Sense and Nonsense on Biogas


Biogas Maize is now grown widely in the Dorset Area of Outstanding Natural Beauty © Miles King

Maize grown specifically for Anaerobic Digesters to produce “biogas” is an increasingly common crop in England, especially in the South West. The area under Biogas Maize increased by 55% in 2016 compared to 2015, to 52000ha. The National Farmers Union set a target of 200,000ha of land under biogas Maize back in 2011, so they are 25% of the way to their target.

Maize is a very environmentally damaging crop, probably the most environmentally damaging crop grown in the UK. Why then is so much of it being grown? Because the Government pays not one, but two subsidies for it to be grown – the generous single payment (now over £200 per hectare annually) for anyone who owns farmland; and on top of this there are a range of payments including the Renewable Heat Incentive and the Renewables Obligation, depending on how big your Digester is, and when it was built. The really ridiculous thing is that producing gas from Maize produces practically no saving in Greenhouse Gas emissions compared with natural gas, because of all the emissions created in its production.

The Government, belatedly, decided to look again at whether all this money for environmental destruction in the name of climate action could really be justified – and held a consultation earlier this year. The results are finally out – and they have decided (at least on paper) to reduce the subsidy for biogas maize by 50%. Although they should have abandoned subsidy for this crop altogether, this is a step in the right direction. It will remain to be seen whether it has the desired effect in a years time when the 2017 planting area statistics are revealed. Given that this reduction only applies to new plants, it will do nothing to reduce the area already covered.

Richard Lowes, renewable energy researcher at Exeter University, points out that if the Government goes ahead with its preferred option, more than 50% of the gas generated from any new AD plant will need to be produced from waste, not crops. As there is a limited (and contracting) supply of organic waste, this should mean that far fewer new plants will be built.


Grass to Gas?

One energy company is proposing to use grass to run biogas plants, instead of Maize. Ecotricity, normally known for its wind turbines (and vegan Football Club) has plans to grow herbal leys (these are mixtures of grasses and other plants) as catch crops between arable crops like wheat or barley. These herbal leys will then be cut, twice or three times a year, and the mowings used to power the AD plants. This sounds great in theory – in practice though to produce enough gas to replace fossil fuel gas would take up all the agricultural land in the country (including upland grassland which is impossible to harvest). Mark Avery has already poured cold water on the idea, and Biofuelwatch recently produced a fairly comprehensive critique. Both actually overestimated how much gas Ecotricity would produce using their system, as herbal leys which don’t receive fertiliser (other than the digestate from the AD plants) will produce much less energy than a standard rye-grass silage crop (on which all the figures for grass to gas are based.) Benefits for wildlife are also likely to be minimal as the areas where the herbal leys are grown will be rotated around different farms. A few farmland birds might benefit.

The sad truth is that biogas from crops, alongside so many other approaches to bioenergy production, deliver very little apart from the opportunity to harvest large subsidies from the public purse, which as we know is rather empty at the moment. If we really wanted to do something about reducing carbon emissions, there are probably better ways of using the money – like a massive national housing insulation project.

After all, what’s the point of producing gas with a slightly lower carbon footprint, if it’s just going to be used to heat air which disappears out of draughty houses?

About Miles King

UK conservation professional, writing about nature, politics, life. All views are my own and not my employers. I don't write on behalf of anybody else.
This entry was posted in Anaerobic Digester, biogas, Maize and tagged , , , . Bookmark the permalink.

23 Responses to Sense and Nonsense on Biogas

  1. Reblogged this on Kitchen Counter Culture and commented:
    We need to keep informed about agriculture oriented towards energy production. In the case of maize in Britain, there’s also a terrible association with soil runoff during excessive rain events that contributes to flooding, as in this piece by George Monbiot with it’s quite shocking video component. A responsible climate change policy would take into account both the importance of good land management (as nudged or not by subsidies) and actual carbon figures, which Miles King, in the post shared below, discusses so clearly.

  2. John Kay says:

    We should be grateful that dairy farmers, facing low returns below the cost of production and growing AD maize as a cash crop, haven’t discovered sugar beet. I think it has maize beat for soil compaction, erosion, run-off potential, pesticide input and gas production.

