Prospects of Concentrating Solar Power (CSP ...

Compendium of National Training Programme On RETScreen International Software for Evaluationof Renewable Energy Projects

Prospects of Concentrating Solar Power (CSP) Generation in India Shashaank Shekhar, M. Tech Student, TERI University and Ishan Purohit , General Manager, Lahmeyer International India (Pvt.) Ltd. Concentrating solar power (CSP) is a large-scale, commercial way to generate electricity through solar energy; and can provide low carbon, renewable energy resources in countries or regions with strong direct normal irradiance (DNI), i.e. strong sunshine and clear skies. CSPsystems comprise concentrated solar radiation as a high temperature thermal energy source to produce electrical power. These technologies are appropriate for the areas where direct solar radiation and number of clear sunny days in the year are high. CSP can provide a reliable source of electricity generation in the regions with strong direct normal irradiance (DNI). In sunniest countries, CSP is tipped to become a competitive source of bulk power in peak and intermediate loads by 2020, and of base-load power by 2025 to 2030. The first commercial CSP parabolic trough system was built in the late 1980s in California. It has produced an accumulated total electricity generation of more than 15 TWh during the last 20 year. The present cumulative installed capacity of CSP plants has grown to 1.17 GW and is further rising as capacity of around 1,800 MW is reported under construction. Capacities over 15,000 MW have been announced in different parts of the world. With incentive schemes, new commercial CSP plants have been built in Spain and several CSP projects are under way. The International Energy Agency (IEA) projects that by 2050, CSP plants would supply up to 11.3% of global electricity. India has targeted 10000 MW capacity of CSP projects across the country by 2022 under Jawaharlal Nehru National Solar Mission JNNSM); in which around 500 MW capacity CSP projects are under construction under the Phase-I. This communication is focused towards the aspects of large scale development, deployment and dissemination of concentrating solar (thermal) power technologies in India from the point of view of the resource and infrastructure availability, appropriateness of the technologies, financial attractiveness and policy & regulatory aspects. The technicality of the projects has been carried out with the optimum information of DNI availability in context of India.

1. Introduction In the language of Physics, Light is described by two theories namely wave theory and the particle theory (Figure-1). The wave theory describes light as electromagnetic waves of various frequencies; whereas particle theory describes light as photons (a particle representing a quantum of light or other electromagnetic radiation) traveling in straight line. Solar radiation is radiant energy emitted by the sun, particularly electromagnetic energy. It is an enormous resource that is readily available in all countries throughout the world, and all the space above the earth. The Earth receives 174 petawatts (PW) of incoming solar radiation at its upper atmosphere. From which approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses.

Corresponding Author Concentrating Solar Power (CSP) comprises solar thermal power generation as well as Concentrating Solar Photovoltaic. In this article CSP comprises solar thermal power generation only.

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Figure 1. Particle and wave nature of light The solar radiation spectrum at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. The spectral distribution of sun indicates (Figure-2) that its surface temperature reaches approximately 5,778 K, which means that solar energy has a very high Exergy (i.e. Available Energy). The intensity of solar radiation at the sun is about 63 MW/m2, but the big distance to be covered lead to a high dilution of the flux, making it possible only around 1 kW/m2 to get to Earth which explains that the solar radiation by itself would supply low temperatures to a thermal fluid, making it necessary to incorporate a concentration ratio of the radiation received in order to get higher solar fluxes/intensities.

Figure 2. Spectral distribution of solar radiation The solar photovoltaic (SPV) cells essentially convert the incident light directly into electricity; however this phenomenon is described using the Particle theory in which the incident photons (light particles) strike on the solar PV cell (made of special grade silicon - a semiconductor) and "knock off" the electrons. These "free" electrons start flowing through a circuit forming an electrical current.

Thermodynamically, the Exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat source.

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There are two ways to generate electricity from light (solar radiation) energy; first converting it into electricity through direct conversion using photovoltaic devices and second by concentrating the incident light rays onto a small surface to produce heat and use that heat to drive a turbine, which in turn drives a generator producing electricity. Solar PV technologies are limited up to decentralized energy generation and large scale grid connected power plants; however there is a wide range of applications of thermal energy generated through solar namely cooking, water/space heating, desalination, process heating etc. up to high grade applications like steam generation for industrial processes to power generation using steam turbines. As solar energy is a dilute energy source hence large scale concentrating collectors are required for high temperature applications like power generation. CSP comprises the heat component of the light; and the phenomenon is described using the Wave theory. When electromagnetic waves are incident on various surfaces, they are mainly absorbed or reflected or they just pass-through the surface; and heat is produced through absorbed waves by the surface. If large amount of "concentrated" waves hit a surface then a large heat is produced which produces a "super-critical" steam and a very high pressure is developed. This "dry" steam at a high pressure drives the steam turbine, which in turn drives an electrical generator to produce electricity (Figure-3).

Figure 3. Schematic diagram of a typical Concentrating Solar Power project CSP plants have a long standing history. As early as 1890, a steam engine was powered by a solar concentrating collector. In 1912, the first solar thermal power plant (500 kW) with Parabolic Trough collectors became operative in Egypt. Unfortunately, the availability of cheap fossil fuel during the 20th century led to decline in interest in solar power plants. However, the oil crisis in the 1970’s caused a resurrection of solar technology. As a result, several research centers were established, mainly in Europe and the USA, to develop new concepts and bring market ready Solar Thermal plants to commercial operation. The 10 MW Solar-One power tower was developed in Southern California in 1981, but the parabolic-trough technology of the nearby Solar Energy Generating Systems (SEGS), begun in 1984, was more workable. The 354 MW SEGS is still the largest solar power plant in the world.

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CSP is being widely commercialized, with about 1.17 Gigawatts (GW) of CSP plants online as of 2011, out of which 582 megawatts of them are located in Spain, and the United States has 507 megawatts of capacity. About 17.54 GW of CSP projects are under development worldwide, and the United States leads with about 8.67 GW. Spain ranks second with 4.46 GW in development, followed by China with 2.5 GW (Figure -4). One of the biggest benefits of CSP is its ability to store thermal heat which ensures continuous supply of power even when the sun is down and when it gets cloudy. Globally, the technology is being used only in the US and Spain at just a few locations. India, with plans to install 550 MW of CSP by 2013, could emerge a major player in this area.

