The story...

Jim Hoffman tells us that FEMAs estimate of 4 x 10 ^ 11 joules of potential energy in each WTC tower was the only source available to pulverise and heat up the concrete created during the WTC collapse.
http://911research.wtc7.net/papers/dustvolume/volumev3.html

Our take...

What Hoffman doesn't point out is the other sources of energy present at the time. Like the energy from the impact of each jet, for instance. And the explosion of the fuel. And the burning materials within the towers. And other energy that you'd expect to be released if any such buildings collapsed: exploding transformers, ruptured gas mains, whatever they might be.

Now yes, some of these are small in the great scheme of things. Others, like heat from the initial impact would have faded, and of course some of the heat from the jet fuel that exploded within the towers would have dissipated. So what difference would all this have made? We don't know, as Hoffman doesn't mention it, however we can say definitively that there's more energy here than his analysis considers.