Case Study Standhill Farm
Standhill Farm has connected dairy farming, anaerobic digestion and commercial tomato production to create a more circular and resilient farming system. Cow slurry, livestock manure, wholecrop rye and lower-quality silage are used to generate renewable electricity, while heat and carbon dioxide from the process are captured and used productively in glasshouses for tomato production rather than wasted. Supported by biomass heating and rainwater harvesting, this integrated system allows the farm to produce around 700 tonnes of tomatoes annually while reducing methane losses, displacing purchased energy and improving the nutrient value of the material returned to the land. The case study provides a practical example of how farm by-products can become valuable inputs, improving on farm efficiencies while also lowering both production costs and the farm’s carbon footprint.
About Standhill
Standhill Farm is a 530-acre family dairy farm in the Scottish Borders. Purchased by the Shanks family in 1951, it has remained in milk production while diversifying significantly over the past decade. The farm now uses anaerobic digestion to convert cow slurry and other farm feedstocks into renewable electricity. Instead of wasting the heat and carbon dioxide created during electricity generation, these outputs are captured and used for commercial tomato production.
Built in 2016, the farm’s four-acre glasshouse contains approximately 55,000 tomato plants and produces around 700 tonnes of tomatoes each year. Plants arrive in mid-January, and the crop is harvested from early April until the middle of November. Two woodchip boilers supplement heat from the biogas engine, carbon dioxide is supplied during daylight hours to support plant growth, and most irrigation water is collected from the glasshouse roof. Bees pollinate the crop, while local labour supports growing and harvesting.
The enterprises are closely connected. Slurry from milk production generates renewable energy; by-products from energy generation support tomato production; and anaerobic digestion improves the availability of nitrogen in the organic material returned to the land. For Standhill Farm, reducing waste is both an environmental objective and a practical way to improve efficiency and resilience.
Finding An Opportunity In Renewable Energy
The concept of integrating commercial tomato cultivation into Standhill Farm emerged in 2009, inspired by an international internship exploring the intersection of renewable energy and agriculture across Sweden, Denmark, Germany, and the United States. In Germany, a promising model was already in operation: glasshouses were co-located with biogas plants, directly capturing the waste heat and carbon dioxide generated during electricity production to cultivate high-yield horticultural crops like tomatoes and cucumbers.
While the farm’s initial objective was simply to identify methods for lowering energy consumption within its core dairy operations, the German biogas systems showed that farms could maximise efficiency by generating renewable energy and reusing all the secondary outputs. This circular model provided the precise framework needed to adapt and optimise the specific resources available at Standhill Farm.
Turning Slurry Into Renewable Energy
Cow slurry is central to the anaerobic digestion system implemented. It is already available as a by-product of dairy production and contains trace elements and micronutrients that help the microorganisms in the digester thrive. Capturing the methane released through digestion allows the farm to generate renewable electricity instead of losing that methane directly to the atmosphere.
Because slurry has a relatively low energy content, it is combined with dung from youngstock, wholecrop rye grown on the farm, and silage that is not considered suitable for feeding to the dairy herd. This includes lower-quality material from the edges and top of the silage clamp, leaving the best forage for the cows.
The digester is fed each day consistently. Stable feedstock, temperature and pH are essential because the microorganisms responsible for gas production perform best under steady conditions. This means careful daily management is as important as the technology itself.
Making Full Use Of The Biogas System
The biogas produced in the digester is passed through an engine to generate renewable electricity. Like any engine, it also produces heat and carbon dioxide. At Standhill Farm, these are viewed as valuable resources rather than waste products. Heat is captured for use in the glasshouse and for drying wood, while carbon dioxide is supplied to the tomato crop during daylight hours to support photosynthesis and plant growth.
This approach reflects a guiding principle across the farm: any useful resource that is wasted will eventually need to be replaced by something purchased from outside the business. Capturing and reusing energy, nutrients, heat, carbon dioxide, and water therefore supports both environmental performance and economic efficiency.
Establishing Tomato Production
While Scotland experiences lower light levels than traditional tomato-growing regions, cool night-time temperatures offer a distinct agronomic advantage by optimising crop development. Combined with robust regional demand for locally grown Scottish produce, these factors underpinned the strategic decision to construct the four-acre glasshouse in 2016.
