Renewable energy comes from sources that are naturally replenished on a human timescale. Examples include solar, wind, hydroelectric, geothermal, and biomass. Non-renewable energy sources (fossil fuels: coal, oil, natural gas; nuclear) are finite and will eventually run out. Which energy source is renewable?

Solar energy is captured using photovoltaic (PV) cells (solar panels) that convert sunlight directly into electricity. Solar thermal systems use sunlight to heat water or air. The cost of solar panels has dropped by about 90% since 2010. Solar is the fastest-growing energy source. What is the main advantage of solar energy?

Wind turbines convert the kinetic energy of wind into electricity. Wind power is one of the fastest-growing renewable energy sources. Wind farms can be on land (onshore) or in the ocean (offshore). Offshore wind is more consistent but more expensive. What is a disadvantage of wind energy?

Hydroelectric power uses the energy of flowing water (rivers, dams) to spin turbines and generate electricity. It is the largest source of renewable electricity worldwide. The Three Gorges Dam in China is the largest hydroelectric plant (22.5 GW). What is a disadvantage of large dams?

Geothermal energy uses heat from the Earth's interior to generate electricity or heat buildings. It is available 24/7 (not intermittent). Iceland gets about 90% of its heating and 25% of its electricity from geothermal. The largest geothermal plant is The Geysers in California (about 1.5 GW). What is the main advantage of geothermal energy?

Biomass energy uses organic matter (wood, crops, manure, agricultural waste) to produce heat, electricity, or biofuels (ethanol, biodiesel). Biomass is considered renewable if the organic matter is regrown (sustainable). However, burning biomass releases CO₂, but it is part of the current carbon cycle (unlike fossil fuels). What is a disadvantage of biomass energy?

Energy storage is essential for integrating intermittent renewable sources (solar, wind) into the grid. Batteries (lithium-ion, flow batteries), pumped hydro storage, compressed air energy storage (CAES), and hydrogen are used. Pumped hydro is the most common form of grid energy storage (about 95% of storage capacity). How does pumped hydro work?

Nuclear power uses uranium (a finite resource) to generate heat through nuclear fission (splitting atoms). It produces no CO₂ emissions during operation, but it is non-renewable and creates radioactive waste. Nuclear waste remains dangerous for thousands of years. Accidents (Chernobyl, Fukushima) have caused widespread contamination. Is nuclear energy renewable?

Fossil fuels (coal, oil, natural gas) are formed from the remains of ancient plants and animals over millions of years. They are non-renewable and release CO₂ (greenhouse gas) when burned, causing climate change. Which fossil fuel is the cleanest (least CO₂ per unit of energy)?

The clean energy transition is the shift from fossil fuels to renewable energy sources to reduce greenhouse gas emissions and combat climate change. Many countries have committed to net-zero emissions by 2050. What is the main driver of the transition to renewable energy?