What is Green Gas?

Green Gas (or biomethane) is a type of gas created from biodegradable material (such as plants) 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 creates a biogas and a natural fertiliser.

The biogas is then purified using a method called “scrubbing” to produce biomethane (or Green Gas), which can be injected into the national gas grid alongside traditional gas (which is fossil fuel-methane drilled from underground).

The main difference between biomethane and fossil fuel-methane is that biomethane is virtually carbon neutral, so doesn’t contribute to Climate Change.

This is because biomethane recycles existing carbon in the atmosphere, which is absorbed by plants as they grow, while fossil fuel methane introduces new carbon into the atmosphere that had been stored harmlessly underground.

What are Green Gasmills?

Green Gasmills are Ecotricity's method of using Anaerobic Digestion to:

  • Produce gas from grass 
  • Improve soil quality
  • Support food production
  • Financially assist local farmers
  • Create wildlife habitats and replace inputs that damage the environment in conjunction with FWAG, Defra and Natural England.

What is Anaerobic Digestion?

Anaerobic Digestion (AD) is a commonly used process that uses bacteria to breakdown (or decompose) biodegradable material – in Ecotricity’s case, it’s grass – in an oxygen-free container. As the grass decomposes, it releases a biogas and creates a natural fertiliser.

(NOTE: The Anaerobic Digester or AD plant is similar to a large compostor, except the process is in an oxygen-free closed loop environment).

The biogas is then ‘scrubbed’ to purify it, leaving biomethane that can be injected straight into the gas grid as a replacement for traditional gas (which is fossil fuel methane).

Why is grass used to create Green Gas?

Ecotricity will use grass as our main input because it is readily available and consistent in quality – which is vital given the high quality and purity of gas required by National Grid.

 1. The first source of grass will be from marginal grassland pasture that is little used for grazing. The latest statistics[i] from the Department of Environment, Food and Rural Affairs (Defra) shows that the UK countryside has 8.4 million hectares of marginal land nationwide.

Also the amount of grassland used for grazing cattle has almost halved since 1990, meaning an increased availability of under utilised grassland that can be harvested.

NOTE: Grazing livestock numbers have declined over the last decade mainly due to changes in subsidies(the transition from a ‘per head’ based agricultural subsidy scheme to a ‘per acre’ based scheme, meaning market forces will determine grazing livestock numbers). Also farming styles have changed over the past two decades with much livestock now housed in large barns for much of the year rather than grazing in fields.

 2. The second source of grass will be a break crop (i.e. grown in rotation for 2-4 years), on lower quality farmland that is currently used to grow feed crops for livestock animals. We will not use medium to high quality land that is used to grow food without providing additional food crop benefit to the land and its environment.

How do Green Gasmills improve land quality?

The Green Gasmills concept improves land quality in two ways:

  1. Introducing crop rotation, with a grass crop grown for 2-4 years, helps break disease and fungal cycles in the soil and its environment
  2. Applying a natural fertilizer, created during the AD process, onto the soil will replace synthetic fertilizers.

Both these changes will help to improve soil health/condition and reduce dependence on synthetic chemicals and fertilisers – meaning after just two years this lower quality land will have improved to the point that it will now support food production for humans rather than only feed production for animals.

In addition, the reduction is synthetic fertilisers and other chemicals will help the surrounding environment and water quality, which can be severely damaged by the over-application of nitrogen-rich artificial fertilisers and other chemicals such as pesticides.

How do Green Gasmills support food production?

The Green Gasmills concept will support food production in two ways:

  1. Improving soil health/condition (see above) to the point that food crops for humans (such as wheat or potatoes) can be grown on the land in rotation with the grass crop – rather than growing feed crops for livestock
  2. Providing the opportunity to improving margin by growing food crops (instead of lower value feed crops) in rotation with grass crops.

How do Green Gasmills financially assist local farmers?

The Green Gasmills concept will financially assist farmers in three ways:

  1. Creating a ‘share-farming’ scheme that introduces a new commercial opportunity to grow grass, helping farmers to diversify and capitalise on land that may be underutilised and needs natural improvement
  2. Improving margins by growing food crops (instead of lower value feed crops) in rotation with grass crops
  3. By reducing the cost of using expensive synthetic fertilisers and pesticides and contribute towards renewable food production.

