In pursuit of alternative back-up energy: a closer look at power-to-gas technologies 

The short term operating reserve market has until recently mainly relied on fuel-generated back-up sources, but the use of combined power-to-gas technologies seems to be a promising and sustainable alternative.

While this method has existed since the nineteenth century and experimental pilot plants were developed in the 1990s, the potential for commercial deployment has only come to the foreground in the last five years.

As power-to-gas engines convert surplus renewable energy into hydrogen gas by electrolysis, splitting water into hydrogen and oxygen, then the generated hydrogen can be conveniently used as a back-up energy source.

Additionally, a small part of it can be added to the mix of gases currently in the grid, since the existing gas storage and transport infrastructure does not support 100% hydrogen.

As part of his research for the Centre for Alternative Technology on the benefits of the technology, Paul Allen, external relations director at the company, points out that “the smart trick that power-to-gas offers is to combine the hydrogen with carbon dioxide to create synthetic methane".

By relying on carbon dioxide from an existing source like biomass or waste to convert the hydrogen into methane it would create a methane gas that is highly carbon neutral. After being burnt, the carbon emitted from the converted methane cycles back into the atmosphere.

This method also benefits from the natural gas storage and power generation systems that are already established, making it cost effective.

Allen’s research also highlights that power-to-gas, “allows the peaks in renewable electricity generation to be used for the storage of significant amounts of energy via the provision of carbon-neutral fuels that can be used directly by industry, by consumers for heating and cooking”, or even used for the production of electricity during the troughs in renewable generation.

According to experts from the Technical University of Applied Sciences in Regensburg, Germany, about 143 power-to-gas hydrogen and methane projects have been developed since 1988 in 22 countries. From them, only 56 hydrogen and 38 methane projects were active in 2019, nearly 45% of which have fed or have planned to feed gas into the local grids or reconvert energy into power or heat.

The application of the method was recently recognised by the EU ‘Store&Go’ project, sponsored under the EU Horizon 2020 programme, a collaboration between 27 partner organisations across Europe. As part of the project, scientists are testing the integration of power-to-methane into the operation of European energy grids. It has three demonstration sites at Falkenhagen in Germany, Solothurn in Switzerland, and Troia in Italy.

French operators Teréga and GRTgaz recently developed power-to-gas demonstration project ‘Jupiter 1000’ in Fos-sur-Mer, in southern France.

The project is set to be the first industrial demonstrator of the technology with a power rating of 1 MWe for electrolysis and a methanation process with carbon capture. As part of the project, green hydrogen will be produced using two electrolysers involving different technologies, entirely from renewable energy.

The company has set a goal for the power-to-gas system to produce more than 15 TWh of gas each year by 2050.

Other companies awaiting approval of their planned power-to-gas projects include Pegasus in Italy, Amprion and Open Grid Europe in Germany, and Swedegas in Sweden.

While the growth in renewables has led to the closure of many coal and gas-fired power plants, experts believe that a mixture of more traditional methods and renewables will work most efficiently in the near future to provide back-up capacity.

Power systems director at WSP, an engineering professional consultancy, Anna Ferguson says: “We need a variety of different back-up sources to meet different needs and timescales. For example, pumped storage traditionally provides large reserve capacities, but batteries are well suited for providing services such a frequency response.”

Similarly, Reid also says that at this stage we don’t see a trade-off of gas over battery or vice-versa.

Instead, he considers another innovative vision where homes, small businesses and large energy assets are connected virtually and in an aggregated way: “They’ll make the stored electricity generated onsite using renewables available to the grid. Equally, some would be incentivised to reduce their demand during peak periods.

“Our Cornwall Local Energy Market project – where 250 homes and businesses are providing flexibility services to both the local and national grid network – is a testbed for this type of market,” he adds.

Ferguson, in turn, believes that in the future, “storage is likely to increasingly be part of the solution, but non-battery storage technologies such as compressed air, which are more suitable for bulk storage, may become cost effective.”

On a larger scale, she projects that “we will have more interconnectors, including potentially connecting Spain and Northern Africa to Northern Europe, to provide balancing with cheap sources of solar".

When combining the trustworthiness of gas-fuelled methods, the potential of batteries and the new renewable methods for the generation of back-up power, one thing is certain – the sector has good availability of options which have to be optimised as to reach a greater scale of energy stability.