    The notion of growing most of our energy needs in real time is so ludicrous it really doesn’t need elaborate calculation. I recall ~1993 the big new thing was short rotation coppice and to supply the entire needs of Manchester an area equivalent to Dorset was required. So many Manchesters and so few Dorsets.

  3. Sue Everett says:

    Excellent synthesis Miles. Sue

  4. wendybirks says:

    I was very disappointed to read that Ecotricity were proposing to do this. I’ve been a customer of theirs for more than ten years, and, because of this I’m afraid they have gone down in my estimation. Shame really! 😦

  5. Ifold blog says:

    Reblogged this on Ifold blog and commented:
    George Monbiot wrote an article in the Guardian a couple of years ago on the damage cause by Biogas plants reliant on maize crops. ‘How a false solution to climate change is damaging the natural world’

  6. Pingback: Sense and Nonsense on Biogas | Ifold blog

  7. I just did a little analysis ( suggesting that the southwest might be able to feed its population from its own agriculture powered mostly by biogas from grass silage in the region. I’d be interested in any critiques, but on the face of it I’d say what’s not to like? The bigger nut to crack indeed is domestic (and industrial) energy use. But inasmuch as people want to scorn the possibility of meeting existing energy needs from biotic or other renewable resources, that’s surely a measure of the mess we’re in. What are the alternatives on the table, aside from ongoing reliance on carbon-spewing fossil fuels? Nuclear? PV? How much of the gap can be closed just by better (retro-)insulation? I’d be interested in people’s thoughts – but I’d be cautious about ruling out biofuels before specifying a plausible alternative energy mix.

    • Miles King says:

      thanks Chris. From reading your post, it seems you’re suggesting it would take 225000ha of permanent pasture to provide the energy needed for farming in Wessex – is that right? We can debate the exact figures – for instance, I suspect an organic grass silage harvest would be far less than half the conventional equivalent. Also, much of the permanent pasture in the south-west would not be amenable to silage harvesting. And have you factored in the fuel cost of transporting the silage to the AD plants? But above all that, the scale of land-use needed to produce gas from grass is enormous; and there will be many other land-uses competing for that land. So, I don’t see it as a solution with the current technology.

      • Miles, the assumptions are 100 litres/ha of diesel equivalent to farm arable, 25 litres/ha to farm grass and an additional 200 l/ha diesel equivalent for both arable and grass to service the off-farm food/biogas economy; I’m assuming 5.5 tonnes dry matter organic silage per hectare or 19.6 tonnes fresh (cf. 45 tonnes for non-organic) and 160 cu.m of gas per tonne of fresh silage – the silage to be made from 25% of the region’s grass (comprising 50% arable leys plus the permanent pasture), amounting to about 200,000 ha in all – on the basis of those assumptions the energy from the biogas exceeds demand by about 50%, though there are some additional energy costs. Fuel costs of transporting to plant aren’t separately factored in, but there is the additional 200 litres diesel equivalent per hectare plus the 50% surfeit to play with. I’m also assuming a population in the southwest of 1 million greater than at present in 2039 (my baseline year) in accordance with ONS projections.

        I guess I’d argue that we need to transition out of fossil fuels, so how are we going to fuel agriculture? Biodiesel from oilseed rape, ethanol from potatoes, methanol from wood, electricity from PV or nuclear? Biogas seems more plausible to me than those alternatives, but I’d be interested to hear alternative suggestions. There may indeed be many other land uses competing for agricultural grassland, but I suspect that ultimately most of them would gain less priority than feeding people (or feeding the machines that are feeding people). Part of my analysis includes assuming 20% of the working population are in agriculture working on low input smallholdings – I suspect it would be hard to push that assumption much further, though of course it is a way of reducing agricultural fuel use.

        You could be right that the grassland is less productive than I’m projecting – I’m modelling it as in rotation with grass-fed cows. I’d be interested in other suggested figures. However, it seems to me that biogas stacks up better than other fuels – unless we assume huge amounts of electrical energy (from nuclear?) that can then be converted into useful agricultural energy. My analysis doesn’t touch on domestic heating (I’m thinking wood & PV for CHP as possibilities?) but I figure there’s no point getting warm if you’re not getting fed.

