Mankins and others estimate the total cost for developing, building, launching and assembling all the components of a space-based solar power plant is on the order of $4 to $5 billion—a fraction of the $28 billion price tag on China’s Three Gorges Dam. Mankins estimates a working scale model with full-sized components could be had for $100 million. By comparison, the Tennessee Valley Authority’s recently completed Watts Bar nuclear plant took 43 years to build, from start to stuttering finish, and cost $4.7 billion all told.
Link: What's Next For Solar Energy? How About Space