Energy mass balanceEquipment sizingCostingBiomass

Dry Batch (Garage) Anaerobic Digester, Garages Count, Percolate Recirculation, Gas Profile

Screening-level mass/energy balance, garage sizing, percolate recirculation loads, CHP capacity, and levelized electricity cost for a dry batch (garage) anaerobic digestion plant.

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

Inputs

Annual feedstock throughput

Total fresh mass treated per year (sum of manure, green waste, biowaste, etc.).

t/year

min 0 · max 500000 · step 100 · t/year

Total solids (TS)

Typical dry batch is >20% TS (solid heap).

min 10 · max 60 · step 1 · %

Volatile solids fraction of TS

VS/TS of the feedstock mix (dimensionless).

min 0.3 · max 0.95 · step 0.01 · ratio

Methane content in biogas

Typical agricultural AD biogas is often ~50–60% CH4.

min 45 · max 70 · step 1 · %

Specific methane yield

Project-specific BMP/expected yield on a VS basis.

Nm3 CH4/t VS

Digestion temperature mode

Select mesophilic or thermophilic; affects heat demand per tonne.

Useful heat utilization

Share of net available heat that can be used/exported (site heat sinks, district heat, etc.).

CHP capacity factor

Fraction of the year the CHP is operating at planned load (availability and dispatch).

Volumes & Cycles

Garage working volume (per unit)

Useful volume that can be filled with the solid heap (excluding headspace/gas dome).

min 20 · max 2000 · step 10 · m3

Bulk density of loaded heap

Average apparent density of the substrate pile in the garage.

min 0.3 · max 1.2 · step 0.05 · t/m3

Batch cycle time (per garage)

Total occupancy time per batch, including digestion and turnaround (loading/unloading).

days

min 10 · max 120 · step 1 · days

Percolate recirculation intensity

Total percolate volume recirculated per tonne of fresh feed (screening aggregate).

min 0 · max 3 · step 0.05 · m3/t

Results

Annual biogas production

Biogas volume derived from methane potential and biogas CH4 fraction

…Nm3/year

Annual methane production

Methane volume from VS and methane yield

…Nm3/year

Number of garages (digesters)

Parallel batch units required to process annual tonnage with chosen cycle

…units

Installed CHP electrical capacity

Average electric power adjusted by batch peak factor and oversize margin

…kW

Net electricity exported

Gross CHP electricity minus auxiliaries (biogas-linked + percolate pumping)

…MWh/year

Net heat available after process heating

CHP thermal output minus estimated heating demand (mode-dependent)

…MWh/year

Costs

Total CAPEX (scaled)

Capacity-based specific CAPEX with economies of scale and a project multiplier

…EUR

Project discount rate (WACC)

Used for CAPEX annualization (CRF). Enter as a decimal (e.g., 0.08 = 8%).

Levelized cost of electricity (LCOE)

Total annualized cost divided by net exported electricity

…EUR/MWh

CAPEX multiplier

Adjusts scaled CAPEX for site complexity, automation level, contingencies, etc.

min 0.7 · max 1.5 · step 0.02 · ratio

Economic lifetime

Amortization period for annualization (CRF).

years

About

Calculator context

Introduction

This calculator provides a pre-feasibility screening model for dry batch / “garage” anaerobic digestion projects, aligned with the operating scope: number of garages, loading cycle, percolate recirculation, batch gas production profile, heating demand, and installed CHP capacity. It is inspired by the ADEME guidance for discontinuous dry digestion (“voie sèche discontinue”) and uses standard project-finance cost annualization to derive levelized metrics.

Methodology

The model combines a feedstock-based methane potential with simplified operational factors (availability/part-load penalty) and equipment sizing rules typical for early-stage development.

