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US DOE: CSP Could Provide Needed Flexibility and Reliability to Grid

November 06, 2017 |
 by Susan Kraemer


Dr. Avi Shultz is the acting program manager for the United States Department of Energy (DOE) SunShot Initiative Concentrating Solar Power (CSP) team, which supports research, development, and demonstration of solar thermal components and systems that can enable wide-spread deployment of low-cost CSP with thermal energy storage.

Every day our power needs fluctuate causing grid operators to make quick decisions to balance the grid. This can happen on hot summer days when people are turning on their air conditioners or in the middle of winter when they crank up the heat. Either way, grid operators must find a way to meet rapid spike in energy demands.

Most concentrating solar thermal power (CSP) systems today are equipped with energy storage, which serves as a battery within the plant and allows utilities to use solar-generated power whenever it is needed. When grid operators have the choice to determine the best way to power the grid, this creates grid flexibility, making CSP a valuable asset as our grid demands evolve.

Despite steady developments in CSP technology, further innovation is needed to use high-tech components in holistically-designed systems that can rapidly and flexibly respond to consumer energy demands at low costs. With support from the Solar Energy Technologies Office’s (SETO) CSP research program, developments in these areas could improve grid flexibility by unlocking new choices for using CSP to better meet grid operator needs.

Concentrating Solar Power 101

CSP systems harness thermal energy from the sun and use this energy to create electricity or heat. State-of-the-art CSP systems use fields of mirrors called heliostats to reflect and concentrate sunlight onto a receiver that sits atop a tall tower. This receiver contains a heat transfer fluid that’s heated to around 565 degrees Celsius and then circulated throughout the system to drive a power cycle that generates electricity.

This thermal energy can be easily and efficiently stored in tanks so it can be used whenever the energy is needed to meet demand, not just when the sun is shining. This enables CSP plants to operate independently and without backup fuel sources much like a conventional power plant.

Size Matters: Flexible Plant Arrangements Can Meet a Variety of Needs

As electricity demands change, CSP’s flexibility as an on-demand resource can be used to the country’s advantage. Smaller systems, with lower up-front costs could be deployed to provide peak power while larger systems with many hours of storage can provide baseload power.

CSP systems are built from similar building blocks: mirrors to collect and concentrate sunlight, receivers to capture it and transfer it to a heat transfer fluid, thermal energy storage tanks, and a power block to convert the heat into electricity.

For example, one 50-megawatt (MW) CSP plant can be configured as a type of peaker plant with less than six hours’ worth of energy storage. This plant can be used to supplement baseload generation when there’s a sudden, high spike in energy demand. That same plant can also be used with more than 12 hours of storage and a much larger mirror field to generate baseload power—allowing the plant to provide solar electricity throughout the day and night.

While CSP plants can be designed in different sizes for different markets, the Energy Department’s solar office is looking ahead to the technology and research needed to ensure that the technology will be cost-competitive.

Its 2030 cost targets for CSP peaker and baseload plants will help the solar industry stay on pace as competitive funding opportunities focus on rapid development. Solar Dynamics, for example, is already investigating the feasibility of a modular, molten-salt tower peaker plant that can be easily replicated and rapidly deployed in 24 months or less.

Spinning and Non-Spinning Reserves Provide Grid Stability

CSP also provides essential grid stabilization features due to the use of a conventional, spinning turbine that adds inertia to the grid. Utilities and independent system operators (ISOs) are charged with meeting customer energy demands, and when there are rapid swings in energy needs, utilities need to ensure the grid remains stable.

For these needs, utilities and ISOs manage frequency and voltage regulation, short-circuit power, and spinning reserves, which is energy that’s already online and synchronized to the grid’s frequency. This makes it easier to maintain system frequency and quickly dispatch more energy. CSP can be a source of spinning reserves for immediate needs and non-spinning reserves for near-term needs, giving grid operators greater flexibility and control for ensuring reliability.

Putting a More Accurate Price Tag on Reliability Benefits

One of the biggest advantages of CSP is its reliability as an energy source and predictable costs. Unlike conventional fuels, there’s nothing to mine, ship, burn, or store as waste; there’s an abundant, unending supply of sunshine. Because the “fuel” is free, costs are predictable over the lifetime of a plant operation and its maintenance costs. In addition, more than 60% of the cost to operate a CSP power plant happens in the first year, enabling investors to have a better long-term understanding of costs and the return on their investment.

To help make the remaining cost of a CSP plant more transparent for project developers and investors, SETO is funding an open source modeling and simulation tool that optimizes CSP plant design and operations. This project accounts for maintenance, field exposure, and even solar generation uncertainties, helping project developers maximize the performance of a plant that that will last for more than 30 years.

This new vision for CSP technology can help grid operators better balance the grid, maximize their available energy resources, and better plan for future energy needs. This increased flexibility empowers grid operators to make the best decisions possible, ensuring the grid remains resilient and secure.

As the country’s energy demands evolve daily, so does CSP technology. While further innovations are needed to create these low-cost integrated systems, the research foundations SETO is laying now—like the Generation 3 CSP Systems funding opportunity—will enable CSP technologies to reach new heights. Its flexibility and predictability will make it a strong contender for meeting our changing energy needs today, tomorrow, and in a 100 years.

Download the graphics and learn more about SETO’s concentrating solar thermal power research.

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