Abstract
Electricity generation through sunlight is one of the fastest-growing renewable energy production sources in the world, and will continue to rise in the coming years. The economic benefits of technologies used to capture sunlight is improving each year, increasing the scope for eco-friendly electricity generation. This article provides a brief overview of a solar energy-based electricity generation system called Concentrated Solar Power (CSP). The article emphasizes the working, merits, demerits, and various applications of CSP technology.
 
Introduction 
Energy decarbonisation is underway on a global scale as part of the post-2020 long-term climate actions called Nationally Determined Contributions (NDCs), prepared and communicated by 193 parties of the Paris Agreement in 2015 to reduce carbon emissions and mitigate the impacts of climate change. In 2017, IRENA (International Renewable Energy Agency) reported that a transition to renewable energy can reduce two-thirds of total energy-related CO2 emission by 2050. 

Nowadays, solar power is a widely used renewable energy source of electricity generation in many countries around the world. While the Photovoltaic effect is used for small-scale electricity projects (like rooftop solar photovoltaics), the massive scale solar thermal capture through Concentrated Solar Power (CSP) is typically used for electricity generation, and other commercial and non-commercial purposes. 

CSP plants in India
The CSP technology is a green and clean source of energy production. Typical CSP plant consists of rows of several mirrors in a large solar field that collect and concentrate sunlight on a system of pipes (receiver) circulating a heat transfer fluid like oil, water and molten salt. This heat produces steam that powers the turbine for sustainable solar thermal electricity generation in the CSP plant.  

 

Figure 1: Types of CSP technology.

 

To reduce its dependence on coal-fired energy production, a total of 470 MW under CSP projects were planned in India under the phase I (2010-2013) of the ambitious Jawaharlal Nehru National Solar Mission (JNNSM). However, only 228.5 MW of total planned capacity is found operational in India as of 2018. 

 

Table 1: Details of CSP projects in India (NA: Not Available). 

S. No.

Project name

Location

Area (acres)

Technology used

Capacity (MW)

Current Status

1

Dhursar Project

Jaisalmer, Rajasthan

840

Linear Fresnel

125

Operational, since 2014

2

Godawari Solar Project

Jaisalmer, Rajasthan

370

Parabolic Trough

50

Operational, since 2013

3

Megha Solar Plant

Anantapur, Andhra Pradesh

600

Parabolic Trough

50

Operational, since 2014

4

ACME Solar Tower

Bikaner, Rajasthan

12

Solar Tower

2.5

Operational, since 2011

5

National Solar Thermal Power Facility

Gurugram, Haryana

NA

Parabolic Trough

1

Operational, since 2012

6

Diwakar Project

Jaisalmer, Rajasthan

NA

Parabolic Trough

100

Under Construction

7

KVK Energy Solar Project

Jaisalmer, Rajasthan

NA

Parabolic Trough

100

Under Construction

8

Abhijeet Solar Project

Jaisalmer, Rajasthan

388

Parabolic Trough

50

Under Construction

9

Gujarat Solar One

Kutch, Gujarat

NA

Parabolic Trough

25

Under Construction

10

Dadri ISCC Plant

Dadri, Uttar Pradesh

NA

Linear Fresnel

14

Under Construction

 
Merits of CSP
In India, the coal-fired thermal power plants utilise 5-7 Cu m water per MWh of electricity generation, however, the CSP systems utilise only 2-3 Cu m water per MWh of electricity generation for cooling and washing of mirror surfaces. The CSP plants with thermal energy storage (TES) technology can store energy, which can be used day or night, and during cloudy weather. The CSP is an economically-efficient technology to offset the carbon emission by replacing the fossil-fuel based thermal power plants, and can be combined as a hybrid system for electricity generation with the existing installed capacities in India.
 
Demerits of CSP
The CSP is a large project (5 to 10 acres of land per MW of capacity). A plant size of 100 MW or more is highly efficient and productive in operation, which makes this project expensive to build. According to the IPCC report, about 22g CO2 emission per unit of electricity from CSP plants, however, this emission is negligible in comparison to 800-1000g CO2 emission per unit of electricity from coal and lignite based power plants in India. Energy investors prefer photovoltaic technology over the CSP plants due to its low techno-economic feasibility. Most of the components of CSP plants like mirrors, tubes and absorbers are imported, which increases its manufacturing cost. The lack of trained man-power to build and operate is another challenge in the successful commissioning of CSP plants in India. 
 
Applications of CSP
This technology is used as an alternative source of energy to heat water and space in domestic and commercial places like hostels or hospitals in a cost-effective manner. For instance, hot water is required in the beverage bottling plants for both production and maintenance. In many parts of the world like India and Sub-Saharan countries, the CSP plant can power absorption chiller refrigerators which can be used to refrigerate food and medicine at about 4-7⁰C temperature, and cooling space in homes, factories and schools. The incorporation of CSP technology in the agriculture sector can benefit greenhouse plants and crops by  maintaining a constant temperature day and night. The heat from CSP plants can be used in biogas processing to raise the temperature of the digestion tank for the conversion of bio-waste into renewable fuel or energy. 
 
Conclusion
The government of India has set up a target of 2000 MW off-grid solar PV application under its National Solar Mission that is to be achieved between 2017-2022. CSP technologies can be commissioned in the states with high solar irradiance like Rajasthan, Gujarat and Tamil Nadu and can be used as alternative energy sources instead of commissioning new fossil-fuel power plants like natural gas, lignite and coal, it can also replace the retiring thermal power plants after their decommissioning. Thus, there is a need for specific policies to ensure that the goals of energy security and climate security can be  achieved in parallel . CSP is an excellent way forward in sustainable energy production  to meet peak electricity demand and maintain grid stability without any significant impacts on the environment.