Category Archives: space based solar power

The different types of Solar power generation

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.

Too cheap to meter?

Lewis Strauss coined in reference to the prospect of fusion power, the phrase too cheap to meter. Mr. Strauss argued that once fusion power would become available, the costs to produce electricity would be so low, that wouldn’t be worthwhile to charge the consumer in respect to their actual energy consumption.

The principal source of energy in Space Settlements is, of course, solar power. Our natural fusion reactor produces such amounts of power, that only a tiny fraction is needed for use by Space Settlers. Hence the question arises whether Space Settlers should be charged for their actual energy consumption?

Though the Sun does deliver its energy for free, it does not mean that the energy consumed by Space Settlers should be free. In order to make use of Solar energy, Space Settlers should convert it into useful forms of energy, such as electricity. This requires the construction of Solar Power Plants (SPPs).

And though a SPP has no fuel costs, it needs money for its construction and maintenance. Further the SPP has to be protected against meteorites and terrorists. It is obvious to someone has to pay for these services. And then we are only talking about the power plants, what to think about the construction and maintenance of the grid? But the good news is that even if we take these cost into consideration, space settlers will receive a considerably lesser energy bill than their terrestrial fellows.

The backside of SPPs is that the initial investment to build them, is quite high (though this would be compensated by the extreme long service life of the plants) and hence vulnerable to emerge of monopolists. After all once a space energy company has built a SPP, it can offer energy at relatively low prices, while the threshold of building a new plant will deter potential competitors.

Since such a monopoly is likely inevitable, it would be best if the governments of space settlements will take care of the production and maintenance of SPPs. This had two benefits: first all profits will flow to public treasury, and secondly price setting by the energy company is subject to democratic supervision.

Time zones and separation of functions

One of the major advantages of space colonization by the use of free space habitats instead of planetary “space” colonies, is the separation of functions. Gerard O’Neill already advocated that residence, agriculture and heavy industry should be separated from each other, i.e. that agriculture and heavy industry should not be done in the same structure where most residences are located.

In regard of the separation of agriculture and residency, O’Neill gives two main arguments. First, in a space settlement we have full control over both climate and day length. However, the climate preferred by most citizens is not necessarily the most optimal climate for the cultivation of crops. Second reason is pest control. If in an isolated space farm a pest will occur, it will be easy to deal with it by sterilizing the farm by increasing temperature above the limit life cannot survive. It’s quite obvious that we cannot do this, in a space habitat populated by humans.

For the separation of heavy industry and residency, the arguments are even more straightforward. Heavy industry impose a great danger to health and safety through its pollution and potential of explosion and similar disasters. By banning heavy industries from space habitats, we create a clean and save environment for people to live.

A second argument put forward by O’Neill is related to his proposal to divide space settlements over three time zones, with a 8-hour difference between each successive zone. Because heavy industry is located outside any space habitat, they can be in continuous operation. And if the industry hires shifts from different time zones, night work which is considered as unpleasant by most, will be avoided.

O’Neill imagined that space settlers employed in heavy industry, would commute each day between their home and their workplace. But technology has improved much since the mid 1970s, that nowadays much work can be automated and where people are still needed teleoperation will allow workers to run factories without leaving their space habitats or even their homes.

Besides the desire the avoid night work, there’s another reason for dividing space settlements among different time zones (which surprisingly is not mentioned by O’Neill). The principal power source of space settlements will be solar power. And since there’s no night in space (in space settlements night has to be created by covering the windows), space based solar power plants will run continuously and hence have a continuous output. But the demand for power is not continuous over the day, causing surpluses at some moments and shortages at others.

If we divide the population of three time zones with an 8-hour difference, the power demand curve will be flattened. This because if one settlement is facing a power shortage at some point, it’s likely that another settlement has a surplus since their population is experiencing another phase of the day.

Rockets

Too many people use the word efficiency when they actually mean efficacy. According to Wikipedia, efficiency is:

Efficiency in general, describes the extent to which time, effort or cost is well used for the intended task or purpose.

Whilst efficacy:

Efficacy is the capacity to produce an effect.

From this we can conclude that efficiency is a relative measure, and that efficacy is an absolute measure. The conflation of efficiency and efficacy is in particular frustrating (on-line) discussions regarding space colonization.

Quite obviously, space colonization requires the use of rockets, both to launch people and equipment from Earth, and to transport resources throughout the Solar System. However, it’s clear to anyone who studies rocketry even shallowly, that there is a wide variety of rocket types. And each different type of rocket has each own advantages and disadvantages.

Before we continue, we need to devote a few words to non-rocket space launch. Though there are many proposals for non-space launch systems, none of those have been tested in practice. The proponents of those systems often claim that their proposals will reduce the costs of space launch. This might be true in the long run, but at the short-term we need to take into account the cost of research and development of such systems.

And since it is uncertain whether these proposals will actually work, or when they will be available, it will be hard to find people who want to invest in such launch systems. On the other hand rockets are proven technology, which enables us to start with space colonization quite soon. This also makes it more likely for people to invest in space colonization.

