On the twelfth day of Christmas
With the festive season now upon us E&T takes a look at what researchers around the world have gifted us this year.
Optimised combined energy use
Engineers from the University of Zaragoza have developed an algorithm that optimises hybrid electricity generation of systems by using a combination renewable and non-renewable energies. It is envisioned that the energy would be stored in batteries or hydrogen tanks.
"The objective of this project is to minimise both the costs and polluting emissions generated by energy production within isolated systems in the electric network, as well as reducing the amounts of unprovided energy," explained Rodolfo Dufo, one of the authors of the study and a researcher at the Higher Polytechnic Centre of the University of Zaragoza.
The engineers looked at isolated installations, which are provided with electric energy from photovoltaic solar panels, aerogenerators and diesel generators, which use electrochemical batteries or hydrogen for storage. They have also looked into the possibility of redirecting the hydrogen for external uses, such as powering a vehicle.
The study is the first time a mathematical algorithm known as SPEA (strength pareto evolutionary algorithm) has been used for the optimal 'multi-objective' designing of hybrid electric energy generation systems. The algorithm provides an optimum range of solutions from which the designer can choose the most appropriate according to the relevant budgetary conditions, acceptable levels of pollutant emissions, and the amount of unprovided energy involved.
Lighter than a battery
Dutch-sponsored researcher Robin Gremaud has shown that an alloy of magnesium, titanium and nickel is excellent at absorbing hydrogen. This light alloy brings us a step closer to the everyday use of hydrogen as a source of fuel for powering vehicles. A hydrogen 'tank' using this alloy would have a relative weight that is 60 per cent less than a battery pack.
In order to find the best alloy, Gremaud developed a method that enabled simultaneous testing of thousands of samples of different metals for their capacity to absorb hydrogen. The well-documented problem of using hydrogen in storage is that it is highly explosive. However, this can be offset using metals that absorb the gas. However, this does make the hydrogen 'tanks' cumbersome.
The battery, the competing form of storage for electrical energy, comes off even worse. Driving 400km in an electric car, with performances comparable to those of the Toyota Prius, would require the car to carry 317kg of modern lithium batteries. With Gremaud's light metal alloy, the same distance would require a hydrogen tank of 'only' 200kg. Although this new metal alloy is important for the development of hydrogen as a fuel, discovery of the holy grail of hydrogen storage is still some way off.
Olive stones can be turned into bioethanol, a renewable fuel that can be produced from plant matter. This gives the olive processing industry an opportunity to make valuable use of four million tonnes of waste in olive stones it generates every year, and sets a precedent for the recycling of waste products as fuels. Researchers from the Universities of Jaén and Granada in Spain have shown how this can be achieved.
Bioethanol is increasingly used in cars, but its production from food crops such as corn is controversial because it uses valuable land resources and threatens food security. It also uses only a small part of the crop. By contrast, extracting energy from olive stones uses food industry by-products.
The team pre-treated olive stones using high-pressure hot water (essentially a pressure cooker) then added enzymes which degrade plant matter and generate sugars. The hydrolysate obtained from this was then fermented with yeasts to produce ethanol. Yields of 5.7kg of ethanol per 100kg of olive stones have been reached.
Secrets from the centre of the Earth
Research that has provided a deeper understanding of the centre of planets could also provide the way forward in the world's quest for cleaner energy.
A team of scientists, led by the University of Oxford, working alongside the Science and Technology Facilities Council's (STFC) Central Laser Facility, has gained insight into the hot, dense matter found at the centre of planets and has provided further understanding into controlled thermonuclear fusion.
This insight could extend our comprehension of fusion energy - the same energy that powers the Sun, and laser driven fusion as a future energy source. Fusion energy is widely considered an attractive, environmentally clean power source using sea water as its principal source of fuel, where no greenhouse gases or long lived radioactive waste materials are produced.
Using STFC's Vulcan laser, the team has used an intense beam of X-rays to successfully identify and reproduce conditions found inside the core of planets, where solid matter has a temperature in excess of 50,000 degrees. The understanding of the complex state of matter in these extreme conditions is one of the grand challenges of contemporary physics.
Thermoelectric materials boost
Thermoelectric materials can be assembled into units, which can transform the thermal difference to electrical energy or vice versa - electrical current to cooling. However, an effective use requires that the material supplies a high voltage and has good electrical, but low thermal, conductivity.
