Windstalker – another way to harness wind

Windstalker is an alternative energy concept designed by Atelier DNA that recently took second place in the Land Art Generator competition. Like wind turbines, the Windstalker installation harnesses wind to produce power, however it does so using a very different method. Essentially it consists of extremely tall and thin structures that sway in the wind, and this kinetic movement can be harnessed to produce the electricity.

In this particular design, there are 1203 of these stalks spaced very close to one another, giving the appearance of a field of wheat swaying in the wind (albeit on a much larger scale!). Each of the stalks is 55 metres in height, and despite being 0.3m diameter at the base taper to only 5cm at the top. The stalks themselves are made up of carbon fibre reinforced resin poles making them extremely strong and are anchored to the ground with concrete bases approximately 10 to 20m in diameter, which define the spacing achievable from one stalk to the next.

How does Windstalker generate electricity?

The electricity itself is produced using piezoelectric ceramic disks, which are stacked upon one another within the stalk, with electodes sitting between them. Piezoelctric substances produce an electric charge in response to applied mechanical stress, so when the wind hits the Windstalker stalks, it causes compression of the disks generating a electrical current through the electrodes, which travels down to a torque generator located in the base of the stalks which produces the electricity that can then be used by consumers.

Like Wind Turbines, the wind stalks will only produce electricity when the wind is blowing and the stalks are moving, therefore electricity production is not constant. In an effort to compensate for this, beneath the Windstalker installation lies an energy storage mechanism that consists of two very large chambers which sit one upon the other. When the wind is blowing and electricity is being produced, some of this power is used to drive water pumps which pump water from the bottom chamber into the upper chamber. When the wind stops blowing, the water is allowed to flow through the pump in the opposite direction, from the upper chamber into the lower chamber, driving the turbine in the pump which connected to a generator can produce electricity, ensuring a more constant source of power.

Windstalker and current commercial proposition

The Windstalker project currently is purely conceptual, but based on technologies currently available to the scientific community.  The estimated power output from an individual stalk is considerably less than a current wind turbine; however the stalks can be positioned much closer to one another, so the actual output per area unit is comparable. In addition this technology would have the benefit of lower noise pollution, less danger to wildlife (wind turbines are a real threat to birdlife), while still producing renewable energy with zero emissions. It will be interesting to see in the coming years whether the Windstalker energy concept is bought to life, and whether it will one day sit side by side with existing proven green technologies.

What is VIVACE?

VIVACE stands for Vortex Induced Vibration Aquatic Clean Energy, and is a technology used to extract energy from flowing water currents.

Vortex Induced Vibrations (VIV) are a physical phenomenon resulting from vortices forming and shedding on the downstream side of a bluff body (e.g a bridge support) in a current. The shredding of the vortices alternates from side to side creating vibrations. For decades, scientists and engineers have worked to try to prevent VIV damaging offshore structures such as oil platforms and bridges

In 2005, Professor Michael Bernistas of the University of Michigan turned this preventive research on its head, trying to maximise VIV and developing a system for harnessing its power. In doing so, he produced a converter unlike any existing technology currently in use, instead of turbines or propellers; the VIVACE converter uses cylinders that move up and down in the water due to the VIV. As these cylinders move vertically in their runners, they move magnets along a coil producing DC current.

VIVACE is the first system that can harness water currents under 2knots, where as conventional turbines and water mills require an average water speed of 5-6knots to operate efficiently. The majority of the earth’s currents travel under 3knots, so this technology is suitable to be situated worldwide and it has speculated that if we could harness just 0.1% of the energy in the ocean, it would support the energy needs of 15 billion people.

Vortex Hydro Energy has exclusive license to commercialise the hydrokinetic power generating device, and is currently running tests in the Detroit River of various types of system.

What are solar updraft towers?

Solar updraft towers use solar energy from the sun to drive turbines, which in turn create electricity. The method that these towers use to generate the power is very different to both solar photovoltaic and concentrated solar power plants.

The solar updraft towers uses the very simple premise that hot air rises as their basis for energy production. Essentially they consist of 3 parts, the first is a massive solar collection area (potentially over 1km x 1km), where the sun hits a greenhouse type structure, heating the air underneath it, and trapping it in.