Figure 4. Global installed capacity of CSP Projects (Source: Concentrating Solar Power in India, IT Power, 2011)

2. Technology Options CSP is a proven technology. Conceptually CSP technologies are of two categories; first the line focusing and second the point focusing (Figure-5). Four main configurations of CSP technologies are commercially available; Parabolic Trough Collector (PTC) Central Receiver System (CRS) Linear Fresnel Reflector (LFR) Parabolic Dish-Engine System Out of above four options the PTC and LFR reflect the incident solar radiation to a linear focus and continuously move the mirrors in one axis to keep the sun focused on the receiver (located at the line focus). However the CRS and Parabolic Dish technologies reflect the solar radiation on point focus and require continuous movement of the reflectors in two-axis.

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Figure 5. Classification of CSP technologies (Source: CSP Global Outlook 2009, report of Greenpeace) As compared with the line focus systems the temperature attainability of point-focus systems is higher hence CRS and parabolic dish system operate at higher temperatures and shows high efficiencies of power generation. The indicative comparative effectiveness of above CSP technologies are presented in Figure-6.

Figure 6. Comparative effectiveness of CSP technologies (Source: ESMAP-World Bank report on CSP, 2010)

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In addition to the CSP technologies there are also non-concentrating solar power systems: Solar Chimney Solar Pond Besides direct irradiation, the non-concentrating systems can also use the diffuse share of solar irradiation. Solar Chimney and Pond technologies are still research stage and not commercialized.

2.1 Parabolic Trough Collector (PTC) Parabolic trough-shaped mirror reflectors are used to concentrate sunlight on to thermally efficient receiver-tubes placed in the trough’s focal line. The troughs are usually designed to track the Sun along one axis, predominantly north–south. A Heat Transfer Fluid (HTF), such as synthetic thermal oil, is circulated in these tubes. The fluid is heated to approximately 400°C by the sun’s concentrated rays and then pumped through a series of heat exchangers to produce superheated steam. This is called a two circuit system due to the two fluids (oil & water) circulating through the plant. Synthetic oil is the most suitable HTF for the current project conditions and represents the state-of-the-art. It has proven good long term reliability at the SEGS plants in California, USA. Alternatively mineral oil, water or molten salt can be used as HTF. The steam is converted to electrical energy in a conventional steam turbine generator, which can either be part of a conventional steam cycle or integrated into a combined steam and gas turbine cycle.

2.1.1 Case Study – 1 SOLNOVA- 4 (Commercial CSP project based on Parabolic Trough Technology) Project Name Location Owner(s) Technology Turbine Capacity Status Land Area Solar Resource (DNI) Solar-Field Aperture Area Solar-Field Outlet Temp Output Type Power Cycle Pressure

Solnova-4 Sevilla, Spain Abengoa Solar Parabolic trough collector (PTC) Net: 50.0 MW Gross: 50.0 MW Operational since 2009 115 hectares 2,012 kWh/m2/yr 300,000 m² 393°C Steam Rankine 100.0 bar Wet cooling 113,520 MWh/yr (Expected/Planned)

Cooling Method Electricity Generation

(Photo Source: http://informeanual.abengoa.com)

2.2 Central Receiver System (CRS) In CRS solar power plant, an array of heliostats (i.e. large individually-tracked mirrors) is used to concentrate the sunlight, whilst a heat transfer medium in this central receiver absorbs the highly concentrated radiation and converts it into thermal energy to be used for the subsequent generation of superheated steam for turbine operation.

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The HTF medium in this central receiver absorbs the highly concentrated radiation reflected by the heliostats and converts it into thermal energy, which is used to generate superheated steam for the turbine. To date, the heat transfer media demonstrated include water/steam, molten salts and air. If pressurized gas or air is used at very high temperatures of about 1,000°C or more as the heat transfer medium, it can even be used to directly replace natural gas in a gas turbine, making use of the excellent cycle of modern gas and steam combined cycles.

2.2.1 Case Study – 2 Gemasolar Thermo-Solar Plant (Commercial CSP project based on Central Receiver System Technology) Project Name Location Owner(s) Technology Turbine Capacity Status Land Area Solar Resource (DNI) Solar-Field Aperture Area Heliostat Tower Height Receiver Outlet Temp Output Type Thermal Energy Storage Cooling Method Electricity Generation

Gemasolar Thermosolar Plant (Gemasolar Fuentes de Andalucía (Andalucía (Sevilla)), Spain MASDAR (40%) Sener (60%) Central Receiver System (CRS) Net: 19.9 MW Gross: 19.9 MW Operational since 2011 195 hectares 2,172 kWh/m2/yr 304,750 m² 2650 Nos. of 120 m2 each 140 m 565 oC Steam Rankine Two tank storage of 15 hours Wet cooling 110,000 MWh/yr (Expected/Planned) (Photo Source: http://climateadaptation.tumblr.com/)

2.3 Linear Fresnel Reflector (LFR) A Fresnel lens is a type of lens invented by the French physicist Augustine-Jean Fresnel in 1819. Originally it was designed for lighthouses. It enables the construction of lenses with large aperture and short focal length. An array of nearly-flat reflectors concentrates solar radiation onto elevated inverted linear receivers. Water flows through the receivers and is converted into steam. This system is line-concentrating, similar to a parabolic trough, with the advantages of low costs for structural support and reflectors, fixed fluid joints, a receiver separated from the reflector system, and long focal lengths that allow the use of flat mirrors. The technology is seen as a potentially lower-cost alternative to trough technology for the production of solar process heat. One of the most important features of the Fresnel lens is the reduction of required material compared to a conventional spherical lens by breaking the lens into a set of concentric annular sections, also known as “Fresnel zones”.

