In December 2013 wind supplied 55% of Danish electricity. On several days, turbines provided over 130% of the total need for power. The variability and overwhelming scale of wind-generated electricity in Denmark poses problems for the grid operator, Energinet. Other countries hoping to emulate Denmark, such as the UK, will face similar concerns.

The last post on this web site moaned about the lack of fundamental research into energy production and storage. Working out how best to run an electricity system that is dominated by a single and rapidly fluctuating source of power is one obvious area where R+D is urgently needed. In Denmark, the national grid operator has just funded over half the development capital for an advanced Power2Gas project at a wastewater treatment plant in Copenhagen. The crucial advantage of Power2Gas is that it can use surplus power, available when the wind is blowing strongly, to turn electricity into natural gas. By contrast, the UK failed to find the capital for a similar proposal here.

The Copenhagen 1MW project may fail. The technology is new and although it has worked very effectively at a smaller scale, there is no guarantee that it will operate successfully in the larger configuration planned for the wastewater plant. But there is no alternative to Power2Gas as a long-run solution to the energy storage problem. The world needs to invest now in risky projects that will eventually show us how to store surplus electricity in the gas grid.

Power2Gas

When the grid has too much power pressing to enter the transmission network, the operator has no choice but to disconnect (or ‘curtail’) some sources of electricity. The power that could have been used is wasted.

One alternative is take the otherwise worthless surplus and use it for the electrolysis of water. This splits water molecules into the constituent hydrogen and oxygen atoms. This is a simple process, carried out in chemistry labs of all the secondary schools in the world. The hydrogen has energy value. When burnt or combined with carbon it can be used as a fuel.

Some people therefore believe that we should run advanced economies on hydrogen. For example, hydrogen can be used in fuel cells for vehicles or home heating. It is perfectly feasible that a large fraction of our total energy demand could be met with H2.

The problem is that the world would have to build huge amounts of hydrogen storage and convert all engines that currently use fossil fuels into machines that use H2 instead. This is almost certainly too expensive and too disruptive to be a realistic option.

An alternative is to take the hydrogen and combine it with CO2 to make methane (CH4) and oxygen. Making methane in this way is also a simple chemical process. Methane is by far the most important ingredient in natural gas.

Since methane can be added in almost unlimited amounts to the natural gas network, it may be possible to convert long surpluses of wind or solar power into an alternative source of power. Germany, for example, has gas storage capacity equivalent to over 200 days of use. It could conceivably store all surpluses of wind or PV electricity in the form of methane, providing a zero carbon source of gas for burning in power stations when renewable energy isn’t sufficiently available.

Among other advantages this might help stabilise the wholesale price of electricity in Germany which has frequently dipped below the production cost of coal-fired power stations in the last few months. On several days power prices have gone severely negative. However much the opponents of fossil fuel may cheer this development, it has had profoundly serious effects on the capacity of electricity generators to fund new electricity generation schemes. The bankruptcy of RWE or E.ON will not solve the climate problem.

Opponents of Power2Gas usually point to the waste of useful energy that is inherent in the two processes of electrolysis and methanation (making methane). Only about 55-60% of the power of the surplus electricity is likely to end up in the form of methane energy. The correct response to this is a) to say ‘so what, it would have been 100% wasted otherwise’ and b) the waste heat from the two processes and the oxygen derived from electrolysis both have potential value that will reduce the loss from conversion.

Why is the first commercial scale electricity-to-methane project sited at a wastewater treatment plant?

Wastewater treatment plants (sewage farms in ordinary English) take human waste and other organic material and decompose it. One output is a biogas that is part methane and part CO2. The CO2 means it cannot be added to the national gas grid. So the biogas is burnt in a gas engine to generate electricity.

However the CO2 is useful for the methanation stage of Power2Gas. The new technology to be used at Copenhagen puts the entire stream of biogas through a reactor that converts the carbon dioxide, along with the hydrogen from electrolysis, into methane. The output from the process is pure enough to put directly into the gas grid.

The company delivering the technology to the project is Electrochaea, an early stage business developed from research at the University of Chicago, that has selectively breed a type of microorganism (methanogenic archaea) to feed off hydrogen and CO2 to make methane. Electrochaea has completed a pilot plant (1kW) in the US and successfully operated a larger pre-commercial system for much of 2013 at Foulum in Denmark, backed by utilities such as E.ON. The Foulum trial took place using biogas from an anaerobic digester, rather than gas from a sewage farm.

A wastewater treatment plant makes more sense. The surplus oxygen from the electrolysis process can be injected into the waste water to increase the rate of decomposition of the organic materials. The surplus heat from the methanation process can be similarly used to speed up the creation of biogas from the sewage.

Biogas can be stored temporarily at a waste water plant meaning, for example, that the electrolysis may well only take place when electricity prices are low, or perhaps even negative. The plant will also benefit from payments for being available to act as ‘frequency reserve’ to the operator of the national electricity grid. This means it will shut down the electrolysis process when the grid AC frequency drops below a safe level and will increase the electricity it is taking when the frequency is too high

Every wastewater plant in the world will eventually have some form of Power2Gas equipment to upgrade the biogas into methane, using electricity when it is in surplus.

The Copenhagen project

At the wastewater treatment works at Avedøre in Copenhagen, the seven commercial partners will install a 1 MW Power2Gas plant, using the proprietary Electrochaea technology for methanation and electrolysis equipment from the Belgian company Hydrogenics.[1] The plant will be built in early 2015 and will run as a trial for the remainder of 2015. A fully commercial Power2Gas system should be available in 2016.

About half of the €7m cost will be borne by the state-owned Energinet, which operates the gas and electricity grids in Denmark. The rest comes from the other others, including car company Audi. Audi’s interest in this venture, which complements its existing Power2Hydrogen research, arises from its wish to find non-fossil fuel sources for its cars. Liquid methane is a potential fuel for vehicles. Other participants include an energy trader and an operator of biogas plants, both of which would benefit from the success of the Avedøre trial.

The importance of this commercial experiment

Without energy storage, the renewables revolution will fail. Denmark and Germany both know this, not least because of the increasingly obvious impact of wind and solar on the functioning of the electricity market in both countries. But it should also be apparent to other countries that the world will need huge amounts of capacity to store electricity. The companies that create the means to convert surplus power into energy that can then be used when supply is tight will become enormously valuable. They will have solved perhaps the most intractable problem of the conversion to a low carbon world.

The UK has yet to understand this. Electrochaea has made sustained attempts to create a network of partners in the UK. Despite sustained interest from Severn Trent, the water and sewage company, and National Grid, the company told me that ‘nobody was able to provide the matching equity’ for its proposal for a trial site in central England. Its applications into competitions for grant funding run by DECC and other bodies have been rejected.

As I said in a blog post of last week, spending multiple billions every year on support for existing technologies through schemes such as feed-in tariffs must be matched by financial backing for raw, risky and unconventional technologies that might radically reduce the cost of a full move away from fossil fuels.

I’m not qualified to judge whether Electrochaea’s technology will work but I do know that backing a trial plant in the UK with a few million pounds is an overwhelmingly sensible idea. Isn’t it about time that someone had the courage to invest in companies that could change the energy world for ever?

[1] I believe the 1 MW refers to the energy value of the methane output, which will be substantially less than the electricity used to carry out the electrolysis.