Biogas Plant Economics: Feedstock Mix, Gas Yields, Methane Content, Electricity & Heat Output, Digestate, Feed-In Revenue and Payback

What you'll build

What you will be able to do

Each lab ends with a concrete result that you build yourself and the checker confirms, cell by cell.

• Turn a year's feedstock plan into dry matter and organic dry matter tonnes, find each feedstock's share of the organic matter and the dry matter of the whole mix: the starting point of every biogas calculation.
• Look up a fictional biogas yield and methane share for each feedstock, turn the organic dry matter into cubic metres of biogas and methane, and express the methane as kWh of energy and as the methane share of the mixed gas.
• Turn four feedstock scenarios into a daily input, the retention time in the digester and the organic loading rate, and label each scenario against the fictional design range of the plant.
• Turn a year's methane into fuel energy, compare three fictional combined heat and power units on electricity and heat output, and check how many full-load hours each would run.
• Price the plant's three products: electricity sold under a fictional feed-in tariff after own consumption, heat sold after warming the digesters, and digestate that is partly sold and partly costs money to get rid of.
• Cost a year of operation: feedstock purchases including a gate fee the plant receives, haulage per tonne-kilometre, CHP and other maintenance, staff and fixed fees, and express the total per MWh of electricity.
• Build 15 years of net cash flows including the start-up year and a CHP overhaul, and judge the investment with simple payback, the cumulative payback year, net present value and internal rate of return.
• Compare upgrading the gas to biomethane with burning it in the CHP, measure how strongly five inputs move the plant's annual result, find the biggest driver and draw a tornado-style chart.