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2.3.1 Case Study – 3 Puerto Errado-1 Thermosolar Power Plant - (Commercial CSP Project based on Linear Fresnel Reflector Technology) Project Name

Location Owner(s) Technology Turbine Capacity Status Land Area Solar Resource (DNI) Solar-Field Aperture Area Solar-Field Outlet Temp Output Type

Power Cycle Pressure Cooling Method Electricity Generation

Puerto Errado 1 Thermosolar Power Plant (PE1) Calasparra (Murcia), Spain Novatec Solar España S.L. (100%) Linear Fresnel reflector Gross: 1.4 MW Operational since 2009 5 hectares 2,100 kWh/m2/yr

270°C Line length = 806m, mirror width in line = 16m, Total lines = 2 55.0 bar Dry Cooling 2,000 MWh/yr (Expected/Planned)

(Photo Source: http://en.wikipedia.org)

2.4 Parabolic Dish A paraboloid dish-shaped reflector (commonly called as parabolic dish) concentrates sunlight on to a receiver located at the focal point of the dish. The concentrated beam solar radiation is absorbed into a receiver to heat a fluid or gas (air) to approximately 750°C. This fluid or gas is then used to generate electricity in a small piston or Sterling engine or a micro turbine, attached to the receiver. The parabolic dish is designed to track the Sun along both axis, predominantly north– south and east-west. Dishes offer the highest solar-to-electric conversion performance of any CSP system. Several features – the compact size, absence of cooling water, and low compatibility with thermal storage and hybridization – put parabolic dishes in competition with PV modules, especially concentrating Photovoltaics (CPV), as much as with other CSP technologies. Very large dishes, which have been proven compatible to thermal storage and fuel backup, are the exception.

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2.4.1 Case Study – 4 Maricopa Solar Project - (Dish Sterling) Project Name Location Owner(s) Technology Turbine Capacity Status Land Area Solar Resource (DNI) Solar-Field Aperture Area Cooling Method

Maricopa Solar Project (Maricopa) Peoria, Arizona, USA Tessera Solar Dish/Engine Gross: 1.5 MW Operational since 2010 15 acres

60 No of Dishes manufactured by Stirling Energy Systems (SES) The SunCatcher does not use water for electricity generation or cooling cycles.

(Photo Source: http://www.roselawgroup.com)

Apart from above four concepts of CSP technologies few alternatives are also available namely typical CSP in hybrid mode through Integrated Solar Combined Cycle (ISCC), Multiple Tower CRS systems etc. The mutual comparability of above four CSP technologies is given in Table 1.

Characteristic

Unit

Plant power Annual capacity factor Focus Type Peak efficiency Annual net efficiency (solar to electric) Maximum cycle temperature Cycle

MW %

Optical concentration ratio (from collector) Area collector/ heliostat

% %

Table 1. Characteristics CSP Technologies Parabolic Power Tower LFR Trough 30-300 100-200 1-100 23-56 20-78 20-25 (without storage) Linear Point Linear 20 19-23 10 11-16 7-20 8-10

Parabolic Dish 5-25 24-25 Point 29.4 12-32

o

300-400

585oC

150-500oC

800

-

Steam Rankine/ Bryaton (Gas turbine)

Steam Rankine/ Organic Rankine

Sterling/ Steam Rankine/ Brayton

-

Steam Rankine/ Organic Rankine 28:1

100:1 -More

8-1

500:1 – 50:1

m2

34-550

40-120

-

92

C

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Characteristic

Unit

Receiver absorptive Receiver efficiency Thermal storage Land requirement Cooling process

Hours m2/MW -

Water consumption Installed generating capacity till 2010 Commercial maturity

m3/MWh MW

Parabolic Trough 0.94-0.99 1-12 40000 Closed circuit 2.9-3.5 943

Power Tower

LFR

> 0.94 7-15 83600 Close circuit

0.94-0.99

2.8 38

2.9-3.5 8 .0

1-12 18000 Closed circuit

Parabolic Dish >0.95 0.90 Not possible 16000 Direct in the power cycle 0.0 1.5

High Medium Medium Low (Source: Global Concentrator Solar Power Industrial Report 2010, CSP Today)

3. CSP Technology Requirements It is well established that solar energy is a dilute source of energy; hence requires more area to collect it for conversion for high temperature attainability and further applications like power generation. From the point of view of CSP technologies, their feasibility is dependent on several parameters.

3.1 Resource Availability- Solar Radiation Resource availability is essentially the soul of project. In case of renewable energy power projects resource assessment becomes most important exercise due to intermittent nature of the renewable energy sources as they varies with location and season of the year and non-uniformly distributed across the globe. Solar energy power applications utilize different types of irradiation in order to convert them into electric energy. For solar PV applications the Global Horizontal Irradiation (GHI) is the solar resource to consider; which is essentially the sum of the direct and diffuse components of solar radiation. The CSP technologies are sensitive for the direct component of GHI which is possible to treat optically and could be focused at any line or point. The intensity of direct component of solar radiation at normal incidence is known as Direct Normal Irradiance (DNI) which comprises the direct sunrays, and is the component to take in consideration for all kind of CSP projects. The DNI over any location is governed by the diffuse component of the GHI. In order to identify regions suitable for CSP projects a long term measured data of at least 10 years is advisable. A straight forward approach to identify the aforementioned high potential regions is screening solar irradiation maps (GHI and DNI) and choosing the regions with the best solar irradiation based on the ground measurements. Based on the best practices the solar resource in the regions of interest should exceed the following minimum requirements: PV: annual sum of GHI > 1000 kWh/m² (preferably above 1600 kWh/m²) CSP: annual sum of DNI > 1900 kWh/m² (preferably above 2100 kWh/m²) Availability of long term measured DNI is the biggest barrier in India towards large scale implementation of CSP projects. In India, Indian Meteorological Department (IMD) maintains a large network of weather stations across the country; however the measurement activities are limited to GHI and other meteorological parameters only. In fact the measured values of diffuse solar radiation are not available for most of the places. In case of unavailability of long term ground data the satellite data is the other option which might be of various resolutions. Presently in context of India several satellite databases are available namely NASA, NREL, SWERA, SOLEMI, 3TIER, SolarGIS, METEONORM etc. which are either purely satellite data or the data generated through interpolation of satellite and ground data. Various databases refer different ranges of DNI over India. The Solar Energy center (SEC) of Ministry of New and Renewable Energy (MNRE) with National Renewable Energy Laboratory of USA has developed GHI and DNI maps of India based on satellite data; which reflects the north-western parts of India (Gujarat and Rajasthan states) receives annual DNI from 1800 kWh/m2 to 2100 kWh/m2; however other satellite databases gives different values. 85


3.2 Land Requirement Selection of the suitable site for implementing CSP project is one of the most important exercises which essentially comprise the detailed study of; Land, Meteorology and Infrastructure etc. (Figure-7)

