Mr. Bill Callanan:

In simple terms, it is down to volume. To reach 5.7 TWh, it takes around 200 plants. If using food waste and other materials, there would be feedstock for around 50 plants rather than 200. The introduction of grass is making up the differential between 50 and 200. It is not going to be 50 plants exclusively on food waste, but the volume of material required across 200 plants requires you to go beyond food waste or animal slurries.