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Concentrating Solar Power

Concentrating solar power (CSP) harnesses the sun's energy through technologies like parabolic troughs, power towers, and thermal energy storage. It can generate electricity even when the sun is not shining by storing solar energy as heat. CSP is well-suited for areas with abundant sunlight like India's deserts and is a key technology for providing renewable energy at scale. While CSP projects are currently capital intensive, ongoing research and larger deployments are expected to drive down costs and allow CSP to compete with traditional power sources.

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Concentrating Solar Power Author: - Saswat Sourav Panda Research Analyst, (Energy & Power) TechSci Research Contact saswat223@gmail.com Across the globe, solar energy is taking off, with increasing investments in “solar power” every day. And, it’s not just solar panels popping up on the rooftops of homes; citizens across the globe are starting to adopt other forms of solar energy, as well. Concentrating solar power (CSP) is a technology that harnesses the sun’s energy potential and has the capacity to provide hundreds of thousands of customers in the world and especially India with reliable renewable energy—even when the sun isn’t shining. The desert and unfertile lands are particularly well suited for CSP because it leverages the nation’s abundant solar energy resources, particularly in the sun-drenched low agricultural productive areas in Gujarat, Rajasthan, and even coastal areas. Every day, enormous amount of solar energy falls on India, in the form of sunlight, more than what the country uses in an entire year. The year 2016 marks a significant milestone in the history of Indian Power sector as it challenges the traditional thermal powered power with cheap, clean, decentralised and cost effective source of energy for millions still living in dark. What Makes CSP Unique A distinctive feature of CSP is that, when deployed with thermal energy storage, it can produce electricity on demand— providing a potential storage source of renewable energy. Therefore, it can provide electricity whenever needed by an electric utility to meet consumer demand, performing like a traditional base-load power plant. CSP with thermal energy storage allows for more use of other renewable energy sources that provide variable or intermittent generation (such as wind and solar photovoltaic). Another distinction of CSP is its ability to integrate with fossil-based generation sources in “hybrid” configurations. Hybrid systems combine traditional fossil-fuel powered plants with emissions-free CSP technology to improve the performance of both systems. CSP is a key enabling technology in the “all-of-the-above” energy strategy for the India. The three key CSP technologies facilitating this shift to clean energy are
1. Parabolic Trough Image source:- www.homepower.com 2. Power Tower Image Source: - www.energy.gov 3. Thermal Energy Storage
Image Source: - www.mtholyoke.edu How Parabolic Trough Works Solar fields using trough systems capture the sun’s energy using large mirrors shaped like a parabola, or a giant “U,” that are connected together in long lines that track the sun’s movement throughout the day. When the sun’s heat is reflected off the mirror, the curved shape sends most of that reflected heat onto a receiver pipe that is filled with a specialized heat transfer fluid. The thermal energy from the heated fluid generates steam and electricity in a conventional steam turbine. Once the fluid transfers its heat, it is recirculated into the system for reuse. The steam is also cooled, condensed, and reused. Heated fluid in trough systems can also provide heat to thermal storage systems, which can be used to generate electricity at times when the sun is not shining. How Power Tower Works Power towers use large, flat mirrors called heliostats to reflect sunlight onto a solar receiver at the top of a central tower. In a direct steam power tower, water is pumped up the tower to the receiver, where concentrated thermal energy heats it to around 1,000 degrees Fahrenheit. The hot steam then powers a conventional steam turbine. In this case, the medium that transfers heat from the receiver to the power block is steam. Some power towers use molten salt in place of the water and steam. That hot molten salt can be used immediately to generate steam and electricity, or it can be stored and used at a later time. A large power tower plant can require thousands of computer-controlled heliostats that move to maintain point focus with the central tower from dawn to dusk. Because they typically constitute about 50% of the plant’s cost, it is important to optimize heliostat design; size, weight, manufacturing volume, and performance are important design variables approached differently by developers to minimize cost.
