There are now almost 8 gigawatts (GW) of concentrated solar power (CSP) projects in the pipeline, compared with the half GW that was installed in 2010. This project pipeline is in stark contrast with recent news about cancellations of CSP power plants. What is going on?
Basically, the CSP industry is at a critical turning point due to a number of factors. The ‘potential’ of CSP is an oft-heard term, and it is true that there are some very attractive aspects of CSP – in principle.
CSP has two key positive and interrelated aspects: it can provide good energy dispatchability, and has the flexibility to support hybridisation. Dispatchability is the ability to provide the energy when the demand wants it, not when the supply generates it. CSP can be configured to have thermal storage and can provide up to six or even eight hours of post-sundown energy.
Hybridisation allows the power plant to have both solar and standard energy for heating. In principle, this capability would allow for 100 per cent capacity– where the power plant is providing electricity over the full 24 hours, and the plant becomes a tunable base load supply – the holy grail for renewables.
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The big ‘however’ is that this all comes at a high price tag, due to the fact that CSP is the most expensive member of the solar and wind club1.
The key to CSP success
The key to CSP's commercial success is developing an economical, effective energy storage capability that will hold the sun's heat and enable clean electricity generation during periods of peak power demand, cloudy weather, and night time hours.
CSP has the potential to address the need for dispatchability through the use of a thermal storage medium. In this regard, there are two intertwined technology paths for CSP – both of which need to be advanced. These are solar collection technology and heat conduction technology. In the latter there are two key elements: Heat Transfer Fluid (HTF) and Thermal Energy Storage (fluids or TES).
The four different approaches to CSP currently include trough, tower, linear reflector, and sterling dish. Except for trough CSP, there is the need for an HTF and in some cases a TES medium. The HTF and TES materials serve as the interface between the solar energy input and the power block.
CSP in Australia
Large-scale solar electricity generation is recognised as a relatively new market in Australia, with considerable uncertainty surrounding future values for a number of key variables that may affect generation costs.
One of the key variables is energy storage. According to the December 2010 Pre-Feasibility Study for a Solar Power Precinct study prepared by AECOM Australia for the New South Wales Department of Environment, Climate Change and Water (DECCW) “Augmenting a solar thermal plant with storage capability is a potential solution to resolve the disparity between solar thermal output and consumer demand.”
According to AECOM, the most important technical issue challenging large-scale solar is connection and integration of its capacity to the electricity network. However, while it does add capital costs, the inclusion of TES to a solar power plant or precinct “may allow electricity to be scheduled for dispatch at peak periods where it can be sold for a higher price and possibly improve financial viability such that the power may become cost-competitive under a Carbon Pollution Reduction Scheme (CPRS) within five to ten years.”
One of the advantages of CSP is that it can be part of a hybrid energy source so that a regular gas-fired plant can also be used to heat the HTF/TES materials during solar down-time.
Installation and testing of innovative solar thermal power plant technology using compressed air and without using water is underway at the Australian National University's Solar Energy Centre in Newcastle, New South Wales. The CSIRO developed new technology that focuses the sun from a field of 450 heliostats onto a 30 metre high solar tower. The heliostats will concentrate the solar resource to create temperatures of up to 1000˚Celsius.
The solar Brayton Cycle system at the site then uses the concentrated solar energy to heat compressed air, which expands through a turbine to generate electricity. This technology also has the capability of hybridisation, as heating can also be performed by natural gas combustion. CSIRO is working in collaboration with Japan’s Mitsubishi Heavy Industries, who views the technology as a good fit for its current range of high-temperature gas turbines. As planned, the solar Brayton Cycle field will be the largest of its type in the world and will generate energy equivalent to the amount required to power nearly 100 homes. Future plans will also reportedly include the option of storage so that clean renewable energy may be provided during peak demand.
The key considerations for development of HTF/TES materials are the ability to vary the operational temperatures, the range of useful temperatures, the heat capacitance and – very importantly – the cost. The latter is essential in the world of solar energy.
The rapid implementation of photovoltaic (PV) in the last year has been accelerated by the dramatic drop in PV prices. It is essential for CSP to achieve some of the same learning curve cost reductions. The solar industry is reliant on incentives, and lowering the cost is a requirement. Further, the ability to introduce new technical solutions is only as good as the ability to provide these technical solutions in a cost-effective manufacturing mode2.
From a commercial perspective, HTF and TES are at very early development stages. Although they can function, the current HTFs suffer from significant shortcomings and TES elements are even more challenging, with only marginal industrial activities. Activity for both remains very much a research and development effort.
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