Lazy Daze Owners' Group

Will heavy shade cut off the solar panels?

June 30, 2018, 01:00:14 pm

No, it does not.
I have always heard that a partially shaded panel will cut off. I accepted that.
We put our RV cover on this week. Some light does penetrate the material. It's "breathable". It passes less light than you would get parked under a fully leafed out oak tree. Isn't that a scientific measurement? 
I was amazed that the panels are producing 1 amp. I suspect they would produce a little more, but the batteries are fully charged.
I can leave the temp controlled exhaust fan on so it can push some of the heat out and I don't have to leave the rig hooked up to shore power. One amp is twice what the fan uses, so no worries about discharging the batteries.

Re: Will heavy shade cut off the solar panels?

Reply #2 – June 30, 2018, 03:43:24 pm

Andy, can you speak about the effect of having, perhaps, 4 panels or 2 panels, with one being partially shaded such as by the AC or the batwing antenna?  Doesn't that dramatically reduce that one panel's output?

Thanks

Ken F in WY

Re: Will heavy shade cut off the solar panels?

Reply #4 – July 01, 2018, 01:34:00 am

"can you speak about the effect of having, perhaps, 4 panels or 2 panels, with one being partially shaded such as by the AC or the batwing antenna? Doesn't that dramatically reduce that one panel's output?"

Shading part of a panel decreases its output, but in my informal tests, the degradation seems to be gradual. I think it depends upon the kind of shade. If you place a piece of cardboard over one cell, completely blocking it, you may see the scenario Steve described: a major loss of power. On the other hand, the shadow of a tree branch is often blurred, and in my experience, causes less of a loss. And overcast skies (with even illumination across the panel) can still yield quite a bit of power.

With respect to multiple panels: it depends on how they are connected. If the panels are all connected in parallel, then even if one panel drops out completely due to a shadow, you'll still have all the other panels producing full power. On the other hand, if all the panels are connected in series, you'd see a major drop in power in that scenario.

In practice, series-parallel pairs have proven to be a good compromise. As I and others have said elsewhere, this configuration gives you the benefits of higher voltage (more efficient MPPT controller operation, less voltage drop, etc.) while minimizing the chances of a shadow bringing down your whole array. Traditionally, RV solar panels have been wired in parallel--that's how I wired Gertie--but with MPPT controllers becoming standard, series-parallel hookups are becoming more and more common.