[mdf]

That 0.00435 is each year, since 87 TWh was the annual use. Multiplying that by 27.25 gets the ~12 % for accumulated percentage by year 2050.

[cycomanic]

Ok I think I misunderstood. You were talking about the land use for coal, which I guess you're right would need some accumulation factor (although I suspect it doesn't grow linearly). But if you would use solar or wind you would not, which was the context of the discussion and hence I misunderstood.