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Anaerobic Digestion (Biogas) Plant

Screening-stage sizing, levelized cost, and operational GHG intensity for an anaerobic digestion biogas unit (agricultural effluents/CIVE/bio-waste).

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alexi

I do low-carbon energy stuff for 10 years & build things I wish existed.

Key Assumptions

Screening estimate of raw biogas yield per tonne of wet feedstock (depends strongly on substrate mix).

Nm3/t

min 20 · max 300 · step 5 · Nm3/t

Typical raw biogas methane content; affects energy content and methane-slip CO2e.

min 40 · max 70 · step 1 · %

Inputs

Total wet feedstock processed per year (effluents agricoles, CIVE, biodéchets).

min 0 · max 500000 · step 1000 · t/year

Fraction of the year effectively operating (used to translate annual energy into an equivalent capacity).

Results

Raw biogas production

Annual biogas volume before upgrading/CHP conversion

…Nm3/year

Digestate output (wet)

Approximate annual digestate mass leaving the plant

…t/year

Net exported energy

Net annual export after parasitic consumption; electricity (CHP) or biomethane LHV (upgrading)

…MWh/year

Export capacity (net)

Equivalent net export capacity based on net annual export and operating hours

…kW

Number of digesters (estimated)

Estimated digester units based on total required volume and a reference unit size

…count

Operational GHG emissions

Methane slip (CO2e) + grid electricity for auxiliaries (if assumed)

…kgCO2e/year

Parasitic energy consumption

Auxiliary electricity demand for reception, mixing, pumping, upgrading (pathway-dependent)

…MWh/year

Cost

Total CAPEX

Scaled total installed capital expenditure

…EUR

Total annual OPEX

Fixed O&M plus feedstock cost (gate fee can be negative)

…EUR/year
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Levelized Cost of Production

Amortization period for annualizing CAPEX via CRF.

years

min 5 · max 35 · step 1 · years

Real or nominal should be consistent with cost basis; used in CRF.

ratio

min 0 · max 0.2 · step 0.005 · ratio

Levelized cost of exported energy

Based on net exported energy (CHP electricity or biomethane LHV)

…EUR/MWh

Operational GHG intensity

Operational emissions per net exported MWh

…kgCO2e/MWh

Delivered feedstock cost; may be negative for waste with gate fees.

EUR/t

min -100 · max 200 · step 5 · EUR/t

End-Use

Choose whether the biogas is primarily exported as CHP electricity or upgraded to biomethane (energy exported on LHV basis).

About

Calculator context

Introduction

This calculator provides a pre-feasibility screening model for a complete anaerobic digestion (AD) biogas unit (reception/pre-treatment, digestion, heating/mixing, biogas storage, digestate output), consistent with typical practice in France/EU project screening. It estimates biogas output, digester sizing, CAPEX/OPEX, levelized cost, and operational GHG emissions intensity using transparent mass/energy balances and standard financial annualization.

Methodology

The model converts annual feedstock throughput into biogas volume, energy, and exportable energy (CHP electricity or biomethane), then sizes digesters by hydraulic retention time (HRT) and estimates costs via scaled specific CAPEX and O&M fractions.

Key equations (with variables):

  • Digester volume:
    • feedstock_daily_t_d = feedstock_annual_t_y / 365
    • flow_m3_d = feedstock_daily_t_d / slurry_density_t_m3
    • V_working_m3 = flow_m3_d * HRT_days
    • V_total_m3 = V_working_m3 / working_volume_fraction
    • n_units = ceil(V_total_m3 / digester_unit_volume_m3)
  • Biogas and energy:
    • biogas_nm3_y = feedstock_annual_t_y * biogas_yield_nm3_t
    • LHV_biogas_MWh_Nm3 = methane_frac * LHV_CH4_MWh_Nm3
    • E_biogas_MWh_y = biogas_nm3_y * LHV_biogas_MWh_Nm3
    • E_gross_export_MWh_y = if(pathway=CHP, E_biogasη_el, E_biogasη_upg)
    • E_net_export_MWh_y = max(E_gross_export − E_parasitic, 0)
  • Costs (IRENA/NREL-style scaling and CRF):
    • CRF = (r*(1+r)^n)/((1+r)^n−1)
    • specific_capex_scaled = clamp(specific_capex_ref*(capacity/capacity_ref)^capex_scale_exponent, min, max)
    • om_fraction_scaled = clamp(om_fraction_ref*(capacity/capacity_ref)^om_scale_exponent, min, max)
    • annualized_capex = capex_total * CRF
    • total_annual_cost = annualized_capex + fixed_O&M + feedstock_cost
  • Operational GHG (IPCC GWP100): methane slip + grid-powered auxiliaries.

