Solar Energy - Applications, Types, Advantages and Disadvantages


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Prelims: General Science

Mains: Achievements of Indians in science & technology; indigenisation of technology and development of new technology

Solar technologies use clean energy from the sun rather than polluted fossil fuels. There are two main types: solar thermal, which uses solar energy to heat water, and solar photovoltaic (PV), which uses solar cells to transform sunlight into electricity.

Global solar adoption is increasing as a result of declining costs and expanding access to clean energy (SDG 7). India can achieve its climate commitments in an environmentally sustainable manner, lessen its dependency on imported fuels, and promote social inclusion (SDG 10) by expanding access to solar applications and increasing solar capacity to 450 GW by 2030. Because of its boundless potential, solar energy is a vital ally for sustainable development.

Solar energy utilises the sun’s radiant light and heat to generate useful energy services like electricity, heating, cooling, lighting, or mechanical work. In recent years, solar technology has emerged as an important renewable energy source with significant potential to meet the world's energy needs in an eco-friendly manner.

Solar Energy - Working and Usage

  • The sun radiates an enormous amount of energy in the form of electromagnetic radiation. Solar technologies utilise various methods to tap this abundant renewable energy source.
  • There are two primary ways solar energy is harnessed -
    • Direct conversion into electricity using photovoltaics.
    • Capturing heat from the sun's rays to generate electricity indirectly.
  • Usage: Solar technologies are scalable and flexible - they can power an entire city through solar farms, provide electricity in remote areas via decentralized systems, and light up homes and commercial buildings by installing rooftop solar panels.
    • For example: Cochin International Airport
  • Significance: The adoption of solar energy provides several benefits, including reducing reliance on depleting fossil fuels, mitigating carbon emissions, improving air quality, and boosting energy access and security, among others.
    • Due to this, solar power's share in global electricity generation is rising steadily.

Types of Solar Energy

Solar energy is captured through three main technologies: photovoltaics (PV), converting light to electricity; concentrating solar power (CSP), utilising the sun's heat for electric turbines; and solar heating and cooling (SHC) systems, gathering thermal energy for hot water, air heating, or conditioning.

Solar Photovoltaic Technology

Solar photovoltaic (PV) technology converts sunlight directly into electricity through the photovoltaic effect. The term "photovoltaics" is derived from the conversion of light (photons) into electricity (voltage), a phenomenon known as the photovoltaic effect.

  • PV cells are made of semiconductor materials like silicon. When sunlight strikes the cell, electrons are knocked loose from the atoms, generating electricity.
    • Grid-connected systems feed surplus electricity back into the grid.
  • In many regions, photovoltaic systems are being deployed at large scales to help power the electric grid.
  • Methods: PV systems come with small rooftop solar installations, solar pumps, off-grid lighting systems, and large utility-scale solar power plants.
  • Cost-effective: The costs of PV systems have fallen dramatically, making solar power cost-competitive.
    • With weatherproof panels and no moving parts, PV systems require minimal maintenance and have long lifespans.
  • Drawback: Solar PV generation relies on sunny weather and output varies throughout the day.

Concentrated Solar Power Technology

  • Concentrated solar power (CSP) systems use mirrors to concentrate sunlight to drive traditional steam turbines or engines that generate electricity.
  • CSP allows thermal energy storage by heating a storage medium during sunlight hours, which can then generate electricity even when the sun is not shining.
  • CSP technologies include parabolic trough systems, linear Fresnel reflector systems, power tower/heliostat systems, and parabolic dish/engine systems.
  • The higher temperatures enable CSP to operate more flexibly than PV power.
  • Large-scale CSP plants have the advantage of inbuilt storage to provide dispatchable and reliable electricity generation.
    • However, CSP systems require direct solar radiation and have not become cost-competitive with PV.

Solar Heating and Cooling Technology

Solar heating and cooling (SHC) technologies harness solar thermal energy for water heating, space heating, cooling, refrigeration, drying, and other applications.

