The ultimate guide to renewable energy sources

Water-based power sources

Water-based energy sources rely on hydrokinetic potential: the energy carried by bodies of water.

From rivers and streams to seas and oceans, there is a reservoir of untapped potential energy sources, all sustainable and relatively carbon-free.

We’ve got info on hydropower, tidal power and wave power (yes – these are all different).

Hydropower

Hydropower typically refers to the energy generated by falling or fast-moving water.

Historically, hydropower has been used for a number of different purposes, from milling grains and wheat to sawing stone and timber. This has developed into the more contemporary practice of generating electricity by funnelling the water through turbine generators.

Perhaps the most iconic example of hydroelectric generation is the Hoover Dam. The huge structure has a generation capacity of 2 GW, supplying energy millions of people across Southern California each year.

Hydropower in the UK amounts to about 1.65 GW of installed capacity, almost 2% of the total capacity. In the US, hydro accounts for 6.1% of energy generation, with installed capacity of 100 GW.

Tidal power

Tidal Power stations make us of the kinetic energy carried by the tide of oceans and seas.

Tides are driven by gravity. The orbit of the moon around the earth exerts a gravitational pull; in combination with the earth’s rotation, this force dictates the pattern and times of high and low tide.

Tidal pattern is continuous, meaning that potential energy generation from the source is stable and easy to predict. This means that tidal is a great renewable energy source that doesn’t face the intermittency issues that wind and solar do.

By placing tidal generators on suitable shorelines – such as the project underway on the coast of Swansea – we are able to take advantage of an infinite resource to generate renewable energy.

Tidal power generation has previously faced issues around cost and site suitability, but its capability for round-the-clock generation means that it could play a huge role in the future energy mix.

There is also some consensus around the potential of tidal streams and ocean currents, though it is yet to be explored.

Wave power

Wave power sounds an awful lot like tidal, but there is a key difference between the two.

While tides are created by the gravitational pull of the moon, waves carry energy potential due to the energy transfer between wind and the water surface; tidal power is generated onshore, while wave energy is generated at sea.

These subtle differences help to distinguish the two sources. Wave power currently plays a very minor role in the global energy mix; the world’s first wave energy unit came online in 2008 and was part of an experimental installation off the northern coast of Portugal at the Aguçadoura Wave Farm.

This has since been followed by experimental projects in Australia, the US, and the UK. While wave energy has not yet reached its peak, estimates indicate that wave energy could supply up to two terrawatts of power.

Solar-based power sources

There’s more to solar power than vast fields of shining solar panels.

From innovatove ways to use sunlight to generate and store heat and electricity, to the scientific exploration of space with dreams of capturing an entirely different kind of solar power, there’s a lot to learn.

Find out about photovoltaic power, solar wind, concentrated solar power and solar thermal.

Photovoltaic

Photovoltaic solar is one of the most iconic forms of renewable energy, and the one most people are likely referring to when talking about solar power.

The photovoltaic effect is the chemical and physical reaction which underpins solar panel technology. The photovoltaic effect is the generation of electric current when sunlight excites (stimulates) the electrons in a material.

This is exactly what happens to solar panels when sunlight falls on them; photons from the Sun excite the electrons in the surface of the solar panel. This in turn creates current.

Photovoltaic is a popular solution for domestic renewable energy generation, as even a small PV installation can help homeowners to reduce their energy consumption while also helping to either reduce bills or earn homeowners money thanks to the popularity of Feed-In-Tariffs.

Solar wind

Solar wind is an optimistic, though currently unavailable, conceptual energy source. The concept involves sending a satellite into space to harness the energy potential of solar wind, the charged particles from the sun which are produced by the natural nuclear processes of the star.

These charged particles flow throughout the solar system, and down on earth we see the evidence of them in the form of the auroras when they collide with our planet’s magnetic field.

To harness the energy potential of solar wind, we would need a Dyson-Harrop satellite in space.

The ‘Dyson-Harrop satellite’ is a theoretical megastructure that would sit in constant orbit around the sun. Made of a metal wire loop, a metal receiver, and an infrared laser, the satellite could collect charged electrons in its ‘sail’ – the magnetic field within the wire loop.

This would pass to the receiver where it is converted to electrical current; this is then transmitted back to a terrestrial satellite in the form of infrared light. On earth, the infrared would be re-converted into electricity.

Again, all of this is conceptual – but a satellite of the correct size could meet the energy needs of the entire planet 100 billion times over.

Concentrated Solar Power

Concentrated Solar Power (CSP) is a less conventional way of harvesting solar energy, though it is becoming increasingly popular in regions where there’s an abundance of intense sunlight; there are installations in Morocco’s Ouarzazate, California’s Mojave Desert, and in Andalusia in Spain.

The system works by using mirrors to reflect the intense sunlight, concentrating light and heat in a particular location. This drives steam turbine, generating electricity.

CSP is mostly used to generate energy throughout the day but in some installations, such as Morocco’s Noor I, molten salt technology is used to store some of the generated heat. This allows the stations to use the heat to generate electricity after sunset.

