All space-based energy systems consist of a method of capturing energy from the sun plus a method of making that energy available to a satellite or transferring it back to earth.
A number of ways of capturing solar energy have been proposed. All but the last two of them are terrestrial solar generators moved to space, either to power the satellites they are attached to or to take advantage of the higher energy flux outside the earth's atmosphere. They are listed here roughly in the order in which they were proposed.
These are simply Concentrated Solar Thermal (CST) systems moved to space. These would use large mirrors to concentrate sunlight onto a boiler. The steam this generates is used to run a conventional turbine generator set. Although popular in SF stories written before the 1960s, these are non-starters due to the enormous expense of lifting the equipment into orbit. In addition, their focussed beams would be extremely dangerous to spacecraft and its not obvious that the system would work unless the entire system is spun to generate a gravity substitute.
This is the currently favoured way of powering satellites. Its simple and relatively light, so easy to deploy, and works well for powering any currently deployed or planned satellite. However, the cost of deploying larger scale systems intended for supplying terresrial grids may be unacceptable because the relative cost of launching a large unit may well exceed a smaller one: launch costs scale as the 3/2 power of the solar panel area and hence of the power output. In addition, the cost of maintenance is likely to be a lot more than that of an equivalent terrestrial generator. In other words, the launch and operating costs may well outweigh the cost of building a similar generator with the same output on earth here on earth.
This is a device that would capture the entire solar output but is entirely impossible with current or forseeable technology. It is a huge sphere 1.66 times the diameter of the earth's orbit with the sun at its centre. It would be built by dismantling and re-using all planets, asteroids and moons in the solar system. People would live in an ecosystem constructed on its inner surface. The entire sphere would be spun to provide the illusion of gravity for the ecosystem. Some sources suggest that, because such a system is unstable, almost all the captured solar energy may be needed to keep the sun centered in the sphere, leaving little to power the ecosystem and the civilisations living in it.
These are relatively light and simple devices designed to extract energy from the solar wind. None have been made or tested so far, but it has been estimated that one with a 300m collection wire connected to a 2m spherical receiver and a 10m diameter annular sail would generate 1.7 MW if sited in the earth's orbit. As the collection wire would only carry 0.44 amps at this power level, it could be quite thin and light. More details are here:
Since this satellite would be built largely of copper or aluminium and be quite light, it can built and launched with current technology.
Transmitting the power to where it is needed is simple enough if the energy capture device is mounted on the satellite it powers. However, if it must power a separate satellite or return the power to earth, things become rather more complex. The only options are to use microwaves or lasers to transmit the power. Both suffer from major problems: