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How much shade affects your solar panels?

Solar panels and battery technology have changed the camping and travel industry for good. However, solar panels only work well when in 100% sun, and it takes the tiniest skeric of shade to virtually kill your solar generation.

This is an interesting test that anyone can do with their solar setup, and it should make you far more conscious of where you park, and how you set your solar up. All you need is a solar system, and an electrical amp clamp, or an inline amp meter.

Custom solar panel rack

A custom solar panel rack on a 4WD that can tilt and spin. Full sun is almost a must for panels

Testing Solar and Shade

Simply have one person read the meter, and the other covering sections of panels. In almost every arrangement I’ve tried, the moment you cover more than about two hands of a panel, you reduce the production of energy down to about 10 percent.

Seriously; the reduction is absolutely massive. What this means is that any shade you have on your panels can hugely reduce its capacity to generate power. Whether its a tree branch, the shadow from your snorkel, the mesh on your roof rack, straps running over the panel or something else, shade is very nasty for your Solar’s energy production.

Solar blankets

The shade from a snorkel is enough to hurt your solar badly

I’ve met a lot of people who think that even if a panel is partly shaded it will still generate a lot of power, and this couldn’t be further from the truth. If you shade more than about 5 percent of most 12V solar panels on the market, you may as well unplug them and put them away.

As an example, I had two 200 watt panels mounted on a boat loader for our camper trailer. These together will put out a maximum of about 290 watts. However, if you cover just three of the little 150 x 150mm squares within one panel, the output drops to below 40 watts. That’s right – not even the size of a tea towel and you lose pretty much all of your capacity.

400W of panels

400W of panels on a tilting boat rack pretty much die when you cover a few squares

Don’t set them up under trees

What this means is that a panel under even a tiny bit of shade really does not much at all. The only way you’ll see this is with an amp meter, which you can get off eBay for pretty cheap and do an awesome job.

Watt Metre

Watt Metres are cheap and easy to use

Trees will badly hurt your solar, and even though you might appreciate the shade, your solar and battery system may not. This is where a portable solar panel is useful, as it allows you to still park in a shady location and to run a lead and panel out into the sun.

Blocking diodes

Solar panels are supposed to come with blocking diodes, which are meant to reduce the impact that shade has when a portion of a panel is blocked off. You’ll get a variety of different types, quantities and qualities of blocking diodes, and its pretty evident with a lot of panels that they don’t do the job they need to.

Series vs Parallel

Most 12V solar panels are wired up in Parallel, but you can do them in series too (like we had on our camper trailer). Series allows for lighter cable size, and will charge for longer during the day as they can run on less light. They are however, far more susceptible to shade, and a bit of shade can take out your entire system.

The general recommendation is to keep them in parallel, and if you want a cheap way of doing it (and don’t mind some heavier panels) you can use old house panels, and a suitable MPPT regulator.

Victron MPPT set up

Testing our Victron MPPT with 400W in series

Have you ever tested what some shade does to your panels? You should; its interesting and helps pick the right place to camp!

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