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Renew | April 2014

Concentrated efforts

With an aim to establish green growth, efforts are being made to harness solar power. But will the Concentrated Solar Power technology manage to achieve its targets?

While the country is trying hard to develop solar power that will help India produce clean energy and contribute to reducing emissions per unit of GDP by 20-25% by 2020, over 2005 levels, Concentrated Solar Power (CSP) is yet to prove its worth with most of the projects running behind schedule. Unlike Photovoltaic as a technology for solar power generation which has struck a chord with developers in India, the challenges of tying up funding, sourcing technologies, unreliable solar radiation data are the main reasons for the CSP story going sour in the country. Globally too, the profitability of CSP technology is raising question marks.

India has sufficient land area with high resource (DNI) for CSP to make a major contribution to its energy mix, along with the will to make this happen. The main enabler for photovoltaic and CSP projects is the Jawaharlal Nehru National Solar Mission, (JNNSM), launched by PM Manmohan Singh in January 2010. It focuses on a target of 20 GW of solar capacity by 2022.

As energy experts point out, what goes against this technology is its current high cost of electricity produced, particularly where the external costs of fossil fuel combustion are not reflected in electricity pricing. The massive upfront need for capital investment further makes it a challenge for CSP technology adoption.

According to a World Bank report, in CSP, where local manufacturing is more complex, India has not been able to manufacture some critical components. Either technology suppliers are limited and their products patented or the lack of natural resources poses an impediment. India should therefore seek to define and develop its manufacturing capabilities in specific parts of the value chain where it enjoys a comparative advantage and can emerge as a globally competitive producer. An earlier ESMAP-World Bank study, Development of Local Supply Chain: A Critical Link for Concentrated Solar Power in India has identified the potential for reducing the costs of CSP components in India through local domestic manufacturing.

Industry players feel that there is a need for a more coordinated and guided approach from the government, in terms of more upfront project preparation before bidding, to move the industry forward in the desired direction. World Bank analysis suggests sound technical due diligence of bidders should be undertaken as a pre-qualification exercise. The relatively long development time of the CSP projects in India stems in part from lack of expertise of the EPCs and lead members of the consortia.

CSP technology
CSP technologies use systems of mirrored concentrators to focus direct beam solar radiation to receivers that convert the energy to high temperature for power generation. There are four main configurations that are commercially available - Parabolic Trough, Linear Fresnel, Paraboloidal Dish and Central Receiver. Typically, this heat is transformed to mechanical energy through a steam turbine and then into electricity. CSP has advantages compared to photovoltaics as it can readily incorporate thermal energy storage and/or fossil fuel boosting to provide dispatchable power. The use of relatively low tech manufacturing methods for solar collector fields, together with the use of steam turbine technologies adapted from the existing thermal power generation industry, makes the prospect of continued, rapid scale-up of CSP capacity very feasible.

Concentrated Solar Power: Attributes
Solar Field
Concentrates solar energy and converts it into heat stored in a medium such as oil or steam. Key components mirrors, absorber tubes or receiver towers, structures, heat transfer fluid, tracking equipment, pumps, piping, medium such as molten salts and storage tanks. Power Block: Uses the medium heated in the solar field to run a turbine and produce electricity. Key components include heat exchangers, steam turbine, generator, control systems and cabling.

Thermal Energy Storage
When used with storage (usually through molten salt technology), CSP can be configured to generate electricity after the sun sets. Storage allows CSP to address both peak and off-peak power.

When used in conjunction with a conventional coal or gas plant, thermal industrial systems or with renewable sources such as biomass, CSP can be configured to use the existing plant's turbines to cost-effectively increase its efficiency and reduce the carbon footprint.

Thermal energy storage and hybridisation allow energy from CSP to be decoupled from immediate solar resource availability. This allows electricity to be despatched on demand, when it is needed the most. Because India's electrical demand peaks after susnset, CSP with storage can play an important role in the country's electrical mix. Grid Flexibility
CSP with storage also builds up grid flexibility and enhances the grid's capacity to accept a larger fraction of energy from variable output from energy sources such as wind and PV, whose output varies with wind intensity and solar irradiation. Connecting CSP plants to grid sub-stations allows for a greater share of wind energy.

Concentrated Solar Power: The challenges
Capital Cost Premium
The cost of a parabolic trough CSP plant in India ranges from Rs 10.5 crore to Rs 13 crore per MW in capital cost. Storage increases the capital cost further but also increases electricity generation. Energy cost optimisation over the lifetime of a CSP plant depends on power tariffs, solar resource, cost of storage and system configuration.

Limited Implementation Record
Parabolic trough is the most mature CSP technology, and more than 80 per cent of CSP plants in operation or under construction globally use this technology. In contrast, linear fresnel and power tower plants are relatively less mature, with less than 100 MW each of global installed capacity. Indian developers have limited CSP experience.

Environmental Concerns
CSP plants require water predominantly for cooling, and also for cleaning. A CSP plant's cooling water requirement is similar to a coal-based plant. Locations suitable for CSP are usually arid regions with a short supply of water. Technology choices to reduce CSP's water demand are available, but affect the levelised cost of electricity. Most water-efficient technologies reduce consumption by 90 per cent, but result in an 8 per cent to 9 per cent increase of electricity tariff.

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