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21 October 2021

What is renewable energy?

Find out about different types of green energy and what you're getting when you buy electricity from different renewable energy companies
Sarah Ingrams

Renewable energy is created from natural sources that are unlimited or continually replenished, such as the sun, wind and water. 

Renewable electricity involves no fossil fuels in its creation and produces zero carbon dioxide emissions when it is generated.

Some 40% of the electricity in the National Grid comes from renewable sources, according to the latest government figures (for 2020-2021).

Types of renewable energy

Wind and solar account for a large proportion of renewable electricity generation in the UK. But hydroelectricity and bioenergy contribute too.

Nuclear power is a low carbon power source, but it's not renewable.

Some sources of renewable power are intermittent, meaning that they are only available in certain conditions (such as when the wind is blowing or the sun is shining).

Read on to find out about the different types of renewable power and their use in the UK, or find out the  differences between green energy suppliers.

If you’re looking to keep your energy bills in check, compare gas and electricity prices using our free Which? Switch service.

Offshore wind farm

Power from wind turbines  

Wind power is the second-largest source of UK electricity. Wind turbines produced around a fifth of the electricity generated in the UK in 2020, according to the government Department for Business, Energy and Industrial Strategy (BEIS).

When wind spins the propeller-like blades of a wind turbine, it turns a shaft inside the turbine. A generator converts the kinetic energy of the shaft turning into electrical energy.

Wind turbines don’t need much wind to turn them. A gentle breeze (around three to five metres per second) is enough.

Onshore wind farm in fields

The amount of wind power generated in the UK increased by 18% between 2019 and 2020.

More of our wind power comes from onshore windfarms than offshore wind farms. But that gap is closing, and the government plans to increase offshore wind generation to 40GW by 2030 (in 2019, we had 8.5GW of offshore wind farm capacity).

Solar farm in fields

Solar energy

Around 5% of electricity generated in the UK in 2020 came from the sun using solar panels. This doesn't include individual solar photovoltaic (PV) panels on people's homes, so the proportion of solar electricity is likely to be higher.

Solar panels use special PV (photovoltaic) cells to convert the sun’s energy into electricity. See more: how do solar panels work?

They can generate electricity as long as it’s light, but the stronger the sunlight, the better they will work.

Most of the UK's solar farms are in England.

If you’re considering fitting solar panels at your home, see our buying advice for solar panels.

Hydroelectric dam with a reservoir behind

Hydroelectric power 

Hydroelectricity was responsible for around 2% of UK electricity generation in 2020.

Hydropower includes:

  • Run-of-river Water in a river or canal is channelled continuously to spin a turbine
  • Storage Water is stored in a reservoir using a dam, and released to spin a turbine and generate electricity
  • Pumped storage Water is cycled between an upper and lower reservoir using pumps powered by surplus energy from the system. Water is released into the lower reservoir to generate electricity. 

All of these involve water spinning a turbine to activate a generator and produce electricity.

Huge waves surrounding a light house

Wave and tidal systems use currents or the power of waves to generate electricity from seawater.

The vast majority of the UK's hydropower is in Scotland.

See our eco shower heads buying guide to save water and money.

Bioenergy and waste 

Bioenergy and landfill gas are the source of a third of our renewable energy although they’re lesser-known sources classed as renewable by the government. Bioenergy includes generation from:

  • Anaerobic digestion 
  • Animal biomass
  • Energy from waste
  • Plant biomass
  • Sewage gas.

Bioenergy isn’t as efficient a renewable source as hydro, wind, wave and solar. Much of the energy content of the fuel is lost in the process of burning it to generate electricity.

Anaerobic digestion breaks down organic matter without oxygen. The organic matter is often food waste or animal waste and is broken down in sealed tanks, producing biogas.

Biogas is then used as fuel in a combined heat and power unit to generate electricity and heat.

Biomass power station

Biomass energy involves burning wood, plants and other organic matter (including manure and household waste) to create steam, which spins turbines and generates electricity. 

It can be considered renewable if the plants or other organic materials burned are from a sustainable source and are replaced, removing carbon dioxide from the atmosphere and storing it. Some biomass plants have carbon capture and storage technology to stop carbon released during burning from being released into the air.

Some big generators, including Drax, have converted coal power stations to biomass and burn wood pellets.

There are concerns about the sustainability of wood biomass, however. It releases greenhouse gases when burnt, which can sometimes be higher than burning gas or coal, depending on the type of biomass burnt and where it comes from, according to UK government research. 

More than 80% of wood pellets were imported from the US or Canada in 2020, according to figures from BEIS. Transporting this has associated emissions.

Energy from waste usually takes residual waste (what’s leftover after recycling) and turns it into energy, including electricity.

There are various ways to do this, but burning it is most common. The government considers it partly renewable because only energy generated from biodegradable materials (such as food, paper and wood) is renewable. Burning oil-based products, such as plastics, is not.

Plants must clean up any waste gases before releasing them to meet pollution limits.

Landfill site with diggers and gulls

Landfill gas, produced as organic material rots, is mainly methane and carbon dioxide. 

This can be collected and used to turn turbines to generate electricity.

Before you put plastic in the bin, check how to recycle it.

Sewage sludge can be used to generate electricity (and heat), too.

The sludge is treated using thermal hydrolysis to increase the amount of methane it can produce. Then it is broken down by anaerobic digestion, producing biogas.