  • SHC systems convert sunlight into useful thermal energy that replaces electricity or fossil fuels.
  • Solar collectors, often mounted on rooftops, absorb and retain heat from the sun which is transferred to a fluid and used via heat exchangers.
  • Common SHC devices include solar water heaters, solar air heaters/dryers, solar cookers, solar stills, and solar absorption cooling systems.
  • Solar thermal systems provide clean energy services and avoid significant greenhouse gas emissions.
  • SHC systems have become popular across the world due to their cost-effectiveness and environmental benefits.
    • However, the potential of SHC still needs to be utilised and needs greater adoption.

Solar Photovoltaic vs Solar Thermal

ParameterSolar PhotovoltaicSolar Thermal
TechnologyConverts sunlight directly into electricity using solar PV cells.Captures heat from sunlight to heat a fluid, which is then used for applications needing heat
Typical applicationsElectricity generation and powering appliances/devices.Water heating, space heating, industrial process heat.
Solar conversion efficiency15-20%50-80%
CostHigher initial investment, lower operating costs.Lower initial investment, higher operating costs.
StorageBatteries used for electricity storageThermal energy storage in tanks/pits used.
SupplyProvides electricity, but needs a grid for overnight/cloudy daysIt provides thermal energy for direct heating applications.
PollutionNo emissions during operation.Some systems use gases with small carbon footprints.
Land requiredAbout 1 hectare per 1 MW for utility-scale.Lower land requirements compared to PV.
Commercial maturityWell-established commercially with rapidly declining costs.Relatively less adoption is key for solar thermal heating.
India potentialHuge potential for both centralized and decentralized PV power.Considerable potential for solar water heating especially.

Applications of Solar Energy

Solar thermal technologies harness solar heat energy for direct thermal applications like:

  • Power generation: Solar PV and CSP plants of utility-scale, rooftop-scale, or off-grid installations generate clean electricity.
    • Example: Bhadla Solar Park in Rajasthan with 2245 MW capacity.
  • Water heating: Solar collectors are used to heat water for domestic, commercial and industrial needs, reducing electricity/fuel consumption.
  • Pumping: Solar PV panels power water pumps for irrigation and drinking water, especially in rural areas.
    • Example: Solar pumps promoted under the PM-KUSUM scheme.
  • Lighting: Solar lanterns and home lighting systems provide clean lighting solutions using small PV panels and batteries.
    • Example: SELCO's solar lighting for rural households.
  • Cooking: Solar cookers with reflective mirrors are used for cooking applications without electricity/fuels.
  • Vehicles: Solar PV cells provide part of the propulsion power for electric vehicles like cars, boats, etc., reducing fossil fuel use.
    • Example - Lightyear One EV with solar-assisted charging.
  • Desalination: Solar thermal energy is used for desalinating seawater to produce potable water.
    • Example - BARC's solar desalination system.
  • Space heating/cooling: Solar collectors provide space heating in winter and cooling in summer.
    • Example - Solar absorption cooling system at TERI office.

Disadvantages of Solar Energy

Some challenges of Solar Energy include:

  • Intermittency: Solar energy cannot be generated at night and output varies due to cloud cover and seasons.
  • Storage: Effective, large-scale energy storage solutions are still being developed to mitigate intermittency.
  • Space requirements: Solar farming requires large land areas with high solar insolation.
  • High upfront costs: The initial capital costs of solar systems can be high.
  • Transmission: Solar farms may require expensive transmission lines to connect to the grids.
  • Efficiency: Most silicon solar cells have efficiencies of around 15-20% with theoretical limits of around 30%.

