The (economic) value of an agricultural crop for biogas is determined by the amount of gas produced per hectare, the costs involved in harvest, transport and handling and the degradability of the biomass in the digester.
Tall fescue and festulolium are together with red clover species having a very high yield potential and they can in many places compete with maize.
Grass and clovergrass fits very well in an anerobic digester together with slurry where it improves the yield of gas.
Grass is a perennial crop with a good environmental profile, grass brings health to the crop rotation and long time benefits to soil fertility.
Scale 1-9, where 9 = best or most pronounced