GS-III · Environment · Renewable Energy · Science & Technology
Solar Energy — From the Sun to the Socket ☀️⚡
Complete UPSC Notes — Solar photovoltaic (PV), Concentrated Solar Power (CSP), Solar Heating & Cooling (SHC), comparison, advantages, challenges, emerging technologies (floating solar, agrivoltaics, perovskite cells, space-based solar, solar trees, BIPV), India's solar journey, all major schemes, and current affairs 2024–2026.
🇮🇳 India: 143.6 GW solar capacity (Feb 2026) | 3rd largest globally (after China, USA)
☀️ Solar: 47% of India's total renewable energy installed capacity
🏠 PM Surya Ghar: ₹75,021 crore | 1 crore households | 300 units free/month
🌊 Bhadla Solar Park: 2,245 MW — India's largest, world's 11th largest (2025)
🎯 India target: 500 GW non-fossil capacity by 2030 | 1,800 GW by 2047
Section 01 — Foundation
☀️ Solar Energy — The Basics
💡 Solar Energy = The Original Power Source of All Life
Every form of energy on Earth — coal (ancient sunlight stored in plants), wind (driven by solar heating of atmosphere), food (photosynthesis), hydro (solar-driven evaporation and rain cycle) — is ultimately solar in origin. Solar technology simply cuts out the middleman: instead of waiting millions of years for plants to turn into coal, we directly capture the sun's energy the moment it arrives. The sun delivers approximately 1,000 watts per square metre of Earth's surface on a clear day — and the total solar energy reaching Earth in one hour is more than humanity uses in an entire year. The challenge is not availability — it's capture, conversion, and storage.
143.6
GW (Feb 2026)
India's installed solar capacity — fastest growing in the world
3rd
Globally
India's solar rank — after China (#1) and USA (#2)
2.63
GW in 2014
India's solar in 2014 — 54× growth to 143 GW by Feb 2026
748
GWp potential
India's estimated solar potential (NISE — National Institute of Solar Energy)
📌 How Solar Energy Reaches Us: The Sun generates energy via nuclear fusion (H + H → He + energy) in its core at ~15 million°C. This energy travels 150 million km as electromagnetic radiation — taking 8 minutes to reach Earth. At Earth's surface, it arrives as: (a) Visible light — captured by PV cells. (b) Infrared radiation (heat) — captured by solar thermal systems (CSP, SHC). (c) Ultraviolet — mostly absorbed by ozone layer. India's geographic advantage: Located between 8°–37°N latitude with 250–300 clear sunny days/year — receives 4–7 kWh/m²/day solar insolation — among the highest in the world.
🔆 Three Main Types of Solar Technology
☀️→⚡
Solar PV
Solar PV
Photovoltaic (PV): Converts sunlight directly into electricity using semiconductor cells (silicon). The photovoltaic effect — photons knock out electrons from the semiconductor → electric current. Applications: rooftop panels, solar parks, solar pumps, portable chargers. Efficiency: 15–22% (silicon cells). Best for: electricity generation at all scales.
☀️→🌡️→⚡
CSP
CSP
Concentrated Solar Power (CSP): Uses mirrors to concentrate sunlight → generates heat → steam drives turbine → electricity. Indirect electricity generation. Key advantage: built-in thermal energy storage (can generate at night!). Types: Parabolic trough, Heliostat/Power tower, Linear Fresnel, Parabolic dish. Best for: large-scale dispatchable solar power. Needs direct radiation (DNI).
☀️→🌡️→🏠
Solar SHC
Solar SHC
Solar Heating & Cooling (SHC): Captures solar heat for direct thermal applications — water heating, space heating, cooking, refrigeration, drying. Uses solar collectors (flat plate or evacuated tube) to absorb and transfer heat to a fluid. No electricity generated — heat used directly. Most cost-effective use of solar energy. Efficiency: 50–80%. Best for: water and space heating, industrial heat.
Section 02 — Solar PV
🔵 Solar Photovoltaic (PV) — Working & Types
⚡ Solar PV — The Photovoltaic Effect
Direct electricity generation
Principle:Photovoltaic effect (discovered by Edmond Becquerel, 1839): When light strikes a semiconductor material (usually silicon), photons knock out electrons from their atoms — these free electrons create an electric current. "Photovoltaic" = photo (light) + voltaic (electricity). First practical PV cell: Bell Labs, 1954.
Material:Monocrystalline silicon (highest efficiency, ~22%), Polycrystalline silicon (lower cost), Thin-film (CIGS, CdTe — flexible, lower efficiency), Perovskite (emerging — potentially >30% efficiency)
Efficiency:15–22% for commercial silicon cells. Theoretical maximum (Shockley-Queisser limit) ≈ 33% for single-junction cells. Multi-junction cells (used in space) can reach 47%.
Output:Direct Current (DC) electricity → converted to AC via inverter for grid use. No moving parts. Silent. Long lifespan (25–30 years).
Applications:Utility-scale solar parks (GW level), Rooftop solar (homes, commercial), Off-grid power (remote areas), Solar pumps (PM-KUSUM), Solar street lights, Solar-powered vehicles, Space satellites (PV powers ISS and most satellites)
Limitations:Intermittent (only generates during sunlight). Output varies with cloud cover, dust, temperature. Needs storage (batteries) for 24/7 use. Land-intensive for utility-scale. ~1 hectare per 1 MW.
