re: Will it be cheaper than tar sands or bio-diesel?
Your almost is a stretch. We can't build any net energy gain fusion reactors, even less ones that burn He3. We can collect solar energy, convert it to electicity, then microwave beam and distribute it.
As you said, basic economics will most probably enable us to use tar sands and biomass first. A wildcard here is that powersats would better enable a hydrogen economy, providing lots of electricity for disassociation of H2 from water. How ARE we gonna generate all that H2 we'll supposedly need for cars, trucks, busses, boats, and home heating?