Mar 9, 2023 · Biogas energy cost equivalency to conventional fuels. The Penn State digester's annual cost of $5,557 produces a net amount of: 1,460,000 cubic feet (42,000 m 3 of biogas from the manure of 100 cows. This biogas has the energy value of 876,000,000 Btu (924,000 MJ).