Farm Biogas Plant Calculator
Estimate what a farm anaerobic digester can produce from cattle manure: daily biogas, electricity, annual revenue, and how long it takes to pay back the investment.
Results
How to Use This Calculator
Enter the number of cattle, the average manure produced per head per day, the gas yield per kg of manure (typically 0.03-0.05 m³/kg), the biogas calorific value (~6 kWh/m³), generator efficiency (~35%), installed plant cost, and local electricity price. Click Calculate.
About This Tool
About
Applicability: Designed for farm equipment and energy planning in North American and European contexts.
How the Calculation Works
Daily gas = cattle × kg manure/head × gas yield (~0.03-0.05 m³/kg dung). Electricity = gas × calorific value × generator efficiency. Annual revenue = daily kWh × 365 × price. Payback = cost ÷ annual revenue. Slurry ≈ 90% of input mass. For 100 head, 25 kg/head, 0.04 m³/kg, 6 kWh/m³, 35% efficiency, $120,000 cost, $0.18/kWh: daily gas = 100 m³, daily kWh = 210, annual 76,650 kWh, revenue $13,797, payback ~8.7 years. Common mistakes: overestimating gas yield, ignoring O&M costs (1-3%/yr), and assuming all gas is used productively.
Reviewed by Agricalc Editorial Team — Agricultural engineers and agronomists with 10+ years of field experience. Our team verifies every calculator formula against peer-reviewed extension publications. For site-specific advice, consult your local agronomist.
References
- US DOE — Anaerobic Digestion Technology
- USDA ERS — Bioenergy and Anaerobic Digestion
- USDA EPA AgSTAR — Farm Biogas
Frequently Asked Questions
How much biogas does one cow produce?
A dairy cow produces roughly 40-50 kg manure/day, yielding about 1.5-2.5 m³ of biogas, which is roughly 9-15 kWh of thermal energy. Beef cattle produce less per head (lower feed intake). Actual yield depends on feedstock and digester temperature.
How long does a digester take to pay back?
On well-managed operations with good feedstock and a feed-in tariff, payback often ranges 6-12 years. Small farm-scale units struggle to reach the economies of scale; revenue from electricity alone is rarely enough, so heat sales, digestate sales and carbon credits matter.
What is the digestate used for?
Digestate is the stabilized, odorless residual material. It is a valuable nutrient-rich fertilizer that can replace synthetic N-P-K, improves soil organic matter, and is easier to store and inject than raw manure.
Do I need to heat the digester?
Mesophilic digesters (35°C) run year-round with heating in cold climates; unheated ambient digesters work only in warm regions and slow in winter. Heating adds energy demand but keeps gas production steady.
What are the main barriers to farm biogas?
High upfront capital, the need for consistent feedstock, O&M expertise, and offtake pricing. Many projects succeed only with grants (USDA REAP, state programs), feed-in tariffs, or partnerships with nearby food-waste producers.