In rocketry efficiency is indicated by the specific impulse I of a rocket, and the thrust T of the rocket. Basically thrust is the product of the specific impulse and the amount of mass exhausted by the rocket. By a given exhaust mass, a higher specific impulse would imply a higher thrust. Hence we should pick the rocket with the highest specific impulse from the catalogue.

Well, if we chose the rocket, we would pick an ion thruster. But is this also the best choice? Not entirely, though ion thrusters have a high specific impulse, they simultaneously have a very low flow of exhaust mass. So low actually, that their overall thrust is low. Because of this, ion thrusters aren’t used for launching spacecrafts from Earth, and is their use limited to deep space. Additionally because of their low thrust, ion thrusters are quite slow.

Although ion thrusters are usually advertised as very efficient, we have to realize that this claim is based on the specific impulse of this type of rockets. However, there are other ways of looking at the efficiency of a rocket. Especially, we should look at the ratio between the energy consumed by the ion thrusters, and the addition of kinetic energy.

Ion thrusters use electricity, generated either by Solar arrays or radio-isotope batteries, to ionize a propellent (usually xenon). The ionization of atoms takes a lot of energy, energy which does not increase the velocity of the spacecraft and hence kinetic energy. Consequently this would decrease the overall efficiency of an ion thruster.

The popularity of xenon as a propellent for ion thrusters, is due to the fact that xenon has a relatively low ionization energy (and hence increasing overall efficiency). However xenon is a rare noble gas, that is present in trace amounts in the Earth’s atmosphere. In order to obtain 1 liter of xenon one has to process 11.5 million liters of air. Hence it’s not hard to imagine that xenon is quite expensive.

For purely scientific space missions these disadvantages of ion thrusters are not that important. A scientific space mission might take several years, if not decades. And scientific mission do not have to return any profit. The humanization of space, however, demands enormous investments, which are only possible if there is a prospect of profit.

What alternative do we have for ion thrusters? An interesting possibility are so-called thermal rockets. Thermal rockets differ from chemical rockets, in that in the former a propellent is heated by an “external” source of energy, instead of a chemical reaction. There are several types of thermal rockets, the most important ones being nuclear and solar thermal rockets.

Nuclear thermal rockets use nuclear reactors to heat the propellent. Given the complexity of reactor technology, and additionally political concerns arising from the launch of nuclear fuels from Earth, we rule out this type of rocket for space colonization in the near future.

Solar thermal rockets (STRs), however, are much simpler. They use solar power to heat up the propellent, and instead of a reactor they need mirrors to concentrate solar heat upon the reactor. For ground launch, however, STRs will not work, so we still need another, most likely chemical rockets, to launch a STR from the ground. But once in space the STR will take over, and bring the spacecraft either to the Near Earth Asteroids or the Sun-Earth Lagrange points.

The main benefit of thermal rockets is that they can be “refueled” with propellent, also in space. Near Earth Objects contain substantial amounts of water which could be used as a propellent. Recall that spacecraft do not need to use their rockets all the time, only to reach the desired speed and to slow down at their destination.

Compared to ion thrusters thermal rockets have a smaller specific impulse, but they have a greater thrust. Consequently they have much shorter travel times than ion thrusters Further thermal rockets do not need to waste energy to ionize their propellent. And finally they don’t require expensive substances as xenon, instead they can use water or ammonia instead.

Japanese to investigate space based solar power

We found on The Independent the following article Japanese engineers plan to turn the Moon into a giant solar panel station. It’s clear that Japan is busy to look for alternative energy resources after the Fukushima disaster of 2011. This plan is a subset of so-called space based solar power or SBSP. The idea is to install solar panels on the Moon which will turn electricity into microwaves which are subsequently transmitted to Earth, and converted back to electricity.

We of Republic of Lagrangia aren’t convinced of the desirability and feasibility of SBSP for terrestrial purposes. We have discussed this topic earlier on this blog. And we have also written about Ocean Thermal Energy Conversion as a solution of Japan’s energy crisis. As an alternative we have discussed Solar Energy Islands as a method of producing energy at sea.

Developments in Solar energy technology

The whole idea of space colonization is founded on two facts: the abundance of extraterrestrial mineral resources and the availability of huge amounts of cheap Solar energy. There are basically two approaches to harvest Solar energy for space settlements: photovoltaic cells and solar-thermal power plants. The latter uses the heat from our Sun to heat a fluid, which is used to drive a turbine.

A challenge for photovoltaic arrays, is their efficiency. But there is exciting news from this field, according to The Science Daily, scientists from North Carolina State University have designed a method to increase solar array efficiency up to 45%. This would mean less Solar cells are needed to produce energy.

Solar Islands and Seasteading

Some time ago we wrote about the feasibility of Space based Solar power (SBSP) for terrestrial use, in that post we argued that SBSP is an unlikely candidate for meeting terrestrial energy needs both because of expected negative reactions from the public and the presence of suitable alternatives. One of those alternatives we mentioned were so-called solar islands.

A few years ago we wrote a sceptical article about seasteading. One of our arguments against seasteading was about their economic suitability. We argued that seasteads had poor economic prospects, with the consequence of a lack of interest from potential investors. However, solar islands might change this.

