3,150 m³ of biogas a day (53% methane) runs a CHP engine of about 299 kWe for 8,000 h/yr, generating 2.39 GWh of electricity and 2.57 GWh of heat. The organic loading rate of 2.4 kg VS/m³·d is within the usual 1.5–4 range. Payback ≈ 13.2 years, but the IRR (2.7%) is below your 6% discount rate: better tariffs, heat sales or cheaper feedstock are needed.
CHP electrical capacity
299kWe
2,201,456 kWh/yr exported
Thermal output
322kWth
1,929 MWh/yr surplus after digester heating
Biogas production
3,150m³/day
1,150 thousand m³/yr
Methane content
52.7%
1,661 m³ CH₄/day
Primary energy (methane)
5.98GWh/yr
683 kW continuous
Digester volume
2,520m³
60 days retention · OLR 2.45 kg VS/m³·d
Digestate
13,821t/yr
37.9 t/day, 10% of the mass converted to gas
Annual revenue
€361,087
crop cost 175,200 €/yr
Payback
13 yr 3 mo
capex 1,345,999 €
IRR
2.7%
Feedstock mix
| Feedstock | t/day | Share of mass | DM % | Biogas m³/t | CH₄ % | Biogas m³/day | Share of gas |
|---|---|---|---|---|---|---|---|
| Cattle slurry | 30 | 71% | 10 | 25 | 55 | 750 | 24% |
| Maize silage | 12 | 29% | 33 | 200 | 52 | 2,400 | 76% |
Typical feedstock values (per tonne fresh matter)
| Feedstock | Dry matter % | Volatile solids % of DM | Biogas m³/t | Methane % | Biogas m³/t VS |
|---|---|---|---|---|---|
| Cattle slurry | 10 | 80 | 25 | 55 | 313 |
| Pig slurry | 6 | 80 | 22 | 65 | 458 |
| Cattle manure (solid) | 25 | 80 | 60 | 55 | 300 |
| Poultry litter / dung | 40 | 75 | 80 | 60 | 267 |
| Maize silage | 33 | 95 | 200 | 52 | 638 |
| Grass silage | 35 | 90 | 180 | 54 | 571 |
| Sugar beet | 23 | 90 | 130 | 52 | 628 |
| Food waste (source-separated) | 25 | 90 | 140 | 60 | 622 |
- Yields are mid-range literature values (FNR/KTBL). Real yields vary ±20–30% with silage quality, dilution of slurry, storage losses and retention time. Lab BMP tests on your own feedstock are worth doing before investing.
- Methane energy uses LHV 9.97 kWh/Nm³. Digestate ≈ input mass minus the mass of gas released; it keeps practically all the nitrogen, phosphorus and potassium of the feedstock.
- Many countries cap energy crops (e.g. maize share limits) or pay tariffs only for waste/manure feedstocks, so check local rules.