What is Green Gas and why is it better than fossil fuel gas?

Green Gas (or biomethane) is a type of gas created from biodegradable material that can be used in the same way as traditional fossil fuel gas for cooking and heating in the home.

Biomethane is created by turning biodegradable material - in Ecotricity’s case, it’s grass – into gas using a process called Anaerobic Digestion. This process creates a biogas and a natural fertiliser.

The biogas is then purified to produce biomethane, which can be injected into the national gas grid alongside traditional fossil fuel gas.

The main difference between biomethane and fossil fuel gas is that biomethane is virtually carbon neutral, so doesn’t contribute to climate change.

This is because biomethane can be made from renewable sources that form part of the natural annual carbon cycle – recycling existing carbon in the atmosphere, which is absorbed by plants as they grow ­– whereas fossil fuel methane introduces new carbon into the atmosphere that had been stored harmlessly underground.

Green Gas can displace fossil fuel gas that is currently imported from overseas and makes a large contribution to UK carbon emissions. It is also a viable alternative to fracking.

What are Green Gas Mills?

Green Gas Mills are Ecotricity’s method of using Anaerobic Digestion to:

  • Produce Green Gas from grass
  • Improve soil quality
  • Support sustainable food production
  • Provide long term income security for farmers
  • Create and improve wildlife habitats and replace inputs that damage the environment under the guidance of FWAG, Defra and Natural England.

What is Anaerobic Digestion?

Anaerobic Digestion is a process that uses bacteria to breakdown biodegradable material – such as grass, in an oxygen-free container. As the grass decomposes, it releases a biogas and creates a natural fertiliser.

The biogas is then scrubbed of any other trace gases, leaving biomethane, which can be injected straight in to the gas grid as a replacement for traditional fossil fuel gas.

Why use grass to create Green Gas?

Grass is common and widespread, covering one quarter of the earth’s land surface,including over 10 million hectares of the UK’s farming environment. Grass is intrinsically part of the natural annual carbon cycle – stripping carbon dioxide from the atmosphere to grow – so produces a fantastic renewable energy source and has a very low carbon footprint.

Grass also provides a range of environmental benefits for the farming environment:improving severely depleted soil nutrition, removing black grass weed infestations, reducing the reliance chemical and artificial fertilisers, creating wildlife habitats, aiding flood mitigation and helping ensure Britain has future food production.

Ecotricity will focus on two sources of grass:

  1. Grass break crops which are grown for 2 to 4 years within an arable rotation.
  2. Permanent grassland where livestock no longer graze and/or where management is needed.

How do Green Gas Mills improve soil quality?

Soils are a really important natural resource and sustainably managing them is essential for farming, yet has been a combination of over-applying chemicals and focusing on mono-culture crops has led to severely depleted soil nutrition.

UK Government report released in 2016 said: “Soil degradation could mean that some of our most productive agricultural land becomes unprofitable within a generation.”

By growing a herbelley break crop – made up of a variety of grasses,clovers and herbs – on severely depleted arable soil, we can improve the soil structure, draw up nutrients deep down beneath the top soil, and increase soil organic matter – which has been in decline in UK soils over the last 20 years. This not only improves the soil’s health and fertility, but can help with its ability to hold and release nutrients and water. On top of that it creates an opportunity for carbon sequestration.

A natural organic fertiliser, which is a co-product in the AD process, is also returned to farmer’s fields, providing fertility to the soil for next year’s grass production, without the need to apply artificial fertilisers.

How do Green Gas Mills support sustainable food production?

By growing our grass break crop in rotation with food crops, soil health and fertility will be greatly improved (how this happens is described above). This is good news for the following food crop in the arable rotation – healthier soils mean more opportunities for farmers to grow a successful food crop.

In addition, with 25% of arable land in the UK suffering from black-grass weed infestation, the grass break crop helps rid the land of this weed, which badly reduces food crop yields.

We will always have a little bit more natural fertiliser than we need and we are currently exploring innovative ways for it to be used in other sustainable food production processes.

How do Green Gas Mills provide long term income security for farmers?

Green Gas Mills create a new commercial opportunity to grow grass, which provides farmers with long-term financial security. Growing our grass break crop will also reduce the need for farmers to use expensive chemicals and artificial fertilisers (sometimes costing up to £200 per ha) for their future crops.

How do Green Gas Mills create wildlife habitats and replace inputs that damage the environment?

By growing our grass break crop and not harvesting field margins, we will allow natural vegetation to grow without being impacted by chemicals. This will create new habitats – benefiting pollinators, such as bees and rebuilding biodiversity.

Whether the grass comes from a break crop or permanent grassland, the land will not receive chemicals and artificial fertilisers. Instead a natural organic fertiliser, which is a co-product in the AD process, will be applied during appropriate times and conditions to replace the massively damaging environmental-impact of farm chemicals, which alone contribute 5% of the UK’s total carbon emissions.

Is Anaerobic Digestion already common in Britain?

Yes, Anaerobic Digestion is a proven technology that is already very common across Britain, with more than 500 plants operating around the country.

These plants mainly use biodegradable material, such as: animal manure, food waste, agricultural crops, crop bi-products, or human sewage; and the biogas is usually burned to create electricity.

There are now over 80 Anaerobic Digestion plants operating around Britain that purify their biogas into biomethane to then inject it into the National Grid.

Our Green Gas Mills are the first of their kind being fed either predominantly or solely by grass.

How much land will be needed to feed a Green Gas Mill with grass?

A 5MW Green Gas Mill could supply 3,500 average homes (based on current consumption rates) and would need around 1,200 hectares of land, or 1.7% of the land within a 15km radius of the anaerobic digestion plant.

Won't food production be reduced on the land you use?

We are committed to making sure our grass never contributes to a reduction in human food crop production.

In fact, our grass break crop will contribute to creating healthier soils for growing food and ridding the farming environment of black-grass weed infestations, which impact 25% of arable farmland and reduces crop yields.

While the availability of permanent grassland has increase over the past 25 years as grazing livestock numbers have declined,due to changes in farming styles (with more livestock housed indoors) and changes to farm subsidies.  For example, despite the amount of grassland in the UK growing since 1990,  Defra data shows dairy cattle numbers have almost halved, overall cattle numbers are down almost a quarter and sheep numbers have fallen by over 20%.

Won’t Green Gas Mills mean lots of extra farm vehicle movements?

Much of the traffic movements will be re-purposing existing farm traffic, with localised tractor and trailer movements happening between the local farms providing the grass to the Green Gas Mill. The farms providing the feedstock will be restricted to a 15km radius around the Green Gas Mill to maximise environmental outcomes by keep transport miles to a minimum. Down the line, a transition to using biomethane powered tractors will further improve our carbon footprint.



...renewable gas could meet up to 50% of UK residential gas demand. Produced mainly via a process of anaerobic digestion (AD) or thermal gasification of the UK’s biodegradeable waste, renewable gas represents a readily implementable solution for delivering renewable heat to homes in the UK.

Report by National Grid January 2009