The future belongs to green gas. For some time now, RAG has been working hard on new approaches to making large amounts of renewable energy conveniently accessible for consumers. Wind + sun = green gas – this is the equation behind power-to-gas. Together with natural gas, this could be the key to the success of the energy transformation. It can make the transportation and storage of large amounts of solar and wind power economically viable. It can mean that climate friendly energy is always available whenever it is needed.
Most of the renewable electricity produced in Austria is generated in spring and summer – outside the heating season. Run-of-river power stations produce twice as much energy in summer as they do in winter, and seven out of every ten kilowatt hours (kWh) of solar power are generated in the summer months. But this energy cannot be stored for extended periods because the electricity storage that would be needed is lacking. Existing gas storage facilities are the answer.
The principle behind power-to-gas could hardly be simpler: Surplus solar and wind power is used to split water into oxygen and hydrogen by means of electrolysis. The hydrogen can then be stored for later use, for example as primary energy in fuel cells. A further process stage is also possible: in methanation, the hydrogen reacts with carbon dioxide (CO2) to form methane, the main component of natural gas (typically making up 98 %). The CO2 can be drawn from the atmosphere or it can come from a biogas or industrial plant. The product of the process is renewable synthetic natural gas.
This means that electricity can be converted into gas, making it storable in large quantities for the first time. The process solves one of the biggest problems posed by electricity storage – shortage of space. It can simply fall back on existing natural gas infrastructure, in the shape of the pipeline grid and the gigantic storage facilities. Instead of developing and rolling out expensive, high-tech storage solutions, power can be transformed into synthetic natural gas and stored in depleted gas reservoirs.The process gives rise to no emissions apart from the oxygen released when the water is split. Today the efficiency of the conversion process is already about 60 % – a lot when one thinks that today surplus electricity is often not used at all owing to the lack of storage capacity, and instead wind turbines are idled or whole wind farms taken off the grid.
Geological history fast forward: over 1,000 metres below ground, where natural gas formed millions of years ago, a microbiological process for producing renewable natural gas is being tested for the first time. It will permit the organic, renewable production of natural gas.
This unique method recreates the process by which natural gas originates, but shortens it by millions of years – like geological history in fast motion. A microbiological process can transform hydrogen and CO2 into methane – renewable natural gas – in suitable gas reservoirs. Converting the energy, increasing the energy density and storing it take place out of sight, in porous rock formations at depths of over 1,000 m.
First, hydrogen is produced from solar or wind energy and water (using power-to-gas technology) in an above-ground facility, and then injected into an existing gas (pore) reservoir. At a depth of over 1,000 metres, in a relatively short time naturally occurring microorganisms convert these substances into renewable natural gas – which can be stored in the same reservoir, withdrawn as needed at any time, and transported to consumers via the existing pipeline network.
The aim of the research project is to use existing gas (pore) reservoirs as natural geological “reactors”. The methanation process and storage take place naturally in an underground pore reservoir. This is the key to the project’s huge potential as it promises to provide the urgently needed flexibility that renewable energy currently lacks. It holds out the promise of achieving the creation of a sustainable carbon cycle.
Laboratory tests, simulations and scientific field tests are being carried out at an existing RAG reservoir in collaboration with a group of project partners. A further objective is to test whether the research results can be repeated in other formations around the world. The striven findings are of great importance as they could extend Austria’s lead position in energy storage, and associated research and development. The goal is to apply the methods developed by the project – both the technology and the expertise – on a global scale.
Initial laboratory tests conducted in the Underground Sun Storage project showed that hydrogen injected into the reservoir with CO2 is converted into methane by microbiological processes. The Underground Sun Conversion project was
initiated on the basis of these findings, and is being implemented by an Austrian consortium led by RAG. The project is being financed by Austria’s Climate and Energy Fund as part of its energy research programme.
Renewable natural gas is carbon neutral if CO2 that is already present – for example, from burning biomass – is utilised and absorbed by the production process. This creates a sustainable carbon cycle.
Renewable energy becomes storable
Solar and wind power output fluctuates due to changing weather conditions, meaning that production cannot be adjusted to demand.
The problem of storing renewable energy is solved by converting it into renewable natural gas.
Use of existing infrastructure
Infrastructure already in place can be used for the natural production process, as well as for underground storage in natural gas reservoirs, and environmentally friendly transportation to consumers.