Fugitive methane emissions from two agricultural biogas plants

•Inverse dispersion was used to measure CH4-losses from two biogas plants over 1 y.•Digestate storage was the largest contributor at both facilities.•Digestate emissions were lower with longer digester HRT and solids removal.•Leakage/venting emissions were intermittent, and were low after maintenance.•Flaring emissions were the smallest contributor (<0.25 %)