🏭 Utility-Scale Solar Parks
- Bhadla Solar Park (Rajasthan): 2,245 MW | 56 km² | India's largest | World's 11th largest (2025) | Jodhpur district, Thar Desert
- Pavagada Solar Park (Karnataka): 2,050 MW | 13,000 acres
- Khavda RE Park (Gujarat): 30 GW planned (solar + wind) — world's largest single-location RE project when complete (Adani). 1 GW commissioned 2024
- 55 solar parks with 40 GW sanctioned capacity across 13 states (Oct 2025)
- Rajasthan, Gujarat, Tamil Nadu — top 3 states; contributed 71% of utility-scale solar installations
🏠 Rooftop Solar
- Solar panels on rooftops of homes, offices, factories — generate electricity for own use + sell surplus to grid (net metering)
- PM Surya Ghar: Muft Bijli Yojana (2024): ₹75,021 crore | 1 crore households target | Up to 300 units free/month | Up to 40% subsidy
- As of Dec 2025: 23.9 lakh households installed | 7 GW capacity | ₹13,464 crore subsidy released
- Grid-connected: excess electricity sold to DISCOMs — earns ₹17,000–18,000/year
- Cochin International Airport: world's first fully solar-powered international airport
Section 03 — CSP & SHC
🟣 CSP & 🟢 Solar Heating — The Other Solar Technologies
🟣 Concentrated Solar Power (CSP) — Solar Thermal Electricity
Storage advantage
Principle:Mirrors/lenses concentrate sunlight onto a small area → intense heat → heats a fluid (molten salt, oil) → steam → turbine → generator → electricity. CSP = indirect electricity (via heat).
Key advantage:Thermal Energy Storage (TES): Heated molten salt can be stored in insulated tanks for 6–15 hours. Turbine generates electricity even at night or on cloudy days. This "dispatchability" is CSP's critical advantage over PV — it can provide baseload reliable power.
4 CSP Types:(1) Parabolic Trough: Curved mirrors in rows focus sun on central receiver tube — most commercial type. (2) Power Tower/Heliostat: Field of mirrors focus on central tower receiver — higher temperatures. (3) Linear Fresnel: Flat mirrors approximate parabolic shape — cheaper, lower efficiency. (4) Parabolic Dish: Dish-shaped mirror + Stirling engine at focus — small scale, high efficiency.
Limitations:Requires Direct Normal Irradiance (DNI) — cloudy/diffuse light doesn't work. Has NOT become cost-competitive with PV (CSP costs have not fallen as fast as PV). Water-intensive (cooling). High capital cost.
India CSP:Rajasthan has highest CSP potential (highest DNI). 2,250 MW Rajasthan Rajya Vidyut Utpadan Nigam (RVUN) CSP project planned. Godawari Green Energy 50 MW CSP plant (Rajasthan) — India's first commercial CSP plant.
🟢 Solar Heating & Cooling (SHC) — Direct Thermal Applications
Most cost-effective
Principle:Solar collectors absorb and retain heat from sunlight → transfer to fluid (water or air) → used directly for heating/cooling. No electricity conversion — heat used directly. Efficiency 50–80% (much higher than PV).
Devices:(1) Solar Water Heaters: Flat plate collectors or evacuated tube collectors. Most popular SHC application — replaces electric geysers. (2) Solar Cookers: Parabolic or box-type — uses reflected sunlight for cooking. (3) Solar Air Dryers: Dries agricultural produce (fruits, fish, tobacco, spices) without fuel. (4) Solar Stills: Distills/desalinates water using solar heat. (5) Solar Absorption Cooling: Solar heat drives absorption refrigeration — cooling without electricity.
India examples:Solar water heaters widespread in Karnataka, Maharashtra, Gujarat. Solar cookers promoted by MNRE. BARC solar desalination systems. TERI office solar absorption cooling. Textile industry (solarisation of process heat).
Challenge:Solar thermal potential still underutilised — needs greater policy push, awareness, and adoption. Industry-scale solar process heat has large untapped potential in India (cement, textile, food processing sectors).
Section 04 — Comparison
📊 Solar PV vs Solar Thermal — Quick Comparison (UPSC Key)
| Parameter | ☀️ Solar PV | 🌡️ Solar Thermal (SHC/CSP) |
|---|---|---|
| Conversion | Light → Electricity (direct) | Light → Heat (→ Electricity in CSP) |
| Conversion efficiency | 15–22% (commercial silicon) | 50–80% (SHC); 30–45% (CSP) |
| Output form | DC Electricity | Thermal energy (heat); AC in CSP |
| Main applications | Electricity for appliances, grid, EVs | Water heating, space heating, industrial process heat |
| Storage | Batteries (electrochemical — expensive) | Thermal storage (molten salt, hot water — cheaper) |
| Initial cost | Higher (but falling rapidly) | Lower for SHC; Higher for CSP |
| Operating cost | Very low (no fuel) | Low (SHC); Moderate (CSP) |
| Intermittency fix | Batteries; grid backup | Thermal storage (CSP) — can generate at night |
| Land | ~1 ha per 1 MW (utility) | Less for SHC; Comparable to PV for CSP |
| Commercial maturity | Very mature; costs dropped 89% (2010–2024) | SHC: Mature. CSP: Less adopted than PV |
| India potential | Huge — 748 GWp estimated (NISE) | Considerable — especially solar water heating |
📌 UPSC Key Fact: CSP's thermal energy storage gives it a critical advantage over PV — it can supply electricity at night (stored heat drives turbine after sunset). This is why CSP is sometimes called "solar baseload power." However, CSP costs have not fallen as dramatically as PV, and PV+battery storage is increasingly competitive. Current solar tariff in India (PV): as low as ₹1.99/unit (L1 bid, 2021) — among cheapest electricity in the world.
