Cost of energy on Mars

Solar array with a Mars settlement in the background. Just one possibility out of a large spectrum of choices, from flexible film unrolled directly on the ground to high powered nuclear reactors.

The cost of energy on Mars is one of the prime parameters required to analyse martian settlement scenarios. To go beyond generalizations and actually evaluate one scenario against another, the cost of energy and the cost of transportation to and from Mars need to be known, or at least estimated to compare on a common basis.

There can be no absolute answer to this question, as the cost of energy will vary depending on the source and the level of development of the colony. If all the energy producing equipment comes from Earth, the cost will be higher than if it is produced in-situ. As the settlement grows larger, economies of scale will come into play to reduce energy costs. As automation increases, and productivity increases accordingly, the cost of energy may go down significantly. Self replication of production equipment may eventually bring down the cost of energy to very small values. This will allow the realization of projects using energy on a scale that will be, literally, cosmic.

But before such a grand time comes, we can estimate a preliminary value for the cost of solar energy on Mars for a growing settlement of a few hundred to a few thousand settlers.

Solar energy

Design

For this estimation we will use a solar panel array built on Earth with the following characteristics:

Solar array characteristics

Characterisitic	Value	References
Efficiency	30%	This would require fairly expensive multijunction production cells. Large volumes of production would keep the cost low.
Fill factor	80%	This is a conventional average for good quality cells.
Mass	3,5 kg/m2	This is the NASA 2018 BIG challenge target of 3 kg/m2, plus 0,5 kg/m2 for ancillary equipment. This corresponds to about 30 We/kg.
Cost on Earth	800 $/m2	An estimate based on an average cost of 500$/m2 for conventional panels on Earth

Transported by SpaceX Starship with other cargo and unfolded on Mars semi-autonomously. For the Cost of Transportation to Mars, we could simply use the cost proposed by SpaceX for their transportation system, 140 $kg to Mars. However, 500$ per kg to Mars may be a reasonable conservative choice, in particular if we apply it to all technologies.

The design is a tracking array. This allows for more energy production with the same peak power characteristics. The added complexity is estimated to be a small cost compared to the transportation costs from Earth. The moving mechanism would be fitted with elements allowing for a self cleaning phase for dust removal. The panels are mounted on a single rotating and extending boom, that allows for tight packing at transportation and can be unfolded using traction from a vehicle that can also serve to transport and set down the array, eliminating the need and mass of self extension mechanisms.

Solar panel cost on Mars

The cost would be 800$/m2 + 3.5 kg/m2 x 500$/kg = 2550 $/m2 of solar panel on Mars. Transportation is by far the largest part of the cost.

Note that 30% is not current but a projection. 22-24% would be closer to the performance of current cells.

Solar panel energy production

The solar constant is estimated at 590 W/m2 over the whole year. Atmospheric dust losses are set at 20%. An additional surface dust factor of 10% is included. Note that such a low surface dust factor assumes that the solar panels will be regularly cleaned, requiring hard physical work over a large area in vacuum suits. If cleaned less often, (out of safety concerns for example), the surface dust factor may be significantly higher.

Under these assumptions, the solar illumination is lowered to 413 W/m2. Using solar tracking can provide peak power for about 7 hours for per day, the available energy per day is calculated as 413 W/m2 x 7h x 3600 s/h = 10 MJ.

The actual energy production should be 10 MJ x 30% x 80% = 2,4 MJ per day.

The installed power, based on the 7 hours of peak operation, should be 413 W/m2 x 30% x 80% = 99 W/m2. The same cells on Earth would have a power of about 99 x 1300/413 = 300 W/m2. The mass ratio metric is then 300 W/m2 / 3 kg/m2 = 100 W/kg. this seems safely conservative compared to recent (2017) NASA projections

The availability of the solar panels is estimated at 95%, to account for repairs, tracking failures and other problems.

So every year a m2 of panel would produce about 2,4 MJ x 365 x 0,95 /1000 = 0,83 GJ/m2.

Note that solar power is intermittent. Either massive batteries, or a base load power system will be required, which is not included in this analysis.

With an estimated life time of 20 years the total energy produced would be 20 x 0,83 = 16,6 GJ/m2. When divided by the cost of 2 550$ the bare cost of the energy would be 153 $/GJ. Majoring in financing, profit and uncertainties, we could expect a multiplying factor of 1.5, for a final cost estimate of 230 $/GJ for martian solar power. In other units this is 0,23 $/MJ, or 0,83$ per kWh. This is a bit more than twice the cost of electricity on the Islands of Hawaii. For 22% efficient cells, the cost might be increased to 310 $/GJ

This is not necessarily the selling price, as there might be taxes added or other costs, such as the distribution system costs. The price for energy might also be modulated; for example, the cost of night time energy, requiring the installation of energy storage systems, might be significantly higher. Or the cost of these storage systems could be factored into the base cost, if the settlement determined this was a useful policy.

This price also has a very broad range of uncertainty, as the cost of solar has been going down steadily, and the cost of SpaceX to Mars is pretty speculative.

