Not too far from the home of Miller-McCune.com, the utility company Pacific Gas & Electric said Thursday it plans to build what's being billed as the largest solar-energy facilities in the world - two photovoltaic plants that at their peak reportedly will able to pump out 800 megawatts.

The two operations proposed for the Carrizo Plains area of California's Central Coast would perch on 12.5 square miles and will join a 177 megawatt solar thermal plant planned for 640 acres nearby.

"These landmark agreements signal the arrival of utility-scale PV solar power that may be cost-competitive with solar thermal and wind energy," PG&E COO Jack Keenan was quoted in a release. And of course, the economy of scale should start kicking in as these projects go forward and presumptive followers start heading down the solar trail.

PG&E also has its back against the wall - the state has required that a fifth of its energy come from renewable sources by 2010, when these two facilities are supposed to come on line.

While Miller-McCune.com has been pretty bullish on solar, a scan of our writings show there's no unanimity on what kind of solar - PV vs. thermal, giant plants vs. rooftops - might be best (or if that's even a silly conceit for a planet with lots of different environments and needs). For the record, while both of the projects PG&E endorsed this week are photovoltaic, the larger uses thin-film and the smaller crystalline solar cells that will track the sun's movement.

But despite our bullishness, the site's proximity to our mothership makes us privy to a cautionary lesson: The Carrizo Plains already hosted what was to have been the world's largest solar energy facility.

The regional oil company Atlantic Richfield (later swallowed by BP) built a 5.2 megawatt solar array in 1983, a relic of ARCO's pioneering work in solar following the 1973 oil shock. The array was purchased by a smaller company a few years later, and when solar's revenues never met its costs, the plant was shuttered and bits and pieces have been sold off over the years since.

We offer this not to dismiss our bullishness, but to temper it. When trudging the soda flats of the solar landscape, make sure those sunglasses aren't rose tinted.