The new knowledge explains why some thermoelectric materials can have the desired low thermal conductivity without degrading the electrical properties. This can be crucial for the conversion of wasted heat, such as that from exhaust emissions. Leading car manufacturers are now working to develop this possibility, and the first models are close to production. The technology is expected to give the cars improved fuel economy, explains Bo B Iversen, Professor at iNANO at the University of Århus. The new knowledge can also contribute to the development of new cooling methods, so that one avoids the most common, but very environmentally damaging greenhouse gas (R-134a). All of which is a gain for the environment.
The researchers have studied one of the most promising thermoelectric materials in the group of clathrates, which create crystals full of 'nano-cages'. By placing a heavy atom in each nano-cage, we can reduce the crystals' ability to conduct heat. Until now we thought that it was the heavy atoms random movements in the cages that were the cause of the poor thermal conductivity, but this is not true, explains Asger B Abrahamsen, senior scientist at Risø-DTU
Smart electric meter
The Power Electronics team from Swansea University's School of Engineering has developed one of the world's most advanced Smart Electricity Meters. And the team is now supplying nearly 1.5MWh per year of free 'Green electricity' to the University, helping to reduce its carbon footprint.
The team, based within the Electronic Systems Design Centre, implemented their prototype Smart Meter to highlight the potential of electricity metering technologies in the near future.
The Smart Meter is to be the focal point for a consumer's personal energy queries. It monitors their energy consumption, giving information not just through a traditional power reading, but in a user-friendly way by displaying animated graphics of money on a large clear screen on the meter.
It also goes one step further than most other potential Smart Meters in that it monitors individual power circuits in the home, including upstairs lighting, downstairs lighting and kitchen sockets. The presentation of consumption information is complemented by the ability to show power generated from micro-renewable technologies in a 'plug and play' manner, similar to the wind turbine currently commercially available, and generic solar panels.
Energy from biomass
Scientists from the Carlos III University of Madrid (UC3M) have developed a system that can improve the efficiency of the conversion process of biomass to fuel gas that could contribute to the production of energy in a more sustainable manner.
One of the challenges that chemical engineers face is placing solid materials in contact with gases to generate certain reactions. One of the options is to use a fluidised bed, consisting of a vertical cylinder with a perforated plate inside which solid particles are introduced using pressurised air. This way, the solid particles are suspended and behave much like boiling water. Solids behaving like a liquid depend on the speed of the air stream, making it key to achieving the desired behaviour. With insufficient air, the particles don't move, but with too much the opposite happens, and they are carried away by the air stream.
Fluidised beds have relevant environmental applications because they allow the gasification of biomass to produce energy. That is, producing fuel gas from crushed biomass which can then be used for energy production. According to one of the authors of the study, Mercedes de Vega from the Energy System Engineering Group of the department of Thermal and Fluid Engineering of the UC3M, using fluidised beds as chemical reactors allows for a more efficient conversion by achieving high mixing degrees and high exchange rates of mass and heat.
Nano solar energy
Professor Darren Bagnall and his Nano Group at the University of Southampton's School of Electronics and Computer Science (ECS) have conducted extensive research into how nanotechnologies can contribute to the creation of solar cells that can be manufactured on cheap flexible substrates rather than expensive silicon wafers. This is done by using nanoscale features that trap light.
The group has investigated biomimetic optical structures, which copy the Nano structures seen in nature so that they can develop solar cells which allow efficient light-trapping. One type of structure is based on an anti-reflective technique exploited by moth eyes. Others are based on metallic nanoparticles that form plasmonic structures.
"It is essential that a solar cell absorbs all of the light that is available," he says. "Thicker devices absorb more light and, unfortunately, the need to use thick layers (particularly in the case of silicon) drives up the cost and often degrades the electronic properties of devices. Effective light-trapping will allow many alternatives and systems to be considered and will allow lower quality (cheaper) material."
Bacteria provides power
Researchers have combined the efforts of two kinds of bacteria to produce hydrogen in a bioreactor, with the product from one providing food for the other. This technology has an added bonus: leftover enzymes can be used to scavenge precious metals from spent automotive catalysts to help make fuel cells that convert hydrogen into energy.
