The availability of Energy is one of the vital requirements for a settlement on Mars. It cannot be brought from Earth in large amounts, with the possible exception of nuclear fuel. An autonomous colony would need its own energy sources.
Since most energy sources are not available continuously some energy storage is required to keep plants alive and production processes running.
Solar panels provide electricity out of sunlight. This source of energy is currently utilized by the majority of space probes, including the Mars Exploration Rovers. Maintenance effort is low, but hi-tech processes are required for their production. The availability strongly depends on the weather conditions and the daytime. Dust storms can last for months during which solar panels are reduced in power. Unfortunately, this energy is not available during the time the greenhouses need additional energy for lighting. The solar energy reaching the surface of Mars is less than half of what reaches Earth. Solar Concentrators may be used to increase the efficiency of solar energy devices. However, these do not work well with diffuse sunlight.
Thermocouples provide electricity out of temperature differences. Thermocouples are used is RTGs, but can also generate electricity out of the temperature difference between the Martian surface and deeper layers. The amount of energy produced with this technology is sufficient for powering sensors or small gadgets for information technology.
New research is done by scientists of the Fraunhofer Institute. They have found a way to use thin electroconductive polymer foils to generate electricity. Those foils could be laid out on large areas and covered with a thin layer of regolith, which is heated up by the sun during the day. 
Wind turbines provide electricity out of movements of the atmosphere and can produce large amounts of energy. Dust storms may have abrasive effect on the rotor blades, increasing the maintenance effort. The availability strongly depends on the weather conditions. This energy is often available during the time that greenhouses need additional energy for lighting.
The atmosphere of Mars is 100 times less dense than the atmosphere of Earth. Thus wind turbines on Mars would generate much less energy than comparable wind turbines on Earth operating in comparable wind velocities. Two elements must be modified: The rotor blades must be enlarged by a factor of 100 to make up for the thin atmosphere, maybe with a different shape. Calculations will show if this is feasible regarding stability and material consumption.
Nuclear power has been considered as the preferred energy source for most plans for medium- to long-term human expeditions to Mars. It does not depend on weather conditions. The availability of radioactive resources on Mars is unclear. Due to the vast effort of the nuclear enrichment process, the nuclear fuel must be brought from Earth until an enrichment facility can be built on Mars.
Industry and construction
Food contains energy for human beings, and hence the production of food consumes a great amount of energy. This may be the biggest consumer of energy for the settlement. Due to the dim sunlight the greenhouses must be lit with additional energy, especially during dust storms.
In-situ production of propellant requires large amounts of energy.