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

For this estimation we will use a solar panel array built on Earth with 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 300 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

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, ideally with automated equipment. If cleaned less often by hand the surface dust factor may be significantly higher, and safety concern might apply.

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.

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. Some dust storms (not this opaque), have lasted for months. (See Dust Storms for more details.) A back up system will be required and the cost of this system must be factored into the cost of solar. Batteries will also 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.

Solar power overall cost

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.

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	-Cost on Earth:|This is the hardest metric to establish. Supposing the entire development cost is excluded and supported by NASA, 200$ per kg for fabrication of the rest would yield about 10 000 000$ in cost.

Nuclear power station cost on Mars

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

Nuclear energy production

The reactor, operating at 98% availability for 10 years will produce 2 000 000J x 10 x 365 x 24 x3 600 x0,98 = 625 000 GJ. When divided by the cost of 37 500 000$ the bare cost would be about 60 $/GJ. If we have the same multiplication factor of 1,5 then the final cost would be 90 $/GJ. this is about one third of the cost of solar.

Alternative nuclear reactor

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 rather than 37 We/kg, all other things being equal they would not be competitive with solar power.

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 kilometres 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

The cost of electrical energy on Mars should be about ten times higher than on Earth, roughly rounded to 300$/GJ or 1 $/kWh for solar, and 100$/GJ or 0,30 $/kWh for nuclear.

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.

• 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 have long term implications but do not influence this model.
• If the solar cells used are lower efficiency than the 30% used in this example, the advantage to nuclear is even higher.
• Solar power would require In Situ production of components to, perhaps, be competitive with nuclear, or cheaper solar panels.
• Transportation costs may be lower or higher and represent a large fraction of the costs of the power systems.
• If solar panel efficiencies are higher than 30% the impact is not sufficient to offset the advantages of nuclear power.
• Future technologies may change the parameters.
• If reactors can be refueled with minimum refurbishment this reduces their cost even further.
• If no market exists on Earth for small nuclear power, or if all development costs are included, nuclear would be less interesting.
• Solar cost for panels keep going down, but significant advances in power/mass would be required to make solar competitive with nuclear on Mars.