Whr Figures, From various sources Options

[djellison]

I've been looking at the new entries at the PDS for WHR quotes, to compile as good a list of actual quoted Whr values as I can......so if you find one, add it to this thread and I'll update this post with figures....any source as long as it's an actual figure and an actual sol.


B0515 - 418 Whrs
B0522 - 462 Whrs

[jamescanvin]

Helvick.

One thing that struck me last night. The amount of incident sunlight absorbed by dust on the panels must be quite inclination dependent. (Think of the size of the shadow of a dust grain, or the path length through a thin dust film as the the angle varies) Maybe this is the reason for the power falling off faster than expected?

If this is the case then as we appoach the solstice the rate of change of this effect should decrease and even better, give more power than expected as spring arrives.

Does this make any sense?

James

[helvick]

Helvick.
One thing that struck me last night. The amount of incident sunlight absorbed by dust on the panels must be quite inclination dependent. (Think of the size of the shadow of a dust grain, or the path length through a thin dust film as the the angle varies) Maybe this is the reason for the power falling off faster than expected?

Interesting idea - this certainly would make sense for beam insolation. The assumption that I made was that the "loss" in power due to dust could be described by a simple efficiency percentage as that seemed to be what the mission planners had thought. Now that I think about it it doesn't make a lot of sense to think it could be so simple.

I think I need to try to model this to see how it might effect power throughout the day and as the Sun's altitude changes from Sol to Sol.

Diffuse light (which accounts for around 30% of power generated at the moment) is definitely not affected in the same way - by definition it comes from all incident angles after all.

[RJG]

Diffuse light (which accounts for around 30% of power generated at the moment) is definitely not affected in the same way - by definition it comes from all incident angles after all.

I'd agree that it is not affected in quite the same way -but the effect will also will affect diffuse light. That element of diffuse light arriving vertically will be affected less than the element of the diffuse light arriving obliquely.

I'll leave you to model it!

Rob

[helvick]

I'll leave you to model it!

Aargh! True there is an effect and it will change the distribution of light on the panel but I have a gut feeling that it will generally cancel itself out. Reflection will play a fairly significant part in it too. Hmmh, some more thinking is in order.

Anyway quick back of the envelope calculations for the beam case show that for the best case situation (midday sun directly overhead) a 33% physical covering of dust would cause a performance degradation of ~45-50%. Exactly the same amount of dust in mid winter (with a maximum solar elevation around 63deg) would cause a degradation of 70-75%.

However that also assumes completely non reflecting dust grains. If they reflect anything (which they do) then a significant percentage of the reflected light will end up becoming available to the panel which could even increase the efficiency of the panel at low solar angles if the dust was quite reflective. Not a simple task to model well I think.

Interesting. Got to think about this more and do some real digging into last years data to see if I can spot any trends.

[helvick]

Just found some great news from the folks at JPL - they definitely disagree with my guess that dust deposition rates were high and getting worse. From todays Spirit update

The deepest part of the Martian winter - that is, the Martian winter solstice - will be on Aug. 8, 2006. The lowest amount of solar energy the rover is expected to receive is 275 watt-hours per sol (a hundred watt-hours is the amount of electricity needed to light one 100-watt bulb for one hour). The rover typically spends at least one sol recharging the batteries following each sol of heavy science activities.

For that to be true the dust deposition rate at the moment would need to be very low (~0.05% per sol). Clearly that's good news.
So to celebrate I've effectively trashed my earlier attempt at the power chart and mapped out a possible version using the above data, a much more friendly dust loss rate from the published table for Spirits panel efficiency for her first year, and including two cleaning events (corresponding to the sol 421 and 520 events).

That would allow for quite a bit of activity (ie like trying to move) from around Sol 1100.

Even without any cleaning events under these conditions she would have enough juice to survive fairly easily and be able to keep up the current programme of long term observation while waiting for a bit of a clean.