Renewable energy sources: definition, types and stocks

Hydroelectric, wind, solar, biomass and geothermal energy are clean and limitless sources of energy. As renewable energies, they play a dominant role in the energy transition. It is essential to promote their development in order to combat global warming.

What is renewable energy?

Energy is said to be renewable when it’s sourced from renewable resources such as the sun, wind, water, or biomass. Renewable energy does not use fossil fuels, coal, or gas, but rather natural resources that can be replenished within the human lifetime.

Renewable energy is generally clean, i.e. it produces little-to-no polluting emissions and thus contributes to the reduction of greenhouse gases in the atmosphere.

While clean and renewable energy can also be called “green”, not all clean energy is renewable. Take, for example, nuclear energy.

Is nuclear energy renewable?

Nuclear energy is a decarbonised and non-polluting energy. It does not emit greenhouse gases into the atmosphere. However, uranium, the fuel used in nuclear reactors, is a limited resource. Nuclear energy is therefore a clean but non-renewable energy.

Unlike wind or solar energy, nuclear energy doesn’t depend on weather patterns and climate to generate power and is therefore likely to stick around for a while and help the UK reach its net zero targets.

Renewable energy and non renewable energy

Non-renewable energy is energy produced by burning fossil sources such as coal, oil, natural gas, etc. Although reserves are vast, they are not inexhaustible and their stocks are slowly diminishing.

At our current rate of global consumption, fossil fuels are running out and, unless things change, will take:

• 50 years for oil;
• 60 years for natural gas;
• 100 years for uranium;
• 110 years for coal.

Fossil fuels are the main cause of CO2 emissions in the UK. It is therefore essential to reduce our dependence on fossil fuels and limit our greenhouse gas emissions by supporting the development of renewable energy.

Like non-renewable energies, renewable energies can produce electricity, heat, gas and fuel (called biogas and biofuel respectively) without emitting greenhouse gases.

What are the 5 renewable energy sources?

The term renewable energy is used to refer to energy that is inexhaustible and available in unlimited quantities. These come mainly from the following five energy sources: water, wind, sun, biomass and earth.

Hydroelectric energy

Hydroelectric power, also known as hydropower or hydro energy, is generated using large areas of water . The movement of the water drives underwater turbines and generators, which then produce electricity. The higher the water pressure, the more energy is produced.

Hydro is a completely renewable and reliable source of electricity generation. Due to the water cycle, this form of generation is extremely sustainable and can be controlled in an efficient way.

Hydroelectric generation relies heavily on geography and topography. The UK is blessed with a rich variety of terrain. However, hydroelectric energy only represents around 2% of the UK’s electricity mix, which is still relatively low given its potential and popularity worldwide.

• The largest capacity hydroelectric power station in the UK is Dinorwig Power Station, near Snowdonia national park in Gwynedd, northern Wales: 1,800,000kW capacity, which has the potential to power over 2,540,000 households at full capacity.
• The largest traditional hydroelectric plant in the UK is Sloy, located on the west bank of Loch Lomond in Scotland: 160,000 kW.

Wind energy

Wind energy is obtained from the kinetic energy of the wind produced by air currents, which spin wind turbines. Like solar energy, wind energy is an inexhaustible but intermittent renewable energy because it depends on the force of the wind.

Wind turbines can be installed on land or at sea, and are called onshore and offshore wind turbines respectively.

• Onshore wind turbines are simpler to install on a technical level;
• Offshore wind turbines are more efficient in terms of energy production.

As we can’t rely on the wind to produce renewable energy in all places 100% of the time, other electricity sources compensate for those areas that experience low wind levels.

• The largest on-shore wind farm currently in operation in the United Kingdom is Whitelee Wind Farm and is located just over 9 miles outside of Glasgow. It is owned and operated by Scottish Power, which has developed this 215 turbine farm with a capacity of 539,000 kW.

Wind energy has expanded rapidly over the last twenty years, mainly due to favourable weather conditions. It is one of the most widely used renewable energies in the world and one of the cheapest and most abundant renewable energy sources in the UK.

In 2019, wind energy contributed to 20% of all electricity produced in the UK, a huge increase over recent years. In August 2020, blustery weather led to a record level of wind generation, with roughly 60% of Britain’s power demand being met by wind turbines.

Is solar energy renewable?

