Renewable energy is energy that comes from practically inexhaustible natural resources, like sunlight, wind and water. Generating electricity using renewable energy sources generally produces very little greenhouse gas. The fuel cost is often very low or even free for such energy sources, but harnessing the energy can be expensive.

The renewable energy source that currently contributes the most to the UK's electricity supply is wind power. The UK also benefits from energy derived from hydroelectricity and solar power.

Wind

Wind turbines use the wind’s kinetic energy to generate electrical energy that can be used in homes and businesses. Individual wind turbines can be used to generate electricity on a small scale – to power a single home, for example. A large number of wind turbines grouped together, sometimes known as a wind farm or wind park, can generate electricity on a much larger scale.

How is energy generated through wind?

Colleagues chatting

A wind turbine works like a high-tech version of an old-fashioned windmill. The wind blows on the angled blades of the rotor, causing it to spin, converting some of the wind’s kinetic energy into mechanical energy. Sensors in the turbine detect how strongly the wind is blowing and from which direction. The rotor automatically turns to face the wind, and automatically brakes in dangerously high winds to protect the turbine from damage.

A shaft and gearbox connect the rotor to a generator (1), so when the rotor spins, so does the generator. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.

The electrical energy from the generator is transmitted along cables to a substation (2). Here, the electrical energy generated by all the turbines in the wind farm is combined and converted to a high voltage. The national grid uses high voltages to transmit electricity efficiently through the power lines (3) to the homes and businesses that need it (4). Here, other transformers reduce the voltage back down to a usable level.

Is wind affordable, secure, clean and plentiful?

Is it plentiful?

Wind is one of those practically inexhaustible sources of energy. The biggest constraint on harnessing the wind is the number of turbines the UK can build, but the move offshore opens up a greater number of suitable windy sites.

Is it secure?

The UK is one of the windiest countries in Europe and obviously the wind does not need to be imported. But there are times when the wind does not blow so backup power plants are needed that can generate at relatively short notice.

Is it predictable?

UK wind farms have an assumed availability at peak of 10%. Wind is intermittent. But this can be addressed by storing its energy output, providing quick-to-respond flexible backup and distributing wind turbines across a wide geographical are

Is it affordable?

By 2020 the cost of generating electricity using onshore wind should be about 8.3p/kWh, and for offshore wind 12.5p/kWh. Wind has high upfront construction costs but once running, the fuel is free.    

It is clean? 

Wind farms have a carbon footprint of 11gCO2e/kWh. Wind energy is not zero-carbon due to emissions from constructing, maintaining and decommissioning wind farms, but it has one of the lowest carbon footprints of the scalable generating technologies.

Solar

Solar panels turn energy from the sun’s rays directly into useful energy that can be used in homes and businesses. There are two main types: solar thermal and photovoltaic, or PV. Solar thermal panels use the sun’s energy to heat water that can be used in washing and heating. PV panels use the photovoltaic effect  to turn the sun’s energy directly into electricity, which can supplement or replace a building’s usual supply.

How is energy generated through solar?

A PV panel is made up of a semiconducting material, usually silicon-based, sandwiched between two electrical contacts. To generate as much electricity as possible, PV panels need to spend as much time as possible in direct sunlight (1a). A sloping, south-facing roof is the ideal place to mount a solar panel .

A sheet of glass (1b) protects the semiconductor sandwich from hail, grit blown by the wind, and wildlife. The semiconductor is also coated in an antireflective substance (1c), which makes sure that it absorbs the sunlight it needs instead of scattering it uselessly away.

When sunlight strikes the panel and is absorbed, it knocks loose electrons from some of the atoms that make up the semiconductor (1d). The semiconductor is positively charged on one side and negatively charged on the other side, which encourages all these loose electrons to travel in the same direction, creating an electric current . The contacts (1e and 1f) capture this current (1g) in an electrical circuit.

The electricity PV panels (2) generate is direct current (DC). Before it can be used in homes and businesses, it has to be changed into alternating current (AC) electricity using an inverter (3). The inverted current then travels from the inverter to the building’s fuse box (4), and from there to the appliances that need it.

PV systems installed in homes and businesses can include a dedicated metering box (5) that measures how much electricity the panels are generating. As an incentive to generate renewable energy, energy suppliers pay the system’s owner a fixed rate for every unit of electricity it generates - plus a bonus for units the owner doesn’t use, because these can help supply the national grid. Installing a PV system is not cheap, but this deal can help the owner to earn back the cost more quickly - and potentially even make a profit one day. 

Is solar affordable, secure, clean and plentiful?

Is it plentiful?

The UK's climate and latitude make it a less than ideal location for harnessing solar energy. But improvements in the performance of solar panels, and using solar energy wherever possible, could go some way to addressing these challenges.

Is it secure?

The UK does not have to import solar energy, so in that respect it is secure. But obviously it does not work at night or in cloudy weather.

Is it predictable?

Solar is an intermittent energy source. The UK does not rely on it for large-scale generation and it is largely confined to microgeneration. In the future, improved storage technologies may mean solar can play a greater role in generating electricity.

Is it affordable?

By 2020 the cost of generating electricity using household solar photovoltaic (PV) panels should be about 25.3p/kWh. Production costs make solar expensive for generating electricity, but costs are reducing as solar technology is developed and commercialised.

Is it clean?

