The Promise of Geographically Distributed Solar-Thermal Power

Contributor(s): 
June 30, 2014

Renewable energy-based grids of the future face technical challenges on a large scale, the most obvious of which is the intermittent nature of most renewable sources of power: Solar and wind power both vary throughout daily and yearly cycles, while both are subject to highly unpredictable weather conditions. While past studies have demonstrated that this variability can be balanced with fast-ramp power stations like hydroelectric or natural-gas-turbine generators, the short-term cost increase and efficiency reduction felt by these “back-up” producers will likely be difficult to mitigate. An immediate solution to the problem of intermittent power sources is grid-scale energy storage. However, traditional means of storing electric energy (a chemical battery, for example) remain significantly too expensive to scale up to a size impactful for a large power grid. A new study published in Nature Climate Change, suggests that concentrated solar power (CSP, also known as “solar thermal power”) can help.

CSP works similarly to a nuclear power plant in that a heat source boils water to generate steam pressure and turn a steam turbine. The difference, of course, is that the heat source for CSP is sunlight and not nuclear fission: light is collected by focusing mirrors onto a collector, which transfers the heat to a thermal fluid. This fluid can either be used to heat the water to generate steam, or stored in insulated tanks to use later. This ability to store energy (in the form of heat) is CSP’s particular advantage over photovoltaic (PV) solar power, which converts sunlight directly into electricity. By storing the energy at a given CSP plant, delivery of power can be tuned to match the grid demand (“dispatchability”), and disruptions in the supply of sunlight due to weather can be smoothed by releasing some of the stored energy. The largest example of such a facility, the recently-opened Ivanpah Solar Plant in California, generates 377 megawatts of power by focusing light from rings of mirrors onto central receiver towers.

The authors of this study examine optimization of large-scale deployment of CSP power stations in four different regions of the world: South Africa, USA, India, and the Mediterranean. Because of anticorrelated spatial weather patterns (sunny in one place means cloudy in another place) in South Africa and the Mediterranean regions, large scale stable-demand CSP would be less costly to implement than in the USA or India, where weather often correlates. In all cases, however, the authors find that increasing the collecting area while fixing the generating and storage capacity, is the most cost-effective method of increasing CSP reliability. By locating several plants in geographically distinct locations, the deficiency in one area can often be met by production in another.

The largest challenges for deployment of such technology are cost reduction of CSP plant hardware (PV solar is currently cheaper) and grid-level coordination of generation capacity. While regulated electricity markets can vary drastically around the world, all projections for highly renewable electric grids require significant coordination by a central planner or heavily modified market systems to compensate for intermittent production (and thus profitability) at any given individual plant. Whatever the eventual solution, it seems clear that the dispatchable nature of power from CSP will be valuable in the renewable, intelligent “grid-of-the-future.”

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Title: Geographically Distributed Solar-Thermal Power Shows Promise for Renewable Baseline Generation

Source: Stefan Pfenninger, Paul Gauche, Johan Lilliestam, Kerstin Damerau, Fabian Wagner, and Anthony Patt, Nature Climate Change, 22 June 2014

DOI: 10.1038/NCLIMATE2276