Explainer

Energy Explained

A plain-English guide to global energy — how we generate power, what the numbers mean, and how the transition to clean energy is unfolding.

Key Facts

Fossil fuels still provide about 80% of global primary energy, though their share of electricity is declining.

Solar is the fastest-growing energy source in history. In 2023, more solar capacity was installed than all other sources combined.

Wind and solar together now generate over 12% of global electricity, up from less than 2% a decade ago.

Renewables (including hydro) produce roughly 30% of the world's electricity — and the share is rising fast.

Battery storage costs have fallen ~90% since 2010, making variable renewables increasingly dispatchable.

Nuclear provides about 10% of global electricity — the largest source of non-fossil baseload power.

The power sector accounts for roughly 40% of global CO₂ emissions — the single largest source.

LED lighting uses ~75% less energy than incandescent bulbs — a simple efficiency gain that saves ~5% of global electricity.

How Global Energy Works

Everything that moves, heats, lights, or computes uses energy. Globally, we consume roughly 580 exajoules (EJ) of primary energy every year. The vast majority — about 80% — still comes from fossil fuels: oil (for transport), gas (for heat and electricity), and coal (mainly for electricity and steel).

Electricity is only one slice of the energy system — around 20% of final energy use — but it's the most important slice for decarbonisation, because clean alternatives (solar, wind, nuclear, hydro) can replace fossil fuels directly. The rest of the energy system (transport, heating, industry) is harder to decarbonise and increasingly relies on electrification: replacing petrol cars with EVs, gas boilers with heat pumps, and coal furnaces with electric arc furnaces.

The energy transition is the generational shift away from fossil fuels. It's driven by three forces: climate policy (Paris Agreement targets), economics (solar and wind are now the cheapest new-build electricity in most regions), and energy security (countries want to reduce dependence on imported oil and gas).

The challenge is speed. Even though renewables are growing exponentially, total energy demand is also rising — especially in developing nations. The atmosphere doesn't care about renewable share; it cares about absolute emissions. As long as total fossil-fuel use keeps rising, emissions keep rising. The inflection point — where global fossil use starts declining, not just growing more slowly — has not yet arrived.

Energy storage and grid flexibility are the missing pieces. Wind and solar are intermittent — they produce power when conditions allow, not necessarily when demand peaks. Batteries, pumped hydro, demand response, and interconnectors between regions are all part of the solution. Green hydrogen may eventually decarbonise sectors that electricity can't easily reach.

Understanding Energy Units

Energy data can be confusing because different sources use different units. Here's a quick guide:

Unit	What it means	Typical use
kWh	Kilowatt-hour	Household electricity bills
MWh	1,000 kWh	Small solar farms
GWh	1 million kWh	Power station annual output
TWh	1 billion kWh	Country-level generation
EJ	Exajoule (278 TWh)	Global energy statistics
GW	Gigawatt (power, not energy)	Installed capacity
gCO₂/kWh	Carbon intensity	Grid cleanliness

Power (W, kW, GW) = rate of energy use at a moment. Energy (Wh, kWh, TWh) = total energy consumed over time. A 100 W lightbulb running for 10 hours uses 1 kWh.

Glossary

Primary energy

The total energy extracted from natural sources before any conversion. Includes fossil fuels burned directly for heat, plus the fuel inputs to power stations — not just the electricity they produce.

Final energy

Energy delivered to end users (homes, factories, vehicles) after conversion losses. Roughly two-thirds of primary energy is lost as waste heat during conversion and transmission.

TWh (terawatt-hour)

A unit of energy equal to 1 billion kilowatt-hours. Global electricity generation is roughly 29,000 TWh per year. One TWh could power about 150,000 UK homes for a year.

kWh (kilowatt-hour)

The standard unit for household energy bills. One kWh = using a 1,000-watt appliance for one hour. A UK home uses roughly 3,500 kWh of electricity per year.

Capacity vs generation

Capacity (measured in GW) is the maximum a power plant can produce. Generation (TWh) is what it actually produces. Solar panels may have 20% capacity factor (produce 20% of theoretical maximum) because the sun doesn't always shine.

Capacity factor

The ratio of actual energy output to the theoretical maximum over a period. Nuclear ≈ 90%, wind ≈ 25-45%, solar ≈ 15-25%, depending on location.

Fossil fuels

Coal, oil, and natural gas — formed from ancient organic matter over millions of years. When burned, they release stored carbon as CO₂. They still supply about 80% of global primary energy.

Renewable energy

Energy from sources that replenish naturally: solar, wind, hydropower, geothermal, and biomass. Renewables now generate around 30% of global electricity.

Solar PV

Photovoltaic panels that convert sunlight directly to electricity. The fastest-growing energy source — solar generation has roughly doubled every 3 years over the past decade.

Wind power

Turbines converting kinetic energy from wind to electricity. Onshore wind is one of the cheapest new electricity sources globally. Offshore wind is growing rapidly.

Hydropower

Electricity from flowing water, usually via dams. The largest source of renewable electricity globally, but limited by geography and environmental concerns.

Nuclear energy

Electricity from nuclear fission (splitting heavy atoms like uranium). Produces minimal greenhouse gases during operation, but faces challenges around cost, waste, and public perception.

Grid

The interconnected network of power stations, transmission lines, and distribution systems that deliver electricity from generators to consumers.

Baseload

The minimum level of electricity demand over a 24-hour period. Traditionally met by coal or nuclear; renewables + storage are increasingly filling this role.

Intermittency

The variability of wind and solar output due to weather and daylight. Addressed through grid storage (batteries), interconnection, flexible demand, and backup generation.

Energy storage

Technologies that store excess energy for later use. Lithium-ion batteries dominate short-term storage; pumped hydro provides 90% of current grid-scale storage.

Electrification

Switching end uses (heating, transport, industry) from fossil fuels to electricity, ideally from clean sources. A key decarbonisation strategy.

Carbon intensity of electricity

Grams of CO₂ emitted per kWh of electricity generated. Ranges from ~0 g (hydro, nuclear, wind, solar) to ~900 g (coal). The global average is about 440 g/kWh.

LCOE

Levelised Cost of Energy — the average cost per kWh over a power plant's lifetime, including construction and fuel. Solar and onshore wind are now the cheapest new-build electricity sources in most of the world.

Energy transition

The global shift from fossil fuels to cleaner energy sources. Involves scaling renewables, improving efficiency, electrifying transport and heat, and developing storage and hydrogen.

Green hydrogen

Hydrogen produced by splitting water using renewable electricity (electrolysis). Potential zero-carbon fuel for heavy industry, shipping, and aviation.

Energy per capita

Total energy consumption divided by population. High-income countries typically use 5-10× more energy per person than low-income countries.

Explore Energy Data

See these concepts in action with real data on our dashboard pages:

Global & Country Energy

Energy mix, renewables, electricity generation

CO₂ Emissions

Country rankings & global trends

Climate Dashboard

Temperature, CO₂ & weather data

Greenhouse Gases

CO₂, methane & N₂O concentrations