The article says that a cow produces about 100 kg of methane a year. At 0.7 kg/m^3, that's about 142 cubic meters of gas per year. Natural gas costs a few dolla

The article says that a cow produces about 100 kg of methane a year. At 0.7 kg/m^3, that's about 142 cubic meters of gas per year. Natural gas costs a few dollars per thousand cubic meters... So even without going into efficiency and the cost of capturing and purifying, it's definitely not going to be worth it.