Power to Gas

Scaling up clean renewable energy systems will generate more electricity than we need. The Centre for Alternative Technology (CAT) have put forward proposals [1] which would generate about 1,160 TWh of electricity in an average year. The average total demand would only be around 770 TWh per year. However, the problem is that the electricity isn't necessarily generated when we need it. There will be a mismatch between supply and demand, with both large surpluses and shortfalls.

The key is to develop large amounts of energy storage which can be saved until needed. At the moment technologies like fly wheels, compressed air, batteries and pumped hydro plants can't store enough energy to keep the lights on when there's reduced amounts of renewable electricity. For example, in 2010 there was little wind but a high demand for electricity due to the cold weather.

The solution is to develop a technology called Power to Gas or P2G.

Hydrogen
Hydrogen can be made by the electrolysis of water – splitting H2O into hydrogen (H) and oxygen (O) using electricity. Electrolysers can use electricity at times when there is abundant surplus of electricity, to create hydrogen gas for storage. In principle, hydrogen can be stored and then used directly to produce electricity using gas turbines or fuel cells. However, hydrogen is a very light gas that needs to be highly compressed for storage. Itis also quite explosive and can even corrode metal. It is possible to store relatively large amounts of hydrogen (a few 100 GWh) over long periods of time, for example in salt caverns. However, compared to natural gas (primarily methane), hydrogen is difficult to store and transport and there is almost no existing infrastructure suitable for it.

Biogas & Synthetic Gas
Biogas and synthetic gas are both produced from renewable sources. Biogas, a mixture of methane and carbon dioxide, can be produced by anaerobic digestion (AD) – the decomposition of biomass (for example, grass, animal manure or food waste) in an oxygen-free environment. Carbon neutral synthetic gas is made via the Sabatier process. Here, hydrogen (made by electrolysis) and carbon dioxide (from burning biomass, or from biogas) are combined to produce methane. Methane is easier to store than hydrogen. The Sabatier process can be seen as ‘upgrading’ hydrogen to a gas that is easier to handle. The process of using electricity to produce gaseous fuel is sometimes referred to as ‘power to gas’ (GridGas, 2012).

Methane gas is also the primary component of today’s fossil fuel natural gas. The methane in biogas and synthetic gas can be stored in very large quantities just as natural gas is currently. The UK today has a highly developed gas infrastructure that includes storage facilities, such as the Rough gas store off the coast of Yorkshire, which has a capacity of 35,000 GWh. However, methane is a powerful greenhouse gas, so it is very important that any escaping from pipelines or storage is kept to a minimum.

Biogas and synthetic gas, once stored, can be burned in power stations (again, like natural gas today) to provide energy when electricity supply from renewable sources is insufficient to meet demand. Gas power stations burning biogas or synthetic gas can be flexible – we can turn them on or off quickly. We can use them as ‘back up’ generation to meet demand when electricity supplies from variable renewables fall short. They can also supply industry for very energy intensive processes which would be difficult to run on electricity.

It is important to remember that burning methane is only carbon neutral when it is produced using biomass and/or renewable electricity. When methane gas is produced from biomass, the amount of CO2 released by burning it is reabsorbed when new biomass plants are grown, resulting in no net increase of GHGs in the atmosphere. Synthetic gas is carbon neutral when the hydrogen used is produced using renewable electricity, and the CO2 used is from non-fossil fuel sources (like
biomass).

The processes involved in creating a significant biogas and synthetic gas back up system have many losses associated with them. As energy is converted between forms (electricity and biomass to gas, and back to electricity), we lose energy in the process – about 50%. However, the ability to store energy in this way forms an integral part of an energy system powered by renewables, and is a good way of using electricity which would otherwise be surplus to requirements.

Who is making the technology happen?

A Sheffield company called ITM Power [2] is developing and installing technology to make Power 2 gas a reality.

References:
[1] http://www.zerocarbonbritain.com/images/pdfs/ZCBrtflo-res.pdf for the full report
[2] http://www.itm-power.com/energy-storage/power-to-gas-energy-storage-solution/

North Sea Renewables Grid

Although critics of wind power suggest that wind is a variable energy source and can’t be relied upon to keep the lights on, this isn’t actually the case when wind power is distributed over a large area like the North Sea. Variations in production at one wind park can be partly balanced by that of another park several hundreds of kilometres away.

