Using the power of the sun is a great, environmentally friendly way to generate power. One popular use of solar panels is for lights, whether that be a security light on your house or small lights guiding the way along a path. But the optimum practical position may not be a position which receives direct sunlight, it could be under a tree or attached to a building. For this reason, a common question is; do solar lights work in the shade?
In short, the answer is yes solar lights will work in most shade but not as effectively and you may not get a full nights charge.
The reality is, the term ‘shade’ can mean a lot of different things and solar lights also vary greatly too, so in this article I will explain this all in more detail, to hopefully give you a better understanding.
How do solar lights work?
To get a better understanding of why a solar light may or may not work in the shade, it is best to have an idea of how they function. There are a few key parts to a solar light that allow it to function.
The Solar Panel
Of course to be able to generate electricity the light needs a way of converting the energy from the sun into electrical energy for the light. This is done by a small solar panel, which is usually built into the top of the light.
The solar panel is a very clever device made up of ‘photovoltaic cells’. These cells are sandwiched between two layers of a substance called silicon (the stuff you find in all your modern electronics). This silicon has been altered by adding phosphorus to one end and boron to the other end, don’t worry, I won’t turn this into a chemistry lesson, but that basically means you have a positive end and negative end and it starts a flow of electrons creating an electric field.
These electrons can be used in an electrical circuit to create electricity, but at the moment they are just moving around and are not useable. To do this they need to be knocked out of the field by something. That something is ‘photons’. For this simple example, imagine a ray of light from the sun as a stream of these photons. So when they hit the solar panel they can knock one of the free electrons out of the field. These could be used straight away to form electricity if required but in solar lights they are not used right away and instead you have a battery.
Every solar light will contain a rechargeable battery. This is because the light needs to be able to capture and store the electrical energy for use when it is needed…..at night. It wouldn’t be much use if your solar lights could only turn on in the daytime now would it?
Rechargeable batteries can store power via a chemical reaction and release them through a circuit when needed.
A standard battery works by having a positive and negative end causing electrons to flow from negative to positive and this flow can be used to generate electricity. A rechargeable battery allows this flow of electrons to be reversed when you apply an external electricity source (in our case the electricity generated from the sun) and the battery re-charges to be used once more.
The light sensor
But how does the battery know when to release the electrons to produce electricity?
This is done by a light sensor. A device usually contained in the top of the solar light that when in darkness will cause the battery to start releasing energy and will cause your light to turn on.
Now you know that in order to recharge the batteries in your solar light you need as many photons reaching the panel as possible. With every second a full stream of direct sunlight is not hitting the solar panel reduces the chances of electricity being generated and stored in the battery for use at night time.
What do we mean by shade?
‘Shade’ is defined as comparative darkness/ coolness which is the result of shelter from direct sunlight.
As you can see, it is therefore quite a broad term that covers a lot of things. Shade could be very dark with virtually no light passing through or it could be just slightly less bright than direct sunlight.
The key thing is; the less light that is passing through the less chance of photons from the light reaching the panel and generating electricity.
So if your panel is behind a wall where it is heavily shaded for a large amount of time, that is different from being under a tree. A tree causes shade but some light is still getting through. You know this because when you enter a woodland, even if all the trees are in leaf and there are lots of them, you are unlikely to be plunged into absolute darkness.
The optimum position for solar lights
With all that taken into account, I’ve run some tests with various solar lights in different shade scenarios. For all these scenarios I waited for the battery to run out of charge first.
Scenario 1 – Direct sunlight all day
I was obviously expecting the best result here, I placed the light in the middle of the garden where it got almost 8 hours of sunlight and the light stayed on all night without any problems.
Scenario 2 – Half day direct sun half day in complete shade
In scenario 2 I placed the light in a position where it would get direct sunlight for about half the day but then once the position of the sun changed it would become shaded behind a fence.
Again the light stayed on all night, it might not have fully charge the battery, but it had enough charge to last the night.
Scenario 3 – Under a tree on a sunny day
Still on a sunny day (as above) but this time I put the light directly under a large oak tree, therefore putting it in the shade most of the day.
The result this time was not as good, the light still turned on but went off after around 4 hours.
Scenario 4 – A cloudy day without shade
On a cloudy day without shade the lights also stayed on all night (over 8 hours).
How much sunlight does a solar light need to stay on all night?
From my test using a small solar light it was clear a full day of direct sunlight was not required to keep a light on all through the night. It also showed that heavy amounts of shade could mean they don’t last all night.
This will, of course, vary depending on the type of light, type of panel and type of battery. There is no single amount of time or amount of sunlight that will guarantee your lights stay on all night. I could give you some formula but the chances of that actually being any use are small.
Most manufacturers claim that 8 hours of direct sunlight will give between 12 and 15 hours of charge. So that is comfortably a full night. But the reality is you aren’t going to want to place all your lights in the middle of a lawn with no shade. But if you can get 4 hours sunlight on them this will give you 6 to 8 hours charge which is a full summers night.
Other reasons why solar lights might not be working
If you move your lights into a sunnier spot and they still don’t work it may be due to another issue such as:
Dirt on the panel
It is common for dirt and grime to build up on the solar panel over time. This will prevent sunlight from reaching it and therefore affect the performance. So make sure you regularly give the panels a quick clean.
Water in the system
Your lights are outside and in the rain quite frequently, there is always a chance some water can get into the panel or circuit and affect the performance of the light.
The batteries are dead
Although the batteries are rechargeable, even they have a finite lifespan and so after a while (probably a few years) they will eventually stop recharging. At this point, you will need to replace the battery (check out this other article where I explain how to do this).
How to get more sunlight to your panels
The first and most obvious option is to try experimenting with some different positions. Observe where the sun is at different times of the day and you may find just moving the lights a meter or so to one side or the other could make a big difference.
Secondly, you could get solar lights that have a separate solar panel, i.e one that isn’t directly on top of the device. This will allow you to still have your lights in a shady spot but keep the panel in the sun…..genius! See the image below for what I’m talking about.
When buying and positioning solar lights there is a good chance the place in your garden that gets the most sunlight and the place where you want your lights won’t match.
However, from my tests, you can get away with less than a full days light and still get a full nights charge.
So yes, solar lights will charge in the shade but nowhere near as well as in sunlight you are better to have some hours of direct sunlight and complete shade than partial shade for the entire day. All I can say is experiment, change the positions and see what happens.