In the short term, solar energy is the simplest way to obtain energy on Mars, which is why we use solar panels on rovers such as Pathfinder, Spirit and Opportunity.
Because Mars is farther from the Sun it receives less incident solar energy per square metre. It’s also smaller than Earth, with about half the radius, which means it also receives less total solar energy.
Mars has a fairly elliptical orbit, which means the distance between Mars and the Sun varies considerably, between about 207 and 249Gm (gigametres, or millions of kilometres). Therefore the intensity of solar energy reaching Mars varies as much as 20% during a Martian year. Earth’s orbit is much more circular, and we don’t see as much variation in solar intensity. The distance between Earth and the Sun varies between about 147 and 152Gm.
We can calculate a ballpark comparison between the amount of solar energy reaching Mars and Earth using average distances:
Average distance between Sun and Earth = 150Gm
Average distance between Sun and Mars = 228Gm
The intensity of solar energy decreases with the square of the distance, because it’s spread out over area. Therefore:
Solar energy at Earth: Ee = k/de2
Solar energy at Earth: Em = k/dm2
where k is some constant of proportionality.
To compare: Em/Ee = de2/dm2 = 1502/2282 = 0.43 = 43%
This calculation suggests that the amount of solar energy per square metre on Mars is only about 43% of that on Earth. In reality, there’s very little cloud cover on Mars and the atmosphere is much thinner than Earth’s, which tends to boost that figure. On the other hand, there’s also a lot of suspended dust in the Martian atmosphere, which tends to reduce it. Overall, the intensity of incident solar energy is about half Earth’s.
This lower level of solar energy on Mars is not as serious a problem as it might first seem. Solar energy is currently experiencing a revolution on Earth – the technology is rapidly advancing, and the price is also rapidly decreasing. The solar energy technology currently being developed now will be available by the time we’re sending humans to Mars. We’ll be significantly better at collecting solar energy in the time frame of human settlement of Mars.
The primary downside of solar energy on a planetary surface is that it’s intermittent (that is, unless the planet is tidally locked to a star). Solar energy can only be collected from a point on the surface of the planet when the Sun is visible from that point; in other words, during the day time. However, methods for storing solar energy are also advancing rapidly.
It’s well-known that Mars is windy. In fact, it’s this windiness that kept the Mars Exploration Rovers, Spirit and Opportunity, rolling for as long as they did, because the wind kept blowing dust off the solar panels. Hopefully the same thing will happen to solar panels at a Mars base, thereby reducing the time and energy required for maintenance.
Wind energy has also experienced a revolution on Earth in recent years, with great improvements in turbine technology and efficiency, and considerable reductions in price, to the point where wind has achieved grid parity or better in many regions. Wind is now one of the most important energy sources in north-west Europe and Scandinavia.
Even though Mars is windy, leveraging wind energy on Mars as a major power source may be difficult. This is because the air pressure is very low, less than 1% of Earth’s, which means that even if the wind is moving fast the amount of force it can generate is very small. Therefore it would not be able to force high turbine speeds or generate much electricity. Nonetheless, Mars’ low gravity could help out here, enabling construction of very tall wind turbines with long blades, which will be able to effectively harness Martian wind.
Another factor is that the air on Mars is full of very fine, suspended dust, which could get into turbine bearings and cause them to wear down. This problem is likely to be solvable with good engineering design, but that may not happen until we have a permanent human presence on Mars.
It has not yet been established conclusively whether or not Mars contains hyperthermal zones (“hot spots”) in the shallow crust that could be utilised for energy. On Earth we refer to this as geothermal energy, however, the word “geothermal” becomes “areothermal” on Mars because we replace the prefix “geo”, which refers to Earth, with the prefix “areo”, which refers to Mars. (Other examples: geology/areology, geography/areography, geosynchronous/areosynchronous, etc.)
On Earth, geothermal energy holds great promise as being the only form of sustainable energy considered capable of providing baseline power. Solar and wind energy are intermittent, and therefore require an energy storage solution such as rechargeable batteries. However, these are generally expensive, inefficient, and not very environmentally friendly.
A reliable source of areothermal energy on Mars will be of exceptional value, possibly superior to all other energy options currently under consideration. Areothermal energy provides a continuous abundant supply of energy, like fission, but without the risk and waste issues. It does not require storage solutions like solar or wind, does not to be launched into space like SSP (Space Solar Power), and can also be used directly for settlement heating or as a source of hot water. If it’s eventually shown that areothermal energy is only available in a few places, these places may well be settled first. Settlements close to both an areothermal energy source and significant water and/or mineral resources will be at a significant advantage.
One of the challenges associated with geothermal energy is efficiently distributing electricity, as geothermal power plants are often geographically distant from users, and distributing electricity through copper wires introduces losses proportional to distance (compare with traditional coal-fired power stations, which can be located close to, or in, cities). However, as with solar and wind, significant advancements have been made in recent years in geothermal technology, and it’s now possible to access geothermal energy in more places. This increases the amount of geothermal energy is available for use, while also reducing distances between sources and consumers.
