How Solar, Wind and Hydro Work — and Why Grids Are Being Rebuilt Around Them

Renewable electricity is generated from sources that replenish naturally — sunlight, wind, flowing water, underground heat and organic material — rather than fuels that are burned and depleted. According to the U.S. Energy Information Administration (EIA), each technology converts a different natural force into electricity through a distinct mechanism, and together they are now reshaping how power grids are planned and operated worldwide.

How each technology converts nature into electricity

Solar photovoltaic (PV) panels use solar cells that convert sunlight directly into electricity, the EIA explains, while a separate technology, solar thermal heating, uses collectors to absorb sunlight and heat water or air for space and water heating rather than generate electricity. Wind turbines, usually grouped into wind farms, capture the kinetic energy of moving air and convert it into electricity; in the United States most wind farms operate in the central region, with offshore projects planned.

Hydropower plants use flowing or falling water from dams and rivers to spin a turbine connected to a generator, per the EIA. A related form, pumped-storage hydropower, moves water between two reservoirs at different elevations, effectively storing energy by pumping water uphill when electricity is abundant and releasing it downhill to generate power when it is needed. Geothermal plants tap heat from the Earth's interior, while biomass facilities burn wood residues, municipal solid waste or biogas to generate power.

Renewables are growing faster than any other power source

Global renewable electricity generation is projected to rise from 9,900 terawatt-hours (TWh) in 2024 to 16,200 TWh in 2030, a 60% increase, according to the IEA's Renewables 2025 report. The agency forecasts that renewables will overtake coal-fired generation by the end of 2025, or by mid-2026 at the latest depending on hydropower output, making renewables the world's largest source of electricity. By 2030, renewables are expected to supply about 43% of global electricity generation, up from 32% in 2024, and to meet more than 90% of the growth in global electricity demand over that period.

Solar PV is driving most of this expansion, accounting for over half of the projected increase in renewable generation to 2030, the IEA says. Wind contributes roughly 30% of the increase, with onshore wind expected to add 732 gigawatts (GW) of new capacity and offshore wind 140 GW — more than double the previous five-year period. Hydropower is projected to add over 154 GW of new capacity, while pumped-storage hydropower capacity is forecast to double to 16.5 GW of annual additions by 2030.

The International Renewable Energy Agency (IRENA) reported that global renewable power capacity reached 5.14 terawatts (TW) by the end of 2025 after 692 GW of additions during the year, according to a summary of IRENA data published by pv magazine USA. Solar accounted for about 511 GW of that growth — roughly 75% of total renewable additions — and renewables made up 49% of all installed global power capacity and 85.6% of all power-capacity expansion added worldwide in 2025.

In the United States, wind and solar hit a new record

National figures mirror the global trend. The EIA reported that wind and utility-scale solar together generated a record 17% of U.S. electricity in 2025; including small-scale rooftop solar, the combined share reached 19% of total net generation. Wind power produced 464,000 gigawatt-hours (GWh), 3% more than in 2024, while utility-scale solar output jumped 34% to 296,000 GWh and small-scale solar rose 11% to 93,000 GWh. Two decades earlier, in 2005, wind and utility-scale solar supplied less than 1% of U.S. electricity, the EIA said.

Why variable power is forcing grids to change

Unlike a fuel-burning power plant that can run on demand, solar and wind output depends on weather and time of day — what the IEA and industry refer to as variable renewable energy. The IEA's Renewables 2025 report says that as solar PV and wind expand rapidly, curtailment — when grid operators scale back renewable output because transmission limits, stability requirements or oversupply prevent the system from absorbing all the power — is happening more often and in more places. Separately, the IEA's Electricity Mid-Year Update 2025 recorded a sharp rise in hours of negative electricity prices, when supply exceeds demand: Germany, the Netherlands and Spain saw negative prices in 8–9% of hours in the first half of 2025, up from 4–5% in 2024.

The IEA describes this as an "urgent need for greater flexibility in supply and demand," pointing to battery storage, demand response and updated market rules as remedies. Addressing the mismatch between variable generation and steady demand requires what the agency calls a comprehensive strategy involving transmission, flexibility and coordinated system planning — rather than any single fix.

What "grid transformation" actually means

• Storage: batteries and pumped-storage hydropower absorb surplus solar and wind output and release it when generation drops, which the IEA cites as central to managing variability.
• Transmission: new power lines move electricity from windy or sunny regions to population centers, part of what the IEA calls coordinated system planning.
• Flexible demand: shifting electricity use to match periods of high renewable output, one of the tools the IEA recommends alongside storage.
• Pumped-storage hydropower capacity additions are expected to double to 16.5 GW a year by 2030, according to the IEA, partly to address integration challenges in Europe.