Amid all the hope and hype about the nascent solar boom under way in California, there’s long been an elephant in the room — transmission. Billions and billions of dollars must be spent to build and upgrade transmission lines to connect dozens of proposed solar power plants to the grid.

Now that elephant has rolled over and squashed one project’s use of innovative solar technology. Last year, California utility PG&E signed a deal with NRG Energy, a New Jersey-based electricity provider, to buy power from a 92-megawatt solar farm called the Alpine SunTower to be built near the desert town of Lancaster, northeast of Los Angeles.

esolar power plantPhoto: eSolarThe power plant would deploy solar thermal technology developed by eSolar, a Pasadena startup founded by serial technology entrepreneur Bill Gross. NRG and eSolar earlier had inked a partnership to build 500 megawatts’ worth of solar farms. In January, eSolar reached an agreement with a Chinese company to supply technology for solar farms that would generate a massive 2,000 megawatts of electricity.

PG&E, however, submitted a letter recently to the California Public Utilities Commission asking approval for a re-negotiated deal with NRG that has resulted in a downsizing of the Alpine SunTower project to 66 megawatts. And instead of deploying eSolar’s fields of mirrors that focus the sun on a water-filled boiler that sits atop a tower to create steam to drive a turbine, the power plant will generate electricity from photovoltaic panels like those found on residential rooftops.

The utility gave no reason for the technology switch. “NRG has not finalized the exact type of panels or the manufacturer of the panels,” a PG&E executive wrote in the letter. “Solar PV panels have been used in installations throughout the world, in both small and utility scale applications.”

However, when I contacted eSolar about the change, I received a joint statement from the company and NRG:

“NRG is returning the project to its originally proposed size to match the transmission capacity available to the project at this time,” it said. “Maintaining the project as previously announced would require waiting for additional interconnection studies and potential transmission upgrades that would delay the project delivery date.”

While solar panels are not as efficient as eSolar’s solar thermal technology in generating electricity, they are modular — meaning you can just keeping adding them to produce a desired amount of power or to match the transmission capacity in an area. ESolar’s power plants, on the other hand, are designed to be built in 46-megawatt units so there’s far less flexibility in scaling them up or down.

It’s too early to say whether this portends other switches from solar thermal to photovoltaic technology, especially as solar cell prices fall and California utilities scramble to meet a mandate requiring they obtain 20 percent of their electricity from renewable sources by the end of this year and 33 percent by 2020.

But the elephant is getting restless.