First of all ... 100%? That shouldn't be your standard. All panels are going to get some dirt on them and lose a wee bit of production. The question is when does it become worth while to clean that dirt off.
Consider that one solar panel (let's say 280 watts) produces about 420 kWh per year. That's most likely between $40 and $80 worth of electricity, depending on rates where you live. Say dirt causes you to lose 5% of that, which is realistic assumption. Well, that's between $2 and $4 you are saving each year by keeping one solar panel squeaky clean. Say you have a 20 panel system, at most you are saving $80 a year. If you do it yourself and it takes you 8 hours (say a few hours each on multiple occasions), maybe you are making the equivalent of $10/hour. Is that worth it to you to clean your own system? You decide. Would you take that pay to clean other peoples' systems? In many places it'd be hard to find someone who would. There's just not enough systems that need enough cleaning to keep someone fully employed.
One point that comes from this: cleaning too often means putting in more effort (or money) for less and less benefit, since the panels will be less dirty and losing less production. For cleaning to be worth it, you really want to get a good jump in production each time you do it, and then ride that for a while.
Also consider that in rainier places, you get less production because of less sunlight, but the rain washes a lot of the dirt away. Meanwhile in sunnier places, you may get less rain washing but you get more production from more sun. So those things will offset each other to some degree with respect to costs.
Bottom line: we don't tell our residential clients that arrays need to be cleaned. Maybe after a few years, if conditions are bad, dirt could be reducing production by 10%, and it's worth cleaning. But the losses usually seem to be much less than that, and rain washes away a lot of dirt, even when it doesn't rain that often. And we don't want to be telling our customers to get on their roof if they aren't used to the dangers and how to safeguard themselves.
If you've got a Megawatt ground-mount, well, it's probably worth an hour or two of someone's time to do some serious math and figure out a real answer.