⚡ Biogas Surplus Calculator

Select your digester, enter daily dung and cooking — see surplus and what it could power.

m³ per kg

Feedstock reference

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Single stove

Default 0.30 m³/hr (SNV/BSP field standard)

Double stove

Default 0.60 m³/hr (2 × single)

The bucket you mix and carry slurry in. Typical: 5 L, 10 L, 20 L jerrycan.

{{ waterToDungRatio.toFixed(1) }} : 1

Parts water per part dung (by weight). SNV/BSP recommend 1:1. Use 2:1+ for fibrous feeds or cold weather.

Define your own digester if it doesn't match the preset sizes. Select "Custom" in the digester buttons above to use these values.

Volume (m³)
Optimal loading — min (kg/day)
Optimal loading — max (kg/day)
Max daily gas output (m³)

🐄 Your inputs

{{ dungKgPerDay }} kg
5 kg Optimal {{ activeDigester.optimalLoadMin }}–{{ activeDigester.optimalLoadMax }} kg/day 120 kg
{{ loadingEfficiency.badgeClass === 'ok' ? '✓' : loadingEfficiency.badgeClass === 'lo' ? '↓' : '⚠' }} {{ loadingEfficiency.label }}
{{ cookingHoursPerDay.toFixed(1) }} hrs
🪣 {{ bucketsOfSlurryPerDay }} bucket{{ bucketsOfSlurryPerDay !== 1 ? 's' : '' }} of mixed slurry per day ({{ totalSlurryLitresPerDay }} L total)
Mix the dung and water together in your bucket first — each {{ bucketSizeLitres }}-litre bucket holds the ready-mixed slurry you carry to the digester inlet. At {{ waterToDungRatio.toFixed(1) }}:1 water:dung, each bucket is roughly {{ (bucketSizeLitres / (1 + waterToDungRatio)).toFixed(1) }} kg dung + {{ (bucketSizeLitres * waterToDungRatio / (1 + waterToDungRatio)).toFixed(1) }} L water. ⚠ Very thick mix — risk of inlet blockages. Increase water ratio in ⚙ Settings. ℹ Thin mix — may reduce hydraulic retention time slightly.

📊 Daily balance

Production

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m³/day

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Cooking use

{{ dailyCookingUseM3.toFixed(2) }}

m³/day

Surplus

{{ dailySurplusM3.toFixed(2) }}

m³/day

Cooking {{ surplusAsPercentOfProduction }}% surplus {{ Math.abs(Math.round((dailySurplusM3 / dailyProductionM3) * 100)) }}% shortfall Surplus
Why {{ Math.round(loadingEfficiency.factor * 100) }}% efficiency? {{ loadingEfficiency.explanation }}
Cooking demand ({{ dailyCookingUseM3.toFixed(2) }} m³/day) exceeds production ({{ dailyProductionM3.toFixed(2) }} m³/day). Try feeding more dung, reducing hours, or switching to a single stove. Marginal surplus of {{ dailySurplusM3.toFixed(2) }} m³/day. Small adjustments could unlock productive use options. You have {{ dailySurplusM3.toFixed(2) }} m³/day of surplus — {{ annualSurplusM3 }} m³/year — going unused. See below what it could power.

Annual surplus

{{ annualSurplusM3 }}

m³/year

Extra cooking hrs

{{ extraCookingHoursPerYear }}

hrs/year

Efficiency

{{ Math.round(loadingEfficiency.factor * 100) }}%

{{ loadingEfficiency.label }}

Production = dung × {{ biogasYieldPerKg }} m³/kg × efficiency factor (Gurung 1997 / SNV BSP). Water in the mix is a carrier — biogas comes from organic matter in the dung. Stove rates are editable in ⚙ Settings.

🏗️ Digester reference

SizeOptimal loadingMax output HRTYour loading
{{ digester.label }} selected {{ digester.optimalLoadMin }}–{{ digester.optimalLoadMax }} kg/day {{ digester.maxDailyOutputM3.toFixed(1) }} m³/day {{ digester.hrt }} {{ dungKgPerDay }} kg — {{ getLoadingPillStyle(digester).label }}

Optimal loading from 30–40 day hydraulic retention time (HRT) for mesophilic fixed-dome digesters (Gurung 1997; SNV/BSP). Below ~25 days HRT, incomplete digestion reduces gas yield and pathogen kill in the bio-slurry.

⚡ What could your surplus power? (tap a card for details)

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Needs {{ use.dailyNeedLabel }}

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⚙ Setup

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💰 Costs (East Africa)

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📈 Economics

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💡 Tip

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Brooder 0.3 m³/hr × 24 hrs; fodder chopper ~0.4 m³/hr × 2 hrs; food dryer 0.5 m³/hr; water heating 0.5 m³/day; lighting ~0.2 m³/evening. Warnars & Oppenoorth (2014) SNV/Hivos.

💡 Think beyond the examples

If a process runs on LPG, propane, or any gas flame — it can almost certainly run on biogas with simple modifications. Use these as conversation starters with your trainer.

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