Dispatchable Solar Power Plant

As penetration of renewable power increases, grid operators must manage greater variability in the supply and demand on the grid. One result is that utilities are planning to build many new natural gas peaking power plants that provide added flexibility needed for grid management. This paper discusses the development of a dispatchable solar power (DSP) plant that can be used in place of natural gas peakers. Specifically, a new molten-salt tower approach has been developed that is designed to allow much more flexible operation than typically considered in concentrating solar power plants. As a result, this plant can provide most of the capacity and ancillary benefits of a conventional natural gas peaker plant but without the carbon emissions. The DSP plant discussed here is based on considerable analyses using sophisticated solar system design tools and in-depth preliminary engineering design. The Arizona Public Service (APS) utility system is used as an example of the benefits resulting from the methods presented. The analysis looks at a 230 MW net power cycle with a range of solar plant ratings. The optimum DSP plant is sized to produce power for preferred periods when capacity is needed. For the APS example this ends up being 5 or 6 hours of generation during the summer months. As a result, the optimum DSP plant ends up having an annual capacity factor of only about 16 to 23%. These results estimate that the cost of the DSP plant is less than 5% higher than a similarly sized and operated natural gas plant when APS reference fuel and emissions costs are included. The DSP plant cost is based on a single, first-of-a-kind plant, and it is likely that subsequent plants would be less expensive. In addition, the DSP plant represents an emission and carbon-free peaking power plant, free of future pricing risk. It provides local Arizona jobs rather than importing fuel from other states. As Arizona has excellent solar resources and lower construction costs than neighboring California, an in-state DSP facility offers Arizona the potential to export carbon free capacity and peaking generation to California to help address the CAISO "Duck Curve."