That's an easy one, yes, unless the rain does it for you.
In the winter it may help if you live in a region where it snows a lot if you can actually reach your panels should they get covered with snow overnight.
In most latitudes your solar panels will be at a sufficient angle to let the rain do its work. If you are at or near the equator it's a different story, some regular cleaning will be necessary.
A better question is 'should solar panels be tracking the sun', and the answer to that one is it depends.
I've lived in Northern Ontario in a house exclusively powered by sun and windpower and even though we had our panels tracking the sun I doubt I would do it again that way.
The reason is that a tracker is a finicky device, fragile and costs a lot of money. Roof mounted panels are much less susceptible to storm damage. The downside is the decreased power, but you can make up for the by investing the money you would otherwise invest in a tracker in several more panels.
Fancy trackers that track on two axis are even more expensive and error prone, but the convenience of not having to do a seasonal adjustment is worth it for some.
Here in the suburbs of a major metropolitan area, and with a lot of agricultural activity further upwind, I find that my car windows develop a film that rain does not remove. Some of the film may be from vegetation (tree sap, etc.), but I can wash the windows and then park in an open parking lot and a driveway with no canapy, and still experience the film.
I wonder whether there are similar issues for solar panels, not solved by rain.
EDIT: Should have read the linked post, first. Rain works well enough for them.
Yes they should be cleaned. (They could have asked any HVAC Engineer to look it up in ASHRAE for them!)
Simply, haze in the atmosphere scatters light and reduces the amount of Solar radiation reaching the earth. Dust on a panel has the same effect! (They could also have asked any photographer that uses a yellow filter on tele-photos).
Index the world's information, organize it and use it!
Empirically, when I wash the half dozen seagull splatters and random dirt off of my panels I can't see a difference in my power production graphs.
I'm sure the output goes up, but it is too small for me to bother with the somewhat uncomfortable chore of washing them with the mop and squeegee on a 16 foot pole.
I snapshotted a picture of the data for those interested. http://jim.studt.net/solar.gif (there are some missing data sections, sorry, the data collection port has some interesting quirks).
The green line is solar panel current delivered to the 24v battery bank (actual panel voltage is several times higher). The red and yellowish lines are various inverter and telemetry loads. In the bottom half the red line is battery bank voltage and the blue is "state of charge" as indicated by the somewhat mysterious Outback DC monitor.
For the sake of cleaning differences, note that I cleaned the panels around 10am on the 11th. Compare the 9am solar output, the first faint vertical line to the left of the noon line on the 10th, 11th, and the 13th(post cleaning). All very similar, a few percent change at best.
I can't let you into the live system to browse, it has an expensive query and the intertubes would crush my server.
A few years ago, I attended a talk about the Mars rovers, where the speaker (Steve Squyres) mentioned that there was a time when one of the rovers had accumulated so much dust on its solar panels that it was in danger of dying. When hopes were fading away for a solution, the rover experienced a few days of strong wind, which cleared off most of the dust, increasing power output 9 fold!
The answer is obvious but the point here is that the average solar panel installer doesn't keep a mountain load o data about the energy output and efficiency of their panels and then make business decisions about it.
In the winter it may help if you live in a region where it snows a lot if you can actually reach your panels should they get covered with snow overnight.
In most latitudes your solar panels will be at a sufficient angle to let the rain do its work. If you are at or near the equator it's a different story, some regular cleaning will be necessary.
A better question is 'should solar panels be tracking the sun', and the answer to that one is it depends.
I've lived in Northern Ontario in a house exclusively powered by sun and windpower and even though we had our panels tracking the sun I doubt I would do it again that way.
The reason is that a tracker is a finicky device, fragile and costs a lot of money. Roof mounted panels are much less susceptible to storm damage. The downside is the decreased power, but you can make up for the by investing the money you would otherwise invest in a tracker in several more panels.
Fancy trackers that track on two axis are even more expensive and error prone, but the convenience of not having to do a seasonal adjustment is worth it for some.