More numbers

Hydrogen has about 141 MJ/kg of energy. It costs about 50 kWh to make and another 15 kWh to liquefy. So penny a kWh power would make hydrogen equal to a gallon of gas for less than 50 cents.

Keep 65 kWh/kg for LH2 in mind, it gets used later.

The only long term source of energy is the sun. Solar power doesn't work all that well on earth because the earth is in the way much of the time. Moving solar power collectors into high orbit, geosynchronous, and very modest concentration gets you close to a factor of ten more sunlight than most places on earth. The way to get the energy down, low density microwaves, has been known for almost 40 years, the block has been high cost to orbit.

Consider a space based solar power project big enough to replace all the coal fired plants in the US in one year, 300 GW. This number is somewhat arbitrary. (The market for new power sats would go on for decades at this rate as fossil fuels run out.) For reasons rooted in geometry and physics, power satellites have to be 5 GW or larger. That means constructing them at 60 per year. At this rate you can ignore RDTE in a first pass analysis.

Could such a project eventually deliver power at a penny a kWh?

Take a year at 8000 hours, and the mass of a power sat at 2kg/kW. So the annual output from a power sat would be in the range of 4000kWh/kg. At a penny a kWh, that's $40. If we allow a capital cost ten times that high (reasonable for long lived projects) then we can afford to spend about $400/kg for parts and transportation to reap $40 of penny a kWh power per year. That's a somewhat arbitrary number. At a kg/kW, we could afford $800/kg installed cost.