Barring a laundry list of technological breakthroughs, space based solar power will not be practical in our lifetimes. I recently did a lit review in this area,

Barring a laundry list of technological breakthroughs, space based solar power will not be practical in our lifetimes. I recently did a lit review in this area, and it's pretty clear that this is a pipe dream for a small group of people that seems to attract bursts of grant money in 10-20 year intervals before collapsing when the people picking up the tab realize what the challenges are. There are a few extant concept designs for space based solar power, but the most mature and most representative example is a design called SPS-ALPHA [1] which came out of a NIAC contract and has been refined by its inventor in the intervening decade. Essentially, the architecture assumes a large structure supporting an array of mirrors in geostationary orbit focused on a sandwich panel. One side of the sandwich panel contains solar cells, the other contains a retrodirective phased array which beams the collected power back to a site transmitting a pilot signal on earth. This design is interesting and solves some issues that plagued the original designs developed in the 70s. The sandwich panel avoids the need to collect and transfer power between separate solar panels and an antenna, and the retrodirective array avoids the need for precise subwavelenth position knowledge of array elements across the antenna. Using mirrors also reduces the number of solar cells required, however, the achievable concentration ratio isn't very high (3x or so IIRC) due to thermal constraints requiring the sandwich panel to passively self-cool. The mirrors are gimballed, allowing the design to maintain peak power generation regardless of the position of the sun. The problem is the sheer size of the structure, and it is dictated by physics constraints. Efficient microwave power beaming over a fixed distance imposes an inverse relationship between the size of the transmitting and receiving antenna: halving the area of the space based antenna doubles the area of the earth based antenna, and vice-versa. Both antennas can be shrunk simultaneously by increasing the frequency of transmission, however, atmospheric absorption caps efficient transmission at around 10 GHz. Most designs, including SPS-ALPHA, assume a 2.4 GHz transmission frequency (probably because of the ISM band and the feasibility of building high efficiency saturated amplifiers in this band). For SPS-ALPHA, this leads to an antenna about 1.7 km in diameter in space and 5 km in diameter on tbr ground. Here's the key part: these dimensions are independent of the amount of power transferred. For efficient transmission, you need to build a spaceborne megastructure regardless of if you're transmitting 1 MW or 1000 MW. You can't really do a small demonstration plant, you pretty much have to go for the whole meal deal. And that structure is huge: the largest thing we've ever built in space by several orders of magnitude, in a very hostile radiation environment (GEO). The costs would be incredible. Could you build it? Technically, yes. But there is no universe in which it makes economic sense. [1] https://www.nasa.gov/general/sps-alpha-the-first-practical-solar-power-satellite-via-arbitrarily-large-phased-array/ https://www.nasa.gov/general/sps-alpha-the-first-practical-s...