Benefits of AD made available to more farmers

When Devon dairy farmer Winston Reed got together with other farmers to found Greener for Life (GfL) Energy, he did so with one clear goal in mind – to enable more farm businesses to share in the benefits anaerobic digestion technology can deliver.

“Farmers are under increasing business pressures, whether from ageing slurry stores or bovine TB. They also have varying access to funds, so just don’t have the time to fully investigate building an AD plant on their farm,” Mr Reed says. “GfL Energy has a team of people with the skills, expertise and funding needed, therefore giving many more farmers the opportunity to diversify their business.

“The AD cycle complements the existing farm business and delivers higher gross margins an acre. As an example, on average we add the equivalent of 2-4p/litre to the bottom line for dairy farmers.”

GfLife Energy has teamed up with City financiers, two British technology providers and a range of other AD industry experts to offer a one-stop shop for anyone looking to build their own plant. It offers to manage all aspects of the AD development process, from initial project feasibility, grid connections and planning, to financing, building and operating the plant.

Mr Reed says funding can be tailored to individual farmer requirements and capital available, although GfL Energy can meet the entire project cost and take all risk, if necessary. It can also tailor plant operation plus manure, digestate and crop management to each business, and offers farmers payments for lease of the site, a performance bonus, payment for manures and a “profit-plus” model for any crops grown that pays a premium over the cost of production.

The company’s focus is on developing plants using “plug flow” digester technology rather than a continuous stirred tank. The plug flow system acts in a similar way to a giant intestine which, Mr Reed says, gives a longer feedstock retention time and up to 20% higher gas yields from the same inputs. Plant size can be anywhere from 50kW to 1MW upwards, depending on individual site circumstances.

GfL Energy also hopes to encourage more collaboration between local farmers, either through setting up clusters of smaller gas-to-grid plants that each pipe biogas to a single site that then cleans the gas and injects it into the grid, or through farmers entering long-term feedstock supply agreements with local plants.

Phillip Mann, partner Bedstone Growers

South Shropshire farmer Phillip Mann installed a 250kW “semi-plug flow” biogas plant last year and believes such technology has a bright future on UK farms.

While his plant was not installed as part of the Greener for Life scheme, the technology is similar to that available through GfL and Mr Mann’s unit is already being used as a demonstration site for interested farmers.

As a family farming partnership, he wanted a plant that would be reliable and flexible enough to fit in with the existing farm business, which centres on 243ha of arable cropping and a 220,000-bird broiler unit supplying Cargill. Eventually, after months of looking at different types of technology and travelling to existing AD sites across Europe, he opted for local British manufacturer Marches Biogas.

“There’s a lot of good technology out there, but I’m proud that we have gone with a British-built plant,” he says.

Getting started

As well as choosing the technology, two of the biggest issues to consider before setting up any AD plant are funding and grid connection, Mr Mann says.

“We were quite fortunate here, because we’re towards the end of a good three-phase connection six miles from the substation. There’s no one else putting electricity into the line [from solar panels or AD], so the grid capacity was there. In fact, there is a feeling that our plant has actually helped even up the variable electricity supply in this area.”

In terms of funding, Mr Mann’s total project cost of £1.5-1.6m was entirely funded through Lloyds Bank, which he says was very supportive throughout the development process. “I think the bank liked the closed-loop system we have here, where we’re in control of producing all of the feedstocks and using the energy in the poultry sheds and applying digestate back to our land.

“Feedstock security is very important for all lenders, because without enough feedstock, the plant obviously can’t generate energy. They key is to make sure you’re in control of feedstock supply, whether that’s by owning, renting or controlling enough land yourself, or by having long-term supply contracts with others.”

Getting planning permission for the AD plant was reasonably straightforward, Mr Mann says, helped in part by the fact he talked plans through with neighbours from the outset to explain what he was doing and why. “In the end there were no objections and the plans went straight through in about three months.”

Performance so far

Since Mr Mann’s plant was commissioned in October 2012, he has been very happy with its performance. It was up to full power output by November and is about 15-20% more efficient than conventional continuously stirred tank reactor systems, largely due to the longer feedstock retention time of about 100 days. Power output of up to 300kW has been achieved during some months when feedstock is particularly good quality, he says. “We actually installed a 400kW capacity engine because of the predicted higher output at certain times.”

Annual feedstock requirement is 5,000t a year, comprising 70% home-grown energy crops (KWS energy beet, maize and grass silage), plus 30% poultry manure. “Energy beet and poultry muck are our preferred feedstocks, with the maize and grass silage fitting in around that. Maize can be quite variable in this part of the country, so it’s about finding a mix of crops that works for the farm and the AD plant.

“The key thing is to size your plant to give yourself enough breathing space to easily meet the feedstock requirements. It doesn’t hurt to have a bit more than needed, because in a worst-case scenario you can sell it on the open market.”

About one-third of the electricity is used to power the adjacent poultry units, with the remainder sold to the national grid. Mr Mann estimates the net benefit to the business from electricity sales, Feed-in Tariff income, power savings and fertiliser value of digestate could be some £500,000-600,000, which would mean the project should pay for itself within three to four years.

Indeed, most of his wheat in the ground for this harvest has only received digestate and next season he expects to remove the need for all bagged nitrogen across the farm, representing a total saving of £50,000-60,000. Typical nutrient analysis for the liquid digestate, which is spread by a contractor using a 24m dribble bar, is 9kg/t nitrogen, 9kg/t phosphorus and 9-12kg/t potassium.

“We’re getting three to four times more nutrient recovery from using the digestate, compared with applying the poultry manure directly,” he adds. “Crops generally look better on it and we’re also getting 15% higher grass yields with the digestate. Much of this is because we’re applying it in the spring when crops need it, rather than having to go on in the autumn as we did with manures.”

He estimates about one-and-a-half hours a day is spent loading feedstock and checking the plant, which means it doesn’t distract too much from the core farm business.

“You’ve got to liken an AD plant to an animal that needs feeding and looking after every day, but we’ve found the daily running doesn’t take as much time as expected, so we’ve still got time to farm,” he says.

Ultimately, Mr Mann says the AD unit has helped keep the farm business sustainable for future generations, giving some element of control over costs and returns for the next 20 years. “You don’t get anything like that stability with agricultural commodities. It’s the best thing we’ve ever done on the farm,” he says.