Concentrating solar thermal power can provide a contribution to the abatement of CO2

The IMDEA Energy Institute’s Manuel Romero outlines why better exploiting solar thermal power can provide a significant contribution to the abatement of CO2 emissions. The high temperature thermal conversion of concentrated solar energy is rapidly increasing, with many commercial projects taken up in Spain, as well as countries such as the USA, India, China, South Africa, Australia, Algeria, France and Italy.

This is the most promising technology to follow the pathway of wind power and PV in order to reach the goals for renewable energy implementation in 2020 and 2050. With 2,400MW connected to the grid in 2013, and 5,000MW expected by 2020, Spain is taking the lead on current commercial developments, together with the USA – where a target of 4,500 MW for 2013 has been fixed – and other relevant programmes like the ‘Solar Mission’ in India, which has recently been approved and is going for 22 GW-solar, with a large fraction of concentrating solar thermal.

Solar Thermal Electricity or STE (also known as Concentrating Solar Power or CSP) is expected to impact enormously on the world’s bulk power supply by the middle of the century. Worldwide, the exploitation of less than 1% of the total solar thermal power plant potential would be enough to meet the recommendations of the United Nations’ Intergovernmental Panel on Climate Change for long-term climate stabilisation. A 1m2 mirror in the primary solar field produces 400kWh of electricity per year, avoids 12 tons of CO2 and contributes to a 2.5 tons savings of fossil fuels during its 25 year operational lifetime.

The energy payback time of concentrating solar power systems is less than one year, and most solar-field materials and structures can be recycled and used again for further plants. But in terms of electric grid and quality of bulk power supply, it is the ability to provide dispatch on demand that makes STE stand out from other renewable energy technologies like PV or wind. Thermal energy storage systems store excess thermal heat collected by the solar field. Storage systems, alone or in combination with some fossil fuel backup, keep the plant running under full-load conditions. This STE plant feature is tremendously relevant, since penetration of solar energy into the bulk electricity market is possible only when substitution of intermediate-load power plants of about 4,000-5,000 hours/year is achieved.

The combination of energy on demand, grid stability and high share of local content that lead to the creation of local jobs, provide a clear niche for STE within the renewable portfolio of technologies. Because of that, the European Commission is including STE within its Strategic Energy Technology Plan for 2020, and the US DOE is also launching new R&D projects on STE.

A clear indicator of the globalisation of such policies is that the International Energy Agency (IEA) is sensitive to STE within low-carbon future scenarios for the year 2050. At the IEA’s Energy Technology Perspectives 2010, STE is considered to play a significant role among the necessary mix of energy technologies needed to halve global energy-related CO2 emissions by 2050, and this scenario would require capacity additions of about 14GW/year (55 new solar thermal power plants of 250MW each).2

However, substantial effort on R&D is still necessary since the current solar thermal power plants are still based on conservative schemes and technological devices that do not exploit the enormous potential of concentrated solar energy.3 Commercial projects operate with thermal fluids at relatively modest temperatures, below 400ºC. The most immediate consequence of these conservative designs is the use of systems with efficiencies below 20% nominal in the conversion of direct solar radiation to electricity; the tight limitation in the use of efficient energy storage systems; the high water consumption and land extension due to the inefficiency of the integration with the power block; the lack of rational schemes for their integration in distributed generation architectures and the limitation to reach the temperatures needed for the thermochemical routes used to produce solar fuels like hydrogen.

1 Herring G ‘Concentrating solar thermal power gains steam in Spain, as momentum builds for major projects in the US, North Africa, the Middle East, Asia and Australia’, Photon International, December 2009, 46-52

2 IEA (2010) Energy Technology Perspectives 2010 – Scenarios and strategies to 2050. ISBN 978-92-64-08597-8

3 Romero M, González-Aguilar J (2011) ‘Chapter 3: Solar thermal power plants’. In: Energy and Power Generation Handbook: Established and Emerging Technologies. K R Rao (Ed) pp. 3.1-3.25. Published: American Society of Mechanical Engineers ASME US, ISBN 9780791859551