Solar concentrator

A solar concentrator concentrates the power of the sun onto a small area. This energy is harnessed in a variety of ways. For example, a system called SCARLET is currently flying on Deep Space I.

Designs

Lenses. A variety of lenses designs are used to concentrate sunlight. A lens may be a simple piece of curved glass or plastic, or a complex Fresnel lens.

Mirrors and reflectors. Fields of mirrors are used in some concentrated solar facilities on Earth. The individual mirrors rotate to track the sun. The construction can be made lightweight from polymers, e.g. Mylar and Hostephan. Computer simulations of radiation damage have shown that an aluminum covering of at least 0.1 mm thickness is necessary(reference).
Fiber Optics

Utilization of Focused Solar Radiation on Mars

Total solar illumination on Mars is the sum of direct and diffuse illumination. Diffuse illumination cannot be focused, and this can significantly reduce the efficiency of solar reflectors on Mars. On average 50% of the light available on Mars is diffuse.(reference) So the surface of reflectors need to be 50% larger than what would be calculated with the total irradiation. Mars is farther from the sun and gets (on average) 43% of the sunlight Earth does. This would make the surface of reflectors needed 2 * 2.32 or 4.64 times larger than an equivalent project on Earth.

Photovoltaics. Solar concentrators are often used in conjunction with solar panels to increase the panel's output. This maximizes the efficiency of a limited number of solar panels. The increase of efficiency on Mars will be lower than on Earth by as much as 50% due to the portion of diffuse lighting.

Thermal Engines. The energy of the sun can boil liquids, causing changes in pressure. These pressure changes are harnessed by thermal engines. It is likely that liquids other than water will be used, due to the low temperatures on the surface. Carbon dioxide and carbon monoxide are both available as working fluids. Common thermal engine designs include the Sterling engine and the steam engine. Since the angular size of the sun as seen on Mars is smaller than it is on Earth, a larger mirror is needed to get the same sized image of the sun at about the same temperature as on Earth. Solar thermal engines should be capable of powering electric generators on Mars.

Thermoelectric Generators. Thermoelectric materials convert heat into electricity.

Photosynthesis. Greenhouses are a good target for solar concentration. The natural sunlight on Mars is less than half that on Earth.

Lighting. Concentrated sunlight can be used to light settlements during the day.

Problems

solar concentrators may present dangers in their utilization and have some operational problems on Mars

Radiation Damage. If solar radiation is concentrated for use in greenhouses or settlements, the harmful parts of the electromagnetic spectrum need to be filtered.

Vision Damage. Looking directly into concentrated sunlight can damage vision.

Heat Damage. Objects passing through the focus of a solar concentrator can be exposed to intense light and extremely high temperatures.

Dust storms. During dust storms direct solar illumination may fall to nothing, while indirect illumination remains and can be used by photoelectric cells. Therefore in some cases photoelectric cells might be more appropriate as an energy source than thermoelectric generators than depend on direct illumination.

Heat Cycling. The temperature cycle for a solar concentrator may range from (say) 1200C in the day time when it is operating, to -70C at night. Temperatures swings of this magnitude are greater than on Earth and care must be taken that the machinery is not damaged by them.

Maintenance effort

The main maintenance cost is likely removing dust. Large dust particles can be brushed off, but tiny particles are sticky and hard to remove. Static electricity control might be useful to reduce the adhesion of dust. Likely, some amount of dust will be considered too difficult to remove and a lower efficiency will be accepted. Donning a space suit is and going on a EVA is always dangerous, and cleaning a large field of mirrors is a non-trivial risk, requiring much time and labour.
The cosmic and solar radiation causes damage upon the concentrator mirrors. The particle bombardment causes blistering and foil carbonization. A lifetime of 10 years is assumed, thereafter the mirrors have to be replaced. (Locally produced mirrors may be more rugged and have longer lifespans.)
Solar concentrators are susceptible to losses due to atmospheric diffraction and dust. During a dust storm concentrators lose most of their efficiency. (95%+ reductions in direct solar power have been experienced by rovers on Mars.)