A source of energy is any material or process that yields usable energy for human activities. For example, sunlight is a source of solar energy used for heating and electricity generation.

Renewable sources are naturally replenished within a short time (e.g., solar, wind), while non‑renewable sources exist in limited quantities and take millions of years to form (e.g., coal, petroleum).

Commercial sources are energy forms bought/sold in markets, like electricity and petrol. Non‑commercial sources are used locally without trade, such as firewood and cow dung used in rural households.

Classification helps in choosing appropriate energy strategies, understanding sustainability, planning resource use and reducing environmental impacts by encouraging renewables over finite fossil fuels.

Solar energy (electricity via PV panels), wind energy (power generation through turbines), and biomass (cooking fuel or biogas production).

Energy security refers to the reliable and affordable availability of energy sources to meet a country's needs, minimizing supply disruptions and dependence on imports.

Conservation reduces demand through behaviour change (switching off unused lights, efficient habits), lowering resource depletion and environmental impact while extending existing supplies.

Coal forms from ancient plant matter buried and compressed over millions of years under high pressure and heat. It is primarily used in thermal power plants to generate electricity and in industries like steel production.

Petroleum (crude oil) is obtained by drilling wells into underground reservoirs and refining the oil into useful products. Major uses include fuels like petrol and diesel for transportation and as raw materials in chemical industries.

Natural gas is mostly methane (CH₄) trapped underground. It produces less carbon dioxide and particulate emissions per unit energy compared to coal, making it a relatively cleaner fossil fuel for heating and electricity.

Burning fossil fuels releases greenhouse gases like CO₂ contributing to global warming, and pollutants such as SO₂ and NOₓ that cause acid rain and respiratory illnesses.

'Peak oil' is the point when global oil production reaches its maximum and begins to decline, signaling potential supply constraints and the need for alternative energy sources and conservation measures.

Combustion releases smoke, soot and gases that contribute to smog and particulate pollution, worsening respiratory health and visibility in urban areas.

Coal ash is the solid residue after coal is burned in power plants. It can be managed by safe disposal in ash ponds, recycling into construction materials, or using dry ash handling systems to reduce environmental risks.

Alternatives are needed because fossil fuels are finite, cause pollution and climate change, and their extraction and use have social and ecological impacts; renewables offer sustainable, low‑emission options.

Energy density is the amount of energy stored per unit mass or volume of a fuel; fuels with higher energy density, like petrol, store more energy in less space than lower density fuels.

Petroleum is a feedstock in petrochemical industries producing plastics, synthetic fibers, fertilizers and numerous chemical products used in daily life.

Photovoltaic (PV) cells use semiconductor materials (usually silicon) that absorb photons from sunlight, freeing electrons and creating a flow of electric current which can be harnessed as electricity.

Solar thermal energy is used for heating domestic water (solar water heaters) and in concentrated solar power plants to generate steam for electricity production.

Advantage: Solar power is clean with minimal operational emissions. Limitation: Intermittency — electricity generation depends on sunlight availability and requires storage or backup systems for continuous supply.

A solar array is a collection of solar panels wired together to increase total power output, enabling installation-scale generation for homes, schools, or utility plants.

By storing energy in batteries (electrochemical storage) or using thermal storage (storing heat in molten salts or insulated tanks) which can supply power after sunset.

Panel orientation, angle, temperature, shading, quality of cells and dust accumulation all affect a PV system's efficiency and overall output.

It reduces dependence on grid electricity from fossil fuels, lowering CO₂ emissions and decreasing transmission losses due to local generation.

Net metering allows homeowners to feed excess solar-generated electricity into the grid and receive credit, offsetting their electricity bills for energy drawn from the grid later.

Wind turbines use aerodynamic blades that capture wind's kinetic energy, rotating a shaft connected to a generator which converts mechanical rotation into electrical energy.

Consistent and strong wind speeds, open terrain or coastal exposure, accessibility, and minimal environmental or social conflicts make a site suitable for wind energy development.

Run-of-the-river projects generate power from flowing river water with little storage, causing minimal inundation; reservoir-based projects store large water volumes behind dams, offering better control and peaking power but more environmental impact.

Pumped-storage uses two reservoirs at different elevations; excess electricity pumps water uphill to store energy, which is released to generate power during peak demand—useful for grid balancing and storage.

Large dams can disrupt aquatic ecosystems, block fish migration, cause sedimentation, and lead to the loss of terrestrial habitats and displacement of people.

Variability leads to fluctuating output requiring storage, diversified geographic distribution or backup generation to maintain reliable electricity supply.

Yes — small hydropower (micro/mini projects) typically require less inundation, cause limited displacement and have lower ecological impacts while supplying local communities.

Offshore sites often have stronger and more consistent winds and allow larger turbines and arrays without land-use conflicts, increasing generation potential despite higher installation costs.

Flooded vegetation in large reservoirs decomposes anaerobically releasing methane (CH₄), a potent greenhouse gas; tropical reservoirs are particularly prone to such emissions.

Biogas is produced by anaerobic digestion of organic matter (animal dung, kitchen waste) in biogas plants; it can be used for cooking, lighting, or electricity generation in rural settings.

Responsible biomass use recycles agricultural waste, reduces dependence on fossil fuels, supports rural energy needs and can be sustainable if harvesting is controlled and emissions minimized.

Tidal energy is site‑specific, dependent on tidal range and coastal geography, has high initial costs and potential ecological impacts on marine habitats and sediment transport.

Geothermal energy uses heat from Earth's interior accessed via hot springs or deep wells; it is most useful in tectonically active regions with accessible geothermal reservoirs for electricity or direct heating.

Biomass energy, such as fuelwood collection, biogas systems, and agro-residue utilization, can provide local employment, reduce cooking costs and enhance energy access in rural communities.

Sustainable biomass use requires proper management of resources, avoiding overharvesting, efficient conversion technologies, and measures to minimize air pollution from burning.

Nuclear plants generate heat through nuclear fission of heavy nuclei (like uranium‑235), which produces heat to create steam that drives turbines to produce electricity.

Advantages: High energy density and low CO₂ emissions during operation. Concern: Radioactive waste management and potential safety risks from accidents or leaks.

Radioactive waste contains unstable isotopes emitting radiation; it is managed through containment, long-term storage in secure facilities, and, where possible, reprocessing to reduce volume and hazard.

High costs arise from complex reactor technology, stringent safety systems, long construction times, regulatory compliance and the need for secure waste handling and decommissioning plans.

Chemical energy in coal → thermal energy by burning → mechanical energy in turbine (steam-driven) → electrical energy via generator, which is transmitted to consumers.

Energy efficiency means achieving the same service using less energy; for example, replacing incandescent bulbs with LED lights provides the same illumination using significantly less electricity.

Conservation involves behavioural changes to reduce energy use (e.g., switching off lights), while efficiency involves using better technologies to perform the same task with less energy (e.g., efficient motors).

Install energy‑efficient lighting (LEDs), promote natural ventilation/daylighting, and adopt rooftop solar panels with awareness programs to reduce consumption and educate students.

Storage (batteries, pumped hydro, thermal storage) smooths variability by storing excess energy for use during low generation periods, improving reliability and grid integration of renewables.

A diversified energy mix ensures reliability, reduces dependence on any single source, balances cost and environmental impact, and improves resilience against supply shocks while enabling transition to cleaner energy.