Investing in biogas: Timing, technological choice and the value of flexibility from input mix

► We study the technology choice problem of a continuous co-digestion biogas plant where input factors are substitutes but need to be mixed together to provide output. ► We show that the degree of flexibility in the productive technology installed depends on the value of the option to profitably re-arrange the input mix. ► Such option adds value to the project in that it provides a device for hedging against fluctuations in the input relative convenience.