        I’m interested in people’s comments, but I don’t really see how we can rule out biogas without specifying alternative renewable fuel sources or assuming that we can continue to rely on imports of food and fossil fuel.

      • Miles King says:

        thanks Chris. Let me have a proper think about what you’ve written and then I’ll reply. In the meantime this is something I wrote a couple of years ago

  8. Joe W says:

    Chris, I haven’t had time to fully digest your comments above, but I thought I’d just comment on one point which is obviously critical to your calculations. You assume 5.5 tonnes DM/ha – to my mind this seems particularly low, I would expect a competently managed organic perenial ryegrass/white clover ley to yield 7t DM/ha, although I’d be expecting around 8-9 t DM/ha in a typical growing season with average grass growth conditions. From an organic italian ryegrass / red clover ley yields of around 9-10 t DM/ha should be expected. Lucerne could be an option on lighter soils, as it can realistically yield around 13-14 t DM/ha in an average season.

    John Kay makes a very valid point about fodder beat, I guess for many farmers, maize is a much easier crop to grow.

    Miles – ‘what’s the point of producing gas with a slightly lower carbon footprint, if it’s just going to be used to heat air which disappears out of draughty houses?’ Yes absolutely- it is absurd that more isn’t done to encourage adequate housing insulation.

  9. murray marr says:

    Excellent analysis, Miles.
    Energy from this subsidised digesting business is amazingly arse-about-face:
    Sweet corn, grains and pulses grown directly on those fields and then eaten is a very effective way to keep any community warm.
    It’s also quite a traditional use of farmland but of course there’s always the need for innovation, enterprise and change, E.g. trying to improve the shape of the wheel.

  10. Thanks for the additional comments. Joe, your figures would make my analysis come out all the better, provided my other assumptions and calculations are valid…

    Electricity to liquid fuel is certainly another way to go, but my feeling is that – as with Miles’s comment on land use – there will be a lot of calls on high grade electrical energy in the future, and only so much to go around.The idea of agriculture providing its own energy needs through biotic means seems appealing to me, though ultimately it’ll doubtless be the price that determines the energy choice.

    I agree that using maize silage to provide for domestic gas needs is not a good idea. But using grass silage to provide for agricultural energy needs is a different kettle of fish…

  11. Pingback: NFU proposals for a new farm subsidy system only fit for cloud cuckoo land | a new nature blog

  12. colin s says:

    It is only fair to be balanced. Maize grown for AD provides green energy. The sustainability criteria looks after emissions and credibility for this practice.
    However, what is the competition for our land bank ? barley for whiskey? wheat for bio-diesel? oil-seed crops? certain specialist crops for the pharmaceutical and make-up industry ? biomass ? Flowers?
    You decide ? Make-up, whiskey, diesel, pharmaceuticals, vanity products ?
    Oh yes, or green energy ?

    • Miles King says:

      Thanks for your comment Colin.

      Am I right in assuming you are the same Colin Steel of Weltec Biopower – world market leader in the production of stainless steel biogas plants?

      No, maize grown for AD does not create green energy, unless you’re redefining green energy as energy from green plants. It does however create a whole range of environmental problems.

      It’s interesting that of all the things you list as competing for UK land-use, food isn’t one of them.

      • colin s says:

        Well done, Linkedin is a fountain of information !!!!

        On this occasion you are wrong, Maize offers very green credentials V the alternatives. Several companies have spent lots of loot to prove this, and examples are available on the web. Extremely detailed Life Cycle Analysis is available, however I am guessing from the tone of your response, this will not suit your agenda.

        Never mind when the lights go out, you can settle down with a Scotch and a face pack..
        end of comments……..

      • Miles King says:

        thanks Colin.

        Always good to get an industry perspective.

  13. Salman Zafar says:

    Reblogged this on Cleantech Solutions and commented:
    Biogas from crops, alongside so many other approaches to bioenergy production, deliver very little apart from the opportunity to harvest large subsidies from the public purse, which as we know is rather empty at the moment.

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