"Under these assumptions each square meter produces an average of 100 watts of power on a 24 hour basis. For 100 megawatts, one would therefore need one million square meters of photovoltaic area. No "few workers" are going to keep that large an area clean."

1 km sq is 1 million sq meters.
A large office building probably has far less than 1 million sq meters of windows, but any city probably has much more 1 sq km of windows which are vertical and which are cleaned every so often.

Example of window cleaning costs:
Residential Window Cleaning Solid Glass Only.

* 1 story up to 3k sq/ft home= $149.00 exterior only.

* 2 story up to 3k sq/ft home= $199.00 exterior only.

* 1 story up to 3k sq/ft home inside & out = $249.00

* 2 story up to 3k sq/ft home inside & out = $299.00

* Mini Pain Glass=$1.50 Per Pain.

Commercial Store Fronts.

* Outside Only= $1.25 per window

* Inside & Out= $1.50 per window
CALL US FOR COMMERCIAL HIGH RISE CLEANING!

And:
Typical costs:

* Generally, window cleaning costs $2-$7 per pane. For a 1,300-square foot home with 20 panes, the cost would run $40-$140. For a 2,200-square foot home with 28 panes, the price would average $56-$196.

I would guess, that if solar panels were designed to allow easy access cleaning them, it would cost less than $1 million dollar per 1 sq km- and therefore require somewhere around 3 to 5 people per 1 million square meters per cleaning. If they were cleaned twice per year, then about 10 man years per 1 million square meters. If one had to clean them every week or every month, then one is looking at a lot of man hours and a lot of costs.

And if one needed to clean every week or less, one would probably need some kind of automation cleaning daily, hourly, or constantly- and still have a crew of around 3 to 5 people per 1 sq km. One kind of automation could be something like a sprinkler system or drip system which captured the water and processed the water to be re-used.

In any case one should be able to keep the cost down to somewhere around 1 million dollars per sq km per year and have less than 10 people doing maintenance, cleaning, and security per sq km- if designed and managed adequately. In other words, it shouldn't cost more than 2 million dollars per year and probably not much less than 1/2 million dollars per year per sq km.

So, if it is 2 million dollars per sq km per year what does this mean?

Say you were in a location which gave an average of 8 kw/h per sq meter per day and you were to give kw/h of this energy, a dollar amount of $.1 per kw/h. So one has .8 million dollars of power per day per million sq meters and 292 million per year. So, less than 1% of the profit.

If one was in a location which gave an average of 7 kw/h per meter per day, it would be .7 million dollar per day and 255.5 million per year- or difference of 36.5 million dollars per year- or 18 times more of a factor than cleaning costs of 2 million dollars per year.

Now, if you are in an area which gave 8 kw/h per day, and if cleaning the solar panel resulted in more than 1 % increase in power, obviously you "make money" by cleaning at whatever level/degree of cleaning gives you a 1% increase in total output.