Section 05 — Pros & Cons
⚖️ Advantages & Challenges of Solar Energy
✅ Advantages
- Infinite & free fuel: The sun provides energy without any cost. No depletion — will last 5 billion years
- Zero emissions in operation: No CO₂, NOx, SOx, or PM during electricity generation — clean air co-benefit
- Declining costs: Solar PV costs fell ~89% between 2010 and 2024. India's tariff: ₹1.99/unit (2021 L1 bid) — cheaper than coal in many cases
- Decentralized: Can be installed at point of use — rooftop, village, remote area — reducing transmission losses
- No water consumption (PV): Unlike thermal power or CSP, PV requires no cooling water — critical for water-scarce India
- Low maintenance: No moving parts in PV — minimal maintenance, 25+ year lifespan
- Energy security: Domestic resource — reduces dependence on imported coal/oil/gas; improves energy self-reliance
- Job creation: India's solar sector generated ~900,000+ jobs by 2025
- Dual use (emerging): Agrivoltaics, solar carports, BIPV — solar on land already being used
❌ Challenges / Disadvantages
- Intermittency: No electricity at night; output varies with cloud cover, seasons, dust — India's grid stability challenge
- Storage: Battery storage still expensive — large-scale, affordable storage remains a key bottleneck
- Land use: Utility-scale solar farms require large land areas — land acquisition challenges in India, conflict with agriculture
- Efficiency: Commercial PV cells: 15–22%. Even with improving technology, much solar radiation is unconverted (heat loss)
- High upfront cost: Despite falling costs, initial capital expenditure is still significant for households and utilities
- Transmission: Solar farms often in remote (sunny) areas — need expensive transmission lines to load centres
- Manufacturing dependency: India imports solar cells/modules from China — reducing Aatmanirbhar Bharat goal. PLI scheme being used to address this
- Grid integration: High share of solar creates voltage fluctuations and grid management challenges
- Dust accumulation: Bhadla Solar Park example — dust reduces panel efficiency, especially in dry regions; frequent cleaning needed
Section 06 — Emerging Tech
🚀 Emerging Solar Technologies — UPSC Focus
Floating Solar PV (Floatovoltaics)
Panels mounted on floating structures on water bodies (reservoirs, lakes, ponds). Saves land. Reduces water evaporation. Water cools panels → better efficiency. India: 600 MW Omkareshwar Dam floating solar (Madhya Pradesh) — India's largest floating solar. 278 MW commissioned as of 2025. Also: NTPC 100 MW Simhadri floating solar (Andhra Pradesh, on ash pond).
Agrivoltaics (Agri-PV)
Solar panels installed above agricultural fields — crops grow underneath in partial shade. Dual land use — same land for food and energy. Shade reduces water stress on crops in hot climates. Solar panels benefit from crop's cooling effect (evapotranspiration). Piloted in Rajasthan, Gujarat, Karnataka. PM-KUSUM scheme promotes agrivoltaic installations for farmers.
Perovskite Solar Cells
New generation semiconductor material — perovskite crystal structure. Lab efficiencies: 25–33% (exceeding silicon). Potentially much cheaper to manufacture than silicon (solution-processable, printable). Oxford PV achieved 29.52% efficiency (perovskite-silicon tandem, 2023). Challenge: long-term stability and lead (Pb) toxicity. Could be transformative if commercialised.
Space-Based Solar Power (SBSP)
Solar panels in Earth orbit (GEO — 36,000 km) capture uninterrupted solar energy (no night, no clouds) → transmit as microwaves to Earth receivers (rectennas) → convert to electricity. Solves intermittency completely. ISRO and European Space Agency (ESA) conducting joint research. ISRO exploring SBSP concept. UK government shortlisted in 2023. Challenge: extremely high launch cost, microwave beam safety.
Solar Trees
Tree-like structures with solar panels as "leaves" on branches. Extremely low land footprint vs conventional solar farms. India has installed the world's largest solar tree (11.5 kW capacity) at CSIR-CMERI, Durgapur, West Bengal. Provides shade for agricultural machinery, water pumps. Central Street Research Institute (CSIR) developing further models. Suitable for urban, semi-urban spaces.
BIPV — Building Integrated PV
Solar cells built directly into building materials — roofing tiles, facade glass, windows. Replaces conventional building material AND generates electricity. No extra land needed — uses building's own surface area. Solar windows (transparent cells) — Ubiquitous Energy's ClearView Power. Bifacial solar cells: capture light from both front AND back surfaces — up to 30% more energy generation. India: BIPV pilot projects at government buildings.
📌 Solar Carports — India's Largest: Solar panels installed as canopies over vehicle parking areas. Tata Motors installed India's largest solar carport (6.2 MW) at its Pune facility. Dual use: generates electricity + provides shade for parked vehicles. Bifacial Solar Panels are increasingly being deployed — they have photosensitive surfaces on both front AND back, capturing direct sunlight on front and reflected/diffuse light on back. 10–30% more energy than conventional monofacial panels.
