worst-case conditions, winter months far north or south of the equator. Figure 3 shows the number of hours of sunlight as a function of the time of year ("areocentric longitude") at various locations north of the equator. Above the Martian arctic and antarctic circles, Mars (like Earth) has no sunlight at all during the winter, and continuous sunlight during the summer. Solar Cells There are three approaches to photovoltaic power. The conventional approach is the use of deployable high-efficiency flat plate arrays. Existing solar arrays used in space use either crystalline silicon (Si) or gallium arsenide (GaAs) solar cells. Silicon is the most well developed solar cell technology, and has been used on all but a tiny fraction of space solar arrays. The conversion efficiency of standardtechnology silicon cells currently flown is about 14.5% under standard space conditions (Air Mass Zero, or AMO) [5]. Note that for calculating operational power, the cell efficiency numbers must be adjusted for the array packing factor and for corrections to efficiency due to intensity and temperature.
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