Farm biogas calculator: would a small manure plant pay off?
Under section 44 of the German Renewable Energy Sources Act (EEG), a small manure plant receives a fixed tariff if it digests at least 80 per cent manure by mass and has no more than 150 kW installed at the site. This calculator shows in seconds roughly how much power and revenue your livestock could deliver.
| Feedstock mass | |
|---|---|
| Biogas | |
| Methane | |
| Energy in gas | |
| CHP size | |
| Tariff (average) | |
| Usable heat | |
| Heat revenue | |
| Investment (assumption) | |
| Operating costs (assumption) | |
| Surplus before depreciation | |
| Simple payback |
A rough guide, not a plant design. Gas yield, costs and tariff depend on dry matter, technology, site and commissioning date. Get quotes and a feasibility check before deciding.
How the calculator works
- Slurry and manure volume from livestock (m³ per place and year, 1 m³ ≈ 1 t) plus bought-in feedstocks.
- Biogas and methane yield per tonne of fresh matter by feedstock.
- Energy in gas = methane × 9.97 kWh/m³; power = energy × CHP electrical efficiency.
- Rated output = annual power ÷ 8,760 h; CHP size = annual power ÷ full-load hours.
- Tariff weighted by rated output (section 23c EEG): tier 1 up to 75 kW, tier 2 from 75 to 150 kW; minus 0.2 ct/kWh with the feed-in tariff, otherwise minus direct marketing costs.
- Heat = energy × thermal efficiency, minus the digester's own demand, of which the used share is valued at the heat price.
Typical values per feedstock
| Feedstock | Biogas per t FM | Methane content | counts as manure |
|---|---|---|---|
| Cattle slurry (bought in) | 25 m³ | 55 % | yes |
| Pig slurry (bought in) | 20 m³ | 60 % | yes |
| Cattle solid manure | 90 m³ | 55 % | yes |
| Horse manure | 63 m³ | 55 % | yes |
| Poultry manure (not counted as manure) | 110 m³ | 58 % | no |
| Maize silage | 200 m³ | 52 % | no |
| Grass silage | 170 m³ | 54 % | no |
| Perennial clover grass | 160 m³ | 54 % | up to 10% |
Slurry per animal place
| Dairy cows | 20 m³ per place and year |
| Young and beef cattle | 9 m³ per place and year |
| Fattening pig places | 1.9 m³ per place and year |
| Sows with piglets | 4.2 m³ per place and year |
Tariffs under section 44 EEG
| Commissioning | up to 75 kW | up to 150 kW |
|---|---|---|
| Commissioned until 30 June 2024 | 22.00 ct/kWh | 19.00 ct/kWh |
| Commissioned from 1 July 2024 | 21.89 ct/kWh | 18.91 ct/kWh |
| Commissioned from 1 July 2025 | 21.78 ct/kWh | 18.81 ct/kWh |
| Commissioned from 1 July 2026 | 21.67 ct/kWh | 18.72 ct/kWh |
Sources: sections 21, 23c, 44, 44a, 51 and 53 EEG 2023 (gesetze-im-internet.de, accessed 19 October 2026); gas yields from the LfL Bavaria biogas yield database, slurry volumes from LfL basic data (table 4b, November 2024), with a wide range depending on dry matter content. Values from July 2024 are calculated under section 44a (for comparison, the VBEW overview for plants commissioned in 2025 lists 21.78/18.81 ct); section 51 (negative prices) is not deducted from revenue. Cost assumptions are rough placeholders, not market prices.
- Calorific value of methane
- CHP electrical efficiency
- CHP thermal efficiency
- CHP full-load hours
- Own heat demand (digester)
- Share of surplus heat used
- Heat price
- Direct marketing cost (above 100 kW)
- Investment per kW installed
- Operating costs per kWh power
Questions about the calculator
How many cows does a 75 kW manure plant need?
With the calculator's typical values (20 m³ slurry per cow and year, 25 m³ biogas per m³, 55% methane, 36% electrical efficiency), around 400 dairy cows reach roughly 45 kW rated output. For 75 kW rated output from cattle slurry alone you would need roughly 670 cows. Solid manure or up to 20 per cent co-substrates by mass reduce the herd size needed considerably.
What is the 80 per cent rule?
Under section 44(2) of the German Renewable Energy Sources Act (EEG), at least 80 per cent manure by mass must be used on average over the calendar year. Poultry manure and dried poultry droppings do not count as manure, while perennial clover grass may count for up to 10 per cent by mass. The calculator checks this using the masses you enter.
Which tariff applies to my plant?
The commissioning date is decisive. Section 44 EEG sets 22 ct/kWh up to 75 kW and 19 ct/kWh up to 150 kW rated output; section 44a reduces these values by 0.5% a year for plants commissioned since 1 July 2024. With the feed-in tariff (up to 100 kW), section 53 deducts 0.2 ct/kWh. Under section 51 EEG, no payment is due for periods with negative spot prices (exception: plants below 100 kW until a smart meter is installed). Your grid operator confirms the binding value.
What is rated output (Bemessungsleistung)?
Rated output is the annual electricity generated divided by the hours in the year, in other words the average output. A CHP unit with 75 kW installed capacity that does not run around the clock has a lower rated output.
Are my inputs stored?
No. The calculator runs entirely in your browser and no inputs are transmitted or stored.
Next steps
- Small Manure Biogas Plants in Germany: Rules and Herd Size
- EEG Feed-in Tariff for Biogas: Section 44 and Worked Example
- Farm Biogas Profitability: How to Run the Numbers
- Biogas Plant Costs on the Farm: Investment and Operation
- Biogas Feedstocks: Slurry, Manure, Silage and Residues
- Planning a Farm Biogas Plant: Five Phases from Idea to Plant