Section 07 — India's Solar Policy
🇮🇳 India's Solar Journey — Key Milestones & Schemes
📜 National Solar Mission (NSM) — 2010
Launched under NAPCC (National Action Plan on Climate Change). India's first dedicated solar policy. Revised targets (2015): 100 GW solar capacity by 2022 (revised from initial 20 GW target). This was aspirational but achieved only in Jan 2025 (delayed by 3 years — still remarkable). NSM paved the way for competitive bidding, tariff reduction from ₹10.95/unit (2010) to ₹1.99/unit (2021).
🌾 PM-KUSUM Scheme — 2019
Pradhan Mantri Kisan Urja Suraksha evam Utthaan Mahabhiyan. Three components: Component A (decentralised ground-mounted solar plants by farmers); Component B (standalone solar pumps); Component C (solarisation of grid-connected pumps). Target: 30.8 GW. As of 2025: 9.2 lakh standalone solar pumps (Component B). 60% subsidy. Converts farmers from energy consumers to energy producers.
🏠 PM Surya Ghar: Muft Bijli Yojana — Feb 2024
India's most ambitious rooftop solar scheme. Launched 13 February 2024 by PM Modi. Total outlay: ₹75,021 crore. Target: Install rooftop solar on 1 crore households by March 2027. Free 300 units/month for households installing 3 kW systems. Subsidy: up to 40% for 1–3 kW; 20% for 3–10 kW. As of December 2025: 23.9 lakh installed, 7 GW capacity, ₹13,464 crore subsidy released. World's largest domestic rooftop solar initiative.
🏭 PLI Scheme for Solar Manufacturing
Production Linked Incentive (PLI) scheme for High Efficiency Solar PV Modules. Launched to make India a global solar manufacturing hub. India's solar module manufacturing capacity: 38 GW (March 2024) → 74 GW (March 2025) — nearly doubled in one year. Solar PV exports: $2 billion in FY2024 (23× rise from FY2022). Target: 100 GW module manufacturing capacity by 2030. India transitioning from net importer to net exporter of solar PV. PLI attracted ₹48,120 crore investment, created ~38,500 jobs.
🌍 International Solar Alliance (ISA) — India's Global Solar Initiative
Proposed by India (PM Modi) at COP21 Paris Climate Conference, 2015. Framework Agreement: Signed November 2015. HQ: Gurugram (Haryana), India — NISE campus. Mission: Mobilise $1 trillion investments in solar by 2030; make solar energy affordable for all member countries. Membership: 125+ member nations (as of 2025) — primarily countries between Tropics of Cancer and Capricorn (sunny nations). India as founding member and host. Works on solar finance, technology transfer, standards, and capacity building. Connected to One Sun, One World, One Grid (OSOWOG) — India's initiative for global solar grid interconnection.
Section 08 — Current Affairs
📰 Current Affairs 2024–2026 (Fact-Verified)
Jan 2025 — 🇮🇳 MILESTONE
India Crosses 100 GW Solar Capacity — Now 3rd Globally
📊 Milestone:India crossed 100 GW of installed solar power capacity in January 2025 (100.33 GW). By February 2026, total reached 143.6 GW. India is now the 3rd largest solar power producer globally (after China and USA). Solar accounts for 47% of India's total installed renewable energy capacity.
📈 Growth:Solar capacity grew from 2.63 GW (2014) to 143.6 GW (Feb 2026) — a 54-fold increase in 12 years. India added a record 24.5 GW in 2024 alone — more than doubling the addition of 2023. Solar tariff fell from ₹10.95/unit (2010) to ₹1.99/unit (L1 bid, 2021).
🏭 Manufacturing:India's solar module manufacturing capacity nearly doubled from 38 GW to 74 GW (March 2024 → March 2025) due to PLI scheme. India's PV exports reached $2 billion in FY2024 — 23× rise from FY2022. India transitioning from net solar importer to exporter.
📚 UPSC angle:100 GW milestone; 3rd globally; 54× growth; 47% of RE capacity; 24.5 GW added in 2024; PLI for solar; Aatmanirbhar solar; India's 500 GW non-fossil target by 2030.
Feb 2024 — 🇮🇳 SCHEME
PM Surya Ghar: Muft Bijli Yojana — World's Largest Domestic Rooftop Solar
📋 Launched:13 February 2024 by PM Narendra Modi. Total outlay: ₹75,021 crore. Aim: Install rooftop solar on 1 crore (10 million) households by March 2027. Target: add 30 GW of rooftop solar capacity in residential sector.
🎁 Benefits:Up to 300 units of electricity FREE per month (for 3 kW system). Subsidy: Up to 40% for systems 1–3 kW; 20% for 3–10 kW. Collateral-free loans via JanSamarth Portal. Surplus electricity sold to DISCOM — earning ₹17,000–18,000/year. Grid-connected: net metering enabled.
📊 Progress (Dec 2025):23.9 lakh households installed, 7 GW capacity, ₹13,464 crore subsidy released, 5.79 lakh collateral-free loans of ₹10,907 crore sanctioned. 1.45 crore registrations on National Portal. 10 lakh milestone reached March 10, 2025.
⚠️ Challenge:Only 22.7% of applications have translated into completed installations — bottlenecks in vendor capacity, DISCOM approvals, and financing disbursement.