Research into using bacteria to produce hydrogen has been revived thanks to the rising profile of energy issues.
We throw away a third of our food in the UK, wasting seven million tonnes a year. The majority of this is currently sent to landfill where it produces gases like methane, which is a greenhouse gas 25 times more potent than carbon dioxide. Following some major advances in the technology used to make biohydrogen, this waste can now be turned into valuable energy.
When there is no oxygen, fermentative bacteria use carbohydrates like sugar to produce hydrogen and acids. Others, like purple bacteria, use light to produce energy (photosynthesis) and make hydrogen to help them break down molecules such as acids. These two reactions fit together as the purple bacteria can use the acids produced by the fermentation bacteria. Professor Lynne Macaskie's Unit of Functional Bionanomaterials at the University of Birmingham has created two bioreactors that provide the ideal conditions for these two types of bacteria to produce hydrogen.
Hydrogen storage powder
Chemists in the US have developed a simple reaction to make ammonia borane - a powder more hydrogen-dense than even liquid hydrogen.
Storing hydrogen safely is tricky, however - pressurising hydrogen gas is potentially dangerous for everyday use, and it can only be stored as a liquid under cryogenic conditions. Chemists like Tom Autrey from Pacific Northwest National Laboratory, US, are addressing the problem by designing materials to store hydrogen safely, such that it can be released at will to power a fuel cell.
Ammonia borane (AB) is a stable white powder which releases hydrogen gas upon heating. Its use as a hydrogen storage material has been hampered by difficulties in making the powder in reasonable yield, but the new research further increases its promise.
Autrey and colleagues discovered a 'one-pot' method of making AB while studying its decomposition pathways. He said the group was "pleasantly surprised that under relatively simple reaction conditions the ammonia borane was formed in very high yields". The group is currently looking at scaling up the reaction to an industrial level. Autrey says the next challenge is to "recycle the solvents to provide the most economical route to synthesise this promising hydrogen storage material".
Roasted energy crops
A process used to roast coffee beans could give Britain's biomass a power boost, increasing the energy content of some of the UK's leading energy crops by up to 20 per cent.
The study, carried out by engineers from the University of Leeds, examined the combustion behaviour of crops grown specifically for energy creation when put through a mild thermal process called 'torrefaction' - more usually associated with coffee production. Torrefaction is increasingly seen as a desirable treatment for biomass because it creates a solid product which is easier to store, transport and mill than raw biomass.
The study examined the energy crops willow, canary grass and agricultural residue wheat straw to see what happened when they went through the torrefaction process and how they behaved at a range of temperatures when they were heated to create an energy-enhanced fuel.
Results showed that the treated materials needed less time and energy to heat to burning point, and also that they offered increased energy yields upon burning.
Willow emerged as having the most favourable properties, in that it retained more of its mass in the torrefaction process and also performed best in terms of its energy yield. As an example, willow was shown to have an 86 per cent energy yield, compared with 77 per cent for wheat straw and 78 per cent for reed canary grass.
"Raw biomass takes up a lot of space and has a low energy density which makes it costly - environmentally and economically - to transport. Plus you need more of it than, say, coal to produce energy efficiently," says Professor Jenny Jones, who worked on this study with PhD student Toby Bridgeman.
Nanosieves save energy
A new type of membrane, developed by scientists at the University of Twente in The Netherlands, can stand high temperatures for a long period of time. This molecular sieve is capable of removing water out of solvents and biofuels. It is a very energy efficient alternative to existing techniques like distillation.
Even after testing during 18 months, the new membranes proved to be highly effective, while having continuously been exposed to a temperature of 150ºC. Existing ceramic and polymer membranes will last considerably shorter periods of time when exposed to the combination of water and high temperatures. The scientists managed to do this by using a new 'hybrid' type of material that combines the best properties of polymer and ceramic membranes. The result is a membrane with pores sufficiently small enough to let only the smallest molecules pass through.
Ceramic membranes, made of silica, degrade because they react with water and steam. In the new membrane, part of the ceramic links is therefore replaced by organic links. By doing this, water does not have the chance to attack the membranes.
Manufacturing the new hybrid membranes is simpler than that of ceramic membranes, because the material is flexible and will not show cracks. What they have in common with ceramic membranes is the rapid flow: an advantage of this is that the membrane surface can be kept small.