How Thermal Storage Works In a power tower that uses molten salt as the heat transfer medium, cold molten salt is pumped up the tower to the receiver, where it is heated, then flows to a hot storage tank. The hot salt then flows through a heat exchanger, where heat is transferred to water to produce the steam that spins the turbine. The molten salt then flows back to the cold storage tank. This hot molten salt retains its heat so well that it can be stored and used to generate electricity at later times. In a parabolic trough solar facility, the heat transfer fluid can be used not only to create steam, but also to heat molten salt stored in tanks near the power block. When the sun goes down, the hot molten salt (rather than the sun- heated fluid) generates steam and electricity. By placing the storage between the receiver and the steam generator, solar energy collection is no longer directly coupled to electricity generation. The sun remains a necessary component of the system, but the molten salt thermal storage enables the plant to continue reliably generating electricity for hours when the sun is not immediately available, such as in the evenings or during cloudy days. Ongoing Projects Although CSP has been in use since decades, however the first historical record of successful utilisation of this technology is accredited to Archimedes, Greek mathematician, who used concentrated solar power to push the evading enemy back home in 212BC. Now, CSP is considered an emerging renewable power with Spain leading the race more than 2500MW CSP power in production, followed by US with a capacity of around 1200MW. India ranks 4th across the globe with an installed capacity of 50 MW, used majorly for powering India’s mega kitchens. A detailed CSP project database is available at :- www.cspworld.org Implementing a CSP is not as easy as it seems, with its unique set of challenges this innovative technology is still in its nascent stage. Analysis of various CSP projects worldwide provided us with the following challenges: - 1. Capital Intensive: - CSP power projects are capital intensive, but have virtually zero fuel costs. Parabolic trough plant without thermal energy storage have capital costs as low as USD 4 600/kW, but low capacity factors of between 0.2 and 0.25. Adding six hours of thermal energy storage increases capital costs to between USD 7 100/kW to USD 9 800/kW, but allows capacity factors to be doubled. Solar tower plants can cost between USD 6 300 and USD 10 500/kW when energy storage is between 6 and 15 hours. These plant can achieve capacity factors of 0.40 to as high as 0.80. 2. Operations and maintenance (O&M): - O&M costs are relatively high for CSP plants, in the range USD 0.02 to USD 0.035/kWh. However, cost reduction opportunities are good and as plant designs are perfected and experience gained with operating larger numbers of CSP plants savings opportunities will arise. 3. High initial production cost: - The levelled cost of electricity (LCOE) from CSP plants is currently high. Assuming the cost of capital is 10%, the LCOE of parabolic trough plants today is in the range USD 0.20 to USD 0.36/kWh and that of solar towers between USD 0.17 and USD
0.29/kWh. However, in areas with excellent solar resources it could be as low as USD 0.14 to USD 0.18/kWh. The LCOE depends primarily on capital costs and the local solar resource. For instance, the LCOE of a given CSP plant will be around one-quarter lower for a direct normal irradiance of 2 700 kWh/m2 /year than for a site with 2 100 kWh/m2 /year. 4. Not enough CSP projects and data: - not enough data exists to identify a robust learning curve. However, the opportunities for cost reductions for CSP plant are good given that the commercial deployment of CSP is in its infancy. Capital cost reductions of 10% to 15% and modest reductions in O&M costs by 2015 could see the LCOE of parabolic trough plants decline to between USD 0.18 and USD 0.32/kWh by 2015 and that of solar power plants to between USD 0.15 to USD 0.24/kWh. 5. Economies of Scale: - Cost reductions will come from economies of scale in the plant size and manufacturing industry, learning effects, advances in R&D, a more competitive supply chain and improvements in the performance of the solar field, solar-to-electric efficiency and thermal energy storage systems. By 2020, capital cost reductions of 28% to 40% could be achieved and even higher reductions may be possible. 6. Choice of Technology: - Solar towers might become the technology of choice in the future, because they can achieve very high temperatures with manageable losses by using molten salt or thermostatic fluid as a heat transfer fluid. This will allow higher operating temperatures and steam cycle efficiency, and reduce the cost of thermal energy storage by allowing a higher temperature differential. Their chief advantage compared to solar photovoltaics is therefore that they could economically meet peak air conditioning demand and intermediate loads (in the evening when the sun isn’t shining) in hot arid areas in the near future. Conclusion For decades, researchers and scientists have explored methods to convert the endless energy potential of the sun into usable electricity. Today, many countries are harnessing the sun’s free and clean energy to power homes, businesses, and communities across the country. By deploying more solar energy capacity in the India and across the globe, we can reduce harmful carbon pollution and keep our air and water clean for future generations. The world is at the brink of shifting its energy economy from to one that is sustained on innovation and cleaner technologies. Energy economies of scale continue to drive down component costs, while policies continue to be developed to address soft-cost obstacles. Meanwhile, developers, investors, and lenders are utilizing financing mechanisms to reduce barriers to obtain funding for solar projects at commercial scale— particularly for leading- edge projects that employ innovative technology. With help from DOE, the United States is becoming a global solar leader, developing and introducing innovative technologies into the marketplace to make clean energy affordable for all Indians.