I already have a working, self-sustaining, exothermic fusion reactor. I made it pretty big, so that the necessary pressure is created by gravity alone. This design produces 400,000,000,000,000 terawatts and is completely maintenance free. It also uses a passively safe design so the reaction can't run away, at least for a few billion years. I managed the containment issues (and the truly excessive power production) by suspending the reactor in vacuum about 100 million miles from any population center. Rather than building a 100 million mile cable, I'm transmitting power wirelessly via medium-wavelength electromagnetic radiation. The reactor uses a simple blackbody emitter to generate the radiation. Unfortunately, I couldn't afford to build a good focusing system at the reactor site, so only about 1/10,000,000,000 of the power (50,000 terawatts) actually reaches my potential collector site. However, we only need 13 terawatts to serve our potential market, and really more like 4 terawatts if we can convert the energy to electricity.
Now I'm just working on a system to convert this medium-wavelength electromagnetic radiation into electricity at the collector site. A lot of the fusion reactor designs I've seen use the radiation to boil a fluid to run a turbine. But I'm thinking it would be much cooler to use semiconductors -- maybe use the electromagnetic radiation to excite electrons across a bandgap and create electricity directly? I've got working prototypes of the solid-state converters, and they're already pretty cheap -- I can produce electricity for about 15 cents per kWh. I think with a few more years' work the whole system will be cheaper than coal power (it helps that I don't have to pay for the reactor or fuel). I figure if I cover 0.05% of my collector zone (the Earth's surface) with 15% efficient converters, I can provide enough energy for everyone on the planet.