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/

Decentralised Energy: Woking Council Case Study

Woking Borough Council has pioneered a network of over 60 local generators, including cogeneration and trigeneration plant, photovoltaic arrays and a hydrogen fuel cell station, to power, heat and cool municipal buildings and social housing. Many town centre businesses are also connected to this local energy supply. The Woking energy model produces dramatic savings in energy use and greenhouse gas emissions. With further help from energy efficiency measures, the council has reduced CO2 emissions associated with the operations of its own estate, including social housing, by a staggering 77% over just 15 years. Some sophisticated engineering solutions have been deployed, including large thermal stores in the town centre car park and at the leisure centre at Woking Park. The balancing of the system is performed entirely by computer, and the control system can be readily accessed by remote engineers or council officers.

The generators are connected to users via private electricity wires owned and operated by Thameswey Energy Ltd – a company set up and partly owned by Thameswey Ltd, a municipal energy and environmental services company itself wholly owned by Woking Borough Council. These private wires have points of connection to the local distribution networks (in turn connected to the national grid), but in 2003 the council’s electricity infrastructure was 99.85% self-sufficient. In the event of a grid power cut the system can switch to island generation mode, meaning businesses and householders connected to the private wires continue to be supplied with electricity with only a short interruption while the system disconnects from the dead grid and restarts using a small black start generator (a generator which can start up with no external power input).



Woking was able to raise capital for energy infrastructure development initially through energy efficiency savings. A fund mechanism was established in a benchmark year for energy expenditure, against which savings accruing from energy efficiency measures were recycled, year on year, into further energy-saving initiatives. The substantial financial savings allowed the council to invest millions in energy supply innovation. Moreover, Thameswey Energy Ltd has attracted investment from Danish pension companies who recognise the steady low-risk return the initiative offers – energy systems like Woking’s are a common component of investment portfolios for pension and insurance companies across Europe.

Developing a private network enabled Thameswey Energy Ltd to avoid charges usually associated with the use of the grid. By circumventing these costs, it has been able to fund wires and generation to deliver low emission electricity in competition with conventional suppliers. For domestic customers in social housing, Thameswey provides electricity below the rate of other electricity suppliers as part of Woking Borough Council’s fuel poverty programme. The council estimates that it supplies heat and power to potentially fuel-poor households for 6–7% of the state pension – well below the 10% threshold of all household income spent on heating that the Government uses to  define fuel poverty.

While the Woking model is widely celebrated in energy circles, its significance for UK energy policy has yet to be fully appreciated. It shows that renewable technologies and cogeneration are highly complementary and lend themselves flexibly to a piecemeal engineering approach as finances allow. The key lesson from Woking is that, liberated from the constraints of centralised rules and infrastructure, cogeneration and renewables can assert their own competitive potential.

See www.greenpeace.org.uk/DecentralisingPower_summary or www.woking.gov.uk for more details.