A Novel Storage Technology Opens New Opportunities for CSP

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1 A Novel Storage Technology Opens New Opportunities for CSP Reuel Shinnar Dept. of Chemical Engineering The City College of The City University of New York

2 The Future of CSP CSP is at presently the only alternative, large-scale energy source that could provide the majority of all energy needs of the U.S. and the rest of the World. This is only slowly recognized as CSP has strong opposition. To become such a source it has to have proper storage and load following capabilities. For the desert it needs to be modified to operate with aircooling, which means backpressure turbines. It is also the cheapest process available for water desalination. 2

3 The Future of CSP (cont.) Sunshine is variable and so are electricity needs, but the two do not match. Furthermore, even in the desert, there are periods of heavy rain. Therefore we need both storage and fossil fuels back up. When we will run out of fossil fuels, we will have to provide the back up fuel from the CSP itself. Ammonia is an available technology for backup fuel. With proper storage and design, CSP can operate like the best power plants. 3

4 Peak Energy As fuel cells cannot become a major energy source the fantasy was promoted that solar cells provide highly needed peak energy, prevent blackouts, and so on. Peak electricity demand occurs between 4 and 9 p.m.. Peak energy has a high value if delivered reliably and only when needed (600 hour/year). Thus, solar cells and CSP without storage are useless as a large reliable energy source, the real value of the electricity is fuel value only or less. Utilities pay a higher price to fulfill their obligation to use alternative energy, and do not care as long as they can transfer the cost to the customers. Solar cells do not prevent blackouts, when sufficient capacity will be built they will actually cause them. 4

5 Hybrid Plants While we need backup with storable fuel fossil, hybrid plants, which substitute natural gas for storage, are not really alternative energy. In steam plants natural gas efficiency is 30 to 38%. In a modern combined cycle plant, the efficiency is 60%. Therefore if we just build a combined cycle plant we get from the same natural gas needed in a hybrid plant almost as much electricity as we get from the hybrid plant, at a quarter of the cost. The CSP community should not repeat the mistakes that led to the demise of Luz in the 1980s, which were hybrid plants, and believing that subsidies can become very large. 5

6 Limitation of Present Storage Technologies I am only aware of two methods actually available. 1. Pressurized boiling water. lowering pressure frees steam. Limited to low temperatures and therefore low efficiency, large storage volume. Heavy penalty when used with backpressure turbine. 2. Molten salt. Limited temperature range. Low top temperature increases required storage volume, reducing efficiency when used with backpressure turbine. Anybody with large experience in molten salt will only use it as a last resort. 6

7 Requirements for CSP Storage Technology CSP has several major hurdles to pass before it can become the energy source: The cost and the footprint have to be reduced. To do so it requires higher plant efficiency. Higher plant efficiency requires higher temperatures. Power plant efficiency is constrained by available materials. CSP efficiency is constrained by storage methods. We need a low cost, high efficiency storage method with no temperature constraints lower than for power plants. 7

8 Requirements for CSP Storage Technology (cont.) In steam power plants, the cost of the materials of construction limits the temperature. It used to be 1200 ºF, today it is ºF. In gas turbines, it is today ºF. We have the collectors for these temperatures. A low cost storage system capable to reliably meet these constraints could give a large cost reduction. In present CSP the constraints is not in the materials of construction, but in the storage. We need to switch it back. 8

9 A Novel Storage Technology for CSP The City University has developed a storage technology that overcomes these limitations. At the Clean Fuels Institute we developed a heat storage technology that is capable to store heat from gaseous and vapor streams and allow its recovery at the same conditions as before the storage. The center of this technology is a unique storage system that can store the heat of a heat transfer medium heated in the collectors on a solid, high temperature storage system design, such that the heat can be recovered on the same heat transfer medium, at the same temperature at which it exited the collectors. The design has a very high efficiency (95 to 98%). 9

10 A Novel Storage Technology for CSP (cont.) Thus, we can store the heat from a hot compressed gas and recover it by feeding the same compressed gas cold to the storage obtaining a gas with exactly the same constant top temperature as in the feed. The same can be done with steam generated and superheated in the collectors. The steam can be recovered by feeding cold water in the storage system. The storage acts here like a boiler and gives the system the same control and load-following capability as a conventional coal power plant. 10

11 A Novel Storage Technology for CSP (cont.) There are no temperature limitations up to 3000 ºF, one can store and recover the heat at the same constant temperature and enthalpy as in the feed. This is true for both gas feed and steam. The only temperature limitations are due to the collectors, and the temperature constraints of the material of construction. 11

12 Readiness for Design The storage technology is based on the experience of the inventor who has successfully used the same technology for completely different applications in chemical reaction engineering. He has also designed vessels with the same filling operating at 2800 ºF. There is nothing in our storage method that requires pilot planting. 12

13 Potential Applications 1. Replacing Dowtherm and molten salt in trough systems with compressed gas using the maximum temperature the trough system allows, especially if the collectors are redesigned. Doing so increases the efficiency and reduces the cost significantly. 2. Storing superheated steam from either trough or tower collectors. In this case the storage unit will function like a boiler and directly feed to a turbine the superheated steam. The storage unit can be controlled for load following just like the boiler of a conventional power plant. This is especially useful for solar towers, as it allows the tower to utilize its main advantage over a trough, namely: the ability to provide high superheat (up to 1350 ºF), like in a regular power plant. This could reduce the cost of present 13 tower designs by a factor of 2.

14 Potential Applications (cont.) 3. Heating the working fluid of a gas turbine in the collectors storing it in the storage unit, and recovering the heat from the storage unit with the compressed working fluid (air, gas) before feeding it to the turbine. 4. The same can be done with the working fluid of any power generating device (Stirling engines, etc.). 14

15 Summary A radically novel storage technology has been presented that offers new opportunities for the design of CSP plants. It shifts the design constraints from the storage technology to the design of the CSP plant itself, allowing high temperatures and much higher thermal efficiency opening the door to drastic cost reduction. The method is ready for large scale implementation, and it is available for licensing from the City University of New York. Interested parties can talk to Dr. Jake Maslow (jake.maslow@mail.cuny.edu) or to Professor Reuel Shinnar (shinnar@ccny.cuny.edu). 15