Power-to-gas and its potential coupling to renewable energies

By Oriol Casal (Cetaqua, Water Technology Centre)

As renewable energies share in the electricity mix increases, so does the impact of its related implementation issue: uncontrolled generation fluctuations. Renewable energies such as hydropower and biomass can be easily controlled, and their power output readily regulated throughout the day. However, other renewable energies such as solar power or wind energy generation depend entirely on external factors that, although can be predicted to a certain extent within a constricted time window, cannot be modulated.

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These fluctuations in power generated can be damped by the other main players in the electricity mix, such as natural gas combined cycle power plants or hydropower itself, provided that their market share is high enough. Nonetheless, as the solar and wind power share increase in the power mix, the flexibility of such key players decreases, and other solutions need to be envisioned, or, otherwise, the stability of the power grid is at stake, and drastic measures need to be taken, such as load shading or, in other words, controlled blackouts.

Power-to-gas as a future solution to renewable energy intermittency

One of the possible solutions with the most potential is energy storage. Conventional energy storage, such as batteries, is not applicable at this scale, neither technically nor economically. Other possibilities, such as storing energy by pumping water to basins with higher altitudes, have very limited potential.

A possible solution would be power-to-gas, in which the excess electric energy in the power grid is used to produce a gas fuel, in which the energy is stored chemically, and can be stored easily, due to the high energy intensity nature of fuels.

The LIFE NIMBUS project: power-to-gas meets biogas upgrading

The LIFE NIMBUS project explores one of these possible solutions: electricity is consumed to generate hydrogen. Nonetheless, hydrogen is not easy to store, due to its light nature and the hazards it presents. Instead, hydrogen is used to upgrade biogas produced at El Prat de Llobregat wastewater treatment plant, in Barcelona, using a technology called biomethanation.

Infographic of the process proposed by LIFE NIMBUS

The resulting gas is biomethane, chemically a substitute for natural gas, which can be considered green and with a neutral carbon footprint, provided that the electricity consumed to generate hydrogen comes from 100% renewable sources. This biomethane purity allows injection into the natural gas grids, or its direct use for transportation. Natural gas is easier to store and transport than hydrogen, whether directly compressed or liquified or injected in the gas grid, which can act as storage itself. In the LIFE NIMBUS project, this biomethane will be used to power a urban bus in the streets of Barcelona.

The future of biomethanation

Applications of this technology could arise in the future in biogas producing facilities, such as wastewater treatment plants, agricultural waste biogas plants or landfills. All these facilities could in the future upgrade from biogas plants to biomethane plants, contributing to the green share of biomethane in the natural gas grid, and improving the flexibility of the power grid. In fact, there is an existing commercial plant in which biogas is updated following the same biochemical route as in the LIFE NIMBUS project, though using a less advanced reactor configuration, in Allendorf, Germany.

Moreover, the possibility of upgrading captured CO2 opens up, meaning that any CO2 emitting facility, such as manufacturing plants, power plants or chemical plants, among others, could potentially become a biomethane production center while greatly reducing its GHG emissions, at the expense of increasing its electricity importation from surplus production at renewable energy plants.

All in all, the technology under investigation in the LIFE NIMBUS project could help tackle the intermittency issue of renewable energy plants, which is only expected to worsen in the coming decades. At the same time, it will help meet the EU target of increasing the share of biofuels, biomethane being one of them, for road transportation, virtually neutralizing its carbon footprint.

Click here more information on the LIFE NIMBUS project.

Photo by Arteum.ro on Unsplash