The glasshouse now houses approximately 55,000 plants, which arrive as two-month-old propagation units in mid-January. Cultivated in a rockwool substrate, the crop benefits from a sterile, highly controllable growing medium where water and tailored nutrients are delivered directly via precision hydroponic irrigation lines. This setup supports a productive harvesting window extending from early April through to mid-November
Biological controls and natural systems are central to the operation; bees are introduced regularly to manage pollination, ensuring consistent fruit set. In addition, by using local labour for daily crop management and harvesting, the diversified enterprise actively supports community employment alongside agricultural output.
Combining Biogas And Biomass Heat
While the initial strategy relied on the biogas engine to fulfil the glasshouse’s total heating demand, operational data revealed that the anaerobic digestion plant lacked the scale to heat the entire four-acre facility. Rather than abandoning the integrated model, the farm decided to introduce two woodchip boilers as a complementary renewable heat source.
The boilers heat water that circulates through the glasshouse. Woodchip also provides heat for the farmhouse and other farm uses. A significant portion of the biomass feedstock was recovered from timber damaged during Storm Arwen, exemplifying a highly resourceful approach to utilising localised waste streams.
This experience highlights the importance of accurately matching renewable-energy supply with demand. Connected enterprises may still require supplementary capacity, particularly when heat demand varies across the year.
Harvesting Rainwater
Tomato production requires a significant amount of water, so the farm captures rainfall from the four-acre glasshouse roof. Water is directed into two storage tanks and then used to irrigate the crop. Scotland’s rainfall and the large roof area make this a valuable resource.
Keeping the roof clean serves two purposes: it maximises the light reaching the crop and ensures that water harvesting works effectively. The farm has invested in a roof washer to maintain glass cleanliness and prevent weeds or debris from interfering with collection.
Outcomes
The main outcome is a circular system in which the dairy, energy and horticultural enterprises support one another are:
- Slurry and livestock manure become feedstocks for anaerobic digestion.
- Rye and lower-quality silage improve the energy content of the feedstock.
- Biogas generates renewable electricity.
- Recovered heat is used in the glasshouse and for drying wood.
- Captured carbon dioxide supports tomato growth.
- Woodchip supplies additional renewable heat.
- Rainwater collected from the glasshouse roof irrigates the crop.
- Digestate returns more readily available nutrients to the farming system.
Using slurry in the digester captures methane that might otherwise be released during conventional slurry storage. Digestion also produces material with more readily available nitrogen, increasing its potential value when returned to the land and managed appropriately.
The system generates value beyond electricity. Captured heat and carbon dioxide support an additional enterprise producing around 700 tonnes of tomatoes annually. Rainwater harvesting, renewable heat and the use of lower-quality forage in the digester also reduce dependence on purchased resources.
Diversification has created several connected outputs, including milk, renewable electricity and tomatoes. The farm’s experience is that lower carbon production can align with lower costs when resources are reused rather than replaced, provided that productivity and output are maintained. Its renewable-energy approach has previously placed it among Tesco’s stronger-performing producers in carbon-footprint terms.
Challenges
The first challenge was matching renewable heat supply with glasshouse demand. Heat from the biogas engine was insufficient for the four-acre glasshouse, requiring investment in two biomass boilers. This demonstrates why farms should consider the quantity, timing and reliability of available heat before developing a connected enterprise.
Anaerobic digestion also requires careful daily management. Changes in feedstock, temperature or pH can disrupt gas production, so a stable and consistent feeding routine is essential.
Scotland’s limited light levels create an additional constraint for tomato growing. The glasshouse must make the most of the available daylight, making roof cleanliness and effective crop management especially important.
Finally, integration creates operational complexity. Dairy production, digester feeding, electricity generation, heat distribution, biomass heating, carbon dioxide supply, water capture and tomato production must all function together. The strength of the system lies in these connections, but maintenance, monitoring and skilled management are essential.
Creating More Value And Less Waste
Lower emissions and lower production costs can go together when farm by-products are treated as resources. Success, however, depends on maintaining output, matching energy supply with demand and managing each part of the system consistently
Standhill Farm demonstrates how the journey towards net zero can be built around practical links between existing farm activities. By using dairy slurry to generate renewable electricity, capturing heat and carbon dioxide for tomato production, supplementing heat with biomass, harvesting rainwater and returning improved nutrients to the land, the farm creates more value while wasting less.
Alistair Trail, SAC Consulting
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