Solar energy has a carbon footprint of 72gCO2e/kWh. Solar does not look so green when the carbon footprint of fabricating the panels is included. But lower-carbon manufacturing techniques can help to bring this down in the future.

Hydropower

A hydroelectric power station converts the kinetic, or movement, energy in flowing or falling water into electrical energy that can be used in homes and businesses. Hydroelectric power can be generated on a small scale with a ‘run-of-river’ installation, which uses naturally flowing river water to turn one or more turbines, or on a large scale with a hydroelectric dam.

How is hydropower energy generated?

A hydroelectric dam straddles a river, blocking the water’s progress downstream. Water collects on the upstream side of the dam, forming an artificial lake known as a reservoir (1). Damming the river converts the water’s kinetic energy into potential energy: the reservoir becomes a sort of battery, storing energy that can be released a little at a time. As well as being a source of energy, some reservoirs are used as boating lakes or drinking water supplies.

The reservoir’s potential energy is converted back into kinetic energy by opening underwater gates, or intakes (2), in the dam. When an intake opens, the immense weight of the reservoir forces water through a channel called the penstock (3) towards a turbine. The water rushes past the turbine, hitting its blades and causing it to spin, converting some of the water’s kinetic energy into mechanical energy. The water then finally flows out of the dam and continues its journey downstream.

A shaft connects the turbine to a generator (4), so when the turbine spins, so does the generator. The generator uses an electromagnetic field to convert this mechanical energy into electrical energy.

As long as there is plenty of water in the reservoir, a hydroelectric dam can respond quickly to changes in demand for electricity. Opening and closing the intakes directly controls the amount of water flowing through the penstock, which determines the amount of electricity the dam is generating.

The turbine and generator are located in the dam’s power house (5), which also houses a transformer. The transformer converts the electrical energy from the generator to a high voltage. The national grid uses high voltages to transmit electricity efficiently through the power lines (6) to the homes and businesses that need it (7). Here, other transformers reduce the voltage back down to a usable level. 

Is hydropower affordable, secure, clean and plentiful?

Is it Plentiful?

As a renewable energy source, hydropower is theoretically inexhaustible, but the best sites have already been exploited.

Is it secure?

As an indigenous energy source hydro is highly secure, but the number of sites where large-scale hydro can be sited in the UK is limited, so it will only ever make a small contribution to the energy mix.

Is it predictable?

UK hydropower stations have an assumed availability at peak of 60%. Hydro might be a minor player in terms of total UK generating capacity, but its inherent reliability contributes to the overall reliability of the electricity supply.

Is it affordable?

It is currently not considered economically viable to build new large-scale hydropower stations in the UK. The affordability challenges facing hydropower are minimal and well-established but possible new sites in the UK are limited.                                                                                                                                      

Is it Clean?

Hydropower stations have a carbon footprint of around 10–30gCO2e/kWh. Hydroelectric dams require significant quantities of carbon-intense concrete but their long life spreads this over years of near zero-carbon electricity generation.  

Marine turbine

A marine turbine converts the kinetic energy of tidal waters into electrical energy that can be used in homes and businesses.

How is marine turbine energy generated?

Marine turbines are installed on the seabed (1) near the shore, where tidal sea water will flow over the turbine rotor blades (2). To generate sufficient electricity, the blades need to turn at a steady quick pace, similar to a wind turbine. So marine turbines are installed where marine currents flow rapidly because they are focused by headlands, straits, inlets and narrow channels in the seabed. The rotor blades are specially shaped so they turn with both the ebbing and flowing of each tide.

The spinning blades are attached to a generator (3). The generator uses an electromagnetic field to convert rotational mechanical energy into electrical current. The operation of the marine turbine is monitored remotely (4).

Thus marine turbines can provide a steady supply of electrical energy four times in every 24-hour period (the ebb and flow of two daily tides). But they cannot increase their output to meet sudden peaks in demand.

Electrical energy is brought to shore via an undersea cable and, via a transformer, converted to the correct voltage for transmission (5). The national grid uses high voltages to transmit electricity efficiently through the power lines to the homes and businesses that need it (6). Here, other transformers reduce the voltage back down to a usable level.

Are marine turbines affordable, secure, clean and plentiful?

Is it plentiful?

Marine energy is practically inexhaustable and the UK has many thousands of miles of coastland. But the marine turbines and wave devices used to harness marine energy are still in the early stages of development.

Is it secure?

Marine energy does not have to be imported, in fact the UK has around half of Europe's available tidal energy. But marine and tidal energy are subject to intermittency.

Is it predictable?

Marine power is one of the more reliable forms of renewable energy but is weather-dependent and thus subject to intermittency. The technologies to harness marine energy are in the early stages of development so it will be some years before their long-term reliability can be assessed.

Is it affordable?

Developing marine energy technology is likely to require significant investment over the coming decade. It is estimated that in 2020, generating electricity using tidal turbines would cost about 18.8 pence per kilowatt-hour (p/kWh), and using wave power would cost about 26.8p/kWh.  

Is it clean?

The carbon footprint of a tidal turbine is about 18 grams of carbon dioxide-equivalent for each kilowatt-hour of electricity it generates (18gCO2e/kWh). Although marine energy does not produce emissions while generating electricity, manufacturing and maintaining marine energy devices does.

You may also be interested in...

Transversal 1

Intro...

Transversal 2

Intro...

Transversal 3

Intro...