Backup power

Due to planet wide Martian dust storms, which can last months, there are periods when solar power may be reduced significantly, or just not be available at all. A back up system will probably be required and the cost of this system should be factored into the cost of solar. This will tend to change the balance of costs in favour of nuclear, or geothermal energy.

If solar is not the primary power source, it becomes more attractive. A Martian colony is likely to be power starved. Some industrial processes could be scheduled for periods of peak sun. For example, a solar furnace could be loaded at night, and in the day time fire ceramics. Solar heat could be moved into masses with high thermal inertia, which would keep the colony warm at night. Growing plants require gigantic amounts of light, and with an approximately 24 hour day, solar is suitable for crops. A fair bit of water is frozen in the subsurface soil of Mars, and solar power could heat patches of ground to release water vapour to be captured and condensed.

Nuclear energy

Design

Nuclear reactor designs for Mars might be based on the Kilopower 10 kW nuclear reactor. It uses Highly Enriched Uranium(HEU), presumably at 20% concentration.

Characteristic	Value	References
Power	10 kW electric 43 kW thermal	Solid core, sodium heat pipe cooled reactor. Stirling engines.
Efficiency	23%
Mass of reactor	7 We / kg	A 10 kWe reactor would include 43.7 kg of 235U and mass about 1430 kg.
Cost on Earth	400 000$	5500 $/kg of HEU (240 000$) 100$ per kg for fabrication of the rest (140 000$).

Nuclear power station cost on Mars

Using 500$ per kg for transportation of 1430 kg and 400 000$ for construction, the cost is about 1 100 000$.

Nuclear energy production

The reactor, operating at 95% availability for 10 years will produce 10 000J x 10 x 365 x 24 x3 600 x0,95 = 3 e12J or 3000 GJ. (If we assume it lasts for 50 years, this value is quintupled.)

When divided by the cost of 1 100 000$ the bare cost would be about 300 $/GJ. If we have the same multiplication factor of 1,5 then the final cost would be 500 $/GJ. this is about 2 times more expensive than solar. If the nuclear reactor could be refurbished and refueled for another ten years, for about 500 x 43,7 + 240 000 = 260 000$ then the cost would be 1 360 000 / 3000 = 226$/GJ x 1,5 = 339$/GJ or about the cost of solar. If the solar cells used are lower efficiency than the 30% used in this example, the two costs, solar and nuclear, will be very similar.

Larger nuclear reactors would probably be more mass efficient. The energy required for in-situ production of enriched uranium is likely to be prohibitive compared to transporting the fuel from Earth. Mars is known to be low in nuclear materials, and the existence of enrichment mechanisms during the earlier periods of Mars' history are unknown. (For an alternate view, see below.) So it is impossible at this time to know if uranium ores would be available.

Note that new reactor types may be less expensive. Molten salt reactors do not require massive containment domes, are much smaller, work at standard pressure, and are considerably more efficient than the light water pressurized reactors designed 70 years ago. If they use thorium fuel, the initial load of fuel salt must come from Earth, but it can be refuelled with metallic thorium which can be reduced from ores with 18th century technology.

The following link discusses a modern reactor which was designed specifically for Martian conditions.

The assertion that Mars is extremely low in radioactive should be discussed. Radioactive ores on Earth are usually found in igneous rocks, and Mars has had a similar history of vulcanism, indeed, Mars has more igneous rocks exposed on the surface than Earth. Thorium and radioactive potassium has been found by the Odyssey orbiter, but it does not detect ore bodies, but dust and surface soils to a maximum of 1 meter deep. (If Odyssey was orbiting Earth, it would not find thorium ores, but rather detect the low levels of Thorium found in soil everywhere.) So I do not consider the low levels of potassium/thorium found by Odyssey to be strong evidence that Mars lacks radioactive ores.

Note that on Earth thorium is about 3 times rarer than lead, and uranium 238 is about ten times rarer than lead. (U235 is ~1400 times rarer tho.) Even if these elements were twice as rare on Mars as on Earth, (which I think is unlikely as there is no reason that the such elements should be discriminated against during planetary formation), there would still be vast amounts of these metals on Mars.

--- This paper discusses a large scale natural paleo-reactor in the Mare Acidalium region of Mars.

--- Analysis suggests that radioactive elements must be more common on Mars than shown in Martian meteorites (shergottite meteorites) which have fallen to Earth.

--- Paper saying that the Th / U on Mars is higher than in typical meteorites, and discusses natural concentrations of radioactives on Mars.

--- Evidence that the bulk of the Martian crust is richer in radioactive materials than the shergottite meteorites.

--- Yet another study saying that the shergottite meteorites are not representative of Mars.

An argument that Mars may be have slightly less radioactive elements Uranium / Thorium / Potassium (U/Th/K) than Earth is suggested by the fact that Mars seems to have better mixed the core materials (Iron and the metals that easily dissolve in iron) with the mantle & crust materials (the silicon loving elements). The radioactive elements U/Th/K are silicon loving elements and a greater proportion of iron (and other core materials) in the crust means that they would be proportionally rarer. This is not to say that there would not be igneous ores, but simply that the proportion in the crust would be lower, and their proportion in Mars' core would be greater.