To demonstrate this concept, Greenpeace commissioned a report based on what would happen if real wind speeds over the North Sea were applied to more than 100 envisioned wind power projects with 10,000 turbines. If all projects from Belgium, Denmark, France, Germany, Great Britain, Netherlands and Norway were built there would be an installed capacity of 68.4Gw.

The top graph below shows how the power output of the propose London Array would fluctuate with changing wind speeds. When combined with all wind farms around the British east coast, the power production starts to level out as a dip in generation around London could be offset by heavy winds around Scotland. The final graph shows how wind production stabilises even more when combining all wind farm output from countries bordering the North Sea.

To capitalise on the balancing nature of distributed wind farms, a large North Sea grid spanning 3,850 miles would be required to connect all of the wind farms together. Such a grid would facilitate trade and increase security of supply by dispatching power from offshore wind farms to different countries depending on the highest demand. Moreover, an offshore grid allows the import of electricity from Norwegian hydro power plants to Britain and other countries. For some hydro plants, excess power (when the wind blows and sun shines) can even be used to pump water back into reservoirs, working like a huge water-battery. Biomass from European countries could also be fed into this grid.

A system of this nature with many thousands of wind turbines is more reliable, and energy production more secure because the impact of maintenance or defects will be negligible when compared to a large coal or nuclear plant going off line. Another advantage of a North Sea grid is that any future wave power, floating wind Turbines and tidal power stations could also be connected up to provide more power, stability and distribution of power between countries.

If this proposal were to be implemented then 70 million homes or 13% of the annual electricity consumption of the seven European countries could be met.

For the full report, see
http://www.greenpeace.de/fileadmin/gpd/user_upload/themen/energie/offshorewindgrid_final.pdf

Electric Car Charging Stations & Grid Storage

Conventional cars need to visit a petrol station to refuel which can often be a time consuming task. In some cases, filling up at a petrol station can add even more miles to a journey depending on its location.

One advantage with electric cars is that they can be plugged in to a normal power socket at home allowing the battery to be changed whenever it is convenient. The task of queuing and paying at a petrol station will be a thing of the past.

For some people, however, it will not be possible to change their cars from their own homes as it would result in power cables running across the pavement. To solve this, additional charging points could be installed outside private homes, workplaces and public locations.
Another advantage with cars being plugged in to charging points is that energy stored in the battery can be borrowed when we need extra electricity for powering our homes and offices. It is better to take this extra electricity from the cars’ batteries than generate it using dirty fossil fuels. These smart chargers would be aware both of the value of electricity, and of the car user’s requirements (for example, “my car must be fully charged by 7am on Monday morning”). The charger would sensibly satisfy the user’s requirements by guzzling electricity whenever renewable energy is available, and switching off when the renewables drops. These smart chargers would provide a useful service in balancing to the electricity grid, a service which could be rewarded financially.

If a car driver needed to make an unplanned long journey and didn’t have time to wait for the car’s batteries to fully charge, the car could be driven to a nearby charging station for a complete battery swap.  In the USA, Better Place have designed a battery switch station to achieve this.

At a Better Place switch station, the driver enters a lane and proceeds along a switch-lane conveyor. The automated switch platform below the vehicle will align under the battery, initiate the battery release process and lower the battery from the vehicle. It will then replace the depleted battery with a fully-charged battery. The depleted battery is placed in a storage room and recharged to be available to other drivers.  The process is completed in just a few minutes, while the driver remains in the car, providing a fast and convenient range-extension solution.

This solution would probably require a number of standards to be developed to swap batteries from different types of vehicles.

For more details on electric vehicles and charging see www.betterplace.com
For more details about how cars can be used as a storage system for intermittent renewables then see page 195 in Chapter 26 at www.withouthotair.com

Green Bio-Gas

According to the energy company, Ecotricity, it is about to launch a brand new initiative to supply green gas.

Green gas - or biogas – can be made during a composting-like process that breaks down food waste and other material that normally gets dumped straight into landfill or burnt in incinerators. Britain currently wastes around 18m tonnes of food alone a year, which could produce enough biogas to supply over 700,000 homes.

Ninety percent of homes in Britain are connected to the gas main and nearly two-thirds of us have a dual-fuel supplier (electricity and gas).

