by Adam Manning
Generating power for Earth from the enormous and constant outpouring of energy in space from the Sun has long been a dream. Solar energy from space has been looked on longingly as a way of benignly solving our world’s ever increasing demand for power and moving civilization on from its dependence on fossil fuels.
These ideas received a great deal of attention in the 1970s with studies by Dr Gerard O’Neill and his colleagues when they set out plans for the colonisation of space. Solar energy from space envisages satellites in Earth orbit collecting energy from the Sun using solar panels. This energy is then converted into a different form, normally microwave transmission or laser beam, and this is transmitted directly down to a receiving station on the surface of the Earth.
Proponents of the idea point to a number of advantages compared to obtaining solar energy from conventional solar panels on the surface of Earth. The Sun’s rays are weakened as they pass through Earth’s atmosphere on their way to the surface whereas in space, there is no atmosphere and so no reduction of this sort applies. Solar energy here on Earth is subject to the vagaries of the weather as when it is cloudy the Sun’s rays provide less energy. In space, the Sun’s energy is constant as there are no clouds. Of course when it is night at a particular point on the Earth’s surface, there is no solar energy at all! By contrast, if the orbit of the satellite is high enough it can receive and transmit energy derived from the Sun nearly continuously. This avoids the need for batteries to store energy that normal solar energy entails so that a continuous supply of energy can be produced for consumers. A typical space based solar power operation of this sort is expected to provide about the same power as an average nuclear power station.
|A Space Based Solar Power Satellite demonstration experiment|
Space based solar energy has been seen as a way to cost effectively solve the energy crisis of the late twentieth century and more recently as a way to provide our civilization with the huge amount of energy it will need in the future without compromising efforts to tackle global climate change. These advantages and hopes for solar energy from space help explain why it is an idea that is revived from time to time with new studies and proposals.
Plans for Space Based Solar Power have also played another role. At the time of the original studies on space habitats in the 1970s, Dr Gerard O’Neill and his colleagues put forward plans for Space Solar Power Satellites as the main reason, at least initially, for the construction of the huge space habitats he and his colleagues proposed. The main purpose for the construction of the Island One space habitat, with a population of 10,000 or so, was to provide living space for the large number of workers that would be needed to construct the satellites.
This was due to the breathtaking size of these solar power satellites, which would have dwarfed, for example, the International Space Station. To ensure that the solar panels on the satellites could obtain enough energy from sunlight to provide the power needed to justify the whole operation, the satellites were expected to be at least a kilometre across and often much larger than that. In the 1970s, there was no other way to realistically envisage an installation of this size being constructed without large numbers of workers being involved. They would need a place to live while this was being carried out in space and so a large space habitat was required. The initial space habitats and solar power satellites took on an almost circular logic, the one justifying the existence of the other.
It is now roughly forty years since the studies by Dr O’Neill and his colleagues and so the question arises, what has changed since? Sadly, space habitats of the size of Island One have yet to be built and there have never been any experiments concerning space based solar power for Earth in space, let alone the construction of the sizeable satellites that an operational energy scheme would necessitate. Why not?
In reviewing the history of solar power from space, one of the most striking developments has been the much wider use of solar energy on the ground accompanied by a parallel drop in its costs. Solar energy was relatively undeveloped in the 1970s and forty years of development have made it far more widespread and mainstream. Solar panels on the roofs of residential homes are now a familiar sight and large solar farms have been constructed to harness more of the Sun’s energy.
One of the key points made in the 1970s studies is that solar energy from space would ultimately be cheap compared to existing energy sources including the then rocketing price of oil, particularly once the enormous infrastructure to generate it was in place. Studies of energy prices in the mid 2010s suggest that this is not the case at present. Oil prices are not as prohibitively expensive as originally foreseen and the cost of solar energy on the ground is much lower than expected. These points already counter an argument for solar power from space based on higher energy costs on Earth compared to solar energy from space. If solar energy from space is not markedly cheaper, why bother?
On this point on costs efficiency it is also important to consider launch costs. The 1970s studies looked forward to launch costs reducing steadily in the future and placed reliance on the space shuttle programme (with descendant programmes developing shuttle technologies) as a major part of this progression. Launch costs have not reduced as substantially as hoped or planned and sending equipment or personnel into space is still very expensive. This is important as a mature space based solar power operation will require a very large number of launches to place the equipment necessary for construction in orbit. This expenditure is exacerbated by the need to ensure the satellite is ultimately functional at geostationary orbit, some 36,000 km from Earth’s surface.
When these huge launch costs are taken into account, solar power from space looks even less cost effective. The point has been made that these costs could be reduced by using materials in space, such as on the Moon’s surface or from near Earth asteroids. This suggestion may have merit but it has to be borne in mind that techniques and technologies for the utilisation of such resources have yet to be fully developed and put into practice and this in itself will be very costly.