2019–2025 — 🇮🇳 SCHEME
PM-KUSUM — Solar Energy for Farmers: 9.2 Lakh Solar Pumps
🌾 Scheme:PM Kisan Urja Suraksha evam Utthaan Mahabhiyan. Launched 2019. Three components: A (ground-mounted decentralised solar plants), B (standalone solar pumps), C (solarisation of grid-connected agricultural pumps). Total target: 30.8 GW.
📊 Progress:Component B: 9.2 lakh standalone solar pumps installed (as of 2025). Farmers receive 60% subsidy on solar pumps. Daytime solar-powered irrigation — reduces diesel consumption. Surplus energy sold to grid — additional income for farmers.
🎯 Significance:Transforms farmers from energy consumers to energy producers. Reduces agriculture's dependence on subsidised diesel. Reduces groundwater over-extraction (solar pumps work only during daytime, not 24/7 like electric pumps). Helps India's emission reduction goals for agriculture sector.
2024–2025 — 🇮🇳 EMERGING
Khavda RE Park + Floating Solar + Agrivoltaics — India's Next Solar Frontier
🌊 Floating Solar:Omkareshwar Dam floating solar (MP): 600 MW planned, ~278 MW commissioned (2025). NTPC Simhadri: 25 MW floating solar on ash pond (Andhra Pradesh). India targeting 10 GW floating solar by 2030. Advantages: saves land, reduces water evaporation from reservoirs, water cools panels (5–10% better efficiency).
🌾 Agrivoltaics:India piloting agrivoltaic systems in Rajasthan, Gujarat, Karnataka under PM-KUSUM. Research shows crop yield maintained or improved under shade of panels in hot conditions. PM-KUSUM Component A specifically enables farmers to install solar on agricultural land.
⚡ Khavda RE Park:Adani's Khavda Renewable Energy Park (Gujarat) — planned 30 GW (solar + wind combined) — set to become the world's largest single-location renewable energy park. 1 GW commissioned by early 2024. By April 2025, construction significantly advanced. Located in Rann of Kutch — one of India's sunniest, windiest areas with minimal agricultural use.
🏆 Solar Trees:CSIR-CMERI (Durgapur, West Bengal) installed the world's largest solar tree with 11.5 kW capacity — recognized internationally. Requires 1/10th the land of equivalent conventional solar. India leading this emerging technology.
Section 09 — PYQs & MCQs
📝 Previous Year Questions & Practice MCQs
PYQ — Prelims 2021 Consider the following statements about solar energy in India:
1. India's total solar energy potential is estimated to be 748 GWp by the National Institute of Solar Energy (NISE).
2. Concentrated Solar Power (CSP) plants can generate electricity even when the sun is not shining, due to thermal energy storage.
3. Bhadla Solar Park in Rajasthan is the world's largest solar park with 2,245 MW capacity.
4. The photovoltaic effect refers to the generation of voltage/current in a material upon exposure to heat.
1. India's total solar energy potential is estimated to be 748 GWp by the National Institute of Solar Energy (NISE).
2. Concentrated Solar Power (CSP) plants can generate electricity even when the sun is not shining, due to thermal energy storage.
3. Bhadla Solar Park in Rajasthan is the world's largest solar park with 2,245 MW capacity.
4. The photovoltaic effect refers to the generation of voltage/current in a material upon exposure to heat.
a) 1, 2 and 3 only
b) 2 and 4 only
c) 1, 2 and 3 only
d) 1, 2, 3 and 4
Statement 1 ✓ — India's solar energy potential is estimated at 748 GWp by NISE (National Institute of Solar Energy), a National R&D institution under MNRE located at Gurugram. This is based on India's land availability, solar irradiance, and technological assumptions — India's actual installed capacity (143 GW, Feb 2026) is still only about 19% of this potential. Statement 2 ✓ — CSP's key advantage over PV is its ability to incorporate thermal energy storage (TES). During sunshine hours, the heat transfer fluid (typically molten salt) is heated and some energy diverted to insulated storage tanks. After sunset, this stored heat drives the steam turbine to generate electricity. CSP plants can typically store 6–15 hours of thermal energy — enabling dispatchable, reliable power generation around the clock. This is why CSP is sometimes called "solar baseload" power. Statement 3 ✓ — Bhadla Solar Park (Jodhpur district, Rajasthan, Thar Desert) has 2,245 MW of installed solar capacity spread across 56 km² (14,000 acres). It is India's largest solar park. As of 2024/2025, it is the world's 11th largest (some sources still cite it as largest — depends on measurement methodology). Statement 4 ✗ — CRITICAL TRAP: The photovoltaic effect is NOT the generation of voltage/current upon exposure to HEAT — that would be the thermoelectric (Seebeck) effect or the thermionic effect. The photovoltaic effect is the generation of voltage/current in a material (semiconductor) upon exposure to LIGHT (photons). "Photo" = light; "voltaic" = electricity. Discovered by Edmond Becquerel in 1839. First practical solar cell created by Bell Labs in 1954. Heat-to-electricity is thermoelectric; light-to-electricity is photovoltaic. Answer: (a)/(c) — Statements 1, 2, and 3 only.
PYQ — Prelims 2020 With reference to 'PM-KUSUM' scheme, consider the following statements:
1. The scheme helps farmers to set up solar power plants on their barren/fallow lands and sell electricity to the grid.
2. It provides standalone solar pumps to farmers for irrigation.
3. It enables solarisation of grid-connected agriculture pumps.
Which of the statements are correct?
