General CST Considerations

Value proposition of CST technologies

The value proposition of CST technologies is excellent. CST technologies have all the attributes of a solution that can become the backbone of a highly decarbonised energy system of the future.

In application, its benefits are varied and cross a number of priority sectors – for example:

  • Electricity sector:
    • CST integrates naturally with storage, and actually becomes cheaper on a $/kWh basis as storage size is increased, which is a unique competitive advantage compared to other storage renewables
    • CST doesn’t need any conventional backup
    • It can perform different roles as needed, from base-load to peaking plants
    • It can provide critical grid stability to increase penetration of non-dispatchable renewable technologies
  • Industrial and transport sectors:
    • CST can provide process heat, fuel and solar chemistry solutions needed to successfully decarbonise these sectors

The intermediate transformation of solar radiation into heat allows CST technologies to:

  • Provide a very large range of energy service options of varying temperature and technological complexity to allow:
    • Heating and cooling;
    • Process heat at high temperatures;
    • Electricity generation; and
    • Solar fuels and other chemistry or metallurgy applications.
  • CST technology can facilitate the integration of hybridisation and thermal storage solutions for a range of industries currently under scrutiny for their carbon emissions or called to question on their strategies to reduce emissions and transition to renewable energy sources and practices. For example:
    • If hybridised with biomass, a CST system can provide continuous 24/7 clean and renewable heat process or electricity production operation.
    • If combined with a thermal storage system, CST can provide the heat for the heat process application or for the delivery of electricity when it is needed most or is economically profitable.

When deployed with conventional power block technology, CST delivers dispatchable clean and renewable electricity and ancillary services to the grid.

The capacity of CST to utilise expertise already available in many countries translates to:

  • High potential for conversion or expansion of existing manufacturing capabilities in a country to serve the CST sector;
  • Local content of CST projects – i.e. built, manufactured and deployed by local companies; and
  • Positive impact on employment, tax revenues and GDP.


Global CST opportunities

Because of its excellent value proposition, CST technologies are expected to play a very important role in the transition to a decarbonised world energy system. According to the 2014 version of the International Energy Agency (IEA) roadmap[1], CST plants will be the dominant technology in the future for Middle East and African countries and they will play a significant role across other regions.

The IEA also predicts that together PV (16%) and CST (11%) could become the largest source of electricity worldwide before 2050.

In fact, PV and CST technologies are beginning to be combined by renewable energy project developers to take advantage of their complementary characteristics, with CST providing the critical thermal storage system to deliver electricity when the sun is not shining.

One should not forget that the production of electricity is just one of the energy applications of CST technologies. Other process heat applications and solar chemistry are much more than niche markets for these technologies.

CST Challenges

Currently, in terms of electricity generation, CST technologies are being deployed at a slower pace than originally foreseen. According to the latest IEA road map, PV technologies are five years ahead in terms of the expectations regarding deployed capacity, while CST technologies are seven years behind.

The main reasons for this are as follows:

  • Although the value proposition of CST technologies is very strong, some of the advantages that CST brings to the table are not fully valued by the markets yet. Some of these advantages include:
    • When integrated with a conventional power block, they:
      • Do not require deployment of conventional backup infrastructure
      • Are able to provide ancillary services to the electricity grid, and
      • Will automatically and almost immediately benefit from any advances in power block technologies.
    • They can be easily hybridised or combined with Thermal Energy Storage systems (TES) to deliver heat or electricity at the time of day when it is best suited or most required (dispatchability).
  • The current state of the art of CST technologies is a utility scale (20 MW – 300 MW) parabolic trough or solar tower power plant with 4 to 7 hours solar thermal storage and a steam turbine based power block:
    • This type of system does not scale-down well, mainly because of the dramatic reduction in performance associated with the reduction in steam turbine power rating, a reduction in performance that unfortunately is not offset by a larger reduction in O&M cost
    • As a consequence, CST technologies are not cost competitive yet in many potential niche markets where smaller plant sizes are needed, even though the costs of large CST power plants have decreased by more than 25% since 2006.

Despite this, the expectations of the IEA and other international bodies are that, in the future, as the amount of non-dispatchable renewable technologies increase and the urge to decarbonise the energy sector continues, the different energy players will appreciate the role that CST technologies can play as an enabler for:

    • Increased penetration of non-dispatchable renewable technologies, such as wind or PV;
    • A provider of ancillary services to the electricity grid; and
    • As a supplier of base, mid or peak load power.

In addition, it is possible to be misled by the claims of different electricity generating technologies about their ability to provide cost-effective electrical storage solutions in the mid-to-long-term future.

In electrical storage terms, the cost of the state-of-the-art commercial thermal storage solution is a third of the cost of commercial-scale electrical battery storage.

In addition, current electrical battery storage technology has not been used to demonstrate the large amount of storage that a typical commercial CST power plant can provide. Obviously, things will improve in the electrical storage as they will in thermal storage, but when comparing different technological options, it is important to try to ensure, as much as possible, that the comparison is fair.

The cost per kilowatt is certainly not the right metric for comparison of CST technology with thermal storage to PV technology with batteries. Comparisons must be made in terms of investment for same yearly production. However, the cost per kilowatt hour is not the right metric either. One should strive to compare ‘system-level-value’ in a per unit energy basis, not cost.

Furthermore, there are other beneficial characteristics of CST technologies that “system value” or “cost” per unit energy alone cannot capture and that should be taken into account when analysing the short, mid, and long-term future of these technologies. One such characteristic is the macroeconomic impact of their very high local content – i.e. the fact that most of the work and goods needed to design, operate, and maintain the plants can be provided by local companies.


IEA (2014a) “Technology Roadmap: Solar Thermal Electricity”, 2014 edition, OECD/IEA, Paris; available from

IEA (2014b), “IEA Technology Roadmaps for Solar Electricity 2014 Editions”, OECD/IEA, Paris; available from