Figure 7. Site assessment for implementing CSP project (Source: Empower, KfW) All CSP technology requires different amount of land per MW depending upon the availability of DNI. Essentially the amount of land required for PTC based CSP project without any thermal energy storage has been reported as 2 ha/MW. Different numbers have been reported in different sources which varies from 6 acres/MW to 10 acres/MW for PTC and higher for CRS technology. In order to make site assessment for CSP projects an average approach of 8-10 acres/MW is essentially adopted for selection. The site selection must address the following dimensions techno-commercially; Meteorology- DNI availability, micro-climatic pattern, local climate etc. Land- Topography, Availability, Ownership, land cover and use, exclusions and risks (seismic, flood etc.) Infrastructure- accessibility, connectivity, water availability, construction power/water, communication, Gas/fuel pipe line (in case of hybrid system) power evacuation facilities etc. However the land need to be free of obstacles (i.e. buildings, trees, hills, mountains, transmission lines, etc.) which can shade the modules or collectors of the solar plant, Free from underground infrastructure (pipes, cables, channels, tunnels, etc.). The maximum up to 2 - 3° or lower than 3 - 5% equator facing slope is recommended for CSP projects depending upon the soil conditions and grading level; however for CSP using PTC technology, shape of land should be rectangular, with minimum North-South elongation of at least 700 m. The land related details of few operational CSP projects are given in Table-2 for all above technologies. Table 2. Land requirement of few operational CSP projects CSP Project

Andasol-1

Extresol-1

Solnova-1

Nevada Solar One

Location (Place/ Lat-Long) Granada, Spain (37°13 3°4 Badajoz, Spain (38°4

PTC

Project Cap. (MW) 50

PTC

50.0

200

2168.0

Sevilla, Spain (37°26 6°14 Nevada, (35°48 114°59

PTC

50.0

115

2012.0

Thermal Energy Storage 2-tank indirect of 7.5 hours 2-tank indirect of 7.5 hours NO

PTC

75.0

162

2606.0

0.5 hours

CSP Tech.

Total land (hect.) 200

Annual DNI (kWh/m2) 2136.0

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Solar Field Aperture Area (m2) 510,120

357,200

510,120

300,000


CSP Project

Planta Solar10 Planta Solar 20 Gemasolar Thermosolar Plant Sierra SunTower Kimberlina Solar Thermal Power Plant Puerto Errado 1 Thermosolar Power Plant Puerto Errado 2 Thermosolar Power Plant Maricopa Solar Project

Location (Place/ Lat-Long)

CSP Tech.

Sevilla, Spain (37°26 6°14 Sevilla, Spain (37°26 6°14 Fuentes de Andalucía, Spain (37°33 5°19 California, USA, (34°46 W) California, USA (35°34 119°11

CRS

Project Cap. (MW) 11.0

Total land (hect.) 55

Annual DNI (kWh/m2) 2012.0

Thermal Energy Storage 1.0 hour

Solar Field Aperture Area (m2) 75,000

CRS

20.0

80

2012.0

1.0 hour

150,000

CRS

19.9

195

2172.0

15 hours

304,750

CRS

5.0

NA

2629.0

NO

27,670

LFR

5.0

12

NA

NO

26,000

Calasparra, Spain (38°16 1°36

LFR

1.4

5.0

2100.0

NO

Line length = 806 m Line width = 16 m Lines = 2

Calasparra , Spain (38°16 1°36

LFR

30.0

70

2,095.0

NO

Line length = 940 m Line width = 16 m Lines = 28

Arizona, USA (33°33 112°13

Dish/ Engine

1.5

6.0

NA

NO

60 dishes of Stirling Energy Systems (SES)

(Source: www.nrel.gov.in)

3.3 Thermal Energy Storage (TES) CSP projects comprise a typical characteristic of daily and seasonal variation of the energy yield from solar field. Consequently, the energy output of the plant fluctuates and the power block size is either too big or too small for most time of the year. In order to make CSP more dispatchable the CSP projects can easily be coupled with thermal energy storage (TES) which can significantly increase the value of electricity delivered to the grid both in terms of capacityrelated and energy-related services (Figure-8). Combining TES system with CSP project the size of the power block can be reduced while the annual production is almost maintained however the actual output depends on the ratio of storage to solar field to turbine size. A proven form of storage system operates with two tanks (with PTC technology). The storage medium for high-temperature heat storage is molten salt; which contain liquid potassium and sodium nitrate as cheap mineral salts that are normally used in synthetic fertilizer production.

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Figure 8. Typical output of a CSP project with TES

The partial loading of power block is greatly reduced by integrating a TES system in the CSP plant design as well as the intermittent fluctuations on the power production due to passing clouds can be eliminated. The approach also gives a higher flexibility for using the optimal tariffs (if available) and, if TES is large enough, it will even allow night time operation. The TES system also provides a high flexibility in time and fuel such as e.g. natural gas or biomass for the use of the auxiliary heating system in CSP projects. Following TES options are available for CSP projects; Molten Salt Storage (One or Two Tank) Thermo-cline Storage with Molten Salt and Filler Materials Concrete Storage Systems Storage by Phase Change Materials DISTOR Concept (Energy Storage for Direct Steam Solar Power Plants) Steam Storage Systems Oil Storage Systems

4. Technology Trends PTC technology is the most commercialized CSP option till date as it consists of around 88 percent of the total operational CSP projects by the year 2010. However ISCC with PTC is also being well adopted by the market. (Figure 9).

Figure 9. Technology status of CSP projects (operational) (Source: http://en.wikipedia.org/wiki/List_of_solar_thermal_power_stations)

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It has been analyzed that the share of PTC is increasing as it consists of around 93% of the CSP projects under construction. (Figure 10). Due to provenness of PTC technology and its suitability with thermal energy storage as well as with hybrid systems its commercialization is faster than other options. Worldwide the most of the established manufacturers are offering the PTC technology.

Figure 10. Technology status of CSP projects (under implementation) (Source: http://en.wikipedia.org/wiki/List_of_solar_thermal_power_stations)

5. Costs CSP is considered to be an essentially proven technology that is at an early stage of its cost reduction curve. Although CSP requires a high capital investment it offers long-term benefits because of lower operational costs. Furthermore, initial investment costs are likely to fall steadily as plants get bigger, competition increases, equipment is massproduced, technology improves and investor confidence in the technology grows. A period of exponential growth in installed capacity together with an exponential decay in cost of energy produced is confidently predicted by the industry. There are wide ranges in the current understood installed cost of CSP systems globally; however actual costs will be technology and project specific (Figure-11). A recent roadmap published by the International Energy Agency, USA for CSP technology presents a highly credible summary of the global situation and way forward. The CSP industry has recommended growth since 2005 with its credibility on 20 years of successful operation on large-scale parabolic trough projects.