Emerging Solar Technologies

Solar power technologies are rapidly evolving and gaining prominence as countries push for increased renewable energy adoption. Key developments include:

  • Floating solar PV farms: Modules are mounted on floating structures on water bodies instead of ground installation.
    • Example: A 600 MW floating solar farm is being set up at Omkareshwar Dam in Madhya Pradesh. It helps overcome land constraints.
  • Solar windows: Transparent solar glass windows that can generate electricity through transparent solar cells while also providing natural lighting.
    • Example: Ubiquitous Energy has developed transparent solar windows that can be installed on high-rise building facades.
  • Perovskite solar cells: Employ perovskites as light absorbers having the potential for high efficiencies and low costs.
    • Example: Oxford PV has achieved 28% efficiency in perovskite solar cells, nearing silicon cell efficiency.
  • Space-based solar power: Captures solar energy in space via orbital PV systems and transmits to the Earth via microwaves/lasers.
    • Example: Potential to overcome intermittency issues and provide baseload power. ISRO and NASA are conducting joint research in this area.
  • Solar fuels: Use concentrated solar thermal energy to facilitate thermochemical reactions to produce clean fuels like hydrogen from water splitting.
    • Example: Heliogen has developed concentrated solar plants integrated with thermal reactors to generate solar fuels.
  • Bifacial Solar Cells: They have both front and back photo-sensitive surfaces to capture reflected light, generating up to 30% more energy than traditional panels. Global installation is rising, given higher efficiency and cost benefits.
  • Solar Trees: Resemble a tree with solar panels mounted like branches on a central pillar. Require minimal land area compared to ground installations while producing equivalent power.
    • Support agriculture activities by providing shaded spaces for machinery, water pumps, etc.
    • India has installed the world's largest solar tree, with 11.5 kW of capacity.
  • Solar Carports: Solar panels are installed as rooftops over vehicle parking areas to generate power while providing shade. Dual land use improves efficiency. Carports with solar tracking to optimize generation are being adopted.
    • Tata Motors installed India's largest 6.2 MW solar carport at its Pune facility.
  • Agrivoltaics: Solar installations on agricultural land in a way that permits continued cultivation underneath.
    • Dual land use improves efficiency while diversifying farmer income. Being piloted in several regions, including India.
  • Building integrated photovoltaics (BIPV): Solar cells integrated into building materials, serving as construction surfaces and electricity generators.
    • It helps avoid separate land requirements but has higher installation complexity and costs.

With enlightened policy frameworks, solar energy can propel sustainability worldwide. The infinite potential of the sun is one of our greatest allies in our collective efforts to combat climate change and achieve the SDGs.

PYQs on Solar Energy

Question 1: With reference to technologies for solar power production, consider the following statements: (UPSC Prelims 2014)

  1. 'Photovoltaics' is a technology that generates electricity by direct conversion of light into electricity, while 'Solar Thermal' is a technology that utilizes the Sun's rays to generate heat which is further used in the electricity generation process.
  2. Photovoltaics generates Alternating Current (AC), while Solar Thermal generates Direct Current (DC).
  3. India has a manufacturing base for Solar Thermal technology, but not for Photovoltaics.

Which of the statements given above is/are correct?

  1. 1 only
  2. 2 and 3 only
  3. 1, 2 and 3
  4. None

Answer: (a)

FAQs on Solar Solar Energy

What are the different solar energy technologies?

The main solar energy technologies are - solar photovoltaics (conversion of sunlight into electricity), concentrated solar power (use of mirrors and lenses to concentrate solar thermal energy and generate electricity) and solar thermal (uses solar heat for applications like heating, cooking, drying etc.)

How do solar panels work?

Solar PV panels contain photovoltaic cells made of semiconducting materials like silicon. When sunlight strikes the cell, photons are absorbed by the semiconducting material, causing electrons to break free generating electron-hole pairs and electric current. The flow of electrons produces DC electricity in the external circuit.

What are the different CSP technologies?

Main CSP technologies include - parabolic trough collectors, solar power tower or central receiver systems, linear Fresnel reflector systems and parabolic dish systems.

What are the main types of solar thermal collectors?

Common collector types used in solar thermal systems are - flat plate collectors, evacuated tube collectors, unglazed plastic collectors and concentrating collectors.