Solar Thermal

Solar Thermal (ST) works on a similar principle as CSP, harnessing heat from sunlight to heat water or air (or both) in either residential or commercial contexts. However, the two methods are not the same.

ST is used to generate heat but can also generate electricity. CSP uses intense heat primarily to generate electricity.

On the small-scale, ST can be used to heat swimming pools; medium-sized applications include heating water in homes and businesses.

Additionally, the generated energy can be stored over the short-term (in day/night cycles) or over the long-term (inter-seasonal), to provide heat on demand.

Waste and material-based power sources

Arguably one of the most efficient forms of renewable energy, power from bio-waste makes use of unwanted by-products of our lifestyle and can be utilised at any time of day, regardless of weather conditions.

Coming in two primary forms, biomass and biofuel, this thrifty source often equates to being carbon neutral, making it a viable choice for low-carbon aspirations (and it’s currently the most-used form of renewable energy in the UK).

Biomass

Biomass is a cleaner, greener alternative fuel which is made from organic materials that would otherwise be thrown away.

Biomass comes from a number of sources, including wood - used by Drax - crop and plant waste, organic animal waste and much more.

Wood biomass typically comes from a mixture of forestry off-cuts and mill residues – normally wood which isn’t of a high enough quality to be used for furniture production and its other well-known uses. It is treated before being converted into fuel form, either pellets or briquettes.

The biomass product is then burned in a boiler, which generates steam and turns a turbine, in turn generating electricity.

Biomass can be burned either in conjunction with coal at traditional boiler stations, or these stations can be converted to run solely on biomass fuel.

Biofuel

Biofuels can be one of two products: bioethanol or biodiesel. While the fuels have similar effects, they come from completely different sources.

Bioethanol is an alcohol made from the fermentation of crops such as corn or sugarcane and is popular across the US and South America.

On the other hand, biodiesel is the most common biofuel in Europe, and is produced from oils and fats such as soybean or vegetable oil.

Both substances are used in conjunction with petroleum fuels to achieve different means; bioethanol is used in petrol engines, primarily to improve engine performance while also reducing emissions. In diesel engines, biodiesel is typically used to minimise emissions.

Biofuels could have a huge role to play in the future. If the ultimate aim is to transition to a low-carbon society, it will not just be electricity generation that has to turn to renewable methods.

Research has been undertaken in to investigate other potential sources of biofuel, with algae having been touted as a potential successor to pure petroleum fuel sources. Watch this space…

Nuclear power sources

The most advanced, most controversial and potentially most lucrative form of sustainable energy – nuclear power.

Fission and fusion are the big two methods, and while they sound similar, they involve vastly different technologies. Whether they can truly be classed as renewable energy is also up for debate, as they technically use finite resources – but in such minuscule amounts that it’s considered by many to be just as clean and sustainable as the classic types of renewable energies.

One is the most common form we know, splitting atoms to create heat. The other is still highly experimental and an international conundrum – which, if solved, could mean changing the face of renewable energy as we know it.

Fission

Nuclear fission is the process that allows us to generate energy in nuclear power stations across the globe.

Fission is the process of splitting one atom into two; the energy resulting from this split is then used to heat water, generating steam which is used to turn a turbine which generates electricity.

The dangers of nuclear reactor failures, as well as concerns around the problems of waste storage, are often cited as the main arguments against nuclear energy.

Additionally, some argue that the supply chain of nuclear energy, from material mining through to waste storage, is no cleaner than fossil fuels.

However, despite these concerns, nuclear energy is hugely efficient, and a much more consistent way to generate energy, which would help combat issues of renewable intermittency in the grid (which can be experienced with the unreliable nature of sources like wind and solar power).

Fusion

This is the big one which takes place on the sun, where hydrogen particles are fused together to make helium. This requires (and releases) huge amounts of energy. At its core, the sun fuses 620 million metric tons of hydrogen per second.

Predictably, this generates huge amounts of energy – although we have yet to be able to find a way to harness fusion power back on earth. More than 60 years of research into the method have been hampered by technological and scientific difficulties, with few advances made.

However, an experimental nuclear fusion reactor is under construction in Saint-Paul-les-Durance, France. The complex invention, known as a ‘tokamak’, is expected to be operational by 2025, and is combining the efforts of thousands of engineers and scientists across the globe. If successful, it could spell a new era for lucrative amounts of renewable energy.

Wind-based power sources

Wind power is one of our most prevalent sources of renewable energy, with the UK ranking as the sixth largest producer of wind power in the world.

With zero greenhouse gases emitted during operation, engineers are coming up with more and more innovative ways to harness wind power. Below, we start with the humble but iconic wind turbine, and then move on to more creative and trend-setting directions that are taking wind generation to the next level.

Traditional turbines

Perhaps the most iconic symbol of the renewable energy era is the wind turbine.

These huge, modern-day windmills are synonymous with green energy. Turbines have become one of the more popular renewable energy sources, helping to generate renewable electricity both on shore and at sea.