Figure 11. Detailed cost breakup of a typical CSP projects (PTC technology) with TES (Source: http://en.wikipedia.org/wiki/List_of_solar_thermal_power_stations)

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As per the CSP roadmap of IEA in 2010 a high credibility summary of global situation and way forward has been presented. The global STPG is projected to grow up to 4700 TWh per year by 2050 with Levalised Energy Costs dropping from US$200/MWh to $40/MWh over the period; with half of the cost reduction achieved over the next 10 years. (Figure-12 & 13).

Figure 12. Growth of CSP Production by Region (TWh/Year) (Source: CSP Roadmap of IEA, 2010)

Figure 13. DNI vs. levelised electricity cost from CSP (Source: CSP Roadmap of IEA, 2010)

6. Scenario of CSP Deployment in India India’s first demonstration CSP project has been implemented at Solar Energy Center (SEC), of MNRE at Gwalpahari (Haryana) of the capacity of 50 kW for Research and Development purposes with German Collaboration. Further for R&D in hybrid mode this project has been combined with biomass gasifier in collaboration with The Energy and Resources Institute (TERI). Further a lot of efforts have been made by MNRE towards commercialization of high temperature solar energy systems but power generation target was not achieved. However high temperature attainability has been received by number of solar systems like Arun Dishes, Gadhia Solar Dishes, Shafler Dishes etc. and successfully demonstrated for industrial process heating applications. The most well-known attempt at establishing utility-scale CSP in India, centred on a proposal for Mathania (Jodhpur), Rajasthan. The CSP project was proposed in integrated Solar Combined Cycle (ISCC) mode; with an average Solar yield of about 35 MW and a fossil field of maximum 3 times the solar field capacity, the total output of around 140 MW. It was proposed to be based on the integrated operation of the PTC plant with a combined cycle gas turbine using fossil

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fuels such as Naphtha, fuel oil or low sulphur heavy stock (LSHS) with an expected capacity factor of 80%. The Mathania CSP project in ISCC mode was designed at solar field of PTC of 219000 m2 to support 35 to 40 MW CSP plant involving two gas turbines each connected the Heat Recovery Steam Generator (HRSG) and a steam turbines connected to both HRSG. This project has not been implemented till date even financially pushed by GEF as well. The main enabler for solar photovoltaic and STPG is Jawaharlal Nehru National Solar Mission (JNNSM) of National Action Plan of Climate Change (NAPCC) of Government of India, which focuses a target of 20 GW of solar power projects capacity by 2022. In its first Phase, 1000 MW grid connected solar power is targeted by 2013 with an approximate 50:50 split between STPG and SPV. The trading arm of M/s NTPC, the NTPC Vidyut Vyapar Nigam Ltd. (NVVN) has been given responsibility for implementing Phase-I. M/s NVVN is offering a 25 year Power purchase Agreement (PPA) for successful solar mission projects at a preferential tariff. Presently 500 MW capacity STPG projects are under construction under JNNSM across the country. Following dimensions are in favor of promoting CSP in India; Renewable Energy Framework Jawaharlal Nehru National Solar Mission Clean Development mechanism Problem on Coal Linkages for thermal power projects Renewable purchase obligation (RPO) of states State’s Solar Power Policies Industry Capability In the year 2009, Ernst & Young rated the attractiveness of various countries for renewable energy investments and ranked India as fourth (after USA, Spain and Italy) in the world for STPG investment attractiveness and scored well above the fifth places country, Australia. There are few barriers towards large scale commercialization of STPG in India; Project Cost Financing Long term DNI data availability Policy risks Land allocation Power evacuation facilities Technology shortcomings Manufacturing scale-up in India Central Electricity Regulatory Commission (CERC) has carried out the capital cost benchmarking of CSP projects in context of India considering the cost trends of various international projects (operational as well as under construction) based on different CSP technologies for arriving at the benchmarking. CERC has benchmarked the cost of CSP projects (without any thermal energy storage) as Rs 13 Cr/MW for the financial year (FY) 2012-13; however it was determined as Rs 15 Cr/MW for FY 2011-12. The cost of STPG projects in India might be lower as compared with their international prices due to possibility of indinization of several equipments (viz. major components of power block, structures of solar field etc.), land (wasteland of deserts owned by Government) and workmanship (cheap labor cost) etc.

7. Feasibility of CSP in India In order to determine the tariff for any financial year CERC make the financial analysis on a flat capacity utilization factor (CUF) of 23 % for all CSP technologies across the country. Similar approach has been adopted in the policy guidelines of JNNSM. It is well established that the technical performance of any CSP project is essentially governed by the availability of annual DNI over any location. However the specific technology and aspects of using TES and hybrid could make significant impact on the system performance. In order to address the feasibility of CSP in India a preliminary exercise has been carried out for several locations covering most of the parts India.

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7.1 DNI Availability Designing of CSP projects is much complicated than the Solar PV projects as is comprise DNI as solar resource for operation. In order to design large scale CSP projects a time series measured data at least of 10-12 years is preferred, which could be statistically processed to generate a reference year or develop a typical meteorological year (TMY) weather data file. Long term measured data gives the high degree of reliability of the energy yield estimations (Figure14).

Figure 14. Uncertainty reduction with long term DNI-Data (Source: S. Lohmann, Solar Energy 80 (2006), Deviation from 18-year mean) Unavailability of long term ground data of DNI over potential location of India is one of the major barriers towards large scale deployment of CSP projects. Indian Meteorological Department is limited to measurement of global horizontal irradiance (GHI), diffuse horizontal irradiance (DHI) at few locations, sun shine hours and other meteorological parameters. Recently MNRE has started a large program towards measurement of DNI across the potential regions of India and implemented 51 automatic weather stations across the country and the data is being processed by Center for Wind Energy Technology (CWET). Recently MNRE has published a database entitled ‘Solar radiant Energy over India’ in association with IMD; in which long term measured values of GHI and DHI over 23 locations have been presented in monthly average daily format. The DNI could be estimated mathematically through the difference GHI and DHI and established earth-sun angles relationships. In case of non availability of ground (measured) data the long term satellite data is preferred; which is available for most of the Indian locations through various satellite databases. However the accuracy of satellite data is governed by the resolution. Following satellite databases provided DNI data over India; NASA (National Aeronautics and Space Administration) satellite through Surface meteorology and Solar Energy NREL (National Renewable Energy Laboratory) Satellite through SEC-NREL link SWERA (Solar and Wind Energy Resource Assessment) satellite database of UDEP

