## TL;DR

Renewable energy comes from naturally replenishing sources: solar (photovoltaic: sunlight→electricity), wind (turbines), hydropower (dams), geothermal (Earth's heat), biomass, tidal. Solar and wind are now cheaper than fossil fuels in most of the world (LCOE). Transition challenge: intermittency — storage (batteries, pumped hydro) and grid modernization needed.

## Core Explanation

Solar PV: global capacity 1.6 TW (2024), growing ~30%/year. Wind: 1 TW (2024). China leads in both manufacturing and deployment. Li-ion batteries: costs dropped 97% since 1991. Duck curve: solar midday surplus, evening deficit — solved by storage + demand response. Nuclear: low-carbon but not renewable, controversial. 'The Stone Age didn't end because we ran out of stones' — energy transitions are about better alternatives.

## Further Reading

- [Sustainable Energy — Without the Hot Air (David MacKay)](https://www.withouthotair.com/)