When wind pushes the large blades of the turbine, they turn a rotor. This then spins the main shaft, within the tall ‘stem’ of the turbine, which in turn spins a generator to generate electricity.

While their large footprint means that they aren’t suitable for every location, they can generate anywhere between 100 kilowatts to several megawatts, and are a popular way of capturing a natural source across the world.

Alternative turbines

Following the traditional turbine come newer, evolved designs that can benefit by being more efficient, cheaper to install or more aesthetically pleasing in a natural landscape.

One innovative example is the proposed Vortex turbine which is completely free of rotor blades.

Instead of wind turning rotor blades, the body of the turbine would oscillate in the wind, in a design that could massively cut down on costs.

These reductions – a 53% reduction in manufacture costs, 51% in operation costs, and 80% in maintenance costs – lower the overall carbon footprint of the device, as well as making it viable for small-scale applications and off-grid communities.

The Vortex bladeless turbine is currently under testing, but it offers an interesting alternative for the future of the turbine.

Crosswind kite technology

‘Crosswind kite power’ is a new wind-based renewable energy technology under research in the UK by Essex-based Kite Power Systems.

The project is based on the principle that wind speeds increase proportionately with altitude. The energy potential in wind varies with wind speed, meaning that a doubling of wind speed equals an eight-fold increase in wind power.

The technique uses a pair of kites attached to a turbine. By flying the kites in circular motion, to research team behind the innovation believes it can take advantage of high wind speeds to both generate energy and make the system self-sustaining, thereby maximising the efficiency of the system.

Kinetic energy and sources

From examining giants of engineering, we scale right down to the minutiae, in the form of imperceptible kinetic energy generation.

This form of renewable energy uses movement to generate electricity, and therefore is well adapted to be fitted into everyday objects that already form parts of our lives.

From paving the floors of dance clubs to sitting inside watches, read on to learn more about kinetic power.

Piezoelectric

Piezoelectricity uses kinetic energy to generate electricity. The source is somewhat limited, with a fairly low output meaning that it is suitable mostly for small-scale purposes. However, there are a few examples of the scale on which piezoelectric can be used.

The concept has been successfully tested in WATT, a nightclub in the Netherlands where a section of the dancefloor is comprised of piezoelectric panels. The movement of club-goers dancing on the panels generates electricity, which is used to power lights throughout the venue.

The company behind the installation at WATT have also demonstrated the product at the football stadium of Feyenoord Rotterdam, where fans generated 1.3 MW over the course of a match.

If the technology can be scaled up – for example, in popular commuting areas with high footfall traffic – kinetic energy could potentially be used to power city amenities such as lighting and display boards, creating a renewable, self-sustained metropolitan.

Micro-generation

Tiny generators inside everyday objects are another way in which kinetic energy can be harnessed.

One micro-generator includes a device which makes use of motion to generate electricity. A tiny pendulum sits within a football, and the movement of the football causes the pendulum to swing, charging up a lithium ion battery to power a lamp.

Biology x technology

When the science community takes inspiration from nature, amazing things can happen.

There are some areas of the biological world that are getting more attention recently, thanks to innovative research learning from and utilising natural resources to generate energy or assist in generating energy.

We’ve covered the studies of bio-mimesis, algaelectricity and bioelectrogenesis below – hard to spell, but fascinating to learn about.

Biomimesis

Marrying nature with technology may sound futuristic, but in the near future it could be one of the ways that we generate electricity.

Biomimetic technology is the hybrid result of mixing technological hardware with ideas from nature. By taking inspiration from natural and biological processes, scientists and engineers are able to play with new ideas and explore new avenues of renewable energy technology.

The field of biomimetic technology is still very primitive, but scientists in America have already developed a prototype biomimetic tree which generates clean electricity.

As the field is very new, developments are likely to be incremental to begin with, but bio-mimesis represents an exciting area with potential for development.

Algaelectricity

Photovoltaic solar could get a boost in the future thanks to experimental science, and algae’s usefulness may extend beyond a source of biofuel.

In 2010, researchers in Gothenburg, Sweden and in Cambridge, England experimented with algae and jellyfish proteins to create a bio-photovoltaic cell which can generate electricity.

By using biological proteins, researchers have created a solar cell which is cheaper and simplified in design.

While the method was not hugely efficient, the symbiosis of nature with technological materials offers a glimpse into the future of energy production, taking bio-mimesis to its logical extreme by fusing nature and technology together.

Bioelectrogenesis

Certain bacteria are capable of transferring electrons to conductive surfaces.

Microbial Fuel Cells makes use of these chemical bacterial processes to generate electricity.

Electricity generation is a welcome by-product of natural bacterial processes. As such, bioelectrogenesis presents a novel way of generating electricity because, under certain conditions, the production of energy can be continuous, meaning that electricity generation could be infinite.

While research is currently limited, microbial and bacterial electric generation could, one day in the future, be scaled up to become an everyday energy source.