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Storage for value

Does CSP with energy storage have economic value? Tex Wilkins of the CSP Alliance speaks exclusively to RET

Wilkins says storage works well with troughs, towers, and linear Fresnel

Is there economic value in concentrated solar power with energy storage? Tex Wilkins, executive director of the CSP Alliance, discusses its latest report.

RET: What are the key benefits of using energy storage technologies with CSP? What are the main challenges that energy storage can help overcome to move CSP forward?

Tex Wilkins: Storage enables solar energy to be used when it is most needed, day or night. It provides needed flexibility to those managing electric grids that have large amounts of intermittent wind and solar without storage. CSP plants with storage can be used to add power to the grid when there is less sun or wind than predicted, or its solar energy can be diverted from the grid to storage if there is more sun or wind than needed.

RET: The CSP Alliance released a report in December 2012 which highlights the "economic value of CSP with storage". Why is this report so important and why is it so significant to the CSP industry today?

TW: Recent analyses from the National Renewable Energy Laboratory (NREL) and the Lawrence Berkeley National Laboratory shows that as the percentage of intermittent wind and solar on the grid becomes larger, storage becomes increasingly important as a tool for injecting flexibility into the grid, helping keep it safe and reliable. As concern over global climate change encourages the increased use of renewable energy, it is important that policy makers understand that along with the benefits of renewable energy, their increased use poses issues that must be addressed.

In addition to flexibility, storage enables CSP plants to provide ancillary services that can displace fossil plants. NREL analysis indicates that these attributes could result in greater use of PV and wind. The addition of CSP with storage strengthens the renewable portfolio, making it possible to safely integrate a larger percentage of renewable energy into the grid.

RET: Among the report's key conclusions is that thermal storage adds energy and ancillary service value to a CSP plant. How does it do this and how does this compare to other solar resources?

TW: Storage enables CSP projects to dispatch electricity to the grid when it is most valuable. During the summer this could be in the afternoon and early evening when air conditioners are being used. In the winter this could be in the morning and evening when people are getting ready for work or returning home from work. Solar resources without storage only provide power when the sun is shining. CSP with storage will be able to shift its power into the grid so that it always dispatches power at the peak value.

Storage also enables CSP plants to provide ancillary services such as spinning reserves, non-spinning reserves, and the ability to quickly increase or decrease its power as required by the grid operator. These services, which are usually met with fossil plants, provide a safety valve for instances when a power plant unexpectedly goes down or additional power is needed in a hurry. Solar resources without storage would not be able to provide them because of their intermittency.

RET: The report says the extra value energy storage gives CSP depends on particular plant designs. What designs excite you in the sector and what designs should solar firms focus on developing, which work best with energy storage?

TW: Storage works well with troughs, towers, and linear Fresnel. It has not been as fully developed for dish technology. As storage temperature increases, its cost decreases. For example, towers that operate at 560°C can provide lower cost storage than troughs that operate at 390°C. Most commercial CSP systems that include storage use molten salt as the storage medium. Steam can also be stored, although not as easily or inexpensively.

RET: The report highlights that its findings are critical for the development of the solar portfolio in regions with high solar potential. Which countries of the world do you think will particularly benefit from energy storage technologies for CSP in the future?

TW: Analyses show that storage becomes increasingly important as grid penetration increases of solar and wind without storage. Any country that plans on using a significant amount of solar energy to combat global climate change will benefit from CSP projects with storage.

RET: Aside from the report, are there other ways the Alliance is looking to promote and develop energy storage for the CSP industry?

TW: The Alliance is taking the key findings summarised in the report to grid operators, state energy regulators, and utilities with the intent of their having a better understanding of how CSP projects with storage can help them meet their goals for renewable energy. The Alliance is aware of on-going studies relating to CSP storage and is helping guide some of those studies.

RET: How do you hope to see energy storage for CSP develop in the next few years? What affect do you hope the report will have on the industry?

TW: The Department of Energy is sponsoring research in new storage materials (advanced salt mixtures, phase change, solids) with the goal of lowering cost by identifying materials with an increased operating range, high heat capacity, and the ability to undergo many thermal cycles. In the next few years I expect there will be introduced new materials that meet this goal. When this occurs, the addition of storage on a CSP system will actually reduce the cost of power because of better utilisation of the turbine/generator and storage will become standard on most utility-scale CSP plants.