The potential of concentrated solar energy

Concentrating solar thermal power could meet from 2% to 10% of future electricity needs, depending on climatic conditions of the different regions.

This is the finding of a recent US study that was compiled by the Pacific Northwest National Laboratory Department of Energy, the University of Maryland and NASA, which introduced a new assessment method to analyze interactions between solar thermal and electrical systems. The aim is to overcome one of the greatest difficulties of economic models that were used up to now for the energy evaluation of solar power, which practically did not take into account the source’s natural variability compared to network loads.

Regarding concentrating solar power, there are essentially two parameters that must be considered: the number of sunny days and the amount of light in those days. That is, the key to a reliable assessment of solar power consists in the exact knowledge of the amount of hours of the day in which the plants have operated and of what action is taken to compensate the energy that was not injected into the grid when the plants were not producing.

The study found that, even considering a substantial development of thermal storage systems and their cost reduction, the widespread adoption of concentrating solar power will require a large number of back-up solar thermal power plants. The latter, for environmental and other type of needs, will preferably be gas or biomass-fuelled, but will significantly affect the total cost of concentrated solar energy, compared to the long term increased cost that is expected for all fuels.

SP technologies hold a promise of clean, domestic power around the world. CSP systems convert the thermal energy in sunlight into electricity. Global use of this technology is projected to grow substantially in the near future with numerous plants under construction worldwide. The potential of solar power technologies is difficult to evaluate, however, because the energy-economic models used to inform decision-makers are not designed to simulate variable renewable resources. The results of this study can be used to produce more realistic estimates of their potential contribution.

The operation of CSP power plants and their interaction with electric loads, by time of day and season, were analyzed to determine how this technology could be realistically incorporated into energy-economic models. A key characteristic of CSP power plants is their ability to supply reliable power through the use of a low-cost backup option referred to as hybrid plants, whereby natural gas, or even biomass, can be combusted in a low-cost boiler or heating unit to supply power on cloudy days.

Plant performance depended on two key parameters: the number of cloudy days in which power plants cannot operate, and the average amount of sunshine on operational days. This research showed that an accurate characterization of the number of such "no operational" days is key to a realistic characterization of this technology. No existing data sets provided global estimates of this parameter, so the necessary values were estimated using regressions developed from the U.S. National Solar Radiation Database in conjunction with a global solar resource data set developed by NASA. The technology representation and data developed in this work were then implemented in the Global Change Assessment Model (GCAM) to examine how CSP technologies might compete with other electricity supply technologies in 14 global regions.

The methodologies and data developed in this research can potentially be used in many energy-economic models to more realistically examine the potential of CSP technologies. A detailed study of the potential of renewable energy more broadly using this and related work using the GCAM model is underway at PNNL. The work reported here highlighted the importance of estimating new solar resource parameters, which may be possible with the next generation of solar resource assessments being conducted by NASA. The role of CSP backup operation should be more thoroughly examined in detailed renewable energy analyses.

Finally, the report stresses the need for further studies in order to better assess how much solar energy used for industrial purposes is truly available in the various regions of the Earth. Subsequently, this will allow to examine the technical and economic aspects regarding to what extent parallel thermal power plants are needed for back-up. Nevertheless, although there have been other more optimistic studies in this field, the possibility that in a few decades concentrating solar alone will be able to meet up to 10% of electricity needs, that is suggested by this report, appears significant.

More information: Zhang Y, et al, 2009. "Modeling the Potential for Thermal Concentrating Solar Power Technologies." Energy Policy 38:7884-7897.