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All these databases show the inter-variance in the data due to their resolution. The limitation of above databases is that they are not available in hourly formats but in monthly average daily sets; however in order to estimate realistic energy outcome through CSP projects hour-to-hour analysis is preferred. There are few databases which offer the time series data over any location either through high resolution satellite data or interpolation of ground and satellite data namely 3TIER, Solar GIS, Solemi, METEONORM etc. In order to carry out the DNI assessment over India all referred data source have been explored and their inter comparability has been assessed. (Figure -15). The DNI assessment has been carried out over 23 reference locations for which long term GHI and DHI data of IMD is available. The DNI through GHI and DHI values of IMD has been estimated for their average daily values, as the NASA, NREL and SWERA data is available in monthly average daily formats.

Figure 15. DNI Assessment over representative locations of India In order to carry out the reliable energy yield estimation and system designing of large scale solar power projects it is preferred to use time series data of multiple years or reference year. Out of above sources only METEONORM gives the long term DNI data in time series (hourly) format. However its accuracy is supposed to be better than other satellite databases as it determines the DNI through interpolation of satellite and ground data. Therefore for energy yield estimation METEONORM has been selected.

7.2 Technical Assumptions and System Sizing The technical evaluation has been carried out using computer software namely ‘System Advisor Model (SAM)’ for performance simulation and energy yield estimations. SAM, originally called the "Solar Advisor Model" was developed by the National Renewable Energy Laboratory (NREL) in collaboration with Sandia National Laboratories in 2005, and at first used internally by the U.S. Department of Energy's Solar Energy Technologies Program for systems-based analysis of solar technology improvement opportunities within the program. It is essentially a performance and financial model designed to facilitate decision making for people involved in renewable energy industry. It makes performance prediction and cost of energy estimates for grid connected power projects based on installation and operating cost and system design parameters that is being specified as input to model (Figure-16).

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Figure 16. System Advisor Model for CSP Project It includes performance models for the following technologies: SPV, PTC, CRS, LFR, Dish-Sterling system, conventional fossil fuel thermal system, solar water heating system, Large and small wind power plant ,Geothermal power and Biomass power etc. It reads weather input files in TM2, TM3, and *.epw format .The TM2 and TM3 formats can be generated from METEONORM where as *.epw formats can be accessed from ASHRAE (and ISHRAE weather files in context of India as well) database. The software also provides parametric, sensitivity, P50/P90, statistical and optimizations analysis for better analysis of the project. In order to put all CSP technologies on a common platform form system sizing and energy yield estimation following assumptions have been done using SAM (Table-2). Table 2. Assumptions for Energy Simulations in SAM Capacity (MW) Life (years) Degradation/year (%) System Availability (%) Solar Multiple (SM) Irradiation at Design Power Block Gross to Net Conversion TES hours

100 30 0.25 96 Optimized Optimized 90% 0

7.3 Optimization of Design Point Radiation (DPR) Optically the line focusing CSP technologies (PTC and LFR) typically track the sun by rotating on a single-axis, which means that the DNI rarely (if ever) strikes the collector aperture at a normal angle. Consequently, the DNI incident on the solar field in any given hour will always be less than the DNI value in the resource data for that hour. The cosineadjusted DNI value; which is essentially the design point radiation (DPR) that SAM reports in simulation results is a measure of the incident DNI.

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Using too low of a reference DNI value results in excessive "dumped" energy; however over the period of one year, the actual DNI from the weather data is frequently greater than the reference value. Therefore, the solar field sized for the low reference DNI value often produces more energy than required by the power block, and excess thermal energy is either dumped or put into storage. On the other hand, using too high of a reference DNI value results in an undersized solar field that produces sufficient thermal energy to drive the power block at its design only during the few hours when the actual DNI is at or greater than the reference value (Figure 17).

Figure 17. Design Point Radiation for CSP system sizing (Source: METEONORM Database and D-VIEW software) In order to optimize the DPR over the selected locations, the product of Cosine adjusted DNI, is plotted and the maximum annual value is recorded for reference DNI or design point irradiance.

7.4 Optimization of Solar Multiple (SM) Solar multiple is defined as the solar field aperture area that, when exposed to solar radiation equal to the design radiation value (irradiation at design), generates the quantity of thermal energy required to drive the power block at its rated capacity (design gross output), accounting for thermal and optical losses. It is well established that at any location the number of annual hours that the actual solar resource is equal to the DPR radiation value is likely to be small, a solar field with SM=1 will rarely drive the power block at its rated capacity. Increasing the solar multiple (SM>1) results in a solar field that operates at its design point for more hours of the year and generates more electricity and CUF. In order to carry out the energy estimation using SAM the SM has been optimized after studying the variation of Levalized Cost of Electricity (LCOE) with solar multiple. The simulation has been carried out with optimized DPR for different values of SM and corresponding value of LCOE were determined. The optimum SM was the value corresponding to minimum LCOE (Figure-18).

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Figure 18. Optimization of Solar Multiple (SM vs. LCOE) (Source: System Advisor Model)

7.5 Energy Yield Estimation The energy yield estimation exercise has been carried out for above mentioned four commercialized CSP technologies using METEONORM weather data under the conditions of without using thermal energy storage. The analysis gives the annual energy yield estimation, capacity utilization factor, water requirement for plant operation etc. however the effectiveness of TES has been analyzed for one representative location with variable Solar Multiple. It has been noticed that when METEONORM database is provided to SAM in TMY2 format it determines DNI internally; which is differ for few locations. In order to analyze this deviation similar TMY2 files have been processed using TRNSYS software and DNI has been determined accordingly. It has been confirmed from the inter-comparability of DNI processed through METEONORM, SAM and TRNSYS software that there is mutual scattering in determination which is not site-specific (Figure-19).