The prevailing view is that Mars has cooled to the point where it’s effectively areologically inactive. However, research by the planetary engineering expert Martin Fogg (see: The Utility of Geothermal Energy on Mars, 1996) shows that regions of Mars with very low crater counts, which have been recently resurfaced by magmatism, may be indicative of regions of above-average heat flow on Mars and may therefore potentially offer sources of areothermal energy. According to his research, regions with the highest probability of offering areothermal energy are almost completely contained in one large area of Mars:
In fact they are almost exclusively located in the planet’s northwest quadrant, from longitude 220° in Elysium eastward to longitude 20° in Acidalia Plantia and north of 15°S and south of 50°N. Such is the clustering of such outcrops in adjacent geographic areas that one can surmise the existence of a distinct province of recent anomalous heat flow on Mars, including Elysium, Amazonis Planitia, Arcadia Planitia and Tharsis.
The challenge for Mars, of course, is that accessing geothermal energy requires deep drilling, a capability we will probably not have on Mars until we have permanent settlements and some sort of industrial base.
Such are the advantages of areothermal energy, if it is shown to be practical for Mars, and if this area is particularly rich in this resource, it may be settled earlier than other regions of Mars. As Fogg writes:
Some of the first permanent Martian communities could spring up around such geothermal oases. By the latter half of the next century, the spa towns of Mars might even be known for offering the best of high life on the high frontier.
It seems very likely that at least some early-stage H2M missions will make use of nuclear fission energy. Almost all Mars mission architectures specify the need for a small nuclear reactor to power the ISSP (In Situ Propellant Production) equipment in an ERV (Earth Return Vehicle) or MAV (Mars Ascent Vehicle), and to provide power and heat to the hab. Modern nuclear reactors are able to produce energy for decades without maintenance, and can provide an abundant supply of energy. Unlike solar, nuclear energy is not subject to diurnal variations and is not affected by dust or weather.
In the past, I have been very opposed to the use of nuclear energy on Mars as well as Earth. My concern was that a Chernobyl-like steam explosion combined with a planet-wide dust storm or even normal Martian winds, would distribute radioactive dust across the whole planet. As you can imagine, this would be disastrous for present and future settlements over almost the entire planet and would significantly compromise scientific studies of Mars, in particular the search for extant life, and could also seriously hamper settlement efforts. I felt that if we allowed even just one nuclear reactor on Mars, it would set a precedent that would lead to hundreds or thousands. Without sufficient qualified people or an industrial infrastructure, it would simply be a matter of time before an accident occurred. In addition, we would be creating a nuclear waste problem. Nuclear waste is hard to manage and dispose of on Earth. On Mars, waste management would be even more difficult, and we may risk ruining the Martian environment before human settlement even gets into full swing.
However, I’ve since learned that this opposition was born of ignorance, that not all nuclear energy is the same, and that appropriate use of nuclear energy is an enabling factor that makes H2M far more possible. The described problems may be characteristic of Generation I and II nuclear reactors (almost all reactors currently in use are Gen II), however, in terms of development we are now up to Generation IV, which encompasses a variety of reactor types that are considerably safer, cheaper and better. The one particular type that I believe holds the most promise for both Earth and Mars is the LFTR (Liquid Fluoride Thorium Reactor), which is fuelled with thorium.
LFTR’s offer significant advantages over current uranium reactors:
- Thorium is a much more common element than uranium, and is abundant on Earth, the Moon and Mars. It’s therefore cheaper.
- LFTR’s can also be made smaller, which is useful for space applications as we want to keep the mass of hardware as low as possible.
- LFTR’s can’t melt down. In a Gen II reactor water is used as a coolant, so if the reactor is damaged and water cannot be supplied, they can overheat catastrophically and melt down. However, if power is lost to a LFTR, the liquid fluoride salt drains away and the reaction stops.
- Gen II uranium reactors must operate at very high pressures, up to 700 atmospheres. However, LFTR’s operate at normal pressures, so there’s no possibility of a Chernobyl-like steam explosion.
- LFTR’s produce very little waste, because they burn almost all of their fuel. In fact, they can even use existing nuclear waste as fuel. That’s right – those pesky stockpiles of nuclear “waste” on Earth could become fuel for the next generation of nuclear reactors. Thus we have a massive, easily accessible energy source, plus the nuclear waste problem becomes solved. Obviously this feature is more important on Earth than it will be on Mars.
LFTR’s are not the only type of nuclear technology currently being developed that holds significant promise. Another is the TWR (Travelling Wave Reactor), which can be completely sealed and operate for perhaps half a century or more without maintenance. However, it seems that LFTR’s offer the most promise, especially for Mars. Both of these reactors are still in development, and not likely to be deployed on Earth for another 2 decades. However, that may well line up with our settlement plans.
Some type of small, self-contained reactors will almost certainly be used on Mars from the beginning. As to what specific reactor type this will be, that remains to be seen. But Mars has plenty of nuclear fuel, and nuclear fission technology is becoming much better.