The field of mirrors at the Sierra SunTower solar power plant, in California's Antelope Valley, reflects Barack Obama's vision of a fundamental change in the US energy supply. Photo / eSolar

The field of mirrors at the Sierra SunTower solar power plant, in California's Antelope Valley, reflects Barack Obama's vision of a fundamental change in the US energy supply. Photo / eSolar

It looks like an epic art installation: 24,000 heliostats arranged in precise rows across the desert floor in the Antelope Valley outside Lancaster, north of Los Angeles.

The heliostats - mirrors that follow the sun's arc across the Mojave Desert sky - sit on the Sierra SunTower site, a demonstration plant built by eSolar, one of a legion of Southern California renewable energy start-ups that are remaking the United States energy industry.

The Pasadena-based company pledges to make solar electricity "for less than the price of coal, without subsidies ... and truly change the world".

It's a promise that fits perfectly with President Barack Obama's vision of a fundamental US energy makeover, moving from fossil fuels such as coal and oil to renewable sources including solar and wind.

Like other solar arrays, the Sierra site, which covers 4ha, uses heliostats to focus sunlight on to a thermal receiver atop a tower (there are two towers at this location).

The sun boils water inside the receiver to create superheated steam, which drives a turbine and generates electricity. The steam cools, reverts to water, and the process repeats itself. The company says it can generate 46 megawatts of electricity from just 65ha, enough to light up 37,000 homes during peak sunlight hours.

But what makes eSolar unique, explains chief financial officer Merrick Kerr, is solar tracking software that calibrates heliostats to the sun's arc - at any time of day, on any day in the year, at any location - to one milliradian, a tiny measurement.

This makes eSolar a world player - a major project with India's Acme Group was announced in March - and illustrates the marriage of clean tech and IT knowledge that is reshaping California's economy.

Eighty kilometres east, outside Barstow, is another desert array, where 1800 heliostats focus sunlight on a receiver to create steam and generate electricity. The array was built by SolarReserve, a spin-off from LA's Rocketdyne, which powered the space shuttle, the Apollo lunar module and the International Space Station.

While many other solar plants work only when the sun shines, SolarReserve touts something new: molten salt that retains heat to produce power 24/7.

"We put the sun's heat into a liquid metal - molten salt or sodium potassium nitrates - and heat it to over 1000F or 550C," explains company president Terry Murphy. "You can put in all this heat then store it in a tank. It's like a solar dam. We capture the sun's energy and then we dam it up, put it in a bottle ... The beautiful thing about molten salts is you've trapped all this energy and a utility can turn the turbines on and off as needed."