Key calculations include:

Operating hours (mandatory E1): load_hours = hours_per_yearcapacity_factor0.01, where capacity_factor is in %.
Part-load penalty (mandatory E2–E3): load_penalty = clamp(1+penalty_coeff*(1-capacity_factor0.01),1.0,max_penalty); effective_consumption = specific_consumptionload_penalty.
Methane and biogas production (mandatory E4):
- VS_t_per_year = feed_t_per_year*(TS%/100)*VS_fraction
- CH4_Nm3_per_year = VS_t_per_year*methane_yield
- biogas_Nm3_per_year = CH4_Nm3_per_year/(CH4%/100)
CHP energy outputs: methane_energy_MWh = CH4_Nm3_per_yearLHV_CH4/kWh_per_MWh; gross_electricity_MWh = methane_energy_MWhη_el; gross_heat_MWh = methane_energy_MWh*η_th.
Auxiliaries: electricity for percolate pumping (m3 recirculated) plus a biogas-proportional auxiliary load (kWh/Nm3).
Garage sizing (equipment_sizing): n_units = ceil(annual_batches_required / batches_per_garage_per_year), with batch mass from garage_working_volume and bulk density.
Installed capacity: capacity is based on average electric power during load_hours, multiplied by a batch-profile peak factor that decreases with more garages.
Costing (mandatory C1–C6): CRF = (r*(1+r)^n)/max(((1+r)^n-1),eps); scaled specific CAPEX and O&M are clamped; total annual cost and levelized cost are computed as annual_cost/net_electricity.

Sources and reference organizations: ADEME (France) for dry batch process characteristics, plus IEA/IRENA/NREL-style screening approaches for efficiencies, scaling, and LCOE formulation.

Applications

Agricultural developer: estimate how many garages are required for a secured manure/green-waste tonnage and what CHP capacity range is implied.
Project financier/analyst: sanity-check annual net electricity and LCOE (EUR/MWh) under a chosen WACC and lifetime.
EPC pre-design: compare mesophilic vs thermophilic heating implications and assess sensitivity to percolate recirculation intensity.

Model

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

86 variables shown of 86

Value	Unit	Depends on
10000	t/year	—
25	%	—
0.8	ratio	—
170	Nm3 CH4/t VS	—
52	%	—
500	m3	—
0.8	t/m3	—
60	days	—
0.5	m3/t	—
1	—	—
50	%	—
90	%	—
0.08	ratio	—
15	years	—
1	ratio	—

Variable	Formula	Unit	Depends on
	`if((<)+(<)+(>)+(<)+(>)+(<)+(<=)+(>)+(<=)+(<=)+(<=)+(<)+(<)+(>)+(<)+(>)+(<)+(>=)+(<)+(<=)+(<)+(>)>,,)`	bool
	`**0.01`	h/year
	`clamp(1+(1-0.01),1.0,)`	—
	`*`	kWh/Nm3
	`/ max(,)`	ratio
	`/ max(,)`	ratio
	`**`	t VS/year
	`*/max(,)`	MWh/year
	`*`	MWh/year
	`*`	MWh/year
	`*`	m3/year
	`*`	kWh/year
	`*`	kWh/year
	`(+)/max(,)`	MWh/year
	`if(==,,)`	kWh/t
	`*/max(,)`	MWh/year
	`*/ max(,)`	MWh/year
	`*`	t/batch
	`/max(,)`	batches/year
	`/max(,)`	batches/year
	`/max(,)`	Nm3/day
	`+ /max(sqrt(max(,)),)`	—
	`clamp(,,)`	—
	`*`	Nm3/day
	`* / max(,)`	kW
	`(*(1+)^)/max(((1+)^-1),)`	—
	`/max(,)`	—
	`clamp(*(max(,)^),,)`	EUR/kW
	`*`	EUR/year
	`clamp(*(max(,)^),,)`	—
	`*`	EUR/year
	`*`	EUR/year

Variable	Formula	Unit	Depends on
	`*`	Nm3/year
	`/max(,)`	Nm3/year
	`max(-,)`	MWh/year
	`max(-,)`	MWh/year
	`ceil(/max(,))`	units
	`**`	kW
	`**`	EUR
	`++`	EUR/year
	`/max(,)`	EUR/MWh