Figure 19. Variation in DNI Estimation by different Computer Softwares (Source: RETScreen, METEONORM softwares)

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7.5.1 Parabolic Trough Collector Under the standards technical parameters in line with best industrial practices the energy generation along with other technical parameters are summarized in Table-3 obtained through SAM using METEONORM database. It is well established that the performance of the project is critically governed by the DNI availability. Out of 23 representative locations of India only 7 locations are able to receive annual capacity utilization factor more than 20 percent using PTC technology if analyzed using METEONORM data. Table-3. Technical analysis of a PTC project over India using SAM Annual DNI (kWh/m2) 1954 1874 2038 1959 1585 1702 1945 2184 2071 1100 1804 1537 1777 1880 1434 1366 1900 1738 1515 2013 1587 1497 1627

Location Ahmedabad Banglore Bhavnagar Bhopal Chennai Goa Hyderabad Jaipur Jodhpur Kolkatta Minicoy Mumbai Nagpur New delhi Patna Portblair Pune Ranchi Shillong Srinagar Thiruvanantpuram Varanasi Visakhapatnam

DPR (W/m2) 880 1040 860 960 980 880 880 880 920 820 920 880 950 880 840 960 980 960 1000 1000 940 840 900

SM 1.75 1.75 1.50 1.75 2.00 1.75 1.75 1.75 1.75 2.00 1.75 1.75 1.75 1.75 2.00 1.75 1.75 1.75 1.75 1.75 1.75 1.75 1.75

NAE (M U) 189.6 153.1 188.5 173.4 162.3 165.4 177.9 214.3 197.0 109.2 182.8 148.9 162.6 187.5 151.7 118.2 170.8 144.3 111.6 164.5 154.1 150.2 158.8

AWU (m3) 810072 661537 795912 778970 718897 727653 771850 865257 803204 526144 787088 664073 704044 781145 678177 549578 726507 693490 484233 641572 681701 666532 705843

CUF (%) 21.65 17.47 21.52 19.80 18.53 18.88 20.30 24.47 22.49 12.47 20.87 17.00 18.56 21.41 17.31 13.49 19.49 16.47 12.74 18.78 17.59 17.15 18.12

(DPR- Design Point Radiation, SM- Solar Multiple, MU-Million Units, NAE- Net Annual Energy , AWU- Annual Water Utilization, CUF-Capacity Utilization Factor)

7.5.2 Central Receiver System Due to utilizability of maximum portion of DNI (two axis), and low thermal field losses, the CRS system attains high temperatures as compared to PTC and shows better energy yield. Table-4 presents the energy yield over the representative locations of the country which increase the number of locations attaining annual CUF more than 20 percent.

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Table-4. Technical analysis of a CRS project over India using SAM Annual DNI (kWh/m2) SM NAE (M U) AWU (m3) CUF (%) 1954 1.75 191.6 713,262 Ahmedabad 21.87 1874 2.00 165.0 617,087 18.83 Banglore 2038 1.75 201.0 731,704 Bhavnagar 22.94 1959 2.00 200.5 725,292 Bhopal 22.88 1585 2.00 164.4 646,433 18.76 Chennai Goa 1702 1.75 161.3 626,037 18.41 1945 2.00 195.0 716,227 Hyderabad 22.26 2184 1.75 214.4 765,061 Jaipur 24.48 2071 2.00 218.4 769,927 Jodhpur 24.93 1100 2.25 117.7 497,451 13.44 Kolkatta 1804 2.00 189.0 711,667 Minicoy 21.57 Mumbai 1537 2.00 159.7 622,528 18.23 Nagpur 1777 2.00 182.2 674,388 20.80 1880 2.00 205.3 742,812 New delhi 23.44 1434 2.25 166.6 639,162 19.02 Patna 1366 2.00 128.9 526,854 14.71 Portblair 1900 2.00 192.9 710,128 Pune 22.02 1738 2.00 171.8 641,586 19.61 Ranchi 1515 2.00 135.8 499,960 15.50 Shillong 2013 2.00 199.8 675,223 Srinagar 22.80 1587 2.00 163.3 631,291 18.64 Thiruvanantpuram 1497 2.00 163.9 626,968 18.71 Varanasi 1627 2.00 163.8 649,036 18.70 Visakhapatnam (SM- Solar Multiple, MU-Million Units, NAE- Net Annual Energy , AWU- Annual Water Utilization, CUF-Capacity Utilization Factor) Location

7.5.3 Linear Fresnel Reflector and Dish-Engine LFR technology is essentially alternative of PTC which comprises low efficiency comparatively; hence requires more solar field area for collecting the solar energy. Hence in case of LFR solar multiple is essentially high. The energy generation patterns of LFR technology over India are found similar as PTC. SAM has recently added module for Dish-sterling system. Ideally this technology should perform best among all CSP technology options as it comprises maximum optical efficiency. SAM slightly underestimates the energy generation through Dish-Sterling system; however the module is at preliminary stage as well and need to elaborate. The energy yield findings of LFR and Dish-Sterling technologies are summarized in Table-5 for selected representative locations of India. Dish-Sterling systems are two–axis tracking system hence does not requires Solar Multiple for area optimization; however this technology does not require water for plant operation.

Location Ahmedabad Banglore Bhavnagar Bhopal Chennai

Table-5. Technical analysis of LFR and Dish-Sterling projects over India using SAM Annual DNI LFR Technology Dish-Sterling System (kWh/m2) SM NAE (MU) AWU (m3) CUF (%) NAE (MU) CUF (%) 1954 1874 2038 1959 1585

2.00 2.00 1.75 1.75 2.25

202.3 162.1 202.1 181.4 171.1

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802,957 657,089 798,222 720,680 716,421

151.2 148.1 159.1 155.3 116.4

22.11 18.50 23.07 20.71 19.53

17.27 16.90 18.17 17.73 13.29


Location

Annual DNI (kWh/m2)

SM

LFR Technology NAE (MU) AWU (m3)

Dish-Sterling System NAE (MU) CUF (%)

CUF (%)