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

The Green Gasmills concept will benefit the environment three main ways:

  1. Harvesting marginal grassland pasture that is little used for grazing, will encourage the growth of wildflowers, creating new habitats for birds and insects such as pollinating bees which will increase biodiversity and improve the seed bank
  2. Providing a natural fertilizer that reduces the need for oil based synthetic fertilizers that have a negative long-term impact on soil quality, water quality and are responsible for 5% [ii] of Britain's carbon emissions
  3. Making green gas that virtually carbon neutral that replaces high carbon fossil fuel gas will help to reduce the UK's overall carbon emissions.

What makes Green Gas better than Fossil Fuel Gas?

Fossil Fuel Gas (also known as ‘natural gas’) is methane,extracted from underground – either by traditional drilling or via fracking.

Green Gas (also known as biomethane) is also methane but it’s derived from living biodegradable material, like plants or algae, which grow by atmospheric carbon sequestration.

What makes Green Gas better than Fossil Fuel Gas is that Green Gas is carbon neutral, so it doesn’t introduce more carbon dioxide into the atmosphere and contribute to Climate Change.

This is because Green Gas recycles existing carbon dioxide taken out of the atmosphere, and absorbed by plants as they grow, while Fossil Fuel Gas introduces new carbon dioxide into the atmosphere that had previously been stored harmlessly underground.

Green Gas can displace Fossil Fuel Gas that is currently imported from overseas and makes such a large contribution to UK carbon emissions. It is also a viable alternative to future fracking.

Isn't Anaerobic Digestion already common in Britain?

Yes. Anaerobic Digestion is a proven technology that is already very common across Britain, with more than 300 plants operating at farms, factories, and water treatment works around the country.

The biodegradable material used at these sites might be slurries (animal manure), crop waste, food waste, human sewage, etc...but the resulting biogas it is primarily burned to create electricity.

So Green Gas isn’t already common in Britain?

Not biomethane. Fewer than 20 of the over 300 AD plants around the UK produce Green Gas that’s made by converting the biogas into biomethane and injecting it into the National Gas Grid.

Most of those 300 existing plants burn the biogas to generate electricity,often to power their on-site operations on the farm, factory, or water treatment works.

The tough part in the Green Gas process is producing a biogas that has a consistent quality or purity, so that it can be converted into biomethane using a process known as scrubbing.

To achieve this, you need a consistent quality or purity of biodegradable inputs.Which is why we are using a grass feedstock to give us a consistent quality of input.

What happens if you don’t have consistent quality of biodegradable material?

The biogas that is produced is far more difficult to scrub and convert into biomethane of sufficient quality to meet the strict gas specifications stipulated by the National Grid.

How much land will need to be turned over to growing grass for gas?

For an AD plant supplying almost 6,000 homes we will need 1670 hectares of land or 5% of land within a 10km radius of the plant or 1% within 15 miles.

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

We will not be using land that is currently used to grow food for human consumption. Only little used grazing land or lower quality land that is used to grow feed for livestock.

In fact, the Green Gas process will improve the lower quality farmland to the point that food crops for humans (such as wheat or potatoes) can be grown on land – in rotation with the grass crop – that was previously only of sufficient quality to growing feed for livestock.

Won’t Green Gasmills mean lots of extra truck movements?

There will be localised truck movements but these will be restricted to trucks driving between the local farms providing the feedstock to the AD plant. The farms providing the feedstock will be restricted to a 15-mile radius around the AD plant to keep transport miles and emissions to a minimum. Down the line, a transition to using green gas powered trucks will further improve the technology towards carbon neutrality.



[i] The latest Defra figures that breakdown land use for 2013, there are:

  • 1.198 million ha rough grazing
  • 5.9 million ha permanent grassland
  • 1.2 million ha temporary grassland

Total = 8.39 million ha

[ii] Synthetic fertiliser and pesticides are bad for the local environment and account for roughly 5% of UK carbon emissions. Greenhouse Gas Emission Projections for UK Agriculture to 2030 Economics Group, Defra August 2011

...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