Like it or not,

Shade is the enemy of solar panels.

If you have an off-grid homestead, RV, van, or even a sailboat you could significantly reduce the power output of your panels.

In this article, I’m going to explain how you can remedy shading on your solar panels.

## What’s so bad about shade on solar panels?

When there is shade on solar panels it will reduce the current of that panel.

Let’s say you have a panel that has a rating of 17.5 Volts and 5.8 Amps, it will produce 100Watts.

Now if shade comes over the panel, the current could drop to 3 Amps, but the voltage stays the same, resulting in 52.5 Watts (3 Amps x 17.5 Volts).

There is really nothing you can do about this if you have a single solar panel.

## What is the effect of shaded PV cells in series and parallel?

The problem arises if you have multiple solar panels.

Multiple solar panels can be connected in series or parallel.

Most of the time, your panels will be connected in series. Want to know why? Check out my article on series and parallel wiring of solar panels.

**Effect of shading in series connections**

If you expect to have shade on your panels, adding panels in series is not the best configuration.

Remember that in series the voltage is added up and current stays the same?

If there is shade on one panel, the current will drop. In a series connection, the current will take the lowest value in the string which is 3 amps in the following example:

The shaded spot on one panel will decrease the string of panels to 3 amps at 52.5 volts. This means that the total wattage will be reduced from 300 Watts (52.5 Volts x 5.8 Amps) to 157 Watts (52.5 Volts x 3 Amps).

Are you keeping up?

Let’s look at what parallel does.

**Effect of shading in parallel connections**

If we do the same experiment with parallel connections, we see that we have a higher power output.

This is because in parallel connections voltage stays the same but current is added together.

Remember that solar irradiance only has an impact on the current and not on voltage?

Therefore we add 3 amps + 5.8 amps + 5.8 amps to become 14.6 amps total. If we multiply this by the voltage of 17.5 we become 255 Watts which is higher than the 157 Watts in a series connection.

If you expect shading on your solar panels, I recommend putting them in a parallel configuration.

If you wire your panels in parallel, the current is higher which means you need to increase the wire diameter. This will increase the cost of your solar system. Therefore, you need to include a combiner box and make the distance between the combiner box and the charge controller as short as possible.

**Conclusion**

If you have no problems with shade, you can wire your panels in series. Wiring panels in series in cheaper and is better for your MPPT charge controller. Most MPPT charge controllers can take a maximum of 100 Volts. If you exceed this, you need a hybrid solar panel setup (series and parallel combination).

If you have an RV or a van and plan to move a lot, you are better off with a parallel connection. This is because you are not always certain if there is going to be sunshine all the time on all your panels. Yes, it will cost you more in wiring but it will pay off in the long term. Especially if your battery bank is running low.

Can you add what happens if the shading of a cell of one panel is so severe that a bypass diode “kicks in” causing the loss of say 1/3 of the panel.

Once the resistance of the cells is high enough, and it’s more than the resistance of the diode, the current will go through the diode. Preventing hotspots for forming on the panel. I don’t know the actual value or time when the diode takes over.

AE Solar makes a panel with a diode on each cell so that shaded cells are bypassed. Shouldn’t that make the loss from shade the same for series as it is for parallel connections of two panels?

From my understanding, that would solve the problem we face with series connections partially. But that will come at a price. It’s certainly promising, but most people always put their panels in the sun. I can see it being useful for RV’s or boats.

The reason I say partially is that the current would still be reduced but in a smaller amount. If you then connect them in series, the panels will drop down to the current of the lowest value panel like shown in the series example. If you expect shade I still recommend using parallel wiring.

My understanding is that when cells are bypassed, it is only volts that are lost. If all the other cells are unimpaired then you wouldn’t lose any current. So, in my example you could lose 1/3 of the voltage of one panel and then you would be better off with the two panels being connected in series. The application I’m interested in is a narrowboat where the panels regularly experience unequal light levels. I’ve heard of people wiring their two panels both ways with a switch so that they can select whichever scheme (serial or parallel) gives the greater output in the prevailing conditions.