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, nuclear or geothermal energy on Mars for a growing settlement of a few hundred to a few thousand settlers.

Solar energy

Design

Solar power is more than just solar panels. Due to the interruptible nature of solar, short term and long term energy storage is required to provide for all the settlement energy needs. In the present cost study, some energy is presumed stored in batteries for short term and methane/oxygen form for long term, with gensets used to produce power during dust storms. The distribution and power transformation systems are excluded, as they are presumed similar across the study. Thermal solar is also excluded, and rather considered as a potential source for specific processes, rather than distributed energy.

Solar panels

Two types of solar arrays are possible, rigid high efficiency panels and flexible film. Although less efficient, flexible film is much lighter.

Rigid solar panels

Rigid solar panel array built on Earth should have about the following characteristics:

Solar array characteristics

Characterisitic	Value	References
Efficiency-peformance	30% - 8,3 We/kg (daily average)	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 0,2 kg/m2 for batteries and 0,3 kg/m2 for other 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 and an allocation for the rest of the required equipment.

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.

Flexible solar film

Flexible solar film may be available at 100 g/m2 for 10% efficiency. Keeping the same power ratios would put batteries at 0,07 kg/m2 and ancillary equipment at 0,1 kg/m2 for a total of 0,27 kg/m2

Either solution would be transported by SpaceX Starship with other cargo and unfolded on Mars semi-autonomously. For the Cost of Transportation to Mars, we can define a range: From the cost proposed by SpaceX for their transportation system, 140 $kg to Mars to a more conservative 500$ per kg(add reference).

Solar panel cost on Mars

For rigid panels, the costs will vary between:

• 800$/m2 + 3.5 kg/m2 x 500$/kg = 2550 $/m2
• 800$/m2 + 3.5 kg/m2 x 150$/kg = 1325 $/m2 of rigid solar panel on Mars. Transportation is by far the largest part of the cost at the higher transport cost.
• Note that 30% is not current but a projection. 22-24% would be closer to the performance of current cells at that price level.

For flexible rolls, the costs will vary between:

• 300$/m2 + 0.27 kg/m2 x 500$/kg = 585 $/m2
• 300$/m2 + 0.27 kg/m2 x 150$/kg = 230 $/m2 of flexible solar panel on Mars. Transportation for the last case becomes as low as 5% of the cost per m2.

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, ideally with automated equipment. If cleaned less often by hand the surface dust factor may be significantly higher, and safety concern might apply. Dust typically reduces solar output by 0.2 % per Sol, see Dust for more information.

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 rigid solar panel would produce about 2,4 MJ x 365 x 0,95 /1000 = 0,83 GJ/m2.

The efficiency of flexible solar film is lower, and sun tracking is not possible, so the energy production will be lower, at about 0,26 GJ/m2.

Short term power

Batteries will be required for bridging between day and night. As the main power loads, food and fuel production, would likely be shut off during the night for a solar based settlement, the actual demand would drop to between 5 and 10% of the daily production. If a 1m2 solar array produces 2,4 MJ per day, then lithium ion batteries storing 1 MJ/kg would require between 0,12 (5%) and 0,24 (10%) kg of batteries per m2 of panel.

For flexible solar panels these values are divided by about three.

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. Dust storms can block unto 95% of the sun's light (tho 30 to 60% reductions are more typical). Some dust storms, have lasted for months. (See Dust Storms for more details.) Rick.

* * *

Because of dust storms, a back up system will be required and the cost of this system must be factored into the cost of solar. A 3500 KW genset on Earth masses about 10 000 kg.

As it would make sense to shut down fuel and food production during storms, the demand during a storm would drop to between 5-10% of the average demand. The mass ratio of the genset is about 350 W/kg, or 3.5 times less than the mass ratio of solar at 100 W/kg. At 10% of the peak demand, the genset would then represent about 3% of the mass of solar panels, so an allowance of 10 grams per m2 of solar panel should be added to the mass of the solar powered system. This fit's into the 300g allocation already provided.

For the first few decades of a Martian settlement, the fuel will be stored in the tanks of the cargo vehicles used to carry the settlement equipment, so no additional mass is required to account for methane and oxygen storage.

If demand during a dust storm can be lowered to 4-5%, as might be possible without fuel and food production, then there will be no need for backup storage in most cases, as the solar panels will be able to supply the required energy.

