Solar and wind exergy potentials for Mars Alfonso Delgado-Bonal a, b, * , F. Javier Martín-Torres a, c , Sandra V  azquez-Martín a , María-Paz Zorzano a, d a Division of Space Technology, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Kiruna, Sweden b Instituto Universitario de Física Fundamental y Matem aticas, Universidad de Salamanca, 37008, Spain c Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Avda. de Las Palmeras n  4, Armilla, 18100, Granada, Spain d Centro de Astrobiología (INTA-CSIC), Ctra. Ajalvir km.4, Torrej on de Ardoz, 28850, Madrid, Spain article info Article history: Received 15 April 2015 Received in revised form 16 February 2016 Accepted 18 February 2016 Available online xxx Keywords: Second law analysis Mars Solar exergy Wind energy Renewable energy abstract The energy requirements of the planetary exploration spacecrafts constrain the lifetime of the missions, their mobility and capabilities, and the number of instruments onboard. They are limiting factors in planetary exploration. Several missions to the surface of Mars have proven the feasibility and success of solar panels as energy source. The analysis of the exergy efficiency of the solar radiation has been carried out successfully on Earth, however, to date, there is not an extensive research regarding the thermo- dynamic exergy efficiency of in-situ renewable energy sources on Mars. In this paper, we analyse the obtainable energy (exergy) from solar radiation under Martian conditions. For this analysis we have used the surface environmental variables on Mars measured in-situ by the Rover Environmental Monitoring Station onboard the Curiosity rover and from satellite by the Thermal Emission Spectrometer instrument onboard the Mars Global Surveyor satellite mission. We evaluate the exergy efficiency from solar radi- ation on a global spatial scale using orbital data for a Martian year; and in a one single location in Mars (the Gale crater) but with an appreciable temporal resolution (1 h). Also, we analyse the wind energy as an alternative source of energy for Mars exploration and compare the results with those obtained on Earth. We study the viability of solar and wind energy station for the future exploration of Mars, showing that a small square solar cell of 0.30 m length could maintain a meteorological station on Mars. We conclude that the low density of the atmosphere of Mars is responsible of the low thermal exergy ef- ficiency of solar panels. It also makes the use of wind energy uneffective. Finally, we provide insights for the development of new solar cells on Mars. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Solar radiation has been a source of energy in space missions as a power source for small satellites, for large structures such as the International Space Station, and for Solar System exploration. It has been very useful in Mars exploration, in particular during the Viking mission and in several Mars orbiters and rovers afterwards. The Mars Exploration Rover Opportunity was able to exceed the baseline mission duration from the 90 sols scheduled initially to more than 3500 sols, continuing nowadays. The complexity of the rovers, and the energy demands of the experiments onboard have increased in the last decades. An example is the Curiosity rover in the NASA's MSL (Mars Science Laboratory) mission [1] currently operating on Mars. As the solar radiation intensity decreases with the square of the distance to the sun, solar energy might become inappropriate to maintain a complex spacecraft. For these reasons, the rover Curiosity is powered by a Radioisotope Thermoelectric Generator (nuclear power) and it is likely that the next rovers exploring Mars will use the same kind of energy source. Although nuclear power could be a partial and temporary solution [2], human colonization of Mars will require a perdurable and renewable source of energy. The transport of nuclear material from Earth to Mars implies large risk and costs. The existence of fossil energy, such as carbon or oil on Earth, seems unlikely to be found on Mars and its transport in spacecrafts is not feasible. Finally, geothermal energy is not feasible on Mars, since no significant geological activity has been recorded on the planet. * Corresponding author. Instituto Universitario de Física Fundamental y Matem aticas, Universidad de Salamanca, 37008, Spain. E-mail address: alfonso.delgado-bonal@ltu.se (A. Delgado-Bonal). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy http://dx.doi.org/10.1016/j.energy.2016.02.110 0360-5442/© 2016 Elsevier Ltd. All rights reserved. Energy 102 (2016) 550e558