References used for typical ranges and structure: IRENA (renewable power cost methodologies), IEA Bioenergy TCP and JRC (biogas/biomethane context), IPCC AR5/AR6 (GWP factors).

Applications

  • Business developer: compare AD project variants (CHP vs biomethane) by levelized cost (EUR/MWh) and size-dependent CAPEX at early screening.
  • Engineering pre-study: estimate digester count/volume from throughput and HRT to sanity-check layout and vendor discussions.
  • Sustainability/ESG analyst: compute operational GHG intensity (kgCO2e/MWh) sensitivity to methane slip and auxiliary electricity assumptions.

Model

77 variables — inputs, calculations and outputs, with their dependencies.

77 variables shown of 77
VariableValueUnitDepends on
2——
30000t/year—
120Nm3/t—
55%—
95%—
50EUR/t—
0.08ratio—
20years—
VariableFormulaUnitDepends on
if(((<1)+(>2)+(<0)+(<=0)+(<=0)+(>100)+(<0)+(>100)+(<0)+(>1)+(<=0))>0,1,0)bool
*0.01—
*0.01—
*h/year
/max(,)t/day
/max(,)m3/day
*m3
/max(,)m3
*m3
*MWh/Nm3
*MWh/year
if(==1,*,*)MWh/year
if(==1,,)kWh/t
if(==1,,)EUR/kW
clamp(*(/max(,))^,,)EUR/kW
if(==1,,)ratio
clamp(*(/max(,))^,,)ratio
*EUR/year
*EUR/year
(*(1+)^)/max(((1+)^-1),)—
*EUR/year
**Nm3/year
*kgCH4/year
*kgCO2e/year
*MWh/year
*kgCO2e/year
VariableFormulaUnitDepends on
ceil(/max(,))count
*Nm3/year
*/max(,)MWh/year
max(-,0)MWh/year
*/max(,)kW
*EUR
+EUR/year
+EUR/year
/max(,)EUR/MWh
*t/year
+kgCO2e/year
/max(,)kgCO2e/MWh

Assumptions

31 assumptions used in the calculations

  • Prevents division by zero in denominators and ensures stable CRF and intensity calculations.

    Market range 1e-09 to 1e-05 (engineering calculators)

    0.000001
    Numerical stability constant

  • Standard hours per (non-leap) year for capacity/energy conversions.

    Market range 8760

    8760h/year
    Calendar constant

  • Used for daily flow and HRT sizing.

    Market range 365

    365d/year
    Calendar constant

  • Converts MWh to kWh for capacity calculation.

    Market range 1000

    1000kWh/MWh
    Unit conversion

  • Converts kWh to MWh for parasitic energy.

    Market range 1000

    1000kWh/MWh
    Unit conversion

  • Wet agricultural/bio-waste slurries are often close to water density at screening stage.

    Market range 0.95 to 1.05

    1t/m3
    Screening assumption for wet feed slurry

  • Provides screening-level digester volume sizing for common agricultural and bio-waste mixes.

    Market range 30 to 90

    60days
    Typical AD design parameter (mesophilic, mixed feedstock)

  • Accounts for freeboard and non-working volume in digester geometry.

    Market range 0.75 to 0.9

    0.85ratio
    Engineering rule-of-thumb

  • Provides a screening estimate of discrete unit count; real projects use vendor-specific sizes.

