead of light to make electricity, only becomes economically feasible when projects are large -- and such large projects can pass the $1 billion mark.

High upfront costs mean Solel will have to raise a lot more money, something the company said it is working on.

The news is only one of several solar-thermal announcements to be announced in recent months.

Earlier this month, German solar manufacturer Schott said it would raise its stake in solar-thermal technology by building a U.S. manufacturing facility to produce concentrating-solar receivers (see Schott to Build Solar Plant Under New Mexican Sun).

In November, startup Ausra said it planned to build a project with the capacity to produce 177 megawatts of solar-thermal electricity in San Luis Obispo, Calif. (see Ausra to Build 177-Megawatt Solar-Thermal Plant). Ausra signed an agreement to sell the energy to Pacific Gas and Electric.

And in September, Oakland, Calif.-based startup BrightSource filed an application to build a 400-megawatt power station in the Mojave Desert.

Despite solar-thermal's high upfront costs, companies say the approach is alluring because it is potentially far cheaper for utilities than other forms of solar electricity.

For example, Ausra claims its technology can deliver power at 10.4 cents per kilowatt-hour today and can potentially cut costs to 7.9 cents per kilowatt-hour in three years. That compares with an estimated 9.7 cents per kilowatt-hour for coal-fired power plants today.

Light vs. Heat

But despite the promise of solar-thermal, the sector still has quite a few unknowns ahead.

For one, none of the recently announced plants have actually been built, said Travis Bradford, president of the Prometheus Institute, which is a Greentech Media partner.

"They aren't past the point of no return," Bradford said.

According to the California Energy Commission, 12 percent of the renewable-energy contracts signed by publicly owned utilities since 2002 have been canceled and another 20 percent have been delayed.

Also, unlike traditional and thin-film solar, Bradford said there are fewer opportunities for technological advances in solar-thermal.

"You make [solar-thermal projects] cheaper by making them bigger," said Bradford, who is working on a research report on solar-thermal technologies slated for publication in the next few months.

He pointed out that 95 percent of concentrated-solar projects are still made up of " parabolic trough" technology, decades-old technology that basically uses curved mirrors to generate steam that in turn powers a turbine to produce electricity.

Still, Bradford said he expects both photovoltaics and solar-thermal technologies to find market acceptance, at least for the next 10 years.

But he does question how solar-thermal technology will fare should companies like thin-film developer Nanosolar realize their full potential.

In December, the San Jose, Calif.-based company said it could profitably sell solar panels for as little as 99 cents per watt (see Nanosolar Begins Production).