Renewable energy explained: a simple guide

Renewable energy is not a niche or futuristic technology — it is already generating a substantial and growing share of electricity in many countries. Understanding the basics helps you make better decisions at home and cuts through a lot of noise in the public debate.

What renewable energy is

Renewable energy comes from naturally replenishing sources — ones that are not used up when you draw on them. The sun keeps shining, the wind keeps blowing, rivers keep flowing. This is in contrast to fossil fuels — coal, oil and natural gas — which formed over millions of years, exist in finite quantities, and are consumed (and converted into carbon dioxide) when burned.

"Renewable" is not quite the same as "clean" or "low-carbon," though there is a lot of overlap. See the FAQ below for the distinction. For practical purposes, most renewable energy sources produce dramatically fewer greenhouse gas emissions per unit of electricity than burning fossil fuels.

Why it matters

• Lower emissions. Burning fossil fuels for electricity and heat is a major source of the greenhouse gas emissions driving climate change. Switching to energy sources that don't burn anything substantially reduces those emissions.
• Cleaner air. Burning fossil fuels also produces air pollutants with direct health effects. Moving away from combustion improves local air quality, particularly in cities.
• Energy security. Countries that generate energy domestically from wind, sun and water are less exposed to price shocks and supply disruptions from imported fossil fuels. Many governments now support renewable energy partly for this reason.
• Cost. The cost of generating electricity from solar and wind has fallen dramatically over the past 15 years and is now among the cheapest forms of new electricity generation in many parts of the world. This makes the transition increasingly attractive on straightforward economic grounds.

The main types explained

Solar energy

Solar photovoltaic (PV) panels convert sunlight directly into electricity. They work on cloudy days (though less effectively) and can be installed on rooftops, in fields or integrated into building materials. Solar PV is now one of the most widely deployed and fastest-growing forms of renewable energy globally.

Solar thermal is different: it uses the sun's heat directly, typically to warm water for heating or hot water systems, rather than generating electricity. Common in some regions for domestic hot water.

Wind energy

Wind turbines convert the kinetic energy of moving air into electricity. Onshore wind is found in open countryside and is one of the lowest-cost sources of electricity in many countries. Offshore wind, built on platforms in the sea, captures stronger and more consistent winds and has become a major electricity source in some regions, though it is more expensive to build and maintain.

Hydroelectric power

Flowing or falling water drives turbines to generate electricity. Hydro is one of the oldest forms of electricity generation and is a significant source in countries with suitable geography — mountainous terrain and high rainfall. Large hydro installations can be highly reliable and provide consistent output regardless of weather, which makes them valuable for grid stability. They do have environmental impacts — on river ecosystems and sometimes communities — which vary considerably by project.

Geothermal energy

Heat from within the earth is used either to generate electricity (in regions with accessible geological heat, like Iceland or parts of the western USA and New Zealand) or for direct heating. For most of the world's population it is not a locally accessible option, but where it exists it provides very consistent, reliable output.

Biomass and bioenergy

Biomass covers organic material — wood, agricultural residues, purpose-grown energy crops — burned or processed to produce heat or electricity. It is renewable in the sense that the source material can regrow. However, the sustainability of biomass varies considerably depending on what is burned, where it comes from, and how it is managed. Burning wood releases carbon; whether this is offset by regrowth depends on the timescales and land management involved. Biomass is a genuinely contested area, and the detail matters enormously.

Tidal and wave energy

These technologies harness the energy of ocean tides and waves. They are still largely at the development and pilot stage in most of the world, though tidal stream generators are operating at small scale in some locations. They are promising but not yet significant contributors to most national energy mixes.

Strengths and real challenges

The main practical challenge with solar and wind is intermittency: they generate more when the sun is shining or the wind is blowing, and less at other times. This is a genuine issue that system designers have to manage. But a few things are worth understanding:

• A grid is not a single source. It combines multiple types of generation — solar, wind, hydro, geothermal, gas peakers, and increasingly battery storage — which together can smooth out the variability of any individual source.
• Weather patterns for wind and solar are at least partially predictable, which helps with grid management.
• Battery storage technology is improving and being deployed at scale, allowing electricity generated at peak times to be stored and used when demand is higher or generation is lower.
• Connecting grids across large areas helps, because it is rarely calm and cloudy everywhere at the same time.
• Demand flexibility — using washing machines, charging electric vehicles, or running industrial processes when electricity is cheapest and most abundant — is an emerging part of the solution.

None of this means intermittency is already fully solved. Managing a grid that is predominantly renewable remains a significant engineering and policy challenge, and the pace and cost of progress vary by country. But the direction is clear, and many countries already run on predominantly renewable electricity at certain times of year.

How it reaches your home

In most countries, electricity flows from generators (of all kinds) through a shared grid to homes and businesses. When you plug something in, you are drawing from that mix. You cannot track which electrons came from which source.

What you can do is support renewable generation through the choices you make:

• Green energy tariffs allow you to pay a supplier who commits to matching your consumption by purchasing renewable electricity certificates or investing in renewable capacity. The details vary by scheme and country — see our guide to green energy tariffs for what to look for.
• Rooftop solar panels generate electricity directly at your home, reducing what you draw from the grid and (in some arrangements) allowing you to sell surplus back. Whether this makes financial sense depends on your roof, your location, your consumption and available incentives — see our guide on whether solar panels are worth it.
• Electrifying your home — heat pumps for heating, electric vehicles for transport — makes it possible to run on renewable electricity rather than gas or petrol. This shift makes sense as grids get cleaner.

Myths, busted fairly

• "Renewables are expensive." This was true in the past. Solar and wind are now among the cheapest sources of new electricity generation in most of the world, and costs have continued to fall. The challenge is investment, grid integration and storage — not generation cost per se.
• "They don't work when it's not sunny or windy." Individual solar panels produce less on cloudy days; individual turbines produce nothing in still air. But the grid draws on multiple sources, and a mix of generation types plus growing storage capacity manages this variability increasingly well. This is engineering and policy — it is being solved, not ignored.
• "They can never power a whole economy." Countries including Norway, Iceland and Costa Rica already generate nearly all their electricity from renewables (largely hydro and geothermal). Denmark regularly generates more wind electricity than it consumes. Full decarbonisation of all energy (including heat and transport, not just electricity) is harder and will take longer, but the trajectory is real.
• "They require too much land." Land use is a real consideration for solar farms and wind parks, but it is much less than the land degraded by fossil fuel extraction and the effects of climate change. Offshore wind uses sea areas. Solar can be co-located with agriculture (agrivoltaics) or installed on rooftops.

What households can do: checklist

• Use less energy first — efficiency and behaviour changes reduce the total that needs to be generated by any source. See our guide to saving energy at home.
• Switch to a green energy tariff if one is available in your area — and check what it actually covers.
• If your home, roof and budget allow, investigate rooftop solar — and check local incentives and feed-in arrangements.
• When replacing heating systems, consider a heat pump rather than a gas boiler — it can be run entirely on electricity.
• When replacing a vehicle, consider an electric option — an EV running on a renewable tariff has very low operational emissions.
• Reduce carbon footprint across the board — see our guide to reducing your carbon footprint.