The Roe family in the south west of England commissioned their first anaerobic digestion plant in 2009 and they did not stop there, as Arable Farming found out.
Based just a few miles out of Bridgwater, the Roe family have farmed 158 hectares of variable land at Cannington, Somerset, for more than 100 years, where, until recently, they focused on arable crops, mainly cereals.
In the 1980s and 1990s potatoes were at the heart of their operation and on the back of this they developed a packing and processing business, including state-of-the-art cold storage facilities. But, when the bottom fell out of this market in the late-1990s, they had to look at alternative uses for their investment, switching to storing food products and eventually establishing a long-standing relationship with Refrecso Gerber, the biggest ambient and chilled fruit juice provider in the UK.
Under a new Cannington Enterprises banner, the Roes now store about 8,000 tonnes of chilled and 2,000t of frozen produce for local food and drink manufacturers, as well as continuing to operate a commercial farm.
When in 2007, electricity costs – which represent almost a quarter of their annual outlay – were set to rise by 72% on the previous two years, they faced another turning point and looked long and hard at alternative means of meeting their energy needs.
This started the family on a journey which has seen them develop what is one of the largest anaerobic digestion (AD) operations of its type and which is now producing the equivalent of 9,300kW of electricity and gas from their Swang Farm base. According to Tim Roe, the family initially opted for a modest crop-based AD plant, largely utilising home-grown maize.
He says: “Commissioned in 2009 and benefiting from strong Feed-in Tariffs available at the time, it helped us produce the 300-400kW of electricity we needed for the cold store and gave a strong income from the surplus 200- 300kW which was fed in to the grid,” he says.
Two years later, the company invested in another 6.8MW capacity plant to increase the amount of energy it exported and at this stage went out of maize, instead utilising food waste – primarily discarded fruit juice materials from Gerber – as an energyrich alternative feedstock
Investing in a unit which extracted the juice from bottles rejected by the manufacturer for use in the biogas plant, they also set up an arm of the business which recycled the waste plastic. As a result, the Roes were not only able to generate power from waste, they were helping improve the carbon footprint of the food and drink companies they serviced.
“Gerber, which is a handful of miles away, for example, now has most of its raw food and drink materials imported straight in to our stores. Any waste is then returned and processed by us, all with minimal movement, helping to meet the low carbon profiles required by its supermarket customers,” says Mr Roe.
But recognising significant growth potential, the Roes’ energy operation did not end there: In 2012 they increased their grid export connection from 1.1MW to 2MW and in 2013 invested further in another 2MW combined heat and power unit taking their capacity up to 3.8MW.
They then bought a gas-to-grid plant which went live in May 2015, meaning they now have the potential to generate 3.2MW of electricity and 1,200cu.m of gas for the grid. To achieve this, they now
use about 60,000-65,000t of food waste per year, but with sources of additional waste material increasingly difficult to find they have forged contract agreements with a number of local farmers to supply a range of biogas crops. “At today’s prices, wheat is hardly tenable on a farm the size of ours, so it makes sense for us – and many local farmers – to look at energy crops which can provide a more stable and tenable income,” says Mr Roe.
In 2015 they ensiled 263ha of maize – much of which was contract-grown and stored locally – and for the first time, specialist energy beet across a total of 182ha.
“There are a number of good reasons for switching from maize to energy beet,” says Mr Roe.
“First and foremost, it helps reduce waste in the plant.
“Ultimately, when we remove the packaging from the food waste, a small quantity of plastic gets into the biodigester tanks.
“Where we use juice co-fed into the AD plant with maize, the ‘non-digestible’ material left after 80-90 days, forms a fibrous mix with this plastic, which at the final screening process is difficult to reclaim and can only be sent to RDF refuse or landfill.
“With beet, there’s virtually no fibrous material left and more of the biomass can be utilised to generate power. As a result, we have little waste to reclaim and that’s a big saving in terms of disposal headaches and costs.
“While most farmers will be looking at revenue per hectare, we focus on returns per cubic metre of the digester space we have invested in.
“While maize and beet may both cost about £30/t to produce, it takes at least twice the length of time in the biodigester to extract the same level of gas from maize compared to energy beet,” he says.
In practice, energy beet delivers about 160-180cu.m of gas/t over a 40-day dwell time in the digester. Maize, in comparison delivers 220cu.m of gas/t, but over a longer, 90- day period.
“We’ve also found that with maize you’ll only ever produce 16-18t/acre, but with beet, 30t/acre is possible.”
But the benefits do not stop there.
“Our plan is to lift the beet when it is needed right the way through winter. This could mean leaving some of the crop in the ground until the end of March in a region which is commonly frost-free.
“As a result, we have focused on keeping the crop growing right through winter using late season fungicides to maintain green leaf. This will not only help pile on the yield in our mild autumn/ winter conditions, it will also help roots to pull moisture out of the soil.”
While the Roes are blessed with free-draining, light land, which will take traffic in winter, they aim to ensure there will be little damage to soils as a result of untimely lifting operations.
In addition, by maintaining a crop on fields most at risk of winter water erosion, soil loss will also be limited. While there are rotational issues with beet – and the farm will be back into other crops this year – they have contracted about 500ha of energy beet for this spring with local farmers.
The farm has also invested in a six-row Ropa harvester to lift the beet alongside a Cross washer to remove any soil and stones prior to feeding into the plant. Working with plant breeder KWS, the Roes have identified a range of varieties which can maximise the level of energy they can generate.
According to KWS, energy beet varieties such as KWS Gerty and Linova have been selected to produce some of the highest dry matter yields per acre with the result every tonne of beet has 25-45% more DM than a typical fodder beet variety.
Cannington Enterprises’ lab tests go some way to confirm this and show energy beet can provide two-and-a-half times more gas than the equivalent weight of maize.
“Not only are yields higher than that from other fodder or sugar beet types, energy beet varieties release more gas per kilogram of root they produce. “In addition, our analyses show a typical fodder beet type yields 112cu.m of gas/t compared to energy beet at 160cu.m,” says Mr Roe, who adds the aim is to ‘grow beet and nothing but beet’ as it fits in with the farm’s system better than maize.
“It is easier to handle, we can lift on demand and because it co-digests well with food waste and has a shorter retention time, we can gain more gas.”
Despite being in a productive growing area, the farm finds maize is just too inconsistent and reliant on the season.
“Despite choosing the best varieties with the most suitable maturity range there’s nothing you can do if the year is against you,” says Mr Roe.
“In 2013, for example, half of the maize crop grown locally grew to little more than 4-5in height. If you are short of AD feedstock, then you have to buy-in from outside, so we feel it is important not to have all our eggs in one basket.”
Alongside the much larger area of beet on local farms, the Roes have already planted 162ha of energy rye and will back this with 243-283ha of maize.
“Rotationally, we recognise we are going to have to use a mix of cropping,” he says.