The deal is done: fossil fuels are on the way out, say the 200 governments who signed the Paris Agreement to fight climate change. Now engineers are looking for ways in which wind can take up the slack.
To some, the whoosh, whoosh, whoosh of slowly turning wind turbines is both annoying and a blight on the landscape. However, with global temperatures increasing, glaciers retreating and sea levels rising, the urgency to make our energy sources cleaner and greener is obvious.
A recently published study warned that ocean life could see its most dramatic change in three million years unless carbon emissions are sharply curtailed.
Governments have got the message, and last December agreed in Paris - after two decades of talk - to phase out the use of fossil fuels to cut greenhouse gas emissions. And wind energy is one of the most promising candidates to fill the resulting energy gap.
For starters, wind is plentiful, cheap, clean and widely distributed. “With costs continuing to fall, wind stands ready to lead us into the future as the cheapest energy source available in the British Isles,” says Amy Cameron, who works for the UK-based climate change campaign group 10:10. “Wind should be - without question - a major component of the low carbon infrastructure needed to meet legally binding carbon targets.”
However, to boost wind’s contribution to the energy mix, engineers first have to make wind energy more efficient, and also solve the problem of inherent supply peaks and troughs as wind speeds rise and fall.
One possible solution is to make wind turbines larger and higher. In many countries, turbine towers are allowed to be not much higher than about 125m, to curtail visual pollution, but there are suggestions to get them as high as 200m.
Height boosts electricity generation: a Swedish study shows that a 5MW turbine's output can be doubled from 7,945MWh to 16,178MWh per year by raising its height from 80m to 125m. There are drawbacks though: the super-sized components still need to be transported to sites, requiring specialised trucks and wide roads, and maintenance so high up could also be more difficult.
Another idea is the wind lens - a conical structure that surrounds the turbine blades, producing low pressure and increasing wind speed. A team developing the design at Kyushu University in Japan claims the wind lens turbine can generate two to three times the power output of a traditional turbine, at the same time reducing noise. Two large 100kW test turbines have been running since 2011, and the researchers are now building a 300kW version. But the design is not without hitches: some point out that it can’t be cost-effective with all the extra material needed for the lens and for the supporting structure.
That’s why researchers are searching for other ways to improve turbines’ efficiency, make them fit better into the landscape, reduce the danger of bird strikes, and cut down on noise pollution.
For the latter, nature shows how it can be done. Nigel Peake, an aeroacoustics expert at Cambridge University, last year examined the downy canopy covering the exposed surfaces of owls’ flight feathers. They smooth the passage of the birds’ wings through the air, greatly reducing noise. Peake and his team hope to replicate the noise dampening features on the blades of wind turbines, decreasing noise levels by 10db without affecting aerodynamics. One side effect could be a higher energy yield, as currently turbines are often ‘braked’ to keep them within noise limits.
Another option is to do away with swooshing turbines completely. Companies such as KiteGen Research in Italy, EnerKite in Germany and Kite Power Solutions in the UK are working to develop so-called ‘energy kites’. According to EnerKite, a 100kW kite yields the same amount of electricity as a 200kW-300kW turbine - meaning cheaper power. “In theory, they could harvest winds which are higher and less variable than those close to the ground,” says wind energy expert Simon Watson of Loughborough University.
Energy kites are based on the concept that huge kites can be flown in strong cross winds, and generate power by turning reels on the ground that are attached to them by tethers. EnerKite promise that their EK1M turbine will be ready by 2018 - and that a kite on a 300m tether could yield twice the energy output of a 190-metre-tall conventional turbine.
Another approach is to take entire turbines to the sky. Two years ago, search engine giant Google bought energy company Makani Power, which is developing wind turbines that look more like planes sporting eight propellers each, fully tethered to a docking station. Once released, the glider and its turbines would rise 450m up in the air, where the wind will make the turbines’ propellers spin and deliver some 600 kilowatts down to Earth.
US firm Altaeros Energies, meanwhile, uses a helium-filled shell instead, with a large but lightweight traditional turbine that sits in its centre. Once again, power is relayed through a wire to a ground station, and the ‘balloon’ can be raised or lowered to get the optimal wind speed. The company claims their invention produces two to three times the power output of a standard turbine, cutting installation and transport costs by 90 per cent.
Canada-based LTA Windpower is working on a similar concept, with an airship that would contain hydrogen.
In terms of energy yield, these are promising solutions, but it will be a while before they take off, says Watson. First, engineers have to overcome major technical challenges to ensure the systems controlling cable movements and take-off are robust and reliable, and avoid material fatigue, although he believes that this will not be an insurmountable challenge.
Who needs blades
Closer to deployment is a more earthbound approach, which bets on turbines without blades. One of the companies working on the concept is Vortex Bladeless in Spain. Instead of harnessing wind through propeller, its turbines rely on ‘vorticity’, an aerodynamic effect that occurs when wind breaks against a solid structure and produces swirling eddies. Engineers usually try to avoid vorticity, for example in tall buildings that must not sway too much.
