Life Support
  Air, Water, and Nutrition
  Waste Management
  Mental Health
  Suits
  Radiation and Zero-G

Habitat On Mars
  Power
  Structure
  Daily Routine

 Overview

It is estimated that the habitat will need a maximum of 28 kilowatts of power at any one time during its stay on the surface of Mars. Fourteen kilowatts will be supplied continously, on average, but power supply will vary to allow for periods of greater need. Power will be provided by fuel cell power plants. In addition, solar panels will be mounted on the outside of the lander, and will be used to store power for such uses as charging space suit batteries.

Specifics

The Ion Propulsion Package (IPP) will carry 20 fuel cell power plants. These will be divided into 5 sets of 4 power plants, with each set providing power for approximately 80 days. To provide power for the habitat throughout its 387-day stay on the surface will require massive amounts of hydrogen and oxygen to be brought along on the IPP. The mass estimate for all components of the habitat's electrical power system is approximately 17 metric tons . All estimates are based on the space shutle's electrical power system. 

The solar panels on the lander will be similar to those used on Pathfinder (manufacturer: TecStar).

Justification

Fuel cells are dependable sources of clean power. They also produce as a byproduct water, which is essential to a manned mission. Specifically, water procuced by the fuel cell power plants can be used for drinking, washing, and hydrating food, or it can be electrolyzed to provide additional hydrogen and oxygen for the fuel cells. The major drawback to fuel cells is the large mass of hydrogen and oxygen that they will require to be brought along.

Another option when pondering how to supply power to the habitat would be to use radioisotope thermal generators (RTGs). RTGs, while more massive than individual fuel cells, do not require the massive amounts of hydrogen and oxygen needed by the fuel cell power plants. The primary reason for rejecting RTGs as the source of power is that they produce no useful byproducts (e.g. water) other than heat.

A third option, solar panels, require no fuel to be brought along with them. A large enough solar array could theoretically power the habitat. However, the uncertainties inherent in depending on solar power are too numerous: potential damage to solar arrays due to atmospheric phenomena (e.g. dust storms), dust accumulation on the panels, radiation damage, and the unknown amount of available sunlight at the landing site. Despite these disadvantages, it would make sense to carry solar panels on the lander if only to assess their capability for future use, given their aforementioned potential and negligible mass (1.2 kilograms per square meter).

Uncertainties

The above represents what appears to be the best way to power the habitat at this time. For all intents and purposes, it does not attempt to estimate the effects of future developments on this solution. It is possible that this plan could be improved upon before the mission's launch date.

Selected References:
http://spaceflight.nasa.gov/shuttle/reference/shutref/index2.html
http://www.tecstar.com/datasheets/gallium.pdf
http://www.ne.doe.gov/pubs/npspace.pdf