As we have argued in an earlier post, the ocean might be a good place for producing synthetic fuels. According to this site seawater contains 15.1% CO2 against 0.03% in air, thus CO2 can easily be extracted from seawater. Energy provided either by solar islands or ocean thermal conversion, can be used to produce hydrogen gas. From CO2 we can produce CO, and from CO and hydrogen we can make synthetic fuels. These fuels can be exported to other places.

The off-shore production of synthetic fuels might be a raison d’être of seasteads. However, it’s doubtful whether the political ideals associated with seasteading can be realised if seasteaders would specialize them in synthetic fuel production. It will depend on who is providing the funding for these projects, if corporations or governments are the primary investors in seasteads then the pursuit of liberty might be jeopardized.

Soon we will discuss the colonization of Antarctica.

Space based solar power?

Introduction

Since the 1970s advocates of space colonization have believed that building space power satellites and transporting space based solar power would be the raison d’être of space colonization. However we do not believe that space based solar power (SBSP) will have any future for terrestrial application.

Public acceptance

The first reason why SBSP will not be a core export product for Space Settlers, is public acceptance. A central part of all SBSP proposals is microwave transmission of power, although this wouldn’t be dangerous for people, a lot of people are afraid of anything related to radiation. An example, in the Netherlands there is broad concern about the health effects for people living in the neighbourhood of overhead power lines. Given that the Netherlands are a densely populated country, a few million people live within two kilometers from an over head power line. Although no scientific study has ever been able to provide conclusive evidence that living near an overhead power line is actually bad for your health, many people believe it is.

Some space advocates believe that we can “educate” the masses through tv shows like man-made marbles, I think this will be a dead-end. It is quite unlikely that it will be possible to educate the masses in this way. First of all, only a selected group of people actually watch this kind of tv shows, and these people are probably already convinced of stuff like SBSP. Secondly, the stronger one’s beliefs are the harder it will be to change these beliefs. Especially beliefs related to health issues are quite strong and therefore difficult to change.

Changing public opinion is difficult and we believe that space advocacy groups shouldn’t waste their time and funding to attempt to eradicate radiophobia.

Necessity

Another issue is whether SBSP is actually necessary. Back in the 1970s photovoltaic technology was in its infancy, solar arrays had low efficiencies and were quite expensive. It was in this time that people like Peter Glasser and Gerard O’Neill were proposing to solve the global energy problem (the 1970s were the age of the oil crises). However, since then both the efficiency of solar cells has been improved and their production costs have been decreased.

In order to provide the world with sufficient energy, we need actually a surprisingly small area: some 62,500 square kilometers or about 2.63 percent of the surface area of Algeria. Of course it will be bad idea to concentrate all of the world’s power plants in the Sahara, but we could spread the solar power plant about the world. In the USA, we could cover a great part of Nevada, Arizona and New Mexico with solar arrays, Western Australia is another place suitable for solar power plants, in Latin America Chile’s Atacama desert will be an attractive site.

An exciting development are the so-called solar islands designed by a Swiss company. Oceans cover two-thirds of the surface of the earth, and are exposed to a large portion or our intake of solar power. So it is a logical idea to harvest solar power at sea.

In a previous post we have discussed the future of Japan’s energy supply, in that post I mentioned the possibility of using synthetic fuels:

One way to do this, is by producing hydrogen through electrolysis. But hydrogen has some severe drawbacks. First the very low density of hydrogen gas requires either storage under high pressure or liquefaction to very low temperatures,  which might cost more energy than can be delivered. The storage problem of hydrogen is one of the greatest obstacles for the transition to a hydrogen economy.

An alternative for hydrogen would be the production of synthetic fuels through the Fischer-Tropsch process from hydrogen and carbon monoxide gas. CO gas can be obtained by electrolysis of CO2 from the atmosphere or sea water. There is also current research of creating fuels directly from water and CO2. Both methods will produce hydrocarbons, like methane gas [main component of natural gas], or alcohols like methanol. These synthetic fuels can easily be transported and because the synthesized fuels are chemically similar to “mineral” gasoline, they do not suffer from the transition paradox. This is the problem that no one will buy hydrogen cars if there are no hydrogen gas station, but no one will build hydrogen gas station if no one drives hydrogen cars.

There is no reason why the production of synthetic fuels couldn’t be done on solar islands.

For more information about solar islands see:

http://solar-islands.com/

Conclusion

It is hard to imagine that Space Based Solar Power will ever been accepted by the broad public, due to concerns about radiation. Any effort to change this attitude is probably wasted energy. Further it is questionable whether SBSP is actually a necessary part of the World’s future energy supply.

On the economy of Space Colonies

This post was originally pubished on blogspot.com on January 19, 2012

In this article, I’ll restrict myself to space colonies in Near Earth space.

Since space colonization cost a huge amount of money, it is necessary that the first space colonies are making profits. For the purpose of this article I’ll assume that space colonies will be financed primarily be issuing corporate bonds at international stock markets. Continue reading On the economy of Space Colonies