Implementing truly dispatchable base-load electricity generation using renewable sources (other than Hydro) is perhaps the most daunting challenge blocking our transition to a sustainable energy environment. Utility-scale storage can be part of the solution if one or more storage technologies become economically viable. In past blog postings I have discussed the use of post-consumer electric vehicle batteries, “Funicular Power” and “Unpumped Storage”. None of these technologies are going to scale up in the next 3-5 years but all have long-term potential worthy of further investigation.
However, there is an opportunity to provide base-load generation from solar power in the Southern U.S. and many other parts of the world in a relatively cost-effective manner.
Photo-Voltaic (PV) solar converts sunlight into electricity through an electro-chemical reaction while Concentrated Solar Power (CSP) generates electricity using steam turbines.
Photo-Voltaic (PV) solar costs have dropped dramatically over the past ten years and are now becoming reasonably competitive with traditional base-load plants on a levelized cost basis. For example, the Energy Information Administration estimates the cost of solar PV at $153/MW-Hour compared to $66/MW-Hour for combined cycle Natural Gas or $111.4/MW-Hour for nuclear. On the other hand, CSP costs have not dropped as rapidly and are still estimated to be about $240/MW-Hour.
As a result PV installations are happening at a rapid pace in many parts of the world.
However, there is one very problematic characterisitic of PV that can be avoided with CSP. PV, with its direct dependence upon sunlight, fades in the late afternoon and is not available in the evening when electricity demands peak. CSP, on the other hand, can be equipped with molten salt Thermal Energy Storage (TES) which can be used to extend electricity production well past sunset.
The Gemasolar plant in Spain generates electricity 7x24x365, as shown by the production graphs below.
The big disadvantages of CSP are cost, complexity of the facilities and the length of time required to construct them. CSP requires the installation of thousands of large mirrors as well as construction of a steam generation plant and salt tanks. All of that takes time; typically 2-4 years or more. For example the Solana plant in Gila, Arizona broke ground in December, 2010 and will be completed in August, 2013.
CSP facilities like Solana and Gemasolar divide the solar energy received into two streams. Part of the energy is used to heat molten salt for energy storage and part is used to produce steam for the turbines that generate electricity during the day.
But what if 100% of the energy was used to heat molten salt? That way a much smaller and less expensive facility could be used to generate electricity using the energy stored in the molten salt into the evening and all night if necessary.
Less expensive PV could be used to supply the electricity needs during the day.
Using this approach would produce the most cost-effective, 100% solar solution possible. All of the grid connectivity and transmission infrastructure could be shared by the two generating sources.
In many parts of the world, including the Southern U.S. this one-two combination of PV during the day and CSP at night would make a lot of sense.