Construction costs might, theoretically, be cheaper now than envisaged in the 1970s due to advances in robotics. Speculatively, it is possible to imagine that robotics can be used to quicken and cheapen construction of the space solar satellites rather than the armies of workers proposed in the original studies. As with using space resources to construct the satellites though this point has a large degree of uncertainty and developing such advanced robotic techniques will entail a great deal of costs by itself. It also abandons one of the main justifications for the construction of the Island One space habitat.
A further point to be considered is the effectiveness of the transmission of power from a space solar power satellite to a receiving station on Earth. These is perhaps less experimental evidence on this as might be hoped considering the four decades that have elapsed from the original studies. The clearest guidance on this point suggests that the microwave transmission from a solar power satellite would transmit around three times as much power to its receiving station on the Earth’s surface than an equivalently sized bank of conventional photovoltaic solar panels would be able to generate, assuming they were placed on a part of the Earth’s surface that is suitable for solar energy production.
The practical problem that proponents of space based solar power face is that it would be much cheaper, easier and quicker to build a solar power facility (or farm as they are referred to) with conventional ground based panels that was three times the size of this receiving station. The same amount of energy would then be produced for much less cost, technical difficulty and time. This saving on cost would allow the use of the batteries that are needed to ensure that solar energy provides a constant supply of electricity in the case of bad weather, for example. An alternative policy might be to build three solar farms in different areas to provide the same power as the satellite for much less cost and time.
Elon Musk is a noted entrepreneur and billionaire with large businesses involved in both space development and solar energy and if anyone were to be a powerful supporter of space based solar energy, it ought to be him. Yet he has, very clearly, set out his view that space based solar energy has no useful advantage over conventional solar panels on the surface of Earth for these reasons.
Space based solar power (SBSP) does have many supporters despite these points. In particular, JAXA (the Japan Aerospace Exploration Agency) has carried out useful experiments on the transmission of energy using technology suitable for SBSP in which energy was transferred over a distance of 500 metres. One result from this was showing how the energy could be accurately directed to ensure it was received effectively.
Japan has in recent years shown particular interest in SBSP in part due to the earthquake of 2011 and the Fukushima Daiichi nuclear disaster. In moving away from nuclear power and with a country with relatively little fossil fuel resources, SBSP must appear an attractive alternative to investigate. China has shown a similar interest. With its huge population coupled with an increasing standard of living, China’s energy needs in the future will be enormous. If SBSP could provide a way to satisfy this need without burning fossil fuels, it could be an ideal solution.
NASA has always had supporters of the concept and from time to time various experiments in this area are proposed, including those involving the International Space Station. The Space Solar Power Exploratory Research and Technology program proposed an ambitious timetable for work in this field.
The US Army War College has also investigated the concept. Whilst noting the attractions and possible advantages of SBSP, they noted that much of the technology required has yet to be sufficiently proven to fully understand the costs and challenges involved. Their report accepts that whilst the main theories concerning the operation of SBSP are plausible, since its earliest days it has always seemed that around ten years of work is needed to ensure the finer practical points are established to get to a position where such a system could be constructed.
Likening it to research into fusion, of which there seems to be rather more experimental work, the US Army War College concluded, like Elon Musk, that at present there was no reason to think it provided any great advantage over conventional ground based solar energy. Interestingly, their report does indicate it might have some use for the military in war zones where they have substantial energy needs without being able to rely on conventional power stations, which are either not present or have been destroyed.
At present there seems to be a clear difference of opinion between proponents of the concept, who often set SBSP within a broader context of the development of space and its long term settlement, and detractors who, whilst freely admiring it and its attractions, conclude that there is no clear, practical advantage to SBSP as matters stand.
In this context the most prudent way to proceed is with more experiments so that a clearer understanding of the practical issues involved can be acquired. The ideal here of course would be experiments involving the transmission of power from the International Space Station to a receiving station on Earth. This body of data may support useful, alternative applications along the way.
If as we hope space development continues to progress, including commercial activities, it maybe that the breathtaking costs involved in the SBSP infrastructure will seem less insurmountable in future than they do at present. This might be the case if Skylon proves to be successful in reducing the costs of access to space. Ultimately SBSP may be useful in providing power to settlements on the Moon or habitats in space itself, such as the Island One, where the absorbing qualities of the atmosphere are not present.
While we have seen reasons why SBSP, despite its initial promise, has never launched off the pages of academic papers and out into orbit, there is still much to learn. In a world seeking to divest itself of its addiction to fossil fuels, it must be right to investigate it further, despite these present difficulties, in case it may one day unlock for us the effectively endless and constant energy pouring out of the Sun.