Householders who sign up to Ecotricity's deal will be supplied from January, although initially their gas will come from conventional natural gas. It is hoped that a small percentage of biogas will be injected into the national grid later in the year.

The company, which has about 30,000 electricity customers, said it wanted to eventually source 50% of its gas tariff from biogas and would match British Gas on dual-fuel pricing.

The owner of Ecotricity is reported to be planning to invest about £50m to build two green gas plants to make the biogas, but would also look at buying in biogas from other sources, including suppliers in Holland.

The National Grid recently produced a report on biogas suggesting that between 15% - 48% of our domestic gas supplies could be met in this way. Some materials such as wood are included in these figures so it isn’t clear if the materials destined for bio-mass projects are counted twice.
  
Extra momentum for UK biogas should arrive in 2011, when the government is due to introduce a renewable heat incentive, giving financial assistance to generators of heat from renewable sources, from householders using ground-source heat pumps to companies supplying green gas such as Ecotricity.

See www.ecotricity.co.uk for more details on green gas.
See www.nationalgrid.com/uk/Media+Centre/Documents/biogas.htm for a small report on the feasibility of using green gas.

Solar Salt Storage

Fossil-fuel proponents often say that solar can't run at night and solar can't run the economy. This might be true without a storage technology, but companies such as Ausra are looking at solutions.

Their solar collectors employ mass-produced and thus cheaper flat mirrors, and they focus light onto tubes filled with water, thus directly producing steam which can be used to generate electricity.
solar-thermal plants are a solution because storing heat is much easier than storing electricity. It is estimated that solar-thermal plants capable of storing 16 hours' worth of heat could provide more than 90 percent of current U.S. power demand at prices competitive with coal and natural gas.

Heat storage is more efficient than electricity storage. Just 2 to 7 percent of the energy is lost when heat is banked in a storage system, compared with losses of at least 15 percent when energy is stored in a battery

The typical method for storing the heat is to use molten-salt storage. Molten salts are inexpensive salt solutions that absorb considerable energy when they melt and give up that energy when they freeze.
For more information see:

• www.technologyreview.com/Energy/19440/
• www.ausra.com/technology
• http://www.solarnovus.com/index.php?option=com_content&view=article&id=5656:areva-solar-us-sandia-labs-join-forces-for-clfr-molten-salt-storage&catid=41:applications-tech-news&Itemid=245

Air Compressor Storage

Copying the idea of carbon sequestration, a coalition of local facilities in Iowa, America, are working on a scheme to store surplus wind energy underground. The idea is to keep it safely locked up when demand is low so it can then be uncorked at a later date when demand is higher.

The utilities plan on building a system that will rely on a gigantic air compressor (as seen in the diagram) to pump air into porous layers of sandstone some 3,000 feet down and sealed from above by dense shale. In essence, the layers of sandstone will act as a giant balloon, allowing for wind energy to be stored until a later time when demand is high - at which point the flow will be reversed, unleashing a large amount of air into a natural gas-fired turbine boosting its efficiency by upwards of 60%. This 268-MW compressed air energy storage (CAES) system is on track to be completed by 2011.

For more detail, and to watch a animation of the technology, see the web site:
http://www.isepa.com/

Energy Storage

Electricity company, E.on, is planning to build a huge battery to store power from sustainable electricity sources. Because sources like wind and solar aren't constantly reliable, some kind of storage is necessary if a 100% sustainable grid is to be created in the future.

E.on's scientists are planning to install the  battery in Nottingham which will be able to hold one megawatt for anything up to four hours. Smaller scale projects have already been underway for some time, but this massive battery should be completed in autumn 2009. Bob Taylor of E.on said, "Green power is only generated from wind farms when the wind blows and that might not be when the power's needed by customers. By researching and developing this battery we can store the power generated by wind farms any time and then use it when our customers need it the most. The storage system will also help the development of localised generation. For example, a school with solar panels can store the power generated at weekends and use it when the kids are back in school."

Solar Power from Deserts

Enormous quantities of energy fall as sunlight on the world’s hot deserts and concentrating solar power (CSP) is a proven technology for tapping in to it. CSP is a relatively simple, mature and practical technology that, with the right political and financial impetus, can be brought into play very soon.
CSP plants in the US Deserts have been operating for more than 20 years.  Since 1984, the solar dish equipment has held the world's efficiency record for converting solar energy into grid-quality electricity. The CSP plants do not use photovoltaic cells but concentrate the sun’s heat to boil a liquid. This is used to generate electricity. Three types of plants exists.

