Wind turbine

Fictional wind turbine on Mars as portrayed in the video game Surviving Mars. Here, the turbines revolve around a vertical axis, allowing for wind capture from all directions, rather than simply horizontally.

Wind turbines can generate electric or pneumatic energy. This would be particularly useful in situations where other methods of power generation are inappropriate, such as during dust storms which can obscure the sun for weeks at a time, thereby rendering solar panels less effective. Missions to the poles of Mars in particular stand to benefit from wind power: polar latitudes may spend half a year with little to no sunlight, and radioisotope thermoelectric generators such as that found on the Curiosity rover give off heat which may be similarly undesirable for the scientific goals of a polar mission.

However, the Martian air is about 0.6% as thick as the air on Earth, so wind power is, at first glance, negligible, and the extremely fine dust is a concern (see below). If Mars' atmosphere were to be thickened by Terraforming then wind power becomes more reasonable.

How will wind power work in Mars' thin atmosphere?

Observations of dust devils and dust storms demonstrate that wind exists in the atmosphere of Mars. Yet, this atmosphere is comparatively thin, with a surface pressure less than 1% of that found on Earth. This means that electricity generation via turbines would require either larger rotor blades (which in turn would pose problems for stability and material consumption) or wind speeds roughly triple those on Earth.

Initial evidence from the Viking and Pathfinder missions did not indicate strong winds, but this data did not include findings from dust storms, which computer modeling and wind tunnel tests have shown can only be created and sustained by high levels of winds. This leads to the possibility of wind turbines which exclusively operate during dust storms, supplementing solar power during the very storms which impede their efficiency. NASA AMES tested a 100 kW wind turbine at their Antarctica station; while this site serves as a general Mars analog due to its harsh conditions, the thin atmosphere was obviously not recreated, and the turbine itself was far too large and heavy for current science missions. A more recent study argued for the feasibility of electricity generation via wind power even outside of dust storm conditions: researchers tested a sample turbine constructed out of parchment paper, straws, wood, and LEGOs in a wind tunnel simulating typical atmospheric conditions on Mars. The experiment utilized a variety of wind speeds based on those found at the Phoenix polar landing site (roughly 2-6 meters/second), finding that more efficiently-constructed turbines could theoretically power a lander equal or smaller in size to the Mars Pathfinder. (Pathfinder generated about 35 Watts from its solar cells, but needed radioisotope heaters to help warm the electronics.)

NASA proposes the following wind speeds: Wind speeds: 2-7 m/s (summer), 5-10 m/s (fall), 17-30 m/s (dust storm) (Viking Lander sites)

If wind turbines are confirmed to be of value, many of the components could potentially be fabricated using Martian resources.

Note that fundamentally wind is powered by solar energy, and strong winds are generated on Earth by the evaporation and condensation of water. Since Mars has about half the solar energy than Earth, and a very limited hydrological cycle, even if Mars' atmosphere was much thicker, there would be less wind energy than on Earth.

Issues arising from dust

Mars has very small dust particles (fines) which must be controlled around moving parts. Windblown dust could clog up or damage moving parts. Maintenance could be expensive, as abrasion cannot be completely avoided. Lubricant may be difficult to produce on Mars and might act differently due to environmental conditions; hence, a nonlubricant-based construction such as pure magnetic bearings without direct contact may be required.

However, dust tight seals are nothing new, and vehicles operate on Earth is extremely abrasive environments, such as alumina smelters and cement plants. Specialty lubricants, such as Castrol Brayco 815Z perfluorinated polyethers have been developed for use in space and on Mars.

Example calculation

A speculative 84m wind turbine, with Spacex Starships in the background for scale. Blade width is tripled for the low air density, and the blade thickness increased by 1.5 times compared to the Earth equivalent. This might produce from 120 to 300 kW, while the Earth equivalent might produce 1,5 MW and need to be reduced in power at high wind velocities. Mass is a big unknown.

P = ½*n*p*As*v3 , where n is turbine efficiency, p is atmospheric density (kg/m3), As is swept area of the turbine (m2), and v is wind speed (m/s). The maximum efficiency is 16/27 (60%) as given by Betz’ law. For a small 10m diameter turbine As=78m2, an efficiency of 31% , air density of 0,02 kg/m3 and a wind speed of 10 m/s, P= 487W. A larger, 40m blade turbine might achieve between 150 and 300 kW of power.

For the above parameters a typical large wind turbine on Earth produces 12W/kg, where the mass includes blades, generator and tower(reference needed). This is less than the 33 W/kg that can be reached by solar on Mars(reference), but the availability may be higher as wind may blow during the night. In particular, during dust storms on Mars the available solar power is very low but the average air speed is higher. As the power is to the cube of the air speed, the average wind power per kg would then be about equal to the sun power per kg, making the two forms of energy complementary. So a Martian settlement might want to have a mix of solar and wind to increase its diversity of power sources.

For the same size of turbine, as the air on Earth is 50 times more dense, the same turbine will produce 50 times more power. However, the Martian wind turbine could be built much lighter as it handles much less power, and possibly have similar overall efficiencies and power/mass ratios. A 2012 study found that the cord length for a Martian wind turbine would be three times longer than on Earth for a 1.5 chord ratio, and that the power and strain on the tower would be one tenth of an equivalently sized tower on Earth.

Airborne wind turbines have been studied with similar parametric changes from Earth to Mars. The same reliability challenges apply to Martian airborne turbines.

Wind turbine mass

On Earth, wind turbines are fairly massive objects: In the GE 1.5-megawatt model, the nacelle alone weighs more than 56 tons, the blade assembly weighs more than 36 tons, and the tower itself weighs about 71 tons — a total weight of 164 tons. The corresponding weights for the Vestas V90 are 75, 40, and 152, total 267 tons; and for the Gamesa G87 72, 42, and 220, total 334 tons.(https://www.wind-watch.org/faq-size.php). Or a power to mass ratio of about 9W/kg. Solar power is about 30 W/kg. However, solar availability is in the order of 25% so the average power is about 8W/kg. The average power of wind turbines depends on the wind availability. If the same power to mass ratio can be built on Mars, with a wind availability of 100%, wind outperforms solar on an energy to mass basis. If the availability is lower, for example 30% as on Earth, then wind power has less than half the energy/mass ratio of solar. There might be areas, for example a base near the poles, where wind power outperforms solar. Both solar and wind require back up batteries that will add significantly to the system mass.

On Earth, the steel tower is anchored in a foundation of more than a thousand tons of concrete and steel rebar, 10 to 15 meters across and anywhere from 2 to 10 meters deep. Shafts are sometimes driven down farther to help anchor it. Mountain tops must be blasted to create a level area of at least 1,2 hectare (12 000 m2 or 3 acres). The foundation is critical to stabilizing the weight of the turbine assembly and resisting the force of the wind.(https://www.wind-watch.org/faq-size.php) A similar foundation would be required on Mars. The fondation might require the need to produce in situ concrete or some form of structural sintered regolith. Rebar (steel bars for reinforced concrete) will add significantly to the mass of the tower.

Emergency use

One of the prime cases for wind turbine use on Mars is to use them during storms, when solar does not function. However, this case must be compared to the possibility of Nuclear power, Flow battery, or adding more solar and using the excess capacity to produce methane. Methane could then be burned in a conventional gen-set to generate emergency power during a storm. A 150 kW gen-set burns about one tonne per day of methane. As all the modern Mars settlement plans include in-situ fuel production, the back-up methane can be part of the normal production process. A 150 KW gen-set might mass about 2 tonnes, while a 150 kW wind turbine array would mass at least 16 tonnes, possibly more.