Biogas Plant Permits in Germany: Building and Emissions Law

A small farm biogas plant such as a small manure plant (Gülle-Kleinanlage) usually needs a building permit. It enjoys privileged status as an agricultural project in the open countryside under section 35(1) no. 6 of the Federal Building Code (Baugesetzbuch, BauGB), provided among other things that the biomass comes mainly from the farm or nearby farms and that the plant can produce no more than 2.3 million standard cubic metres of biogas a year. A permit under the Federal Immission Control Act (Bundes-Immissionsschutzgesetz, BImSchG) is only required above certain thresholds in the 4th Ordinance (4. BImSchV). Water law (AwSV), safety rules such as TRAS 120 and grid connection requirements apply as well.

Building law: privileged status in the countryside

Biogas plants are almost always built in the outer zone (Außenbereich), meaning outside villages and local development plans. Construction there is only permitted by exception. Section 35(1) no. 6 BauGB (German only) privileges plants for the energy use of biomass if they serve an agricultural or forestry business, a horticultural business or a commercial livestock business. Four conditions apply:

1. The project has a spatial and functional link with the farm.
2. The biomass comes mainly from the farm, or mainly from the farm and nearby farms.
3. Only one plant is operated per farmstead or site.
4. Biogas production capacity does not exceed 2.3 million standard cubic metres a year.

A small manure plant is far below this capacity limit. On paper, a plant with 75 kW rated output produces roughly 300,000 cubic metres of biogas a year. You should still document the other three conditions carefully, especially the origin of the feedstocks.

Thresholds in the 4th BImSchV

Whether an emissions control procedure is needed in addition to or instead of the building permit depends on Annex 1 of the 4th BImSchV (German only). These entries are the most relevant for biogas plants (V stands for the simplified procedure, G for the formal procedure with public participation):

A typical small manure plant processes roughly 30 to 40 tonnes of slurry a day, produces well under 1.2 million cubic metres of raw gas and has a CHP unit clearly below 1 MW rated thermal input. The digestate store deserves a closer look: digesting 11,000 to 12,500 cubic metres of slurry a year and holding several months of storage can bring you close to 6,500 cubic metres. The gas holder should also be checked against the 3 tonne threshold. If the livestock unit itself holds a BImSchG permit, the biogas plant may also be treated as an ancillary installation within that permit.

Major accidents law

The Major Accidents Ordinance (Störfall-Verordnung, 12. BImSchV) only applies above certain quantities of hazardous substances on site, for biogas in the range of several tonnes. Small farm plants with gas holders of a few hundred to a few thousand cubic metres are usually well below this. For larger plants with several gas stores, an expert should calculate the quantities.

Water law: the AwSV

Slurry, digester feedstock and digestate count as generally hazardous to water. Biogas plants therefore fall under the Ordinance on Installations for Handling Substances Hazardous to Water (AwSV). Section 37 AwSV contains specific requirements for biogas plants using agricultural feedstocks:

• Single-walled tanks for liquids need a leak detection system.
• Installations where leaks can occur above ground level need a bund that holds at least the volume of the largest tank.
• Underground tanks must be double-walled with leak detection if they may reach the groundwater or are in protection zones.
• Earth basins are not permitted for storing digestate.

The bund is often underestimated at the site planning stage. It affects the layout, earthworks and costs. Inspections by approved experts are also required before commissioning and at regular intervals.

Installation safety: TRAS 120

The Technical Rule on Installation Safety 120 (TRAS 120) describes the state of the art in safety for biogas plants. It covers explosion protection, gas holders, overpressure protection, gas flares and lightning protection, among other topics. For plants with an emissions control permit it is a key benchmark, and for smaller plants authorities often use it as guidance. The Industrial Safety Ordinance (Betriebssicherheitsverordnung) with its risk assessment and explosion protection document applies as well. See the guide to biogas plant safety for more.

Grid connection and registration

Alongside the permit, submit a grid connection request to the local grid operator. The operator determines the connection point where the plant can feed in. A distant connection point can add substantially to cable costs and the timeline. Around commissioning, the plant must also be registered in the Federal Network Agency’s core energy market data register (Marktstammdatenregister), otherwise EEG payments are at risk.

Other areas of law

Beyond building, emissions and water law, further rules come into play. Fertiliser law sets how much storage capacity for digestate is required and when and how it may be spread. Fire protection calls for a concept covering the CHP room, gas holder and access routes. Depending on the site, nature conservation, listed building protection or flood zones may be relevant too. The authority checks many of these points within the building permit procedure, but they should already be reflected in the site plan.

A practical sequence

1. Hold a preliminary meeting with the building and emissions authorities and clarify the procedure.
2. Request the grid connection and ask where the connection point will be.
3. Have a site plan drawn up showing separation distances, bund and digestate store.
4. Submit the application with an operating description, feedstock list, fire protection concept and water law documents.
5. Transfer the conditions in the permit into the detailed design.

Most farms work with a planning office for the application and with approved experts for inspections. You will find partners under planning and engineering and experts and surveyors. The overall process is described in the guide to planning a farm biogas plant.