Last reviewed 16 Sept 2026 · Facts as of 16 Sept 2026 · 9 min read
Energy basics
Energy — capacity to do work (SI unit joule). Commercial electricity is billed in kWh (1 kWh = 3.6 MJ).
| Classification | Types |
|---|---|
| Forms | Mechanical (kinetic, potential), thermal, chemical, electrical, nuclear, radiant (light) |
| Primary energy | Found in nature — coal, crude oil, natural gas, uranium, sunlight, wind, flowing water, biomass |
| Secondary energy | Converted forms — electricity, petrol, diesel, hydrogen, steam |
| Commercial | Traded — coal, oil, gas, electricity |
| Non-commercial | Traditional — firewood, crop residues, cattle dung (rural areas) |
| Non-renewable (conventional) | Finite — fossil fuels, nuclear fuels |
| Renewable | Naturally replenished — solar, wind, hydro, biomass, geothermal, tidal |
Common units: 1 kcal ≈ 4.187 kJ; 1 kWh = 860 kcal; tonne of oil equivalent (toe) ≈ 41.868 GJ (10⁷ kcal); 1 hp ≈ 746 W (imperial) / 735.5 W (metric).
Why energy conservation?
- Fossil fuels are finite and largely imported (oil) — energy security and foreign exchange.
- Greenhouse gas emissions and air pollution.
- Cost savings for consumers and industry; reduced need for new power plants ("negawatts").
- Affordable access to energy for growing demand.
Energy conservation vs energy efficiency
| Energy conservation | Energy efficiency |
|---|---|
| Reducing energy use by changing behaviour or avoiding waste (switching off lights, using natural light) | Using less energy for the same output/service through better technology (LED lamps, efficient motors) |
Both are complementary; efficiency usually requires investment, conservation requires awareness.
Legal and institutional framework in India
Energy Conservation Act, 2001
- Provided the legal framework for energy efficiency; established the Bureau of Energy Efficiency (BEE) (operational from 2002) under the Ministry of Power.
- Key provisions: standards and labelling of appliances, energy conservation building codes, designated consumers (energy-intensive industries) with mandatory energy audits, energy managers and targets; state designated agencies.
- Energy Conservation (Amendment) Act, 2022 — enables a carbon credit trading scheme, mandates use of non-fossil energy sources by designated consumers, expands building codes to larger residential buildings, and strengthens penalties.
BEE programmes
| Programme | Description |
|---|---|
| Standards and Labelling (S&L) | Star ratings (1 to 5 stars) on appliances such as air conditioners, refrigerators, ceiling fans, geysers, motors, transformers, LED lamps — more stars = more efficient |
| Energy Conservation Building Code (ECBC) | Minimum energy performance for commercial buildings (first 2007, revised 2017; later updated as the Energy Conservation and Sustainable Building Code) |
| Eco Niwas Samhita | Energy code for residential buildings (2018) |
| PAT (Perform, Achieve and Trade) | Market-based scheme for energy-intensive industries: targets for specific energy consumption; energy saving certificates (ESCerts) traded by over-achievers |
| Designated consumers | Energy-intensive sectors (thermal power, cement, iron and steel, fertiliser, aluminium, textiles, pulp and paper, chlor-alkali, railways, refineries, DISCOMs, etc.) |
| Demand side management, energy managers and auditors certification | Capacity building |
UJALA
- Unnati Jyoti by Affordable LEDs for All (launched 2015) — distribution of LED bulbs (and efficient tube lights and fans) at subsidised prices through EESL (Energy Efficiency Services Limited); with the Street Lighting National Programme (SLNP) replacing conventional street lights with LEDs.
Energy audit
Energy audit — systematic examination of energy use to identify saving opportunities.
| Type | Scope |
|---|---|
| Preliminary (walk-through) audit | Quick assessment using available data; identifies obvious savings and areas for detailed study |
| Detailed (comprehensive) audit | Measurements, energy balance, detailed techno-economic analysis of savings measures |
Steps: data collection (bills, equipment inventory) → measurement (power analysers, lux meters, flow meters, thermography) → energy balance and benchmarking (e.g. kWh/m² for buildings) → identify energy conservation measures (ECMs) → cost–benefit and payback analysis → implementation → monitoring and verification.
Energy efficiency measures
| Area | Measures |
|---|---|
| Buildings | Orientation, shading, insulation, cool roofs, efficient glazing, daylighting, natural ventilation, efficient HVAC (inverter ACs, VRF), BMS, star-rated appliances, green building ratings |
| Lighting | LEDs (much lower power than incandescent/CFL for similar light), occupancy and daylight sensors, task lighting |
| Motors and drives | High-efficiency (IE3/IE4) motors, variable frequency drives (VFDs) for pumps and fans, correct sizing, power factor correction |
| Pumping systems (water supply, irrigation, sewage) | Efficient pumps at best efficiency point, reduced friction losses, leak control, VFDs, solar pumps; pump power ∝ flow × head |
| Construction | Efficient equipment, reduced idling, planning haul routes, energy-efficient materials (blended cements, fly ash bricks), prefabrication, LED site lighting, solar-powered site offices |
| Transport | Public transport, electric mobility, efficient logistics |
| Industry | Waste heat recovery, cogeneration, process optimisation |
Renewable energy sources
Solar energy
| Technology | Principle | Applications |
|---|---|---|
| Solar photovoltaic (PV) | Semiconductor cells convert sunlight directly into DC electricity; inverters convert to AC | Grid-connected solar parks, rooftop solar, solar street lights, solar pumps |
| Solar thermal | Collectors absorb heat | Solar water heaters, solar cookers, dryers, concentrated solar power (CSP) |
| Passive solar design | Building orientation, thermal mass | Heating/cooling of buildings |
- Output depends on solar irradiation, panel orientation/tilt, temperature, shading and dust; India has high solar potential (many regions with roughly 4–7 kWh/m²/day irradiation).
- Grid-connected (net metering/gross metering) vs off-grid (with batteries).
Wind energy
- Wind turbines convert kinetic energy of wind: — power ∝ cube of wind speed; Betz limit .
- Onshore and offshore wind; best sites in coastal and plateau regions (e.g. Tamil Nadu, Gujarat, Karnataka, Maharashtra, Rajasthan).
- Issues: intermittency, land use, noise, bird strikes.
Hydropower
- ; large hydro, small hydro (in India generally up to 25 MW, classified as renewable), mini and micro hydro; pumped storage for grid balancing.
- Clean and flexible, but environmental and rehabilitation impacts for large dams.
Bioenergy
- Biomass combustion and cogeneration (e.g. bagasse in sugar mills), biogas (anaerobic digestion — roughly 55–65% methane), compressed biogas (CBG), biofuels — ethanol blending with petrol, biodiesel; waste-to-energy plants.
Other renewables
- Geothermal — heat from the earth (limited sites in India, e.g. Puga valley in Ladakh has been studied).
- Tidal and wave energy — potential in the Gulf of Khambhat, Gulf of Kutch and Sundarbans (largely untapped).
- Ocean thermal energy conversion (OTEC) — temperature difference in ocean layers.
Green hydrogen and storage
- Green hydrogen — produced by electrolysis of water using renewable electricity; used for fertilisers, refineries, steel, heavy transport. (Grey hydrogen from natural gas; blue with carbon capture.)
- Energy storage — battery energy storage systems (BESS), pumped hydro storage — essential to integrate variable solar and wind.