Brittany Kelp Biogas Cooperative Profit Modeler

Turning Brittany’s kelp into cooperative biogas revenue

Brittany’s coastline produces more than 60,000 tonnes of kelp annually. Traditionally harvested for alginate extraction, the seaweed increasingly ends up as a feedstock for anaerobic digestion. Cooperative fishers and farmers want to capture that opportunity without ceding control to multinational utilities. The Brittany Kelp Biogas Cooperative Profit Modeler walks stakeholders through the economics of pooling harvests, digesting kelp, selling electricity under France’s tarif d’achat, distributing waste heat, and marketing nutrient-rich digestate to organic farms. With inputs tailored to Armorican realities, the tool aims to help cooperatives draft bankable business plans and align member expectations.

The feedstock section captures the biological fundamentals. Kelp arrives at the digester with high moisture content; the dry matter percentage indicates how much of that mass contains volatile solids that generate biogas. Biogas yield, expressed in cubic metres per tonne of dry matter, reflects lab trials conducted by the French National Institute for Agronomic Research. Methane share determines the energy content—higher methane fractions translate to more usable energy. Combined heat and power (CHP) efficiency determines how much of that energy becomes electricity eligible for feed-in tariffs, while the remainder exits as low-grade heat for district heating loops or algae drying.

Revenue streams extend beyond electricity. France’s tarif d’achat for biogas-fed electricity, currently around €0.185 per kWh for sub-500 kW plants, forms the backbone of cooperative income. Heat recovery is increasingly monetized as local greenhouses pay for steady thermal supply. Digestate, rich in potassium and micronutrients, substitutes imported fertilizers; regional organic farms pay between €5 and €15 per tonne depending on transport distance. The calculator lets users adjust each revenue coefficient to match supply contracts or conservative estimates during early negotiations.

Operating costs include kelp collection, transport, grinding, digester operation, and residual waste handling. Cooperative models often rely on member labour, but cash costs remain for diesel, enzyme additives, and regulatory compliance. Maintenance covers pump overhauls, CHP servicing, and monitoring staff. Capital expenditure reflects the digester, CHP unit, storage tanks, and connection fees to Enedis. Many cooperatives secure grants from the Brittany Region, ADEME, or the European Maritime, Fisheries and Aquaculture Fund; the grant field reduces the net upfront investment.

The model’s engine converts wet tonnage to dry mass, multiplies by biogas yield, and calculates methane volume. Assuming 10 kWh of energy per cubic metre of methane—a standard engineering approximation—the calculator splits energy into electricity and heat based on the CHP efficiency. Multiplying electricity by the feed-in tariff yields energy sales revenue. Heat output, converted to megawatt-hours, earns additional income at the user-specified price. Digestate revenue scales with wet tonnage, assuming one tonne of digestate per tonne of kelp after dewatering.

Cash flow is then computed by subtracting operating and maintenance costs from total revenue. The initial investment equals capital expenditure minus grant support. Each subsequent year features the same net benefit unless users adjust inputs to represent escalation or degradation. Net present value is calculated via

where I₀ represents net capital outlay, R_y annual revenues (electricity, heat, digestate), C_y annual costs (operating plus maintenance), and r the cooperative’s discount rate. The calculator also reports payout per member—useful for co-ops distributing surplus to fishers and farmers based on patronage.

Imagine a cooperative across Saint-Malo and Cancale harvesting 40 tonnes of kelp per week during peak season and storing excess for winter digestion. At 18 percent dry matter and 320 m³ of biogas per tonne of dry matter, the digester produces roughly 370,000 m³ of biogas annually. With 60 percent methane, that equates to 222,000 m³ of methane, or 2.22 GWh of energy. Operating a CHP with 35 percent electrical efficiency yields about 777,000 kWh of electricity, worth €143,000 at the tariff. The remaining heat—1.44 GWh—sells to a nearby oyster hatchery at €32/MWh, adding €46,000. Digestate sales contribute another €16,000. Against €93,000 in operating costs and €110,000 in maintenance, the cooperative posts roughly €23,000 in annual surplus. Distributed across 24 members, that is nearly €960 each, before setting aside reserves.

The comparison table spotlights how harvest scale and contract pricing affect outcomes. Three scenarios—baseline cooperative, expanded harvest with premium heat sales, and conservative pricing—illustrate sensitivity.

The calculator reinforces cooperative governance by showing how payouts per member respond to pricing, grants, and maintenance budgets. Members can discuss whether to reinvest surpluses into kelp harvesting gear, debt service, or community dividends. Lenders can inspect the CSV export to stress-test low-price scenarios or model debt coverage ratios.

Limitations remain. Biogas yield varies with kelp species and storage; storm-damaged kelp may contain sand that lowers volatile solids. Feed-in tariffs can decline in future tender rounds, so cooperatives should update the tariff field whenever the French Energy Regulatory Commission publishes new rates. Transport logistics matter: if members harvest across scattered bays, trucking costs could rise beyond the default operating cost input. The calculator assumes constant annual production; in reality, maintenance shutdowns or algae blooms could reduce output in certain months. Finally, cooperative statutes determine how surpluses are shared—this tool provides per-member figures for discussion but does not replace formal accounting.

Despite these caveats, the model equips Brittany’s coastal communities with transparent numbers. By combining scientifically grounded conversion factors, policy-specific tariffs, and cooperative governance metrics, it helps residents evaluate whether kelp biogas can diversify incomes, decarbonize energy supply, and valorize marine resources without sacrificing local control.