[Author here]

The LUIE figure we found for dedicated biomass is 580 m²/MWh/y: 580 square meters to generate one megawatt-hour per year. You multiplied this by hectares, meaning you multiplied area times area. If you want to determine the amount of energy you can produce from a given area (e.g. 1 billion hectares), you need to divide by 580, not multiply by 580.