In the centre of the collect area is a large diameter concrete chimney structure, which vents the hot air into the atmosphere (as the hot air rises). As the hot air moves from the solar collection area to the chimney structure, it drives the third element of the solar updraft tower, the electricity producing turbines, these are either situated around the base of the chimney, or actually in a horizontal plane within the chimney itself.

The 2 primary factors in solar updraft towers

There are two factors that are critical for successful operation of a solar updraft tower. The first is the size of the collection area; put simply, the bigger, the better. The more air that gets heated in the greenhouse collection area, the larger the volume of warm air that will travel up the chimney.

The second factor is the chimney height, when again bigger is better (750m plus). The higher the chimney, the greater the pressure generated by the temperature differences, resulting in a larger stack effect. The stack effect relates to movement of hot air through the tower, so the higher the tower, the more electricity can be produced.

Practicality of solar updraft towers

A Spanish man called Isidoro Cabanyes first proposed solar updraft towers in 1903, however it was not until 1982 that a small scale solar updraft tower was built south of Madrid. This test power station was operational for 8 years, before the tower collapsed due to a storm as the result of inexpensive materials used in it’s production. The chimney was 195m high, and the collection area was approximately 11 acres, giving the plant a maximum electrical output of 50kW.

It really then became a forgotten technology until about 5 years ago when numerous proposals were put forward to build much larger solar updraft towers than the Spanish test facility. One of the major issues with this type of solar power station is that for them to be a worthwhile investment, a large collection area is required. This makes it unsuitable for areas that have high cost per acre.

In addition there are high associated initial capital costs for the construction of these plants. When compared to solar photovoltaic plants and concentrated solar power plants, these solar updraft plants also are incredibly inefficient, only capturing a fraction of the solar energy that hits the ground.

Despite this, in October 2010, Enviromission announced plans to build 2 200MW solar updraft towers in Western Arizona, which have the potential to supply 100,000 homes with electricity.

There are also additional benefits when comparing the updraft towers to traditional solar photovoltaic and concentrated solar power stations. In addition to creating free clean electricity supply, unlike other solar sources that are intermittent, relying on the sun shining to produce electricity, solar updraft towers can produce power 24/7 if special materials are used under the collection canopy that reduce the heat slowly through the night.

In addition underneath the collection area canopy, condensation created at night allows the soil to be used for arable land, enlivening potentially otherwise barren desert. In addition there is sufficient clearance between the canopy of the collection area and the ground allowing farming equipment to move freely.

Finally if the towers were associated with air filters (potentially carbon dioxide), this technology could also act as a CO₂ scrubber (a CCS Technology) potentially helping to avert global warming.

The future of solar updraft towers

Solar updraft towers certainly have the potential to become a useful tool to help combat climate change. If production costs can be reduced, these would be ideal in third world countries where there is lots of cheap space to build the plants.

There are also patented designs that replace the large concrete chimney with a low cost fabric designs held in position using successive tubular balloons filled with lighter than air gas (such as helium). These would make the plants far cheaper to produce, although these have not been tested on a commercial scale.

A lot will depend of the success of Enviromission’s two planned solar updraft plants in Arizona, which will be completed in the next couple of years.

The sun and solar energy from space

Our sun is the largest known energy source in the universe. In the vicinity around the earth, each m² receives 1.4KW of solar radiation, however as this solar radiation travels through the atmosphere and hits the ground, due to day-night cycles, summer-winter cycles and weather, each m² receives just 250W.

If we were able to harness a single KM wide band around the earth in geosynchronous earth orbit (the height at which a satellite would sit), it would receive approximately the same solar energy in one year as the total amount of energy contained in the combined recoverable oil reserves on earth today (~211 Terawatt years compared to ~250 Terawatt years).

How does space-based solar power work?

