Following their success in Europe, compact biogas systems, commonly known as mini digesters, are making significant inroads into the North American market. These systems, celebrated for their efficiency and swift installation, are quickly becoming a preferred solution for farm-based energy generation.
Mini digesters have established a solid foothold due to their appealing features: rapid deployment, ease of monitoring remotely, minimal maintenance needs, and lucrative returns on investment. Their popularity is on the rise, with an increasing number of installations projected across North America. Originating in Europe, a Belgium-based company, Biolectric, has successfully installed over 220 mini digesters on small to medium-sized farms across Belgium, the Netherlands, France, Italy, Poland, Sweden, and the United Kingdom.
In collaboration with Martin Energy Group, a U.S.-based engineering and consulting firm, Biolectric expanded its reach with installations in Ontario in 2018 and Pennsylvania in 2019. Further discussions are underway to extend their reach to additional farms in Pennsylvania and Vermont.
The contrast between these smaller systems and traditional full-sized digesters is stark. “Full-sized digesters involve extensive construction, significant investment, and comprehensive engineering and environmental assessments,” explains John Hawkes, project development manager at Martin Energy Group. In contrast, “a mini digester is a streamlined product, rather than a complex project. It arrives with pre-assembled parts ready to be set up on a simple concrete base within days, substantially reducing costs and complexity.”
Mini digesters in action
At Harcolm Farms in Beachville, Ontario, dairy farmers Rob and Rachel McKinlay have demonstrated the potential of mini digesters. Installed in 2018, the digester was assembled by eight people in just four days, highlighting the system’s ease of installation. The digester, comprising a 20-kW capacity split between internal use and grid supply under Ontario’s MicroFIT program, exemplifies efficient and sustainable farm management.
Rob McKinlay, reflecting on the project initiated eight years prior, recognized the importance of securing financial support through Ontario’s feed-in tariff program and additional funding from Bloom and Bioenterprise Canada. These funds were instrumental in realizing the installation and ensuring its financial viability.
The McKinlays appreciate the dual benefits of the digester: it meets their farm’s energy needs and provides a sustainable way to manage dairy waste. The system’s design allows for simple operation, significantly reducing fugitive methane emissions and enhancing nutrient management on the farm.
Optimizing manure use in mini digesters
Mini digesters are engineered primarily to process manure, yet Rob McKinlay of Harcolm Farms supplements his with a modest amount of stale grain feed. Currently, with 65 milking cows, he enhances the digester’s feed with about half a skid steer bucket of grain daily. McKinlay estimates that the manure from 100 cows would be adequate to consistently generate 20 kW of energy, and plans to expand his herd to reach this capacity as milk quotas allow.
The McKinlays also cleverly utilize the byproduct heat from their digester. During the colder months, they repurpose this energy to heat their barn and other farm structures, optimizing the system’s utility beyond just electrical output. Remarkably, their mini digester produces more thermal energy than electrical, enhancing its overall efficiency and utility on the farm.
Furthermore, following the anaerobic digestion process, the remaining digestate is processed through a screw press. This procedure separates the solids, which McKinlay recycles as bedding for his cows, while the liquid component is applied as a nutrient-rich fertilizer to his fields. This comprehensive use of all byproducts underscores the environmental and operational efficiency of mini digesters, making them an increasingly popular choice for small to medium-sized farms.
Financial viability
John Hawkes from Martin Energy Group highlights that their mini digesters are designed to recoup both capital and operating costs within eight to ten years, assuming appropriate funding mechanisms are in place. Rob McKinlay, who runs one such mini digester on his farm, corroborates this financial viability, noting minimal operating expenses and substantial efforts to reduce initial costs by locally sourcing more components rather than relying on imports from Biolectric.
Hawkes also points out available funding programs that bolster the adoption of such renewable technologies in North America, including Pennsylvania’s Alternative and Clean Energy Program (ACE), Vermont’s FIT program, and the federal REAP program in the U.S. These incentives are crucial for making such sustainable investments feasible for farmers.
Initially concerned about the reliability of his mini digester, McKinlay now reports no issues, emphasizing the importance of financial preparation, such as securing favorable exchange rates, and practical measures like ensuring proper system winterization to prevent downtime in cold weather.
The McKinlay mini digester has generated considerable local interest, demonstrated by the success of multiple open house events. This interest is expected to mirror in the ongoing Pennsylvania project. Hawkes notes the discrepancy in subsidy programs between Europe and North America but remains optimistic about the potential expansion of similar incentives, especially given the substantial number of small dairy farms in northeastern America. He estimates that even a modest uptake by these farms could lead to the installation of around 500 mini digesters over the next decade, showcasing a significant shift towards renewable energy solutions in agriculture.
