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What is renewable energy?

Which? explains the renewable energy sources we use in the UK, including solar energy and wind turbines
Sarah Ingrams
Marianne Calnan

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. 

Over 40% of the electricity in the National Grid comes from renewable sources, according to government figures (for October-December 2021).

Types of renewable energy

Offshore wind farm

Wind and solar account for a large proportion of renewable electricity generation in the UK, but hydroelectricity and bioenergy contribute as well.

Nuclear power is a low carbon power source too, 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, as well as find out the differences between green energy suppliers.

Power from wind turbines 

Onshore wind farm in fields

Wind power is the second-largest source of electricity in the UK and the most efficient renewable form of energy. It produced 29% of the electricity generated in the UK in the first quarter of 2022, according to government figures from the 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 then 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 sufficient.

The amount of wind power generated in the UK increased by 3.9% in the first quarter of 2022.

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. By comparison, in 2019, we had 8.5GW of offshore wind farm capacity.

Solar energy

Hydroelectric dam with a reservoir behind

Some 2.5% of electricity generated in the UK in 2021 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 PV cells to convert the sun’s energy into electricity. The panels can generate electricity as long as it’s light, but the stronger the sunlight, the better they will work. Read our advice guide to find out more about how solar panels work.

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

Hydroelectric power

Huge waves surrounding a light house

Hydroelectricity was responsible for almost 7% of UK electricity generation in the first quarter of 2022 owing to lower rainfall than the previous quarter.

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.

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

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

Bioenergy and waste 

Biomass power station
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 

This 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 energy 

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 
Landfill site with diggers and gulls

Energy generated 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 gas

This is 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 

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.

Geothermal energy

Geothermal energy is a source of renewable energy due to its low environmental impact.

It is created using heat from the earth's core, which is continually produced. Geothermal energy comes from heat generated during the original formation of the planet and the radioactive decay of materials. The energy is stored in rocks and fluids in the centre of the earth.

Wells that are around a mile deep or more are drilled into underground reservoirs to tap into the geothermal resources. 

Geothermal energy is constantly available because heat is continuously produced inside the earth. 

It can be used for bathing, to heat buildings, and to generate electricity.  

What is the best type of renewable energy?

Bulb energy renewable energy 485629

Figuring out the best source of renewable energy will depend on which one is right for you and your household's energy use.

The best type also comes down to which factors you prioritise, which could be your budget, energy efficiency or reducing your energy bills, so there's a lot to consider.

Some types of technology have specific requirements for installation. For example, solar photovoltaic (PV) and solar thermal systems will depend on the way your roof faces, solar thermal, heat pumps and biomass require space inside and outside your property, while hydropower systems require a nearby stream or river. 

Once you've narrowed down the technologies that are suitable for your property, you can then rank them based on how well they would perform for your needs. The Energy Saving Trust recommends you consider the following questions:

  • Are you hoping to replace your current heating system? 
  • Are you looking to save energy and make your home more sustainable, or looking for which technology could save you the most money?
  • Should the system provide all your energy needs, or will it work in support with another?

If you need to replace your boiler or central heating system, this is an opportunity to move away from a fossil fuel heating system like a gas boiler. Should your priority be to save carbon dioxide, consider a heat pump, a large wind turbine or large solar PV system. If you live in an isolated rural property with no mains electricity, you may get the most reliable off-grid supply from hydro or from a mixture of wind and solar PV.

You should also weigh up the products that are available, their costs, the size of systems and any special requirements for installation before reaching out to installation providers.

Find out more about heating your home with renewable energy

Advantages and disadvantages of renewable energy

Research on laptop

Renewable energy is a way for consumers to up their green credentials as they do not directly produce any pollution. Renewables will not run out, can reduce environmental waste and tend to have lower maintenance requirements. 

Plus most energy generators, such as wind turbines or hydroelectric power stations are pricey to set up but cheap to run.  

Renewables are being heavily incentivised for companies and members of the public by the UK government too. It revealed its Contracts for Difference (CfD) scheme in September 2021 to encourage investment in low-carbon electricity. This is open to projects operating in Great Britain and comes with £265 million worth of investment to give developers of projects with high upfront costs and long lifetimes with protection from volatile wholesale prices. The government said the CfD scheme will ensure consumers don’t pay increased costs when electricity prices are high.

As for consumers, the government introduced the Boiler Upgrade Scheme in May 2022, offering grants of up to £6,000 towards the cost of replacing your traditional boiler with a low-carbon heating system such as a heat pump.

But renewables have high upfront costs and can be intermittent, with sources such as wind turbines and solar cells rely heavily on the weather. For instance, if it is not a windy day, wind turbines will not turn, and if it is not sunny, solar cells will not produce much electricity. 

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