commercially available energy from nuclear fusion by 2020 ?
Dream on.
At the moment there are two main pathways towards fusion. Inertial confinement (lasers, such as in this story) and magnetic confinement (tokamaks such as JET or ITER that will be build in France).
Don't let those people over at the inertial confinement facility convince you that they are in this for fusion. It has more to do with high power lasers for the military and simulation of nuclear explosions. Nuclear test explosions has been banned. That is why France quickly did a few more before the ban started, and why the USA and France (and probably others as well) are so interested in inertial confinement.
That leaves magnetic confinement. The timescale here is that by 2020 ITER will be finished, up and running. But ITER is a test facility, designed to prove that the energy output is greater than the energy input. If you want to get to a reactor that will actually provide energy to a grid, then you will have to wait another 20 to 30 years. Thus energy to the grid around 2040 - 2050, from a reactor called DEMO that has to prove the commerciality of fusion energy. By that time, we'll probably just be happy to get any energy at all from any source (unless solar lives up to its promise).
A single reactor by 2050, how many are we going to need to power the world? After DEMO, it will probably take another 10 to 15 years (a guess, based on the build time for ITER) to get that total power production up to something significant.
Yes, I am a big proponent of fusion, and we absolutely need to do it, but some realism won't kill us.