Hybridizing Solar with Fossil Fuel
Back to Fossil?
Why solar-fossil hybridization? The world has been running away from dependence on fossil fuel. The reasons were strategic and environmental. Supply of fossil fuel from the Middle East was unreliable, and use of fossil fuel adds to global warming with all its ill effects. Solar energy is green, and becoming financially viable, but it has a serious limitation-despatchability. Solar energy is intermittent, and in a commercial solar power system cannot be depended upon to provide a continuous supply to customers. Integrating electric power generation from fossil fuel with power from concentrated solar power (CSP) is a viable alternative giving multiple advantages.
Concentrated Solar Power
Concentration of solar power before conversion or storage has advantages of reduced infrastructure and economy. Concentrated solar power can then be either converted to electric power or used as such. Conversion to PV is not really attractive because concentrated power heats up the cells and their efficiency goes down. On the other hand, concentrated solar can be used directly for heating, thermal PV or integration to a thermal power plant. This last process is called solar-fossil hybridization.
Advantages of Hybridization
In solar-fossil hybridization, solar energy (when available) partly substitutes the fossil fuel consumption. Advantage is taken of the presence of an existing thermal generation system, which normally uses a combined cycle gas generation system. This system has three major advantages:
· Reduced overall cost– This reduces the total cost of production because an existing infrastructure of generation, transmission, and control is already available and functional.
· Reduced Carbon foot-print– Hybridization of concentrated solar power reduces greenhouse gases which are an essential result of generation from fossil fuels. The more sunlight is available and used, the lower the emission of greenhouse gases.
· Intermittence of Solar power is eliminated– A combined cycle gas generation is normally used for generation. The solar power can be fed as the heat source without too many changes. When the sun is down, the normal fossil fuel can take over again, producing a continuous power output.
Integration of solar power to an existing fossil fuel generating system can be done at two levels. These are thermal, or chemical
· Thermal– This is the method escribed above. Solar power provides the heat to replace or augment that from fossil fuel. This is the method normally used. This entails modifications to the plant to be able to quickly switch over to a different heat source.
· Chemical– the integration is via a chemical process driven by sunlight. An example is gasification of coal using solar power. The gas can then be directly fed to the existing gas generation plant to generate power. The plant needs no modification. Switching is as simple as turning a valve to change the source of gas. The US Pacific Northwest National Laboratory, under the US Sunshot Initiative, is aiming to increase the solar thermochemical augment as much as 28% by the year 2020. The target is to achieve a levelized cost of electricity (LCOE) of under 6 cents per KWH.