Assumptions

30 assumptions used in the calculations

Prevents division-by-zero and unstable ratios in screening calculations.
Market range Not applicable
0.000001
Tokenizer/division guard
Non-leap year hours used for capacity factor conversion to annual load hours.
Market range 8760
8760h/year
Calendar constant
Used to convert annual flows to daily averages and batch cycles per year.
Market range 365
365days/year
Calendar constant
Converts kWh to MWh for consistent annual energy reporting.
Market range 1000
1000kWh/MWh
Unit conversion
Approximate lower heating value of methane at normal conditions to convert Nm3 CH4 to energy.
Market range
9.97kWh/Nm3 CH4
Thermochemistry constant (LHV)
Represents a typical mid-scale biogas engine-generator electrical efficiency at/near rated load.
Market range
0.4ratio
Screening CHP performance
Represents typical recoverable heat fraction from a biogas CHP unit (jacket + exhaust).
Market range
0.45ratio
Screening CHP performance
Represents non-pumping auxiliary loads proportional to biogas production (controls, mixing where applicable, flare/compression).
Market range
0.02kWh/Nm3 biogas
Screening auxiliary electricity intensity
Increases effective auxiliary electricity intensity when capacity factor is reduced (start/stop and under-utilization effects).
Market range
0.5
Heuristic part-load penalty coefficient
Prevents unrealistically large auxiliary penalties at very low capacity factor.
Market range
1.5
Heuristic cap on penalty
Aggregated electricity per m3 of percolate recirculated (accounts for head losses and pump efficiency).
Market range
0.2kWh/m3
Screening pumping energy
Approximate net process heat required per tonne of fresh feed for mesophilic operation (heating percolate/structure losses).
Market range
25kWh/t
Screening process heat demand
Higher heat demand per tonne for thermophilic operation due to higher setpoint and typically higher losses.
Market range
45kWh/t
Screening process heat demand
Captures higher peak-to-average gas rates for a small number of garages; peaks reduce as garages increase.
Market range
1.5
Batch-production smoothing heuristic
Limits peak-to-average sizing multiplier to avoid unrealistic capacity requirements at extreme conditions.
Market range
2.5
Heuristic cap on peak factor
Adds a practical margin for engine selection, degradation, and operational flexibility.
Market range
1.1ratio
Sizing margin
Defines the capacity at which the reference specific CAPEX applies for the scaling correlation.
Market range
250kW
Reference sizing point for scaling
Represents an order-of-magnitude installed CAPEX for a garage-based dry batch AD + CHP system at the reference scale.
Market range
6000EUR/kW
Screening CAPEX reference (garage dry batch tends higher civil works)
Models decreasing specific CAPEX with larger installed capacity.
Market range -0.05 to -0.3
-0.15
Economy-of-scale exponent
Prevents unrealistically low specific CAPEX from scaling at very large capacities.
Market range
2500EUR/kW
Clamp lower bound
Prevents unrealistically high specific CAPEX for very small projects due to scaling extrapolation.
Market range
12000EUR/kW
Clamp upper bound
Represents annual fixed O&M as a fraction of total CAPEX (maintenance, labor share, consumables).
Market range
0.05ratio
Fixed O&M fraction reference
Models modest economy of scale in O&M fraction at larger capacities.
Market range -0.15 to 0.0
-0.05
O&M scale exponent
Avoids unrealistically low O&M fraction for large projects.
Market range
0.03ratio
Clamp lower bound
Avoids runaway O&M fraction for very small projects due to scaling extrapolation.
Market range
0.1ratio
Clamp upper bound
Represents variable costs proportional to gross electricity (e.g., engine service hours, consumables).
Market range
8EUR/MWh
Variable O&M placeholder
Improves readability and avoids inline literals for clamps and invalid checks.
Market range 0
0
Numeric constant
Improves readability and avoids inline literals for checks and factors.
Market range 1
1
Numeric constant
Used for validating two-option select inputs.
Market range 2
2
Numeric constant
Used for validating percentage inputs.
Market range 100
100
Numeric constant

Sources

1 external source

Guide-methanisation-voie-solide-discontinue-2018-ADEME.pdf