How Much Energy Does a Biodigester Generate?

A biodigester generates energy through the methane in its biogas. As a practical benchmark, each cubic meter of biogas (with ~60% methane) holds on the order of 6 kWh of primary energy. Run it through a combined heat and power (CHP) unit with 38–42% electrical efficiency and you get about 2–2.5 kWh of electricity per m³, plus an additional 40–45% as usable heat. In other words: 1,000 m³/day of biogas roughly equals 2,000–2,500 kWh of electricity per day, enough for a continuous output of around 90–110 kW.

The method: from cubic meters of biogas to kWh

Biogas energy lives in its methane. Pure methane has a lower heating value (LHV) close to 10 kWh/m³. Since biogas is a mix of CH₄ and CO₂, its energy content is proportional to the methane percentage:

Biogas energy (kWh/m³) = %CH₄ × 10 kWh/m³

At 60% methane: 0.60 × 10 = 6 kWh/m³. That is the gross energy content. What you actually capture depends on the conversion equipment:

• Combined heat and power (CHP): a gas engine coupled to a generator. Typical electrical efficiency 38–42%, plus 40–45% recoverable heat from hot water and exhaust.
• Boiler: heat only, at 85–90% efficiency on the LHV. The choice when the plant needs steam or hot water rather than electricity.
• Upgrading to biomethane: CO₂ and H₂S are removed to inject into the grid or use as vehicle fuel; it generates no on-site electricity but maximizes the gas value.

For electricity the formula becomes:

Electricity (kWh) = Biogas (m³) × 6 kWh/m³ × CHP electrical efficiency

Reference table: energy per m³ of biogas

Indicative engineering values for biogas at ~60% methane.

Conversion path	Efficiency	Output per m³ biogas	Typical use
Gross energy content	—	~6 kWh	Reference
CHP — electricity	38–42%	2.3–2.5 kWh electric	Self-supply / grid sale
CHP — recoverable heat	40–45%	2.4–2.7 kWh thermal	Reactor heating, process
Boiler (heat only)	85–90%	5.1–5.4 kWh thermal	Steam / hot water

Note that cogeneration delivers electricity and heat: total useful efficiency of a CHP is around 80–85%. Part of that heat keeps the reactor at mesophilic temperature (35–38 °C), and the surplus is available for the process.

Worked example: a plant producing 343 m³/day of biogas

Take a co-digestion dairy producing 343 m³/day of biogas at 58% methane (the case from the yield-by-substrate article).

Step 1 — Energy content

• Energy per m³: 0.58 × 10 = 5.8 kWh/m³
• Daily primary energy: 343 × 5.8 = 1,989 kWh/day

Step 2 — Electricity with CHP (40%)

• Daily electricity: 1,989 × 0.40 = 796 kWh/day
• Annual: 796 × 365 ≈ 290,000 kWh/year (290 MWh)
• Equivalent continuous output (operating ~22 h/day): 796 ÷ 22 ≈ 36 kW electric → specify a ~40 kWe genset

Step 3 — Recoverable heat with CHP (43%)

• Daily heat: 1,989 × 0.43 = 855 kWh thermal/day
• This heat covers digester heating and leaves a surplus for process hot water.

Result: the plant generates on the order of 290 MWh of electricity per year plus useful heat. For a rural or mid-sized agribusiness load, that offsets a significant share of the electricity bill and of the diesel or wood used for heat.

What reduces the real available energy

• Plant self-consumption: mixers, pumps and reactor heating consume 5–15% of the energy generated.
• CHP availability: maintenance and stops; design usually assumes 8,000 h/year, not 8,760.
• Biogas quality: H₂S and moisture must be treated before the engine; dirty gas cuts efficiency and engine life.
• Biological stability: an overload or a cooldown reduces methane and, with it, the kWh.

These kWh are the basis of the return on investment: to turn them into payback years, review biodigester payback in agribusiness, and to understand the equipment that produces the gas, what an industrial biodigester is. Tech Tank delivers turn-key biogas and biodigester plants, sizing the reactor, gas holder and CHP to your substrate and your load profile.

If you want to know how many kWh and how much heat you can generate from your waste, tell us your case and we will prepare an energy and economic estimate for your project.

Frequently Asked Questions

How many kWh does 1 m³ of biogas generate?

A cubic meter of biogas at 60% methane holds about 6 kWh of energy. In a CHP unit with 40% electrical efficiency you get roughly 2.4 kWh of electricity per m³, plus a similar amount of usable heat.

Why isn't all the biogas energy captured as electricity?

Because no engine converts 100% of the fuel into electricity. A CHP turns about 40% into electrical energy and another 40–45% into heat; the rest is lost to exhaust and friction. That is why using the heat too matters: it lifts total capture to 80–85%.

Is it better to generate electricity or heat?

It depends on the site's demand. If there is electrical demand or the option to sell to the grid, cogeneration is standard because it also delivers heat. If the plant only needs steam or hot water, a biogas boiler captures more energy per m³ (85–90%).

What generator power do I need?

It is calculated from daily biogas production and operating hours. As a rule, divide the daily electric kWh by the operating hours (typically 20–22 h) to get the continuous output, and select a genset with some margin above that value.

Do methane and biomethane deliver the same energy?

Biomethane is biogas upgraded to over 95% methane, so it yields close to 10 kWh/m³, almost double raw biogas. That is why upgrading makes sense when the goal is grid injection or using the gas as vehicle fuel.