    Market range 1500 to 6000

    3000m3
    AI

  • LHV(CH4) ≈ 35.8 MJ/Nm3 ≈ 9.94 kWh/Nm3; used to compute biogas energy from methane fraction.

    Market range 0.0097 to 0.0102

    0.00994MWh/Nm3
    Methane LHV conversion

  • Screening net electrical efficiency for CHP electricity export pathway.

    Market range 0.25 to 0.40

    0.35ratio
    Typical biogas engine electrical efficiency

  • Represents methane recovery/energy retention from raw biogas to biomethane export (excluding parasitic electricity handled separately).

    Market range 0.93 to 0.99

    0.97ratio
    Biomethane upgrading energy retention

  • Represents mixing, pumping, reception, basic gas handling for CHP-oriented AD plants.

    Market range 10 to 40

    20kWh/t
    Auxiliary loads rule-of-thumb

  • Adds upgrading compression/separation electricity to base AD auxiliaries.

    Market range 20 to 70

    35kWh/t
    Auxiliary loads rule-of-thumb

  • Represents modest mass loss to biogas and water evaporation/handling; digestate remains close to input mass on wet basis.

    Market range 0.85 to 1.05

    0.95ratio
    Screening mass yield factor

  • Reference capacity used for CAPEX and O&M scaling curves.

    Market range 200 to 2000

    500kW
    Scaling reference point

  • Models decreasing specific CAPEX with increasing capacity at screening stage.

    Market range -0.30 to 0.00

    -0.15
    Economy-of-scale exponent (specific CAPEX)

  • Prevents unrealistic underestimation at very large capacities in a screening model.

    Market range 2000 to 4500

    2000EUR/kW
    Clamp bound for scaled specific CAPEX

  • Prevents unrealistic overestimation at very small capacities when applying scaling.

    Market range 4500 to 10000

    8000EUR/kW
    Clamp bound for scaled specific CAPEX

  • Representative midpoint for AD + CHP installed CAPEX at screening stage.

    Market range 2500 to 4500

    4000EUR/kW
    CHP pathway reference CAPEX

  • Represents AD + biogas upgrading to biomethane; higher than CHP-only pathway at screening stage.

    Market range 3500 to 7000

    5200EUR/kW
    Upgrading pathway reference CAPEX

  • Models weak reduction in fixed O&M fraction with capacity due to scale effects.

    Market range -0.15 to 0.05

    -0.05
    Economy-of-scale exponent (fixed O&M fraction)

  • Lower bound to avoid unrealistically low fixed O&M in screening.

    Market range 0.02 to 0.04

    0.02ratio
    Clamp bound for fixed O&M fraction

  • Upper bound to limit overestimation in small plants while reflecting higher O&M intensity at small scale.

    Market range 0.05 to 0.12

    0.08ratio
    Clamp bound for fixed O&M fraction

  • Represents fixed O&M as a fraction of CAPEX for AD+CHP.

    Market range 0.03 to 0.08

    0.05ratio
    CHP pathway fixed O&M fraction reference

  • Upgrading adds complexity and maintenance; O&M fraction slightly higher than CHP-only case.

    Market range 0.04 to 0.10

    0.06ratio
    Upgrading pathway fixed O&M fraction reference

  • Captures residual methane emissions from handling, storage, and small leaks at screening stage.

    Market range 0.002 to 0.03

    0.01ratio
    Operational methane slip assumption

  • Used to convert methane slip volume to mass for CO2e conversion.

    Market range 0.65 to 0.75

    0.716kg/Nm3
    Methane density at standard conditions

  • Converts methane mass emissions to CO2e for 100-year horizon.

    Market range 27 to 30

    28kgCO2e/kgCH4
    IPCC methane GWP100 (approx.)

  • Represents the fraction of auxiliary electricity assumed to be imported from the grid (rest self-supplied), for operational GHG estimation.

    Market range 0.0 to 1.0

    0.2ratio
    Screening assumption

  • Used to estimate CO2e from grid electricity consumption for auxiliaries; not region-calibrated.

    Market range 50 to 700

    300kgCO2e/MWh
    Generic electricity GHG factor (screening)