Though there is broad consensus that Solar power will be the principal energy source for Space Settlements, several methods of converting Solar power into useful forms of energy have been proposed. In most cases this means to conversion of solar energy into electricity, but also the production of thermal energy of industrial importance.
In most Space colonization plans space habitats and solar power satellites are proposed as separate structures. This because space habitats have to rotate in order to generate “artificial gravity”, whilst solar power satellites are preferentially kept stationary. Most proposal suggest microwaves as the method of power transmission to space habitats (or even to Earth), where the microwaves are converted into electricity.
In Space colonization literature two main types of Solar Power Satellites (SPS) have been proposed: the first type uses Solar energy to heat a fluid (such as helium) to drive a turbine to generate electricity. The second type uses photo-voltaic cells to convert Sunlight directly into electricity. Both types use electricity to produce microwaves, which are then beamed to the consumer.
Type I satellites are by far the most simple SPSs to construct, and have been proposed since the 1960s. Basically you only need a mirror, tubes, a compressor, a turbine and a working fluid to build one. Back in the 1970s photo-voltaic cells were much less developed than today. And for that reason most early proposals for Solar Power Satellites were of this type.
Another advantage of type I satellites of type II ones, is that photo-voltaic cells will deteriorate due to their exposure to Solar winds. And consequently type II satellites will decrease in power output over time.
But on the other hand type I satellites are much more vulnerable to meteorite impacts. A small hole in one of the tubes caused by such an impact, will cause the working fluid to leak from the system; which will render the entire plant useless. However, if a type II satellite, which is composed of a multiple photo-voltaic cells is hit by a meteorite, only the cells which are hit will be destroyed, whilst the others will still be in operation.
Compared to type I satellites, type II satellites are less massive and hence require less material resources to be built. Also type II satellites have no moving parts, which are subject to wearing off.
Besides these two main types, several other types of Solar power satellites have been proposed. An interesting proposal are Solar-pumped lasers. These are laser which are powered directly by Solar power, without the intermediate step of producing electricity. The generated laser beam can then be used to transmit energy over great distances. This has several potential applications.
First, such lasers can be used to propel solar sails throughout the solar system. A second application is to transmit power to settlements at great distance from the Sun. The amount of Solar power one receives, decreases with the distance to Sun squared. For instance Saturn is located 10 times as far from the Sun as Earth, and receives per squared meter a 100 times less energy. A solar power satellite in the neighbourhood of Saturn needs to be a 100 times larger than a comparable satellite in the neighbourhood of Earth.
Since laser beams are highly concentrated, a solar-pumped laser in our neighbourhood could power a SPS close to Saturn. And that SPS could be considerably smaller.