Renewable Energy

Renewable energy (also called sustainable energy) is energy derived from natural sources that replenish on a human timescale, such as the sun, wind, flowing water, geothermal heat, and biomass (material derived from living organisms). It differs from fossil fuel energy—coal, oil, and gas—which takes millions of years to regenerate.

Most forms of renewable energy originate ultimately from solar energy: wind arises from temperature differences in the atmosphere, and water cycles depend on evaporation driven by the sun. Geothermal energy and tidal energy caused by the moon are the two exceptions.

Major types

Solar energy is captured by photovoltaic panels that convert light directly to electricity, or by systems that collect solar heat. Wind energy is generated by turbines with blades that convert air movement into mechanical rotation. Hydroelectric energy from dammed rivers has long been one of the largest sources of renewable electricity. Geothermal energy is used for electricity generation and heating buildings, while biomass and biofuels are made into fuels, plant material, and animal waste products.

Technical challenges

Solar and wind are intermittent sources: their output depends on time of day and weather. For this reason, electricity systems require energy storage (batteries, pumped hydroelectric storage), extensive grids connecting regions, and demand management. The cost of solar panels and batteries has fallen in recent years, expanding their use.

Climate and policy

Because electricity generation from these sources produces far less carbon dioxide than fossil fuels, governments have made renewable energy part of their commitments to reduce greenhouse gas emissions. International agreements, financial incentives, and electricity market rules drive this transition.