Bio-digester to power farm’s milk floats

DOOR-TO-DOOR milk deliveries powered by cow poo. Well maybe not literally, but delivered by electric milk floats using batteries charged by electricity generated from biogas produced by Sorbie Farm’s anaerobic digester.

This is the ambition of Ayrshire farmer Alan Hogarth, who is using a bio-digester which converts the slurry from 250 dairy cows into biogas used to generate electricity and heat.

“We are making our farm system as sustainable as possible, buying in as little from outside as we can,” says Alan, whose family has farmed at Sorbie for 50 years.

“Our cows are fed as much as possible from feeds produced on the farm, we breed almost all our own replacements and the slurry goes through the anaerobic digester.”

The digester produces gas which is burned in boilers to produce heat, and the digestate goes on to the land to grow the grass and crops to feed the herd.

Alan hopes the next stage will be to use the gas to power an electricity generator and utilise a part of it to charge the batteries on the milk floats.

“We market our milk as being locally produced and from a sustainable system in which our cows are kept under as natural conditions as possible,” he explains.

Full circle

“Being able to say our milk floats are powered by electricity produced from cow poo would bring things full circle.”

The 243ha (600-acre) farm carries a 250-strong Holstein milking herd, calving all-year-round. The farm is all grass apart from about 41ha (100 acres) of spring cereals – mostly barley with some triticale, all for home-feeding.

In 2004, Alan was offered the chance to take part in a Scottish Government programme to improve the quality of the bathing waters off the Ayrshire coast and to reduce the levels of faecal indicator organisms (FIOs) in the water. It was believed slurry from farms was one of the factors involved.

The initiative encourages Scotland’s dairy farmers to make a big contribution to meeting the Scottish Government’s ambitious targets to cutting greenhouse gas emissions, as by 2050, the region must reduce 1990 emission levels by 80 per cent.

Part of the deal was the Scottish Government would provide and commission an anaerobic digester on the farm, plus maintain and operate the unit for five years.

At the end of the five-year period, ownership of the digester was to be passed over to the host farmer who agreed to run and maintain the unit.

Alan took over the Sorbie digester unit in April this year which, apart from its original purpose, has brought many benefits to his farm business.

Reducing odour

Among other considerations, Alan was conscious the farm was situated on the edge of a large urban conurbation and it was important to minimise any pollution risks and to keep farm smells to a minimum. He is also a strong believer in sustainable farming systems and the digester offers the desired results.

The digester runs on a continuous feed system with automatic scrapers delivering slurry from the dairy housing to a lagoon from which it is pumped, as required, into the digester. Digestion produces biogases which are drawn off, and the digestate which is delivered on to the land.

The heat generated in the digestion process means the digestate is sterilised and virtually odour-free.

The hot water and steam clean the dairy and wash the traditional glass bottles used by the milk delivery business Alan, and wife Lorraine, run in the area. It is estimated its use has enabled farm fertiliser costs to be cut by up to £10,000 per year over the past 4-5 years, based on soil analysis.

The gas is also used to fire a steam boiler used in the dairy, plus boilers in the farmhouse and neighbouring cottage and Alan estimates this is worth about £4,000-£5,000 per year.

“It all makes great sense”, says Alan Hogarth, “I can make really good use of the liquid fertiliser for grass and crops. It saves me buying in as much fertiliser and helps reduce my farm’s carbon footprint, too, and our customers like the fact their milk hasn’t travelled far before it reaches their doorstep.”

He also hopes to take advantage of a proposed grant scheme offering up to 50 per cent of the cost of a biogas-powered electricity generator. This, he hopes, will bring at least major reduction in the farm’s £20,000 per year electricity bill and, ideally, meet all the farm’s electricity needs – giving a payback time of three years.

Key marketing aid

Sustainability was also to become a key marketing aid when Alan decided to move into selling milk direct to the public.

“Sorbie Farm is on the edge of a town and we have about 100,000 houses within a five-mile radius of the farm.

“We did not see why we should be getting a low price for our milk to be taken to Glasgow and brought back here for sale at a much higher price. I believed I could do better myself and cut out all the middlemen.

“We were advised against door-to-door deliveries, but there was said to be strong demand for local produce, so we decided to give it a try.”

He bought a couple of electric milk floats off e-Bay and, for the dairy, started with just the basics – buying a new pasteuriser and separator and everything else second-hand ‘to keep risks as low as possible’.

The start-up budget was around £50,000, though in practice, Alan says the cost was nearer £75,000 as the business developed. “We started working outwards from the farm, delivering a free bottle of milk and a leaflet to each house.”

His marketing strategy worked and the business has now been running about 18 months, gaining around 1,000 household customers and supplying 50-60 retail outlets. Around 40 per cent of yields are supplied direct to householders or to local shops and businesses with the remainder sold on to wholesale market.

Steady growth

Looking forward, Alan sees steady growth rather than any major developments in the farm business.

Until now, the incentives for generating electricity from renewable sources like biogas have not been enough to interest farmers. But a new Feed-in Tariff scheme (FIT) will pay renewable energy producers a FIT rate for each unit of electricity generated with more for each unit sold to the National Grid. It comes into force in April next year and Alan and Lorraine plan to use the new FITs for electricity which they do not use themselves.

Selling milk direct will continue to be a key focus and it is hoped to eventually sell all the farm’s production this way, with ‘locally produced’ and ‘sustainable farming’ as key marketing messages to existing and potential customers.

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