Space-based solar power captures sunlight in orbit where it is constant and stronger than on earth. This then gets converted to coherent radiation and beamed down to a receiver on earth. The typical design for this would be a satellite sitting in geostationary orbit with kilometres² of photovoltaic arrays situated either side capturing the sunlight producing the electricity. This would then be converted to radio frequencies that are best suited to atmospheric transmission and beamed down to a reference signal on earth, where the beam would picked up by a rectifying antenna and converted into electricity for the grid, delivering approx 5-10GW of electrical power to the grid.

Space-based solar power does not require any scientific breakthroughs or new physics to become reality. Since the idea was first put forward in 1968 by the Nasa engineer Peter Glaser, these breakthroughs have taken place, and all of the technologies involved have come on leaps and bounds. The international space station currently has solar panels the size of football pitches powering it, as do most satellites currently orbiting above the earth.

Space-based solar power is currently being held back as a viable energy solution by the high cost to orbit. It could not be achieved without safe, frequent (daily or weekly), cheap and reliable access to space, and the current lack of this makes it prohibitively expensive.

What are piezoelectric materials?

Piezoelectric materials are materials that produce an electric current when they are placed under mechanical stress. The piezoelectric process is also reversible, so if you apply an electric current to these materials, they will actually change shape slightly (a maximum of 4%).

There are several materials that we have known for some time that posses piezoelectric properties, including bone, proteins, crystals (e.g. quartz) and ceramics (e.g. lead zirconate titanate).

However, in May 2012, it was announced that University of California Berkeley lab scientists have found a mechanism of harnessing piezoelectricity from viruses. This is the first time a biological material has been used to make piezoelectricity.

Why are piezoelectric materials of interest?

Imagine walking down the street and charging your phone as you walk, charging your laptop by typing, or powering a nightclub by dancing on a piezoelectric floor! The concept of piezoelectricity has been around since the 1880s and was discovered by Jacques and Pierre Currie. Despite already being used in things like lighters to create the spark that ignites the gas, using it as an everyday energy source is still a long way off.

Issues with current piezoelectric materials

There are 3 issues that we are currently faced with in trying to tap into piezoelectricity as a viable electricity production method:

• The major issue one is that the quantity of electricity produced is so small, so unless vast installations were set up, it simply would not have the strength to power our latest gadgets.
• The current is only produced when there is mechanical stress being applied, so as soon as you stop compressing the material, there is no charge produced.
• The final issue is that up to now, many of the starting products needed to produce the piezoelectric materials are toxic and difficult to work with.

Why newly identified viral piezoelectric material could be the answer

There are many reasons why this finding could revolutionise the piezoelectric field. Firstly, viruses replicate incredibly quickly, producing millions of identical viruses within hours, so your supply is potentially limitless. In addition, as it is a virus, scientists can relatively easily genetically engineer it, thereby improving its piezoelectric characteristics. The virus itself is shaped as a rod, so when many come into contact, they naturally orient themselves into a amazingly organised film.

If you look at the Windstalker technology, you will see that the engineers behind it looked at ceramic piezoelectric materials being positioned within the wind stalks to harness the wind’s energy. This new research completed by the Berkeley lab, could make this potential technology more viable, as there is now a cheaper source of the piezoelectric material.

The future of piezoelectricity

Piezoelectricity is an exciting field of Nanotechnology, and there are already tests being run outside labs to try and harness this form of power. In many places including Japan’s subway, dance floors across the world and football stadiums, engineers have already put in place piezoelectric floors that use the high volume of footfall to decrease their demand for electricity from the grid. With a bit of luck in the years to come, piezoelecticty will become another weapon which we can use to reduce our reliance on fossil fuels and to derive the energy we need.

What is nanotechnology?

Nanotechnology is a relatively new field of science that involves any technology where its components are less than 100 nm. 100 nm is one-billionth of a metre, or another way of looking at it is that a sheet of paper is about 100,000 nanometres thick.  Nanotechnology can be used in many walks of life, but there is great focus on using it within the energy industry.

Uses of nanotechnology

Efficient energy conversion

As fossil fuels become scarcer, nanotechnology will be used to reduce losses during energy conversion. Nano-catalysts could improve the conversion of crude oil into various petroleum products.

