With the present global dust storm on Mars appearing to be on the wane, I thought I'd raise an issue which I can't remember ever seeing raised elsewhere (although I guess it must have been at some point somewhere).
If a global Martian dust storm like the present one can cut sunlight reaching the surface by 99% or more, and do so for weeks on end, and such storms are semi-regular events, then obviously they will inevitably impact on the viability of operations on the surface of a manned expedition to the Red Planet which relies on solar power for its outposts, vehicles, etc.
Unmanned installations like the MERs may be able to hunker down, cut power usage to a bare minimum, and wait out such storms, but doing would appear to require them to endure the kind of temperatures which would kill a human crew. So quite apart from anything else a certain level of power would need to be available simply to keep at least some part of the interior of their outposts or vehicles at some suitable temperature, and they will need to be able to do so for at least several weeks, a length of time likely to outlast any battery-backups such installations may have available.
The most obvious solution may or may not be viable. Even supposing such storms could be predicted years in advance, the requirements of celestial mechanics may or may not preclude arranging an expedition such that their stay on the surface spanned a storm-free (or at least likely storm-free) period.
Something similar might be said for the next most obvious: liftoff back into orbit to wait out the storm (assuming a fully fuelled vehicle is available for such a purpose). Unless those vehicles could return the expedition to the surface once the storm was over, then obviously that would mean:
1) the end of further surface exploration during that expedition; and
2) a maybe lengthy stay in orbit until the next scheduled Earth departure came around.
And of course if such a storm came along suddenly enough (say with only a week or so's notice) some expedition members may well be caught away from the main outpost. For example, on a hundred mile trek to some geologic site in a self-contained but solar powered vehicle.
Other solutions such as using the fuel from an ISRU unit (or even the fully fuelled lift off vehicle) to survive the storm may or may not be viable.
That inevitably raises the question of whether using solar power would be viable even for comparatively short-term manned expeditions to Mars--ie those with a stay on the surface of, say, a year or less--if there was any chance at all of such a storm catching an expedition on the griound.
Will such storms mean that nuclear power will need to be at least available (in the form of RPGs even if not necessarily a full blown reactor) as a backup even for the first few expeditions, and more or less a necessity for longer term ones? (That is, will it mean that the more people there are on Mars at any given time the less viable solutions of other sorts may become?)
(PS to Doug: if this thread is not suitable subject-matter for the forum feel free to delete it.)