A human mission to Mars would require a substantial amount of electrical power on the surface. It seems there are two main options for producing a lot of power on Mars: solar and nuclear fission. Both a large array of solar panels and a nuclear reactor would be difficult to deliver to and deploy on the Martian surface.
Solar power has the advantage of being safe and technologically reliable. There is no public resistance to solar power. Since non-tracking solar panels have no moving parts, they do not frequently fail to operate. We can also expect solar panel technology to develop significantly over the next decades because there are a variety of terrestrial applications and initiatives that employ it. Unfortunately the solar flux at Mars is less than half what it is at Earth, and the amount of insolation will decrease at non-equatorial latitudes and during the Martian winter. Accumulation of dust on solar panels, a phenomenon for which Mars is notorious, will further decrease energy outputs. If solar panels are thin and flexible, a stern wind could lift unrestrained panels off the ground. Of course, solar power must be stored during the day with a battery or regenerative fuel cell for nighttime use.
Nuclear fission on the Martian surface can offer much more power per unit mass than solar power. It produces energy at a constant rate and could be used equally at any surface location. These characteristics make the fission reactor an attractive candidate to power a production plant for in-situ resource utilization—machinery that will surely consume loads of power. A nuclear reactor, of course, produces dangerous radiation and therefore must be placed a significant distance from crew members. Typical designs contain numerous moving parts to convert heat into electricity, which introduces complexity and risk of failure. Small-scale nuclear reactors have little application in terrestrial settings, so most development efforts may have to fall on space agencies like NASA. And we are all aware of the political obstacles to developing a nuclear reactor and launching it into space.