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More on Space Based Solar Power …

Published on Oct 15, 2007 at 2:24 pm. 2 Comments.
Filed under solar energy.

Wow. I just noticed that it has been three days since I posted! I have been so busy the past few days that it is unbelievable. For today, I thought that I’d write a bit more about Space Based Solar Power (SBSP). This continues my prior posting.

Mirror in Space

SBSP has been kicked around for decades now. As I said before, it is only now just becoming feasible. One of the earliest proposals was to use giant mirrors in space to focus light onto the Earth below. In fact space mirrors were proposed by Hermann Oberth in the 1920s. The idea would be that ordinary ground based solar energy stations would benefit from having extra bright sunlight with which to work. There were proposals to also use these mirrors to light cities at night, eliminating the need for streetlights and many other artificial light sources, thus saving electricity. Russian Space Mirror (artist impression, had it worked) In 1999, Russia even attempted to build and test a mirror in space, though the mirror did not unfurl. Had it done so, a five mile wide swath of light would have swept from Germany, through the states of the former Soviet Union, across Seattle, in the northwestern portion of the continental United States, and across part of southern Canada. Interestingly, a similar solution has been proposed for the Austrian town of Rattenberg. In the case of Rattenberg, though, the mirrors would be located on adjacent mountains directing light into the town that is in the shadow of other mountains all the winter. Proponents of the space mirror idea pointed out that such mirrors could be used to provide temporary broad lighting for disasters, for military operations, and for special outdoor nighttime sporting events. The space mirrors have also been suggested for crop management purposes.

But, the mirror in space idea has problems. For one thing, the mirrors are just that: mirrors. They reflect sunlight across the visual, infrared, and ultraviolet spectrum. Not all of that light is useful. There are environmental concerns. What would perpetual light do to the circadian rhythms of animals? What would be the psychological effect of perpetual light on humans? And, while the amount of additional sunlight directed towards Earth would be tiny compared to what Earth already gets, what effect would this have on weather and the climate? We are already talking about global warming. Do we really want to shine more sunlight on Earth? In fact, one proposal to deal with global warming is to put objects in space to shield the Earth from some of the Sun’s energy! Weather is very susceptible to very small changes in conditions. Do we really know what such small effects would do over long periods of time? Darnell Clayton from over at Colony Worlds mentioned the weather factor in a comment on my last posting, and this is something that bears looking into. And, it has even been suggested that solar mirrors could be used for weather and climate modification, so that suggests that there could well be some unintentional weather effects. Personally, I would suspect that the change would be no more than we make anyway by cutting down forests and filling the land with houses built so close together that there is no room to plant trees: just concrete and roofs. But, then we know that such building styles lead to the urban heat island effect, and who knows what else. So, it may well be that solar mirrors would not be environmentally neutral. Clearly further research into the environmental effects needs to be done before we undertake beaming more sunlight to Earth.

Space mirrors A second issue with the solar mirrors in space issue is that the solar energy reflected to Earth is that they are just as susceptible to weather as regular sunlight. That being so, clouds, even haze, would drastically reduce the solar energy making it to the ground. Furthermore, there is always waste heat in the conversion of solar energy into usable energy. Only some of the sunlight is used in any solar energy conversion scheme. The rest produces even more waste heat. Furthermore, not all wavelengths of sunlight pass equally well through the atmosphere. Large mirrors reflecting sunlight to Earth are an easy concept to grasp, but perhaps they are not the best approach if the idea is to provide solar power. The mirrors are fairly passive in that all they do is reflect sunlight. They would be quite an engineering feat, of course, as they would have to be large and they would have to move to track the Sun and perhaps to beam the light to different targets on the ground. Still, the only technological hurdle is to determine how to build such large structures in orbit that would remain stable and could be adjusted as needed. But, all the mirrors do is make more sunlight falling on Earth. Then, standard usages of the sunlight would be employed on the ground. There is no real new technology here. And, given that only a portion of the Sun’s energy being reflected to Earth would be used, the strategy is rather inefficient, too.

This is where Peter Glaser’s proposals come in. As I said yesterday, in the late 1960s Glaser championed a new type of space based solar power satellite. His proposal was to build solar power stations that would actively intercept sunlight and convert it into electrical. This electrical energy could then be converted into microwaves that could be directed on a tight beam to receiving stations on Earth below. Those receiving stations would then convert the microwaves back into usable electrical energy. The waste heat from converting the sunlight into electricity would then be generated and released (in the form of radiators, if needed) in space, not on Earth. Any of a number of ways of generating electricity could be employed, from photo-voltaic cells to solar boilers creating steam to drive turbines. Each method has its pluses and minuses.

Solar Power Satellite

The advantage of the Glaser plan is that microwaves are less affected by the weather. That is not to say that weather has no effect on the microwaves. Anyone with satellite television knows that massive storms can interfere with reception. Water interferes with the microwave transmissions. However, the effect is small with just clouds. You normally need larger drops of water, like with rain. Still, there is some microwave absorption, so the issue as to how this might affect weather sill is a valid concern that needs to be addressed. But, if solar power stations replace fossil fuel burning power plants on Earth, then the environmental impact from the space based solar power may turn out to be less than what we already experience. Note that I say may. Before we commit to this approach, we need to see what the effects really are. Perhaps one or two experimental space based solar power stations would give us the data that we need.

But, the key here is the assumption that solar power will replace power generated on the ground using terrestrial resources. Sadly, I don’t see that as really happening. Look at hybrid cars. The first ones were far more energy efficient than the later ones. They used the hybrid technology to replace the traditional automotive engine. But, later hybrids used the technology largely to augment conventional engine performance, so that you get more horsepower out of a smaller engine. That does far less to improve fuel efficiency. I may be a pessimist, but I fear that what will happen is that space based solar power stations will be built on the promise of providing good clean energy replacing all of the old polluting power plants that we currently use. But, then with more electricity available, we are apt to use more. So, then we’d have the solar power in addition to what we have already. That would not only not alleviate any of the environmental concerns, but it may make them worse if space based solar power is not as environmentally neutral as is promised by its proponents. What we really need is a policy to conserve energy and to use what we have available wisely. Then, perhaps SBSP may be the way to go.

-Astroprof

(Images courtesy of NASA)