Solar energy is a renewable energy obtained from the sun's electromagnetic radiation. It is renewable energy because it is obtained from a natural and inexhaustible source. However, this energy is not continuously available. It is an intermittent source of energy that depends on sunlight.

It is important to distinguish between two types of solar energy:

• Photovoltaic solar energy, which is when electricity is produced via photovoltaic solar installations;
• Solar thermal energy, which is when heat is generated by thermal collectors.

Solar energy is one of the easiest renewable energy sources to produce, especially solar photovoltaic.

• The largest solar farm currently in operation in the UK is in Bournemouth, southern England. It’s called Chapel Lane Solar Farm and covers around 310 acres. At full capacity, it can generate 51,300 kW, which is enough to power around 60,000 homes.
• The Cleve Hill Solar Park in Kent is set to overtake Chapel Lane as the largest solar plant and is expected to provide enough clean electricity to power over 91,000 local households when it opens in 2022.

Biomass

Biomass energy comes from the combustion of wood or the methanisation of organic matter. It operates on the composting principle but scaled up to an industrial level.

Biomass power can produce electricity, heat or fuel.

The UK generating capacity for green gas has grown rapidly in recent years. The primary reason is that green gas can be made out of many different kinds of biomass and organic waste slurries, and the technology involved here is scalable and fairly cost-effective.

• The Veolia biogas plant in Northallerton, North Yorkshire has been generating biomethane gas for a number of years. It is estimated to be able to fuel around 3,000 local homes and businesses using solely renewable energy sources, showing that biogas does have the potential to progress and have a large effect.

This concept is still at an early stage and has not made a considerable impact as of yet. However, according to the Renewable Energy Association, biomethane has the potential to meet around 20% of the UK’s gas demands eventually.

Is geothermal energy renewable?

Geothermal energy is the extraction of heat from the ground. Depending on the depth at which it is extracted, geothermal energy can produce both heat and electricity.

It is one of the only renewable energies, along with biomass energy, that is not intermittent and therefore not dependent on weather conditions.

Geothermal energy contributes very little to the UK electricity mix. A 2012 report in The Guardian claimed that geothermal energy had the potential to fuel around a fifth of the UK’s electricity demands. However, as of yet, we have not seen any great advances on this claim.

• One of the most notable sites is the Eden Project in Cornwall. This plant has a capacity of 3,000 - 4,000 kW, which, working to its full capacity, could power a maximum of around 5,650 households in real-time per hour.

Other renewable energy sources

In addition to the five most common sources of renewable energy, there are a few other lesser known and underused renewable sources, which show promising results in the years to come.

Is tidal energy renewable?

Tidal energy, like hydroelectric energy, relies on the flow of water to generate electricity. The power and consistency of tides can be effectively utilised to make clean electricity. There are a couple of different approaches to getting power out of tidal currents:

• With a network of underwater turbines in locations where there is a significant height difference between incoming and outgoing tides (estuaries and bays for example).
• A tidal barrage that completely blocks off a bay or estuary. This type of low-lying sea wall design has turbines embedded in its base. These are activated by the ebb and flow of the tides. Parts of the tidal barrage can also be opened up to enable the free flow of maritime traffic and additionally, they can provide new transportation links by cutting distances along a bay.

The UK seems to be currently favouring the more scalable freestanding underwater turbine designs which have lower start-up costs, represent a smaller overall risk for financially skittish investors and bring significant logistical flexibility.

Hydrogen energy

Hydrogen energy is perhaps the least explored of the renewable energy sources. It involves the generation of electricity through the combination of hydrogen and oxygen atoms. Current technology means that hydrogen fuel cells are disproportionately heavy - a 300kg tank would provide only a few hours of electricity - but the abundance of hydrogen in our atmosphere makes it a promising source of energy for the future future, particularly for cars.

What is the UK target for renewable energy?

In June 2019, the UK became the first G7 country to set a legally binding net-zero emissions target, aiming to reduce all greenhouse gas emissions by 100% (compared to 1990 levels) by the year 2050.

One year later, in April 2020, the UK hit a new renewable energy milestone. The country started running purely on renewable energy for the first time ever.

Switching to a renewable energy supplier

Switching to renewable energy can help reduce your energy bills and cut your carbon footprint at the same time.

One easy way to cut down on fossil fuels is by switching to a renewable energy supplier. Many providers offer green tariffs, with electricity generated from sustainable sources. To learn more, visit our guide to renewable energy providers.