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Green gas – your questions answered

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20 Mar 2023

Lots of customers have sent us questions about our first green gasmill, near Reading, which will be producing vegan gas by summer 2023. The questions are on a wide variety of subjects including biodiversity, feedstocks, soil health and the comparison with hydrogen. Simon Pickering, Principal Ecologist at Ecotricity, has written this article to cover all those questions and many more, in the context of today’s climate and energy crisis.

Why do we need green gas?

Let’s put this in context. In an ideal world, the UK would be phasing out the last use of gas for electricity generation, as well as hot water and heating in our homes and buildings, by 2030.

However, owing to abject failures of policy and policy implementation by successive governments over the past 30 years, 78% of our homes and buildings still have gas heating and hot water – and, as a country, we still generate 40% of our electricity from gas.

This is not only a betrayal of those suffering the effects of climate change right now (as well as future generations), but it’s also one of the factors pushing up energy prices.

The best industry prediction suggests that gas use will only halve in the next 30 years. Hydrogen, when the technology is fully developed and the gas grid network has been upgraded, may replace 50-60% of fossil fuel gas by 2050. Even with a massive programme of insulation for buildings, there will still be a gap in energy requirements for heating and hot water.

Green gas can help fill that energy gap.

How will the green gasmill work?

Our green gasmill is drawing from best practice from anaerobic digesters across Europe. It is being built to much higher standards than current anaerobic digestion facilities.

There will be specialised pre-treatment with the addition of seaweed extract to boost efficiency in biomethane production. It will have the technology to capture and upgrade any waste CO2 to food grade standard.

The main feedstock will be herbal leys, which have a wide range of benefits. They provide high yields of green gas, improve the soil, sequester carbon, improve drought tolerance and are a brilliant habitat for insects and pollinators. With lots of insects, they provide a feeding habitat for a wide range of farmland birds by day and bats by night.

Where will we grow the herbal leys?

They will be integrated into farming practices, replacing monoculture grasslands used for dairy herds or as a break crop for several years in an intensive arable system to get rid of black-grass infestation.

What are the benefits of herbal leys to the soil?

Herbal leys include deeper rooting clovers, lucerne and sainfoin which draw up minerals from deeper in the soil. This is important for the health of microorganisms. These deeper rooting species enhance water percolation and drainage, reducing the risk of surface water runoff and loss of topsoil.

Clovers and legumes have small nodules in their roots which contain symbiotic bacteria and cyanobacteria, which can extract nitrogen from the air.

The digestate which is left over after the biomethane is extracted in the green gasmill is an excellent source of minerals and nutrients. So, it will be returned to the soil as an organic fertiliser.

How will green gasmills affect biodiversity?

Biodiversity has declined dramatically across much of lowland UK due to the intensification of both arable farming and monoculture grasslands. Species-rich herbal leys won’t be carefully managed nature reserves, but they will support a much higher density of insects, bees and other pollinators than any intensively managed grassland or arable fields.

This is because there’s much greater species diversity, including flowering plants such as clovers, sainfoin and lucerne providing both pollen and nectar. The fact that we won’t be using artificial pesticides or agrochemicals is also a huge help to biodiversity.

The herbal leys will provide a feeding habitat for insectivorous birds, from skylarks and yellow wagtails to whitethroats and grey partridges. They’re also great foraging areas for bats.

Herbal leys also have longer growing seasons than intensive grasslands, which allows us to put longer spacing between the two main cuts, avoiding the peak bird breeding season. Actual management regimes will be considered on a site-by-site basis in partnership with landowners and our ecologist. Herbal leys are always cut high to maximise regrowth, which will avoid nest damage.

What effect do the herbal leys have on carbon?

The herbals leys absorb carbon dioxide during the growing season, acting as a carbon sink with 60-80% of the carbon dioxide captured below ground.

Just a small increase in soil carbon content can have a huge beneficial impact on microbial activity, as well as the soil’s ability to hold moisture, which is important in these times with increasingly hot dry summers.

What emissions are there from burning grass for gas?

Green gas recycles atmospheric carbon and does not release any additional fossil carbon into the atmosphere as the carbon contained in biomethane is biogenic and part of the carbon cycle.

A proportion of the carbon dioxide captured by the herbal leys during the previous growing season within the above ground harvested leaves (less than 50%) will, of course, be released when the biomethane is used for heating our homes and hot water.

However, much of the land on which it is to be grown would have been used for animal farming. Imperial College has calculated that taking into account the switch from high- input animal farming and the high specification of our green gasmill, there will be greenhouse gas savings of 87% compared to business as usual. You can see the full breakdown of figures on emissions in Section 5.5 (p28) of the full report: Green gas | Ecotricity.

What waste products are created, and how are they disposed of/recycled?

From the process of anaerobic digestion, we get two main outputs: biogas and a digestate, which isn’t wasted but used as a rich source of organic fertiliser. There will also be a small amount of carbon dioxide which we will capture and upgrade to food standard, for use in our bar at Forest Green Rovers and potentially other pubs.


How are the herbal leys harvested?

Our initial aim is to get the green gasmill up and running as soon as possible, producing low-carbon green gas.

We currently have to use diesel tractors to harvest and transport the feed stocks. However, we’re looking to install a compressing plant, which will allow us to use biomethane farm equipment to make further greenhouse gas emission savings.

Is this the right time for green gas?

We’re in a climate and cost of living emergency. We can't wait around for the theoretical perfect solution. In a very rapidly changing world on the verge of a climate change catastrophe, it’s vital “not to make the perfect the enemy of the good”.

Green gas could make a really meaningful contribution. Combined with a massive deployment of renewables, insulation of buildings, hydrogen, smart grids, energy storage and heat pumps in suitable buildings, it could contribute to the UK becoming carbon zero and energy independent by 2030.

Read our Green gasmills fact sheet for more frequently asked questions and if you missed it – watch Dale Vince talk about Green gasmills at the House of Commons.

Further articles referred to in the blog:

Centre for Ecology & Hydrology & Rothamsted Research (2018) Quantifying the impact of future land use scenarios to 2050 and beyond - Final Report. Committee on Climate Change
Dimbleby (2021) The National Food Strategy: The Plan – July 2021

Audsley et al. (2010) Food, land and greenhouse gases. The effect of changes in UK food consumption on land requirements and greenhouse gas emissions.

Department for Environment, Food & Rural Affairs, UK Government (2022) Statistical data set. Agriculture in the United Kingdom data sets

Stewart et al. (2021) Trends in UK meat consumption: analysis of data from years 1–11 (2008–09 to 2018–19) of the National Diet and Nutrition Survey rolling programme. The Lancet, Planetary health, 5(10):e699–e708.

Navigant 2019. Pathways to Net Zero: Decarbonising the Gas networks in Britain

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