Commercial solar panels currently run at between 15-24% efficiency, due to the reflection of sunlight amongst other things. Nano-technology could be used to boost this energy conversion process, potentially by improving the material properties of the solar cells by embedding carbon nanotubes within them, or by taking advantage on nano-crystals.

Within wind turbines, carbon nanotubes can be used within the blades themselves making them stronger and lighter, thus improving energy efficiency. These blades are 50% lighter than glass-fibre blades, but far stronger. This means that larger blades can be used, which will start operating at lower wind speeds.

Energy storage

Nanotechnology is also being favoured to increase the efficiency of energy storage, taking up more energy and holding it for longer. This can be achieved by coating the electrodes with nano-particles, which increases the surface area, allowing more current to flow between the electrode and the chemicals in the battery. In addition, the liquid part of the batteries can be separated from the solid electrodes when the battery is not in use, so it holds its charge for longer. With renewable sources providing increasing amounts of the UK’s energy, it may well be commonplace in the years to come that a household contains an energy storage device to act as buffer from fluctuations in energy availability, such as when the wind stops blowing, or there is limited sunlight.

Nano-technology is also being looked at as a means of storing hydrogen more efficiently in hydrogen-powered cars. Researchers are using graphene layers (an atom thick sheet of carbon atoms) to store the hydrogen – this storage mechanism has exhibited a capacity of 14% by weight at room temperature, which far exceeds any other material found to date.

Efficient energy transmission

Currently, electricity is produced in limited locations and is then transmitted along power lines to all the places it is needed. The further the end destination from the electricity producing unit, the more electricity gets lost along the way. Nano-technology could be used to create new kinds of conductive materials that are much more efficient, losing less electricity as it travels through the power lines. There is a great deal of research currently taking place questioning whether nano-coating power lines can decrease electricity losses.

What is bioethanol?

Bioethanol is an example of a renewable energy source because the energy is produced by using an organic substance and sunlight, which cannot be depleted. Up to now, bioethanol has been primarily produced for fuel and used in vehicles, but experts believe this technology can be applied to electricity generation as a green, low carbon alternative. Recent trials have shown that burning bioethanol as a fuel vs. other fuels such as natural gas and diesel fuel emits a reduced level of greenhouse gases such as nitrogen oxides, carbon dioxide and sulphur oxide.

Bioethanol fuel production

Bioethanol is an alcohol made by fermenting the sugar components of plant materials and is made mostly from sugar and starch crops. Creation of ethanol starts with the growth of plants via a process known as photosynthesis which grows a series of feedstock such as sugar cane and corn. These feedstocks are then processed into ethanol, first using enzyme digestion to release sugars from the stored plant starch, which are then fermented, distilled and finally dried. Bioethanol is already the most commonly used biofuel in the world, and is especially prominent in Brazil.

Bioethanol used for electricity generation

Burning bioethanol via combustion produces a lower thermal energy output than other thermoelectric generating processes from fuels such as coal or oil. To generate the same level of energy and electricity a much larger stock of Bioethanol is required. The advantage however is that this is a carbon neutral fuel. During the plant growth process, the plants remove CO₂ from the atmosphere, and when they are burnt they release this gas back into the atmosphere, therefore the whole process is carbon neutral where as burning coal or oil adds CO₂ to the atmosphere.

The future of bioethanol in producing electricity

The world’s first bioethanol power plant is located in Brazil, opened for testing in early 2010, with an 87MW capacity, enabling it to provide power for over 150,000 inhabitants. The power plant is looking to generate electricity on a commercial scale using sugar-cane bioethanol as one of the key fuels. Testing on emissions from this power plant have shown a 30% reduction in greenhouse gases such as nitrogen oxide, without an impact on its power generating capacity.

In the UK we are probably not best suited to expolit this fuel as a green electricity generating source; with Windfarms, Wave and Tidal Energy probably being the best suited to our unique topography. Bioethanol on the other hand is heavily used as a blended transportation fuel in the US and Brazil. This is because mass production and cultivation of high yielding crops currently takes place in those countries.

