Farm Diversification

The Howgarth family have been milking cows at Sorbie Mains, Ardrossan, North Ayrshire for over three generations. The 250 cow mainly grassland unit is now managed by the young family of Alan and Lorraine. Having grown increasingly frustrated by a low farmgate milk price and seeing a gap in the local market, the husband and wife team took the decision to invest in processing equipment and start retailing their own milk to doorstep and local shops in the adjacent coastal towns.

Why install renewable energy?

An Anaerobic Digestion (AD) plant (also known as a biogas plant) was originally installed as part of a bathing water quality initiative. That said, the Hogarths are now convinced of the business benefits. The airtight bio-digester converts the slurry into biogas. The Hogarths are now investing in a combined heat and power (CPH) generator to harness this biogas to create renewable electricity and heat. The electricity will supply the farm, milk processing and power electric milk floats. The hot water and steam already clean the dairy and wash the traditional glass milk bottles.

The system will provide nearly 100% of energy requirements (equivalent to clean renewable energy for around 40 small family homes).

Making use of renewable power is reducing energy bills, reducing their carbon footprint and adds to the sustainability ethos that the Hogarths are adopting in other areas of the business e.g. encouraging the return of the traditional glass milk bottle and sale of unhomoganised milk. Milk is also being delivered, within 24hours of milking the cow, to customers within view of the green slopes of Ardrossan, where Sorbie farm is located – ensuring freshness and low food miles, all adding to the selling points for this family farming unit.

The liquor (know as digestate) from the AD unit retains all the original nutrient value of slurry but becomes less polluting. The process does, however, enhance the structure and availability of nitrogen for growing crops. This digestate has also contributed towards reducing purchased fertiliser requirements. Together with increased slurry storage and regular soil sampling has enabled fertiliser bills to be reduced by some £10,000. The AD process effectively eliminates odour from manure, which was a welcome bonus for surrounding residents.

How did you identify the type and scale of the renewable energy project?

The size of the digester was based on slurry throughput from the dairy herd with no other feedstocks being used. Youngstock manure is stored separately and transferred to the AD unit during the summer when cows are out at grass. This means there can be relative continuity of supply throughout the year and consistency of product – based on manure only.

With regards to the electricity generator, a 25kW system was calculated to closely match biogas production from the slurry, ensuring the generator is running to near capacity for as much of the time as practical and making most effective use of the money invested.

Researching the idea

An AD plant was originally installed on farm as part of a Scottish Executive Environment and Rural Affairs Department pilot study with the aim to enhance bathing water quality. The Hogarths together with neighbouring units were invited to participate in the scheme, being located in a priority catchment area – Saltcoats South Bay.

Having been introduced to the idea, Alan saw an opportunity to improve the farming operation while harnessing a renewable energy. The AD process also has the advantage of utilising existing manure, which can be made available all year round, which is more consistent than e.g. wind energy.

Establishment

Compared with most livestock operations this dairy unit has a near continuous electricity requirement to cover the daily milkings and pasteurisation. Fortunately the pattern of AD energy generation more closely matches the consumption pattern than many other renewable energy types. Off-setting purchased electricity provides the biggest financial incentive, and further benefits from the Feed In Tarriff (FITS) scheme. Since the business also makes full use of the heat generated, the Hogarths will also be eligible to claim Renewable Heat Incentive (RHI) scheduled to be launched in 2011.

Problems encountered

Establishment: Unlike larger commercial AD units, farm-scale versions are closely linked to the farming system and are generally in close proximity to the existing farm steading. Although a relatively new technology it makes use of familiar farm structures (above ground cylindrical steel stores) therefore provided it is not visually intrusive it will present few planning constraints. The Hogarths identified that involving Scottish Environment Protection Agency at an early stage did help the process.

If connecting to the national grid it will be necessary to confirm whether there is sufficient line capacity. This can be costly (depending on the proximity to a transformer). Booking until connection can take several months; something often underestimated in the project timeline.

Issues once established: Unlike larger AD units which incorporate feedstocks from many different sources, ‘rationing’ the digester to create a balanced environment for bacteria to breakdown the organic matter is a skilful process. Using only manure reduces complications.

Alan could think of very few problems except a blockage which lowered the digester temperature, consequently reducing bacterial activity and subsequent biogas yield. It then takes a few weeks to get the system back up to full production again.

Where the business is now
Importantly, the combination of diversification and the adoption of AD renewable technology fits with the existing farming system and makes use of existing resources. This helps keep the system simple, especially important on a very busy farm such as this.

Critical success factors
Having a system that can make use of the electricity and heat is particularly important. Availability of manure throughout the year and land to spread the digestate near to the holding also reduces cost and increases viability.

Contact

For further information contact Alan or Lorraine on 01294 605013 or email contact@sorbiefarmdairies.com.