1. The scheme helps farmers to set up solar power plants on their barren/fallow lands and sell electricity to the grid.
2. It provides standalone solar pumps to farmers for irrigation.
3. It enables solarisation of grid-connected agriculture pumps.
Which of the statements are correct?
a) 1 only
b) 2 and 3 only
c) 1, 2 and 3
d) 1 and 3 only
All three statements are correct — they correspond to the three components of PM-KUSUM. Statement 1 ✓ = Component A: Decentralised ground-mounted solar plants of 500 kW to 2 MW capacity set up by individual farmers, cooperatives, panchayats, or farmer producer organisations on their barren/fallow/agricultural land. Power generated is sold to DISCOMs (electricity distribution companies) at a fixed tariff — providing farmers with a steady, guaranteed income from energy production. This transforms farmers from passive energy consumers to active energy producers. Statement 2 ✓ = Component B: Installation of standalone solar pumps of up to 7.5 HP capacity for farmers with no grid connection. Replaces diesel-powered pumps — eliminating fuel costs and running expenses. Farmer pays only 10% of cost; 30% state subsidy + 30% central subsidy + 30% bank loan. Up to 9.2 lakh standalone solar pumps installed by 2025. Statement 3 ✓ = Component C: Solarisation of existing grid-connected agricultural pumps. Solar panels installed alongside existing electric pump systems — solar powers the pump during day, with grid as backup. Any surplus solar electricity is fed back to the grid, earning the farmer additional income. Also encourages efficient irrigation — solar availability is finite and daytime-only, naturally discouraging nocturnal over-pumping that depletes groundwater. Answer: (c) — all three statements are correct.
Q1 With reference to PM Surya Ghar: Muft Bijli Yojana (2024), consider the following statements:
1. It targets installation of rooftop solar on 1 crore households with a total outlay of ₹75,021 crore.
2. Eligible households can get up to 300 units of free electricity per month.
3. The scheme is restricted only to rural households and does not cover urban areas.
4. Households can earn additional income by selling surplus electricity to distribution companies.
1. It targets installation of rooftop solar on 1 crore households with a total outlay of ₹75,021 crore.
2. Eligible households can get up to 300 units of free electricity per month.
3. The scheme is restricted only to rural households and does not cover urban areas.
4. Households can earn additional income by selling surplus electricity to distribution companies.
a) 1 and 3 only
b) 1, 2 and 4 only
c) 2 and 4 only
d) 1, 2, 3 and 4
Statement 1 ✓ — PM Surya Ghar: Muft Bijli Yojana was launched on 13 February 2024 by PM Modi. Total outlay: ₹75,021 crore (~US$9 billion). Target: Install rooftop solar panels on 1 crore (10 million) households by March 2027. It is the world's largest domestic rooftop solar initiative. The scheme operates through the National Portal (www.pmsuryaghar.gov.in) — consumers register, select vendors, apply for subsidy and loans. Statement 2 ✓ — Eligible households that install 3 kW rooftop solar systems receive up to 300 units of electricity free per month. This is enabled through net metering — the solar panels generate electricity during the day, reducing/eliminating grid consumption for most households. Smaller systems (1–2 kW) generate proportionally less free units. Statement 3 ✗ — WRONG: PM Surya Ghar is NOT restricted to rural households. It covers ALL households across India — rural AND urban. Urban households (apartments, independent houses) can also install rooftop solar and avail subsidies and loans under the scheme. Many early adopters are actually urban middle-class households. There is no rural-urban restriction in the scheme. Statement 4 ✓ — Households that generate more solar electricity than they consume can sell the surplus to their local DISCOM (electricity distribution company) through net metering. A typical 3 kW solar system can generate more than 300 units per month, allowing households to earn ₹17,000–18,000 per year by selling surplus electricity. This income-generation aspect is a key selling point of the scheme. Answer: (b) — Statements 1, 2, and 4 only.
Q2 Which of the following correctly distinguishes Solar PV from Concentrated Solar Power (CSP)?