For vorticity turbines though, it’s a different matter. They look like inverted cones made from fibreglass and carbon fibre, and are built for maximal movement as vortices break synchronously along their entire length. Two rings of magnets near the base sustain this initial movement regardless of wind speed; each swing of the mast is repelled by a magnet, intensifying the return swings.
Classical propeller turbines are still better at capturing the wind’s energy, and across a wider area - but, says David Suriol, chief executive of Vortex Bladeless, twice as many Vortex turbines fit into the space taken by one propeller turbine, maximising efficiency. Other advantages are a lack of gears or bearings, which means neither noise nor any need for lubricants. It could turn vorticity turbines into the “solar panels for wind power,” says Suriol, making them much more suitable for residential areas, and deliver huge cost savings.
However, Watson isn’t sure that these claims will stand up to scrutiny. “The effective cross sectional area from which the device is extracting energy is very small compared to that of the swept area of a conventional bladed turbine,” he says.
Still, Vortex plans to release its first domestic model within a year. Three metres tall, it will combine with solar panels to power household appliances. By 2018, the company aims to have built a 149 m structure which may power 400 households. Such height, however, may make the turbines bend significantly, says Watson. “It is hard to imagine machines like this surviving for long.”
That’s why there is continued investment in the tried and tested approach with propeller-powered wind turbines, especially off-shore, where winds are about 90 per cent stronger than on land, according to a 2005 study evaluating global wind power. Last year, more than 3,000 megawatts of offshore wind power were connected to the European grid alone, twice as much as in 2015. “The offshore wind industry has in recent years risen to the challenge to reduce [the] cost of electricity,” says Feargal Brennan, energy expert at Cranfield University.
Traditionally, off-shore turbines have been fixed on the sea floor, but there are now attempts to make installation easier by using floating platforms such as the Hywind project, which will soon be installed in the North Sea off Peterhead. The small array will consist of five turbines, built by Norwegian energy firm Statoil. The turbines will stand on a platform that is tethered to the seabed through a three-point mooring spread and anchoring system. Electricity will be transported using a cable, and the project could power up to 19,900 homes.
Last August, Japan built the largest offshore floating wind turbine. The 7-megawatt machine is 105 m tall and is weighed down by four 20-tonne anchors. The chains are slackened, so that the structure can withstand storms and even tsunamis. The deployment - four years after the Fukushima nuclear disaster - is part of Japan's attempt to tilt its energy mix towards renewables.
A need for storage
However, a major hurdle for the long-term success of all this renewable energy is the fact that supply can never be quite guaranteed. To smoothen the peaks and troughs of when the wind blows, companies are developing energy storage solutions, not least for the home.
One much watched solution is Powerwall, a low-cost home battery pack developed by electric carmaker Tesla. Also developing home energy storage solutions is Californian company SimpliPhi Power. “There is a critical need to eliminate the intermittency… so that power is available even when the sun doesn't shine and the wind doesn't blow,” says chief executive Catherine von Burg. In the US, nearly half a million people experience power interruptions on a daily basis, and such cuts are always accompanied by “quantifiable economic consequences - as much as $150 billion in 2014,” she adds.
The installation of energy storage projects in homes and businesses is soaring worldwide, says a report by Citigroup; the total amount of energy storage, excluding the electric car market, could reach 240 gigawatts by 2030, with batteries being the main technology.
Most commonly used at the moment are alkaline, lead-acid and lithium-ion batteries. But innovators are exploring other approaches, such as flow batteries that store electricity in two tanks of liquid separated by a membrane. This would make it possible to store large amounts of energy over long periods of time, although they would be bulkier than lithium-ion batteries.
California-based Primus Power had developed a slightly different flow battery design, with one tank instead of two, and using titanium instead of plastic for its electrodes, thus boosting energy production. The company recently won a contract with Kazakhstan’s biggest electricity company, Samruk-Energy.
Researchers are also working to find cheaper and less toxic materials to build flow batteries, replacing vanadium, iron, zinc and bromine. At Harvard University, scientists are building a battery made of non-toxic organic materials that could perform as well as vanadium while costing less, making it environmentally-friendly and non-corrosive.
Another firm developing energy storage solutions is Good Energy. “We’re exploring and trialling peer-to-peer energy schemes, which will help us unlock the potential that’s out there,” says Will Vooght, the company’s head of innovation. In one trial, so-called Maslow battery systems will be deployed in 150 residential homes; another trial, called Piclo, will be the UK’s first marketplace where both private consumers and large electricity generators can buy and sell energy to each other.
In the US, Orison is offering a plug-and-play energy storage system. Its domestic storage devices are charged from the grid during off-peak hours. “Regardless of what energy storage solution homeowners choose, creating the means to harvest, store and manage energy from renewable resources on a local basis promises to reduce energy costs… as well as greatly reduce greenhouse gas emissions,” says von Burg.
However, the success of all these green energy innovation ultimately comes down to public support, says 10:10’s Amy Cameron. “Wind should, without question, be a major component of the low carbon infrastructure needed to meet legally binding carbon targets. But if we're to see wind take its rightful place at the forefront of our move to a low carbon future, we need a greater recognition of its public popularity and economic potential”.