In order to exploit the theoretical potential of small manure anaerobic digestion (AD) plants for flexible power generation, the technical retrofitting and the prospective additional revenue generated by direct marketing is assessed for two different manure AD plants by means of a profitability analysis. Due to the variation in the economic profitability by the individual direct marketing models, the economy of three plants was simulated in four different scenarios: basic feed-in tariff, direct marketing, electricity balancing market, and flexible operation. Economical operations were calculated and the additional revenue for small manure AD plants taking part in the direct marketing system was calculated.