Power Towers use a large field of sun-tracking mirrors to concentrate sunlight on to a receiver on the top of a low tower, to raise steam and thus generate electricity.
Trough Systems use parabolic trough-shaped mirrors, each one of which focuses light on to a tube containing oil or similar fluid that takes the heat to where it can be used to raise steam and generate electricity.



Dish/Engine Systems uses a large sun tracking mirror with a Stirling engine generator at its focal point to convert heat energy into electricity.
Some detailed projections prepared for the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) show how, even allowing for increases in demand, a combination of CSP with other technologies can enable Europe to cut CO2 emissions from electricity generation by 70% by the year 2050, and phase out nuclear power at the same time
Every year, each square kilometre of hot desert receives solar energy equivalent to 1.5 million barrels of oil. Multiplying by the area of deserts world-wide, this is nearly a thousand times the entire current energy consumption of the world. At the moment, only a small area of desert will need to dedicated to CSP plants to generate enough electricity to power the world.
Are there any problems?
The first thing most people say is that the sun doesn’t shine at night. This is true, but deserts in the US, Africa and Australia all receive sun light at different times. Furthermore, techniques exist for storing the energy in melted salt or other substances. The clean electricity can also be used to produce hydrogen which can be stored.

How do we get the power from the deserts to the UK? It is feasible and economic to transmit electricity to the whole of Europe, the Middle East and North Africa using modern high-voltage DC (HVDC) transmission lines. Average transmission losses over modern high-voltage DC transmission lines (HVDC) are about 3% per 1000 km. In round figures, this means that electricity can be transmitted from North Africa to London with only about 10% loss of power. Since the fuel for CSP is free, any such loss is quite acceptable.

Other benefits
Besides generating electricity, the power plants in deserts could help the economies of Africa and other desert countries. The CSP plants can make use of the waste hot water to desalinate sea water which could have a major impact in alleviating shortages of water throughout the world, a problem that is likely to become increasingly severe with rising global temperatures
Although the area under solar collectors is in shadow, it should still receive a lot of light, quite sufficient for growing plants. Thus land that would otherwise be useless for any kind of cultivation could become very productive. An obvious problem is that plants need water and that is not plentiful in hot deserts. But desalination of sea water is another potential by-product of CSP and this may provide the fresh water that would be needed for CSP horticulture.

The potential of CSP in deserts is so huge that by 2050 the UK could be importing 70 TWh from this source. (1 TWh is enough to power 50 billion x 20 watt low energy light bulbs for an hour)

For more details contact Dr Gerry Wolff on 01248 712962 or by email at gerry@mng.org.uk
The web site can be found at: www.mng.org.uk/green_house

Flywheel Energy Storage

The electricity supply system is linked together on the ‘National Grid’. Your wall socket connects you to this. The Grid has to match demand with supply and keep things running at a steady level. Demand is not 100% predictable so we need ‘just in case’ supply to guarantee the lights stay on. But this safety net is a polluting fossil fuel power station.

An American company called Beacon has produced a flywheel which can store excess energy from power stations when there is no demand for it. When the demand increases, the flywheel technology can re-supply the stored electricity for use on the grid. This reduces the need for polluting power plants to provide standby energy.

A flywheel collects energy in the form of kinetic energy. The energy stored is similar to the stored energy that powers a rubber band car. As you twist and tighten the rubber band by pulling the car backward, energy is stored in the rubber band. Once the car is released, the potential energy stored in the rubber band is transferred into usable kinetic energy making the car go forward. The flywheel spins around an axis, the motor-generator rotor, by the use of magnets in a vacuum

A full-scale facility is designed to provide an important revenue-generating service, while at the same time help facilitate increased use of renewable energy sources, reduce air pollution, and make the grid more reliable. Comprising 200 high-speed, high-energy flywheels and associated electronics, a fully equipped plant will be able to provide 20 megawatts of “up and down” regulation – equal to a 40-megawatt swing.

The flywheel storage system can help renewable technologies like wind and solar by storing unused energy until it is needed at a later time. When the wind isn't blowing or the sun isn't shining the storage system can be used to provide power.

Click here to read more details about the flywheel storage technology