1. Solar PV converts light directly to electricity; CSP converts sunlight to heat to electricity.
2. CSP systems can generate electricity at night using thermal energy storage; PV cannot without batteries.
3. Solar PV requires Direct Normal Irradiance (DNI) to function; CSP works with diffuse sunlight as well.
4. Commercial solar PV cells have efficiency of 15–22%; CSP plants have power cycle efficiency of 30–45%.
1. Solar PV converts light directly to electricity; CSP converts sunlight to heat to electricity.
2. CSP systems can generate electricity at night using thermal energy storage; PV cannot without batteries.
3. Solar PV requires Direct Normal Irradiance (DNI) to function; CSP works with diffuse sunlight as well.
4. Commercial solar PV cells have efficiency of 15–22%; CSP plants have power cycle efficiency of 30–45%.
a) 1 and 2 only
b) 1, 2 and 4 only
c) 2, 3 and 4 only
d) 1, 2, 3 and 4
Statement 1 ✓ — This is the fundamental distinction: Solar PV uses the photovoltaic effect (photons → electrons → DC electricity) — a direct conversion with no intermediate heat stage. CSP uses mirrors/lenses to concentrate sunlight → generates intense heat (500–1000°C) → heats fluid → steam turbine → generator → AC electricity. CSP is an indirect conversion pathway (light → heat → motion → electricity). Statement 2 ✓ — This is CSP's critical advantage over PV: CSP plants can incorporate Thermal Energy Storage (TES) — typically molten salt stored in insulated tanks. During the day, some heat is diverted to storage; after sunset, this stored heat drives the turbine for 6–15 hours. CSP thus provides "dispatchable" (on-demand) power — like a conventional thermal plant but fuelled by stored solar heat. PV without batteries stops generating at sunset. PV+battery storage is increasingly competitive but still more expensive for longer durations. Statement 3 ✗ — EXACT REVERSE: It is CSP (NOT PV) that requires Direct Normal Irradiance (DNI) — the direct beam component of sunlight that can be focused by mirrors. CSP CANNOT use diffuse, scattered sunlight (cloudy, hazy conditions). Solar PV, on the other hand, can work with both direct AND diffuse sunlight — PV panels still generate electricity (at reduced efficiency) on cloudy days. This is why PV is deployable in more locations (including cloudy regions like Germany, UK) while CSP is mainly viable in high-DNI desert regions. Statement 4 ✓ — Commercial silicon PV cells have efficiency of 15–22% (monocrystalline typically 20–22%; polycrystalline 15–17%). CSP plants' steam turbines (Rankine cycle) have thermal-to-electrical efficiency of 30–45% depending on temperature. However, the mirrors' optical efficiency and heat losses mean overall solar-to-electricity efficiency for CSP is 15–20% in practice. Answer: (b) — Statements 1, 2, and 4 only.
Section 10
🧠 Memory Aid — Lock These In
🔑 Solar Energy — All Critical Facts for UPSC
INDIA STATS
Solar capacity: 2.63 GW (2014) → 100 GW (Jan 2025) → 143.6 GW (Feb 2026). 3rd globally (after China, USA). 47% of total RE capacity. Solar potential: 748 GWp (NISE estimate). Record 24.5 GW added in 2024. Solar tariff: ₹10.95/unit (2010) → ₹1.99/unit (2021). Top solar states: Rajasthan, Gujarat, Tamil Nadu.
3 TYPES
PV (light→electricity, 15–22% efficiency, intermittent, no storage). CSP (light→heat→electricity, thermal storage=generates at night!, needs DNI, not cost-competitive yet). SHC (light→heat for direct use, 50–80% efficiency, water heating, most cost-effective). TRAP: PV needs both direct AND diffuse; CSP needs ONLY direct (DNI).
KEY SCHEMES
NSM (2010): National Solar Mission, 100 GW target (achieved Jan 2025). PM-KUSUM (2019): 30.8 GW target, 3 components (A: ground plants, B: standalone pumps 9.2 lakh, C: grid pump solarisation), 60% subsidy. PM Surya Ghar (Feb 2024): ₹75,021 crore, 1 crore HH, 300 units free/month, 23.9 lakh installed (Dec 2025), 7 GW. PLI Solar: 38 GW→74 GW module capacity in 1 year, $2B exports.
MAJOR SITES
Bhadla Solar Park (Rajasthan, Jodhpur): 2,245 MW — India's largest, world's 11th (2025). Pavagada (Karnataka): 2,050 MW. Khavda RE Park (Gujarat, Adani): 30 GW planned (world's largest single-location RE when complete). Omkareshwar floating solar (MP): 600 MW planned. Cochin Airport: first fully solar-powered international airport.
EMERGING TECH
Floating solar (floatovoltaics) — saves land, less water evaporation. Agrivoltaics — crops + solar on same land. Perovskite cells — high efficiency potential (>30%), cheaper than silicon. Space-Based Solar (SBSP) — no day/night, ISRO+ESA research. Solar trees — CSIR-CMERI world's largest (11.5 kW, Durgapur WB). BIPV — solar in building materials. Solar carports — Tata Pune 6.2 MW (India's largest). Bifacial solar — 30% more energy.
ISA
International Solar Alliance — India proposed at COP21, 2015. HQ: Gurugram (Haryana). 125+ member nations. Target: $1 trillion solar investment by 2030. One Sun One World One Grid (OSOWOG) — global solar grid interconnection. Connects with ISA's "LiFE" and "Panchamrit" goals.
TRAPS 🪤
• Photovoltaic effect = LIGHT→electricity (NOT heat). Thermoelectric = heat→electricity (different!). • CSP needs DNI (direct); PV works with direct + diffuse (cloudy too). • CSP can generate at night (thermal storage); PV cannot without batteries. • Solar thermal efficiency (50-80%) > Solar PV efficiency (15-22%). • Bhadla = 2,245 MW — India's largest solar park (NOT Pavagada). • PM Surya Ghar = for ALL households (rural + urban; NOT only rural). • ISA HQ = Gurugram (NOT Delhi or Mumbai).
Section 11
❓ FAQs — Concept Clarity
What is the photovoltaic effect? How is it different from the thermoelectric effect?
