Using consistent power from an AD to power 6 automatic milking robots

At Alderstone Mains Farm in southeast Scotland, the team milks 350 cows across six Lely robots on 350 acres of land. Faced with volatile electricity prices and a constant demand for power, they took the decision to install a small-scale anaerobic digester to turn slurry into electricity, heat and fertiliser.

“We first started looking at small-scale AD to take control of some of our costs,” Andrew explains. “Electricity prices had been very volatile and we wanted to find a way of making them a bit more secure, and also make use of the resources that we already had on the farm.”

Why look at farm‑scale AD?

The starting point was cost control and risk reduction. With robots milking around the clock, the farm’s electricity use is both high and continuous, making it especially exposed to price swings. AD offered a way to link that steady demand with equally steady on‑farm generation.

By focusing on a technology that could use slurry as a feedstock, Andrew saw an opportunity to turn a necessary by-product of the dairy into a strategic asset. Instead of just managing slurry, the farm could use it to produce energy and a more consistent fertiliser.

From slurry to electricity, heat and fertiliser

Since commissioning the digester, the farm has been using slurry to generate electricity and heat, while producing a high-quality digestate for use on the fields.

“Turning the slurry into electricity has reduced our electricity bill,” Andrew says. “Milking on the six Lely robots, we have a constant requirement for electricity and we felt that on‑farm AD matched the requirements of electricity with the production we could get from the plant.”

Alongside the digester, the farm also operates a 50 kW wind turbine and 50 kW of solar, with the digester adding 44 kW of additional capacity. Andrew highlights that it is the consistency of the digester’s production – generating power 24/7 – that particularly suits the dairy, providing a reliable backbone of supply for the robots.

On the nutrient side, the remaining digestate is now spread on the fields. “We can now spread that on the field as a very consistent product,” he explains. “We started spreading it in October and so far so good. It’s definitely a very powerful fertiliser.” While it is too early for exact like‑for‑like comparisons, he notes that it has been a good grass‑growing season so far.

Fitting into the day‑to‑day running of the farm

Despite adding new technology, the day‑to‑day workload has remained manageable. Andrew describes the operation as simple and largely automated.

“The day‑to‑day running is fairly minimal,” he says. “A lot of it’s automated. It’s just to take a look inside the reactor every day and check over a few of the settings on the app. But other than that, it’s not much work.”

The digester also fits neatly into existing infrastructure. The sheds were already built with automatic scrapers and a collection channel at the end, so the main change was in the slurry route. “All that we’ve done is we’ve diverted the slurry through the digester before going to our storage towers,” Andrew explains. As he puts it, the digester “has added into our business well” and supports their electricity requirements while ensuring all on‑farm resources are used to their full potential – something he says is “ever more important in the dairy industry”.

Impact on the electricity bill

Although exact numbers are not quoted, Andrew is clear that the financial impact has been positive. Using slurry to generate electricity on site has reduced the farm’s electricity bill and made costs more predictable.

By combining wind, solar and AD, the farm has built a more resilient energy mix. The digester’s round‑the‑clock output is particularly valuable for covering the base load, smoothing out the effect of market volatility on the business.

The future of farm‑scale AD in British dairy

Looking beyond his own farm, Andrew believes the technology has a strong future in the wider dairy sector. “I think on‑farm AD has the ability to produce power from a waste product while maintaining a quality resource in the digestate,” he says. In his view, the investment can pay off in the short to medium term, especially when electricity prices are unpredictable.

He also sees a reputational benefit for the industry. “I think it’s a good look for the dairy industry to be producing our own power from our own materials, especially with it coming from methane, which has been criticised in the past,” Andrew says. “So I think it’s a good thing.”

The system in one sentence

Summing up the role of the digester at Alderstone Mains Farm, Andrew describes it as a system that has “added into our business well,” fits their demand for electricity and helps use every resource on the farm to its full potential. In practice, that means turning slurry from a challenge into both a source of power and a reliable fertiliser for the fields.

Explore what AD could do for your farm

If Andrew’s experience at Alderstone Mains Farm sounds relevant to your business, we’d be happy to help you explore the options. Get in touch to find out how farm‑scale AD could help you stabilise electricity costs, make better use of slurry and build a more resilient dairy operation.