Goa 1702 2.00 178.2 728,752 124.9 14.26 20.34 Hyderabad 1945 1.92 188.4 750,700 134.6 15.37 21.18 Jaipur 2184 1.75 209.1 808,908 178.1 23.87 20.33 Jodhpur 2071 2.00 208.7 799,085 167.2 19.08 23.83 Kolkatta 1100 2.50 132.2 567,188 15.08 76.7 8.76 Minicoy 1804 2.00 191.3 781,625 21.83 139.8 15.96 Mumbai 1537 2.00 161.6 670,141 18.44 113.1 12.92 Nagpur 1777 2.00 169.6 684,826 19.36 136.6 15.59 New delhi 1880 2.00 195.2 771,990 144.8 16.52 22.28 Patna 1434 2.25 162.1 676,149 18.50 108.4 12.37 Portblair 1366 2.25 138.6 585,558 15.82 98.6 11.25 Pune 1900 2.00 181.6 728,464 20.73 151.8 17.33 Ranchi 1738 2.00 158.0 640,010 18.04 139.4 15.91 Shillong 1515 2.00 121.2 472,953 13.84 122.0 13.92 Srinagar 2013 2.00 165.8 617,213 18.92 164.3 18.76 Thiruvanantpuram 1587 2.00 163.8 683,579 18.70 117.8 13.44 Varanasi 1497 2.00 157.5 653,258 17.98 113.3 12.94 Visakhapatnam 1627 2.00 168.1 703,310 19.19 115.1 13.14 (SM- Solar Multiple, MU-Million Units, NAE- Net Annual Energy , AWU- Annual Water Utilization, CUF-Capacity Utilization Factor) Above numerical findings are explaining the technical performance of the CSP projects over representative locations of India. The locations of Rajasthan and Gujarat seem more favorable than the rest locations as it is possible to achieve annual CUF more than 20 percent using METEONORM database.

Impact of TES It is an established fact in context of CSP technologies that the CUF can be increased using TES; however implementation of TES is not possible with Dish-sterling technology. Most of the proven projects with TES are based on PTC technology. Essentially the TES is used for enhancing the number of operating hours and hence increasing the CUF. There are several CSP projects operational at CUF more than 50 percent. Optimization of suitable capacity of TES critically depends upon the techno-commercial aspects of the project. SAM analyzes the TES in different way as it stores only that energy which is found in excess throughout the day. With fixed area, the total energy collected remains the same with optimized storage is meant the using the incident energy in most efficient way. As per SAM the systems with TES can increase system output (and decrease the LCOE) by storing energy from larger solar field for use during times when the solar field output is below the design point. However, the TES system's cost and thermal losses also increase the LCOE. In order to obtain the optimum combination of SM and TES capacity for CSP projects based on PTC technology the simulation has been carried out with optimized DPR. The simulation has been carried out to study the mutual behavior of three parameters simultaneously i.e. SM, LCOE and TES hours. Table-6 summarizes the combination of SM and TES hours are the optimised storage hours at specified location with the calculated Solar Multiple. Location Ahmedabad Bangalore Bhavnagar

Table – 6. Optimization of TES hours and corresponding Capacity factor DPR (W/m2) SM Optimized NAE AWU (m3) TES (hr) (MU) 880 2.25 4.0 267.16 1112770.0 1040 2.00 3.0 195.38 836769.0 860 2.25 5.0 296.57 1211610.0

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CUF (%) 30.50 22.30 33.86


DPR (W/m2)

Optimized NAE AWU (m3) CUF TES (hr) (MU) (%) 960 2.25 3.0 235.73 1026970.0 26.91 Bhopal 980 2.00 1.0 177.25 787150.0 20.23 Chennai Goa 880 2.25 4.0 234.17 999716.0 26.73 880 2.25 4.0 262.62 1111368.0 29.98 Hyderabad 880 1.75 1.0 231.96 935403.0 26.48 Jaipur 920 2.00 2.0 238.79 960783.0 27.26 Jodhpur 820 2.25 2.0 137.02 642046.0 15.64 Kolkatta Minicoy 920 1.75 1.0 197.98 855835.0 22.60 Mumbai 880 2.25 3.0 202.87 877766.0 23.16 950 2.00 2.0 196.12 838360.0 22.39 Nagpur 880 2.00 1.0 217.00 893642.0 24.77 New Delhi 840 2.25 2.0 184.95 810090.0 21.11 Patna 960 2.25 3.0 161.08 727093.0 18.39 Portblair 980 2.25 3.0 230.75 959061.0 26.34 Pune 960 2.00 2.0 175.98 831836.0 20.09 Ranchi Shillong 1000 2.25 3.0 154.24 655148.0 17.61 1000 1.75 1.0 177.12 695927.0 20.22 Srinagar 2.00 2.0 188.96 825023.0 21.57 Thiruvanantpuram 940 840 2.00 2.0 181.44 788748.0 20.71 Varanasi 900 2.00 2.0 193.76 849770.0 22.12 Visakhapatnam (DPR- Design Point Radiation, SM- Solar Multiple, MU-Million Units, NAE- Net Annual Energy , AWU- Annual Water Utilization, CUF-Capacity Utilization Factor) Location

SM

In order to get the idea of the trends of the variation of CUF and LCOE of a typical PTC based CSP project under different SM has been presented in Figures 20 to 22. The project cost is indicative only as per the database of SAM; however the trends are well representative in context of India as well.

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Figure 20. Thermal Energy Storage vs. Capacity Utilization Factor

Figure 21. Thermal Energy Storage vs. Levalized Cost of Electricity

Figure 22. Solar Multiple vs. CUF/LCOE

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8. Way Forward Concentrating Solar Power technology is still at nascent stage in context of India as there are no established manufacturers of the technology and no operational commercial projects till date (except few demonstrations plants of small capacities). The sector is getting attention due to JNNSM and likely to commercialized in India. The non availability of long term ground (bankable) DNI data, infrastructure, water availability, manufacturing base, high project cost, provenness of the technology in Indian conditions etc. are the major challenges in the direction of large scale CSP technology deployment. In the present scenario of CSP development in the country the project developers are totally dependent to international suppliers; however the project cost is being a big challenge for the financing of the projects. From the preliminary analysis using METEONORM database it has been observed that within the best performance parameters selection it is not possible to achieve 23 percent annual capacity utilization factor for most of the Indian locations. Hence CSP potential is limited to few states of India only; however good quality high resolution satellite data with real time energy yield simulation could give the clearer image of CSP feasibility in context of India. There are several policies upcoming in India to promote CSP in big way namely JNNSM, REC etc. Presently as per the available policy guidelines TES and Hybrid systems are not encouraged; however it could make the CSP projects technocommercially more attractive. In addition CSP with biomass could be one suitable option in context of India. In order to make CSP attractive and feasible the present measures towards financial viability need to be continuing in a programmatic manner. However support for research and development, standardization as per Indian climatic/operating conditions, capacity building of industries, financial institutions and stakeholders is also essential.

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