However with recent trends forcing the pricing of crops and food upwards has meant that enthusiasm for this fuel source as a full alternative to conventional fossil has been slightly reduced.

Benefits

• Renewable energy source – it relies on sunlight & photosynthesis process which doesn’t diminish.
• Reduced emissions of greenhouse gases from the combustion process vs. other fossil fuels.
• Works well as an “add-on” fuel, a blending substance to conventional fuel.

Limitations

• Bioethanol relies on crop yields and crop prices as an input – therefore higher prices make the substance less economical.
• The combustion process produces less energy than conventional fuels such as oil and coal.

Airborne wind turbines

The total energy contained in wind is 100 times the amount needed by everyone on the planet. But most of this energy is at high altitude.

The average surface wind speed across Europe is 3 m/s (6.7mph). Most commercial turbines sit around 80m from the ground where the wind speed is almost 5 m/s (11.2mph). However at a height of 1000m, average wind speed rises to 9 m/s (20mph). Wind at these higher levels is also more consistent – so what does this all mean?

Well by doubling the wind speed from 5mph to 10mph, the power in the wind increases by a factor of 8. Increase the wind speed from 10mph to 100mph, the power increases 1000 times! So the effect of having the turbine at 1000m instead of at the surface means that the turbine will be in contact with wind 27x more powerful, but how do we harness it?

Airborne wind turbines – this high energy source of the future is of particular relevance to the UK, the Netherlands, Ireland and Denmark due to the high-speed jet stream.

How do wind kites generate energy?

Utility companies can tether giant kites up at very high altitudes (potentially miles up) where these high strength winds consistently blow. These kites pull with an enormous amount of force on their tethered cords, and this force can be used to spin the shaft of an electric generator stationed on the ground next to the anchor point of the kite, or spin a generator held up in the air. There are many types of wind kite; we discuss several designs below.

Kitegen is an Italian-based company. Its Airborne Wind Turbine (AWT) offering is based on a large foil ‘wing’. When the wind hits the kite it will spin out of a funnel attached to a pair of high resistance cables able to control the kite’s angle and direction. The kite is flown in a figure of eight trajectory pulling the lines out from a spool that coupled with a dynamo, produce current. A radar system can direct kites within seconds in case of any interference, for example birds or even light aircraft. When it has reached its maximum height, it is reeled back down in a controlled process to minimise the energy needed to retract the kite.  Done correctly, the initial phase should generate approximately 5 times the power as spent reeling in the kite.

Makani Power are currently testing a 30kW mini prototype version of its AWT known as the M30; resembling a conventional propeller plane, this AWT is designed to operate to a maximum altitude of 110m. Also in the pipeline are the M600 (a 600kW) version and the M5 which is the commercially viable 5MW version that will have an operational altitude of 350-600m. The AWTs themselves are essentially conventional propeller planes, with the propellers acting to get the kite airborne, and then once in position the propellers work in reverse, spinning as the wind hits them acting as small electric generators, the electricity comes down the tether cable to the ground station. It was announced in May 2013 that Google has moved to acquire Makani Power under its Google [x] research arm.

Another company currently working on an AWT is Magenn Power. Magenn’s AWT product is know as MARS, which is a 100kw unit and is a tethered inflatable turbine held in position in the sky by helium, rotating about a horizontal axis. Following successful prototype model (a 10kw model in 2008), the MARs unit is about to enter commercial production. The MARs unit comes with a 750ft tether however it is possible to get an extension to 1500ft, and it is ideal for both remote locations or where existing electricity infrastructure is limited / missing. Pricing for the MAR model has not yet been finalised.

SkyWindPower favours a rotorcraft type Flying Electric Generator (FEG), resembling a tethered elementary helicopter, with four rotor blades each 5m in diameter capable of generating between 6 – 100 kW of power.  The FEG will operate up to 2,000 feet where winds are stronger for better power production. The rotors spin in opposite directions, and when powered via electricity position the craft to the correct altitude. Once airborne the wind turns the motors, which acts to hold the AWT in position and produce electricity which travels down the tethered cable. Sky WindPower is at the final prototype phase and expects to be in production in late 2013 or early 2014.