^{DISCUSSION: This argument seems to assume that long duration dust storms never block more than 10% of the solar energy, which is wrong.}

Solar power overall cost

The prices below have 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.

Rigid solar panels

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

Flexible solar film

With an estimated life time of 20 years the total energy produced would be 20 x 0,26 = 5,2 GJ/m2. When divided by the cost of 230$ the bare cost of the energy would be 44 $/GJ. Majoring in financing, profit and uncertainties, we could expect a multiplying factor of 1.5, for a final cost estimate of 66 $/GJ for Martian solar power. In other units this is 0,07$/MJ, or $ per 0,25 $/kWh. This would be the minimum likely cost, with the lowest transportation cost.

So the total cost might be somewhere between 66 $/GJ to 310 $/GJ. Flexible solar film offers the bet value.

These is not necessarily the selling prices, 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.

Nuclear energy

Design

The MINERAL reactor is proposed for this cost estimate. Nuclear systems scale very well. As they follow a cube law, doubling any dimension creates an order of magnitude of increase in capabilities. The MINERAL reactor produces 2 MW of power for a total mass of 53 tonnes .

Characteristic	Value	References
Power	2 MW electric 5,8 MW thermal loss	Solid core, CO2 Brayton cycle power production. six 400m2 radiators.
Efficiency	25,5%
Mass of reactor	37 We/kg, 27 kg/kW

Cost of a nuclear reactor

This is the hardest metric to establish. The cost of new nuclear reactors is between 6-9 billion$ for 1100 MW on Earth(reference). So from 6 to 9 million$ per MW. This might put the construction cost somewhere between 12 and 18 million$ for a Mineral type reactor. However, a certain amount of financing is required to develop the reactor. The cost of preparing special nuclear fuel may also be significative. As a fist order approximation we might suppose 30 million dollars per reactor for a few dozen reactors. However, this is probably optimistic for any early nuclear reactor.

Nuclear power station cost on Mars

• Using 500$ per kg for transportation of 53 500 kg and thirty million$ for construction, the bare cost is about 56 000 000$.
• Using 140$ per kg for transportation of 53 500 kg and thirty million$ for construction, the bare cost is about 37 000 000$.

Nuclear energy production

The reactor, operating at 98% availability for 20 years will produce 2 000 000J x 20 x 365 x 24 x3 600 x0,98 = 1 250 000 GJ. When divided by the cost of 56 000 000$ the bare cost would be about 45 $/GJ, and 30$ per GJ for the lower transportation cost. If we have the same multiplication factor of 1,5 then the final cost would be 45 $/GJ to 70 $/GJ. This overlaps the cost of solar.

Alternative nuclear reactor designs

Nuclear reactor designs for Mars based on the Kilopower 10 kW nuclear reactor are probably insufficient for any sizable settlement. Since their mass fraction is only 7 We/kg (143 kg/kW) rather than 37 We/kg (27 kg/kW), all other things being equal they would not be competitive with solar power.

Future modular reactors (which are designed to be mass produced and can be shipped in a single shipping container) would be much cheaper.

Molten salt reactors such as LFTR could be largely built with local materials. It is possible that the Li6 or the nickel alloys for the plumbing would be sent from Earth for early settlements. Note that several companies are developing these, and China is building a commercial reactor to be completed in 2029.

Geothermal energy

Mars has had volcanic eruptions in the last 10 million years (the present in geological terms), and there is evidence that there may be active vulcanism now. Hot rocks kilometers before the surface take hundreds of millions of years to lose their heat, so there is every reason to suspect that regions of Mars could have useful amounts of geothermal heat within drilling distance.

Geothermal energy is unsuitable for exploration bases, or early colonies, but once Mars has local industry sufficient to make pumps, drill bits, pipes, condensers, etc. Geothermal power becomes attractive. In addition to providing power, it can likely bring up hot, liquid water, a valuable commodity in its own right.

Hot water brought to the surface vacuum will flash to steam, making a very efficient turbine possible.

However, the temperature of the rocks, the possibility of liquid water, the depth to drill, the cost of local materials, the value of liquid water, the cost of electricity and heat, are all not known.

Therefore, for this study, the cost of geothermal is not calculated.