This distinction is one of the most common UPSC traps in the solar energy topic. The Photovoltaic Effect (discovered by Edmond Becquerel, 1839): When light (photons) strikes the surface of a semiconductor material (like silicon), the photon energy is absorbed by electrons in the semiconductor's valence band. This energy allows electrons to break free from their atomic bonds and jump into the conduction band — where they can flow as electric current. The direction of current flow is determined by the p-n junction (a semiconductor junction between positive and negative doped silicon) — which creates a built-in electric field that pushes the freed electrons in one direction, creating a direct current (DC). Key words: LIGHT (photons) → electricity. Solar PV panels use this effect. The Thermoelectric Effect (Seebeck Effect, 1821): When there is a temperature difference between two junctions of dissimilar metals or semiconductors, it creates a voltage — which drives a current. This converts HEAT GRADIENT → electricity. Thermoelectric generators use this (e.g., in space probes like Voyager). Different from solar PV. The Photothermal Effect: Light → Heat (solar thermal collectors work this way — they absorb light and convert it to heat, not electricity directly). CSP plants use heat to drive turbines (heat → mechanical → electrical). So the three are: Photovoltaic = light → electricity. Thermoelectric = heat difference → electricity. Photothermal = light → heat → electricity (in CSP) or heat for direct use (in SHC). For UPSC: PV = photovoltaic = photons → voltage = light → electricity. If the question says "heat" → it's thermoelectric, not photovoltaic.
Why can CSP generate electricity at night but PV cannot?
This is about energy storage mechanisms — and why CSP is sometimes called "dispatchable solar" while PV is "variable solar." PV's situation: Solar PV panels convert sunlight to electricity at the moment of sunlight hitting the cell. No sun = no electricity. To store PV electricity, you need an external battery (electrochemical storage). Current lithium-ion batteries can typically store 2–4 hours of power for most grid applications. 8-hour overnight storage is expensive. CSP's thermal advantage: CSP plants use mirrors to concentrate sunlight → heat a fluid (like synthetic thermal oil or molten salt) to 400–600°C. This fluid flows through pipes. During peak sunshine, some of this hot fluid is diverted to large insulated tanks (thermal energy storage). The stored hot fluid retains its heat for hours (insulated tanks lose only 1-2% per hour). After sunset, this stored hot fluid flows through a heat exchanger → creates steam → drives a turbine → generates electricity for 6–15 hours. The stored thermal energy is much cheaper than equivalent battery storage (molten salt tanks cost $10–30/kWh; lithium batteries cost $150–300/kWh). Why CSP hasn't dominated despite this advantage: PV costs fell 89% between 2010 and 2024, making PV + battery storage increasingly competitive. CSP costs have not fallen proportionally. CSP also requires Direct Normal Irradiance (DNI) — it cannot use diffuse, scattered sunlight (works only in very sunny, clear-sky desert regions). PV works even in partly cloudy conditions. CSP also has higher water consumption for cooling turbines — a problem in arid solar regions. For UPSC: CSP = can store thermal energy → generate at night. PV = cannot generate at night (needs battery for storage).
What is agrivoltaics and why is it significant for India?
Agrivoltaics (also called agri-PV or agri-solar) refers to the simultaneous use of land for both solar energy generation and agricultural production. Solar panels are installed above crops — typically on elevated structures that allow farming equipment to operate underneath. This dual land use is particularly important for India for several reasons: India's land scarcity challenge: India has limited available land for utility-scale solar. Agricultural land covers 60% of India's land area and is essential for food security. Agrivoltaics allows the same land to serve both purposes. How crops benefit: Partial shade from solar panels can REDUCE water stress on crops (less evapotranspiration) — important in hot, dry conditions. Studies show yields of certain crops (lettuce, spinach, wheat, grapes) can be maintained or even improved under partial shade. The microclimate under panels is cooler and more humid. How solar benefits: Crops' evapotranspiration (water released by plants as vapour) cools the air under the panels — keeping panels cooler. Cooler panels operate more efficiently (solar panels lose ~0.4% efficiency per degree Celsius above 25°C). How farmers benefit: Agrivoltaic farmers earn from both crops AND electricity sales — diversifying and de-risking their income. PM-KUSUM Component A specifically encourages farmers to install ground-mounted solar on their barren or agricultural land and sell electricity to the grid. India's specific advantage: India's farmers face water scarcity, heat stress, and income volatility. Agrivoltaics addresses all three. Rajasthan, Gujarat, Karnataka are leading pilots. Challenges: High installation cost of elevated structures; crop management complexity; coordination with DISCOMs for grid connection. For UPSC: Agrivoltaics = dual land use (solar + agriculture) = addresses India's land constraint + farmer income + energy transition simultaneously. Connects to PM-KUSUM, farmer welfare, SDG 2 (food) + SDG 7 (energy).
Section 12
🏁 Conclusion — UPSC Synthesis
☀️ From 2.63 GW to 143 GW — India's Solar Decade
In 2014, India had 2.63 GW of solar capacity. In January 2025, it crossed 100 GW — a 38-fold increase in just a decade. This trajectory, which placed India among the world's top three solar nations, was driven by policy innovation (NSM, KUSUM, PM Surya Ghar), market discipline (competitive bidding brought tariffs from ₹10.95 to ₹1.99/unit), and geography (India's location gives it solar insolation among the world's highest). The journey ahead — from 143 GW to the 500 GW non-fossil target by 2030 — will require solving the harder problems: grid integration, 24/7 storage, manufacturing self-reliance, and ensuring that solar's benefits reach every farmer, village, and rooftop.
The PM Surya Ghar scheme, with 1 crore household targets and 300 units of free electricity, aims to make every Indian home an energy producer. Agrivoltaics, floating solar, and the Khavda mega park show that India is solving the land constraint creatively. The PLI scheme, which doubled solar module manufacturing capacity in one year, is making Aatmanirbhar solar a reality. The 748 GWp of untapped potential ensures the journey has barely begun.
