Geothermal part 1: time to tap California's potential?

By Jonathan Marshall



One of California's oldest sources of renewable energy—geothermal—may be ripe for expansion to meet the state's ambitious greenhouse gas reduction goals, according to a new status report issued by the Geothermal Energy Association, the industry's leading trade association.

You'd expect them to say that, of course, but a study by the U.S. Geological Service confirmed the existence of about 5,000 megawatts (MW) of potential new geothermal development in California, and extrapolated that another 11,000 MW of geothermal resources are waiting to be found in the state.

Some 32 geothermal projects are in some stage of development within California, mostly in Imperial, Siskiyou or Sonoma counties. Sonoma County is home to The Geysers, the world's largest geothermal field. Utility-scale power production there was pioneered by PG&E in 1960. As of 2012, just over a quarter of PG&E's renewable electricity came from geothermal resources.  

One of the most promising areas for new geothermal development, by all accounts, is the Salton Sea area in Imperial County. “This area's unique geology created the perfect circumstances for hot geothermal fluids to seep to the surface to generate power," according to the new GEA study. The basin's likely geothermal capacity ranges from 1,700 MW to 2,900 MW, depending on the estimate.

That's significant for several reasons. Counting all elements of plant operation, geothermal energy has low life-cycle carbon emissions; the very best geothermal plants create as little in the way of GHG emissions as hydroelectric plants and less than solar photovoltaics, according to a study by Argonne National Laboratory.

Second, geothermal plants run reliably around the clock, making them good substitutes for 'baseload' coal plants. In contrast, intermittent wind and solar plants require more complicated strategies for predicting and managing their variable output.

Last but not least, geothermal plants use far less land than many other types of renewable generation—and are thus less likely to run afoul of concerns over habitat and species loss. On the other hand, some geothermal plants may release toxic brine, raising legitimate environmental concerns

So why don't we see more geothermal in California? One reason is the high cost of exploration and drilling — typically accounting for a third of project costs — which raises the financial risk of failure. Many developers don't have sufficiently deep pockets to drill multiple holes, several kilometers into the Earth's crust, until they find a suitable steam basin or reservoir of hot rocks to tap.

But the biggest reason highlighted in the GEA report is the distance of many promising geothermal sites from available electric transmission lines. Building new transmission is expensive, time-consuming, and fraught with permitting issues.

I could imagine a new transmission line in the Salton Sea area serving both geothermal and new solar projects, spreading the cost among many developers and enabling significant new renewable energy production.

As it happens, the Imperial Irrigation District came up with the same thought before I did. A study it released in December estimated that renewable generation in the area could raise $2,150 million in revenue from 2016 to 2045, nearly all from geothermal, but some from solar as well. The caveat: a 500-kilovolt transmission line to serve this area would cost about $500 million.