Proposed cost

Compared to a cost of 20 $/GW (0,06$/kWh) on Earth, the cost of electrical energy on Mars should be about three to five times higher, roughly rounded to a range 60$/GJ (0,18 $/kWh) to 100$/GJ (0,3 $/kWh). The cost of thermal energy would be about one tenth of that value, with a very high availability from nuclear power, and requiring some form of thermal energy storage for solar. Much of the range is a result of the large uncertainty on transportation costs.

Discussion

Nuclear vs solar energy is an endless source of discussion and contention. The aim of this section should be to establish a reasonable cost of energy on Mars to be able to evaluate projects, and to offer a basis of comparison with Earth. Unless a technology is clearly better by an order of magnitude, the costs should be similar and we should not try to choose the technology here.

• If the solar cells used are lower efficiency than the 30% and 10% used in this example, the advantage to nuclear is higher. Lowering the system mass has more impact than increasing efficiency. (Note 10% cells are no longer produced on Earth, but early Martian cells may be lower efficiency.)
• If solar panel efficiencies are higher than 30% the impact is not sufficient to offset the advantages of nuclear power. However, more efficient solar film, or less expensive solar film, eventually wins out, but the advantage gets limited by the cost of storage systems.
• This article assumes that dust is cleaned off solar cells regularly (never more than 10% loss of power). This is a huge effort for a large field of solar cells, and the dangers of many trips onto the surface is a concern. Low efficiency, locally made cells, require more space and increase this disadvantage.
• The higher cosmic ray flux will slightly lower the lifetime of solar cells on Mars.
• The very high thermal stress on Mars may increase maintenance costs for large fields of solar panels. Doing repairs outside is difficult and always somewhat dangerous, but perhaps we can assume that these are rare enough not to matter.
• The discussion above seems to assume that there are not months long dust storms with 30 to 60% reduction in power.
• Solar power using In Situ production of components could be competitive with nuclear in certain long term cases as the transportation costs would be reduced. In particular, cheap local batteries would be very advantageous to solar. See Flow battery.
• Transportation costs may be lower or higher and represent a large fraction of the costs of the power systems.
• Based solely on surface quantities of Thorium, radioactive elements may be rarer on Mars than on Earth. This is discussed in detail in Radioactive Rarity on Mars and could make early thorium mining more difficult. However, even low grade ore will provide plenty of thorium once wide spread mining is established. Also note that thorium does not require enrichment.
• If we use CANDU reactors, they can use natural uranium, so no enrichment is needed. Note that deuterium is 5 times more common on Mars, so this reactor will be cheaper on Mars.
• The new Supercritical CO2 turbines are 10 times less massive, and improve the efficiency of power extraction by 10%. This makes nuclear more attractive.
• If reactors can be refueled with minimum refurbishment this reduces their cost further. Note that molten salt reactors can be continuously refuelled.
• The NASA horizon for nuclear is 10 years, but the calculation uses 20 years, a number often used for Earth based 'nuclear batteries'.
• 20 years of operation without a major overhaul may be optimistic for nuclear. At ten years, the nuclear advantage goes away.
• Maintenance should be included in the 1.5 surcharge proposed in the text, but has not been checked in detail.

.... Future technologies will surely change the parameters discussed above.

.... If we add development costs for nuclear power, we can make it uneconomical.

• If no market exists on Earth for small nuclear power, or if all development costs are included, nuclear would be much less interesting and would cost more than solar power.
• The development cost of a 40 kW nuclear reactor for Artemis has been floated at 1 billion$. This would make any nuclear reactor uncompetitive for decades.
• The study for the Prometheus reactor cost 400 m$ and never produced a prototype. Just attributing this cost to less than a dozen early nuclear reactors would make them uneconomical.
• Solar cost for panels keep going down, but significant advances in power/mass would be required to make solar competitive with nuclear on Mars if a reactor such as the MINERAL is developed and the developments costs are omitted.

^{DISCUSSION: The author above suggests that future advances will make solar cheaper, so shall we assume that the Mars colony will solely pay the cost of such improvements? If we assume we are using off the shelf solar technology, then we should assume we are using off the shelf nuclear tech as well. Detailed calculations on the costs and tradeoffs of future systems, when we have no idea of the transportation costs, and have no idea of what local industry can produce, seem futile. However, I suggest that this page remains, as the structure of the argument may be of use to people. Rick}

References

• Nuclear reactor development cost. https://spacenews.com/nasa-plans-for-lunar-fission-power-systems-face-fiscal-challenges/