Planning a Farm Biogas Plant: Five Phases from Idea to Plant

A farm biogas plant is best planned in five phases: feasibility check, business case, design and permits, construction and commissioning, and operation. Each phase ends with a clear decision on whether and how to proceed. The basis is reliable data on slurry volumes, herd size, heat demand and the grid connection. From idea to commissioning often takes one to two years, depending mainly on the permit and the grid connection.

The five phases at a glance

Phase 1: feasibility check

The feasibility check establishes whether a plant makes sense on your farm at all. Key points:

• Slurry volumes: record volumes over a full year if possible. Wash water, grazing and bedding change the figures considerably.
• Herd size and outlook: payments under Germany’s Renewable Energy Sources Act (EEG) run for 20 years. Ask yourself honestly whether the herd will remain stable for that long and who will run the farm.
• Site: space close to the barn, distances to dwellings, ground conditions and groundwater.
• Grid connection: ask the grid operator early about the likely connection point.
• Heat: the farmhouse, barns, workshop or neighbours can use the waste heat and improve the economics.

The feasibility check should end with a simple overview: available slurry volume, possible co-substrates, a suitable site, distance to the grid and potential heat users. This overview is also the basis for first talks with suppliers and your bank.

For a small manure plant under section 44 EEG, also check whether you can meet the rule of at least 80 per cent manure by mass permanently. The guide to small manure biogas plants explains the details.

Phase 2: business case

Now volumes become figures. The biogas calculator gives a first estimate. A detailed calculation should follow, covering investment, financing, revenue from electricity and heat and all running costs over the whole support period.

Work with scenarios: what happens with less slurry, higher maintenance costs or rising interest rates? A plant that only makes a profit in the best case is a risk for the whole farm. The guide to biogas plant costs describes the main cost blocks. Clarify at this stage whether investment grants are an option, since many programmes require the application before the first binding order.

Phase 3: design and permits

Once the decision is made, obtain comparable quotes. Pay attention to identical scope, reference plants and after-sales service. Many suppliers of small manure plants also prepare the permit documents. Alternatively, work with an independent planning office.

Three strands run in parallel:

1. Permit: a building permit for a privileged project in the countryside is usually enough. Above certain thresholds, a procedure under the Federal Immission Control Act (BImSchG) is required. See the guide to biogas plant permits.
2. Grid connection: the formal grid connection request stating output and site.
3. Financing: talks with the bank based on the business case and the quotes.

A standard checklist helps when comparing quotes: what is included, what has to be provided by you, which gas yield and CHP running hours are guaranteed, and how are maintenance and response times arranged? Only with such a list do prices become comparable.

Only sign the supply contract once the permit, grid connection and financing are reasonably secure, or agree corresponding withdrawal rights.

Phase 4: construction and commissioning

Building a small farm plant usually takes several months, with standardised systems being quicker. Before commissioning, inspections are due, for example by approved experts under water law and for explosion protection. The digester is then filled and the biology started up gradually. It normally takes a few weeks until gas production is stable.

During construction it pays to be on site regularly or to appoint someone to supervise the works. Deviations from the permit, for instance in separation distances or the bund, are easier to correct before acceptance than afterwards.

Keep two dates in mind. The plant must be registered on time around commissioning in the core energy market data register (Marktstammdatenregister), otherwise EEG payments are at risk. In addition, the commissioning date fixes the reference value for the whole support period. Since values for new plants fall each year on 1 July, a date shortly before can make a small financial difference.

Phase 5: operation

Commissioning marks the start of the longest phase. Daily routine includes the feedstock log, inspection rounds, CHP maintenance, recurring inspections and reports to the grid operator. Regular evaluation of the plant shows early on when gas yield or running hours decline.

Plan your own working time realistically and arrange cover for holidays and illness. A maintenance contract with short response times protects the running hours of the CHP unit.

Common mistakes and where to get support

Many problems in farm biogas plants originate at the planning stage. These mistakes come up again and again in practice:

• Overly optimistic slurry volumes: the plant is sized larger than the herd supports and runs at part load permanently.
• Heat not planned for: without heat users, a large share of the energy is wasted, although heat can improve the economics considerably.
• Grid connection clarified too late: a distant connection point makes the project more expensive and delays the schedule.
• Quotes that cannot be compared: different scopes make cheap quotes look better than they are.
• Labour underestimated: even an automated plant needs daily checks and documentation.
• Grant conditions overlooked: an order signed too early can cost the grant.

Independent planning offices are a good fit for the feasibility check and business case, while specialist contractors and service firms support construction and operation. The provider directory lists companies by category, from planning and engineering through plant construction to service and maintenance.