The key factor when it comes to solar power plant efficiency – be they of the photovoltaic or concentrated solar power (CSP) variety – is the amount of light that can be captured by the light-absorbing material and converted into electricity or heat. Researchers at the University of California, San Diego (UCSD) have developed a new nanoparticle-based material that promises to improve the efficiency of CSP plants with its ability to absorb and convert over 90 percent of the sunlight it captures into heat.

Unlike photovoltaic (PV)-based solar power plants, which convert light directly into electricity, CSP plants generally use sunlight, concentrated onto a small area, to generate heat and drive a steam turbine to generate electricity. Because this is similar to the process used by fossil fuel power plants, CSP technology has the potential to be retrofitted to existing power plants to make them more environmentally friendly. The technology also has advantages over PV plants with its ability to generate electricity 24 hours a day by storing heat captured during the day in thermal tanks.

CSP plants commonly uses large numbers of mirrors to focus sunlight onto a tower spray painted with a black paint material that is designed to maximize sunlight absorption. However, being subjected to such high temperatures day after day degrades the material, meaning such plants usually need to be shut down once a year or so to allow the degraded light-absorbing material to be chipped off and a new coating applied and cured.

To overcome this problem, the US Department of Energy's (DOE's) SunShot program challenged UCSD researchers to develop a material able to operate at higher temperatures than existing materials and for much longer. With financial support from the SunShot program, a multidisciplinary team at UCSD developed a material using particles ranging in size from 10 nanometers to 10 micrometers.

When spray-painted onto a metal substrate for thermal and mechanical testing, the researchers found that the "multiscale" surface these particles form is able to withstand not only temperatures in excess of 700° C (1,292° F), but also years of exposure to air and humidity. The structures are also able to trap and absorb around 90 to 95 percent of light, while letting less than 30 percent of infrared light at near the peak of 500° C (932° F) black-body radiation escape.

The researchers say CSP plants currently account for around 3.5 gigawatts of power worldwide, but that this number is set to increase significantly with construction underway on plants that will provide up to 20 GW in the near future. The material developed at UCSD could help improve the efficiency and cut maintenance costs of CSP plants, going some way to achieving the goal of the Sunshot Initiative launched by then-Energy Secretary Steven P. Chu in 2010 that aims to make solar power cost competitive with other means of electricity generation by 2020.

Details of the material can be found in a paper published in the journal Nano Energy.

Source: UCSD

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