Well, it's a pretty handy power supply. Already now it is being used in the most favourable locations (geothermal vents + cold weather which hot water can be used for heating and greater temperature differential for power generation). I can only surmise that it will grow as a proportion of energy sources. But it really will follow a trend of all power sources, surmised as follows:
Hey, gee it's windy here -> Let's build some wind farms.
By golly there's a lot of cheap sugar source here -> lets make ethanol fuel.
Gee there's three spectacular gorges here -> let's build some hydroelectric dams.
Hey we're near the equator and near some deep water -> lets build some ocean thermal differential power-stations/desalinators/cold water airconditioners.
Does the sun ever stop here? -> Let's build some big solar power generators.
Already, service stations have to supply auto-gas, unleaded, diesel, ethanol blends etc. They will just have to make more options.