Greener Solar Plants Turn to Biofuels By Night


How do you make those solar thermal power plants, which are being built in California’s desert, even greener? Add biofuels to the mix. At least that’s what San Joaquin Solar (a subsidiary of power gear company Martifer Renewables) is doing. The company is building solar plants, which when the sun goes down, switch over to power its steam turbines via biofuels. How cool is that? And the company got a big customer this morning: Northern utility PG&E says it has entered into two contracts that will deliver 106.8 MW of solar thermal-biofuel hybrid power.

San Joaquin Solar will build these solar-biofuel projects, expected to begin operation in 2011, near Coalinga, Calif., which is smack dab in California’s Central Valley, between Los Angeles and the Bay Area. The plants are expected to deliver a total of 700 gigawatt-hours per year of renewable electricity for PG&E’s California customers. PG&E says that each hybrid project will require 250,000 tons of biofuel per year, which will come from local wastes, both from agriculture and livestock.

How do these things work? During the peak times of available sunlight, San Joaquin Solar’s projects will function the same way other solar thermal plant are supposed to — using the suns rays to heat liquid to run turbines that generate electricity. But at night, or when there’s little sun, the steam turbines will kick over to run off of biomass, solving one of the key problems of solar generation.

While it sounds like a good idea, we’re not sure how much output the biofuels-run turbines will add to the plants (we have a call to Martifer and are waiting to hear back). The added biofuels generation also sounds like a system that can be easily copied. If it works, those 11 solar thermal companies building plants in the desert should follow suit.



“How do you make those solar thermal power plants, which are being built in California’s desert, even greener? Add biofuels to the mix.”

Adding biofuels does not make anything automatically greener. In fact, it can easily do the opposite. The number of unsustainable biofuel projects in operation far outnumbers the sustainable ones. In fact, I haven’t heard of a sustainable one yet.

“……those 11 solar thermal companies building plants in the desert should follow suit.”

You mean those 11 solar thermal plants hundreds of miles away from the nearest consistent source of biomass? It is estimated that the San Joaquin hybrid project will require the transport of 250,000 tons of biomass annually, presumably with fossil fuels. Plus, our “agriculture” system is really just a soil mining industry and is utterly unsustainable. With 10 fossil fuel calories being consumed for every single biomass calorie produced from the average industrial farming operation, it is a crisis that needs tending to immediately by returning biomass to the soil. When done properly, this reduces water and energy use on the farm by orders of magnitude, increases crop resilience to pests, disease and harsh weather and cleans up our coastal zones and groundwater supplies.
Soil mining should be considered criminal behavior, with the perpetrators being prosecuted for crimes against humanity.

For solar hybrid plants located near agricultural operations, it may make more sense to invest in more solar thermal storage using molten salts (which can add a 7 hours or more to the power plant’s daily solar output) and replace biomass burning with biochar production through pyrolysis, producing combustible gases to drive the turbines and precious biochar to return to the croplands where the original biomass was sourced. Of course, this only begins to make sense with more efficient transport, meaning at the very least plug-in serial hybrid diesel trucks. If the fossil energy used per ton-mile is not reduced, it is a losing proposition to burn the biomass for energy production and is anything but “green.”

Please pay attention to energy return on investment, folks. Literally, our lives depend on it.

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