Reuel Shinnar, co-director of The Energy Institute at The City College of New York offers a four-point criterion for CSP to become a major source of reliable energy

Storage technologies are considered to be a key aspect for CSP plant exploitation as their availability allows reliable power production forecasting.

According to Reuel Shinnar, Co-Director, The Energy Institute, The City College of New York (CUNY), half the CSP plants built in the US have no storage and “they are useless as an energy source because they save fuel at too high a cost.”

“Also, it does not make sense to build plants which use water in dry locations. The States and the utilities must get together to find a way to avoid such problems,” said Shinnar, speaking to CSPToday.com, which is scheduled to conduct a session on the significance of storage during the forthcoming 3rd Concentrated Solar Power Summit US, to be held in San Francisco on June 30 – July 1 this year.

There is no dearth of theories about the utility of storage in CSP.

In fact, in recent analysis posted by CSPToday.com (Depth adding and dispatching thermal energy storage system) it was discovered that much effort would be required to develop viable high-temperature storage. The article also discovered that presently the share of solar power in the grid is small, and it is felt that all the power can contribute to consumption in daytime. When solar becomes a more dominant part of the power mix, storage will certainly have to be addressed as a high priority.

Shinnar disagrees, saying, “CSP is the only technology for which affordable storage has been invented. The only reason that half the CSP plants are built without storage is that they receive the same subsidy whether or not they are built with storage even though CSP plants with storage are much more valuable,” he explained.

Emphasising on the significance of storage in CSP, Shinnar referred to a four-point criteria for CSP to become the main source of alternative energy.

In fact, according to Shinnar, the only source of alternative energy that can become the main input for the national grid is CSP, provided the following criterion is met:

·CSP must be equipped with adequate thermal storage - at least eight hours a day for intermediate loads and more for load-following. Regrettably, half the plants being built today lack storage. We have created the fantasy that solar energy is peak energy and therefore, that there is a large need for CSP without storage says Shinnar. In reality, peak consumption occurs between 5:00 and 9:00 in the evening. The utilities don’t seem concerned that CSP plants lack storage because they are mainly interested in meeting state-imposed quotas.

·CSP must have oil or gas backup for rainy periods, but, not as a substitute for storage. In the future, the fuels needed for backup will be produced by CSP. Rather than storing solar energy, the old Luz plants supplemented CSP with fossil fuel backup not only for rainy days but on a daily basis. It is unfortunate that BrightSource and others have taken up this practice again. As gas fired steam power plants have a much lower efficiency than combined cycle power plants, such hybrid plants waste so much natural gas that they can hardly be considered “alternative” energy.

·Water should not be used to cool the condenser in CSP plants as it is a scarce resource. Where all the CSP plants that have been permitted in California to be built, no sweet water would remain for other uses. Obviously, this will not happen, but, it has helped encourage the growth of a strong movement against CSP. Unlike traditional power plants which require relatively small land tracts and can therefore be built along the densely populated California coastline, CSP plants must use large amounts of sweet water as they cannot be built near the ocean. The amount of water used is inversely proportional to the efficiency of the power plant. This problem could be avoided easily by using air cooling. The negative impact of air cooling on efficiency is reduced when the operating temperature and thermal efficiency are high.

·CSP must have load following capability to stabilise the variability of other alternative technologies that can contribute to our energy supply, e.g., wind, solar cells, etc. Compensation for variable energy sources has already become a serious problem in California. In addition to storage, load following capabilities require a large increase in the capacity of the power plant. The unique advantage CSP can give to load following, however, has never been utilised. When the capacity of the power plant of a 100MW CSP plant is doubled, it attains the same the load following capability as a 200 MW coal power plant. Yet, the cost increase for the CSP plant is only 10% of the total investment whereas, achieving the same capability in a coal power plant would require double the investment. The most effective way to narrow the gap between the costs of CSP and fossil fuel energy is to design CSP plants especially for load following; this would make CSP much more attractive to utilities.

Focus on the cost of the electricity produced

As far as the costs are concerned, according to Shinnar, the question is not the cost of storage, but rather, the cost of the electricity produced.

“Molten salt and Dowtherm limit the operating temperature of the power plant and this lowers the efficiency and increases costs. For this reason, The City University of New York developed a high temperature storage system that is available for licencing. It has no practical temperature limitations and a low storage cost. The cost of electricity produced by CSP plants can be reduced by 30%. This invention is based on good engineering and not on abstract research,” said Shinnar.

CSP plants should adopt heat transfer fluids (HTF) that are able to withstand the higher temperatures used in modern power plants today, points out Shinnar.

“This would greatly increase efficiency and thus, reduce the cost of the electricity produced. CSP plants are too expensive because they have been using heat transfer fluids which limit the temperature at which they can operate and thus, lower their efficiency,” explained Shinnar.

Shinnar claims that with CUNY’s method, the capacity of a plant can be increased with almost no incremental investment. Furthermore, the temperature differential that can be achieved is much larger than with molten salt and this decreases storage costs dramatically. The higher temperatures that are made possible by the CUNY technology makes it much easier for CSP plants to meet the four criteria itemised above.

“Our storage method is cheap enough to be added to any CSP plant that was originally built without storage with no increase in the cost per Kwh because adding storage makes it possible to utilise the full capacity of the power plant. The higher operating temperature and the higher efficiency that can be reached also reduces the negative impact of air cooling on efficiency substantially. Industry and the utilities need to cooperate in building CSP plants they will want to use rather than to build in order to meet quotas,” said Shinnar, who feels if appropriate action isn’t taken at this juncture, then there is a chance that the industry may lose this opportunity to secure a reliable alternative energy technology for the future.

3rd Concentrated Solar Power Summit US

CSPToday.com is scheduled to conduct the third edition of Concentrated Solar Power Summit US in San Francisco on June 30 – July 1 this year.

For more information, click here: http://www.csptoday.com/us/agenda.shtml

Or

Contact: Sara Lloyd-Jones by email sara@csptoday.com

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