PG&E contracts 107MW of fully renewable solar thermal-biomass hybrid power

California utility PG&E Corp has contracted with a renewable energy unit of Portuguese conglomerate Martifer for 106.8 megawatts (MW) of solar thermal-biomass hybrid power. Solar power is an intermittent source of energy: it cannot deliver reliable baseloads and peakloads, and doesn't work at night. Energy storage systems are currently inefficient or not commercially viable. Therefor, in practise, solar-thermal energy is dependent on other energy sources, most often fossil fuels like coal or natural gas. But when coupled to biomass, which does deliver baseloads, a fully renewable energy system emerges capable of supplying electricity around the clock.

Solar-biomass hybrid concepts can be described in other terms: the solar thermal system converts solar energy directly into electricity, whereas biomass uses solar energy to build cheap but highly efficient structures (strong plant cells) capable of storing this energy for later use.

The two planned solar thermal-biomass hybrid power plants - the first of their kind - will be managed by Martifer subsidiary San Joaquin Solar LLC and will provide enough power for nearly 75,000 homes in northern and central California. They combine solar thermal technology with steam turbines powered by gas made from locally available biomass (agricultural waste and livestock manure.)

The plants will be located near Coalinga, California, in the center of the state, and will help PG&E reach the state-mandated goal of increasing the amount of electricity it produces from renewable sources. The projects are expected to begin operations in 2011. PG&E has already invested heavily in biogas research (more here) and recently it started feeding upgraded biogas (biomethane) into its natural gas pipelines (previous post).

This biogas expertise will now boost the solar thermal power technology. Solar thermal plants use the sun's heat to run steam turbines that produce electricity and are mostly located in sun-drenched states such as California. Advocates say the technology could one day become a viable replacement for fossil-fueled power plants due to their large scale. But critics argue the power produced is too inconsistent because it requires the sun to be shining at all times, which it obviously doesn't. After sunset, when electricity demand can be high, the plants stop working altogether. Therefor solar thermal plants are forced to rely on other, polluting sources to ensure continuous power supplies. The hybrid solar-biomass system effectively solves this problem.

When the sun is shining during peak hours, it will just be the solar facility. As the sun sets, biomass will be available to support the solar generation, and then at night the biomass will run purely on its own. - Andrew Byrnes, project developer

Ricardo Abecassis, president of Martifer Renewables Solar, said that power generated by the solar thermal-biomass hybrid plants would be cost-competitive with energy from conventional power plants, such as those fueled by natural gas or coal:
energy :: sustainability :: biomass :: bioenergy :: biofuels :: biogas :: solar thermal :: intermittency :: baseload ::

Earlier in Germany, a consortium of renewable energy companies and universities demonstrated that in principle an entire country can be powered on the same principles, independently of coal, natural gas or nuclear.

This so-called 'Kombikraftwerk' project consisted of coupling intermittent renewables like wind and solar power to biomass, which delivered the reliable baseload and kicks in at night. This way, a fully functional renewable energy system was designed capable of supplying electricity around the clock regardless of weather conditions and electricity demand. Peak and baseloads were supplied as reliably as in conventional fossil fuel based systems (previous post).


The PG&E contracts filed with the California Public Utilities Commission are part of the company's broader renewable energy portfolio. Since 2002, PG&E has entered into contracts for over 2,500 MW of renewable power. California law requires each investor-owned utility to increase the share of eligible renewable generating resources in its electric power portfolio to 20 percent by 2010. PG&E has made contractual commitments to have over 20 percent of its future deliveries from renewables. For 2008, PG&E expects to have 14 percent of its energy delivered from renewable sources.

References:
Biopact: Germany is doing it: reliable distributed power based on 100% renewables - December 29, 2007

Biopact: California's Pacific Gas & Electric starts feeding biogas to its natural gas pipelines - March 05, 2008

Biopact: Pacific Gas & Electric Company to research large-scale biomethane resources for its customers - January 25, 2008