Solar garden lights come in many different shapes and sizes and are an easy way to add some points of interest to your garden. One of the main advantages is that these lights don’t need to be plugged into your mains electricity, which is handy considering you are going to want to have the flexibility to place them anywhere in your garden without having to worry about where the nearest socket is! Despite them not needing a constant supply of electricity and generating their power from the sun instead, you may still wonder if these solar garden lights need batteries to function.
The short answer is yes, solar garden lights work by using the energy from the sun to recharge rechargeable batteries within the solar light unit. But most of the time batteries will come with the units and you don’t need to buy your own.
But now you know that, you may have some other questions regarding these batteries; are they provided? Will they need replacing? How long do they last? Well in this article I will try and answer as many of these common questions as possible.
How do solar garden lights work?
Without this becoming a complex physics lesson I will quickly try and explain how solar garden lights function.
You will notice that your solar garden lights will all be fitted with a small solar panel probably on the top so they get maximum exposure to the sunlight in the day time.
This tiny panel is a mini version of the larger panels you may see on roofs or in gardens. It is comprised of very clever things called ‘photovoltaic cells’.
These cells are housed between some sort of semi-conductive material which could be silicon (the substance found in pretty much all your electronics) or even glass. Without anything being done to them, these semi-conductors are very stable and all the atoms are bonded together with the electrons within the silicon not moving around. This means under normal conditions they don’t conduct electricity very well, they must be altered in some way.
To start these electrons flowing, phosphorus is injected into one of the layers of silicon which causes electrons to start moving around (this is known as the N side). The other layer of silicon is injected with the element boron, which has the opposite effect and creates things known as ‘holes’ (this is known as the P side).
The electrons from the N side will move toward the P side to fill the holes that have been left there. Because electrons have a negative charge by them moving away from the N side to fill the holes on the P side, the N side is left with a positive charge and the P side becomes negatively charged.
So within each cell, there are two types of silicon; N-type silicon which has extra electrons and P-type silicon which has extra holes for electrons.
Between these two regions, you have a region known as the depletion region where there are no free electrons or holes.
This is where sunlight comes in. If you imagine sunlight as a stream of particles known as photons, these photons enter the cells and travel into this depletion region where they strike electrons, knocking them free and starting them moving, in there place they also leave a hole. This newly free electron moves towards the N side where there is a positive charge with the holes moving to the P side.
Wires can then be connected to the P and N sides and this creates an electrical current as the electrons will want to flow towards the holes.
This is the electrical current that powers the solar garden lights
Why do solar lights need batteries?
Solar garden lights aren’t much use in the day time and this is of course when the sun is shining, the photons are hitting the cells and the power is being generated. At night time no power is being generated as there is no sunlight available. Sorry if this sounds like I’m stating the obvious here.
So because we want to use this energy at night time, we need a way to store it temporarily and this is where the batteries come into it.
What type of batteries are in solar garden lights?
The batteries within solar garden lights are pretty much always going to be rechargeable. These rechargeable batteries might be either lithium-ion batteries, which are the same type of battery that comes in other rechargeable devices such as your smartphone. These batteries are more expensive and you are therefore more likely to get them in higher end solar garden lights such as security lights.
In cheaper, smaller solar garden lights you are more likely to have nickel cadmium (NiCd) or nickel metal hydride (NiMH) rechargeable batteries, which are similar to that found in a rechargeable camera.
In lithium-ion batteries, lithium is chosen as a substance as it has a very high tendency to lose electrons. When a charge is applied, in the case of your solar lights via the sun in the process described earlier in this article, these lithium ions move from one side of the battery (the cathode) to the other to a material, usually graphite (the anode), where they are stored. This is now a ‘charged’ battery.
When night time falls a light sensor tells the solar light to switch on. The lithium ions then move back from the graphite layer where they were stored back to the cathode. This energy is then converted from electrical energy into light energy and your garden lights should work.
How long do the batteries last?
Rechargeable batteries do have a life cycle and will eventually self-discharge so they will no longer function. You may notice this in a laptop or smartphone which also utilize rechargeable lithium-ion batteries, eventually, you find the charge lasting less and less time, until eventually, you feel like it is constantly having to be plugged in!
This is because the chemical reaction in the battery is not perfect and so every time it is recharged.
The average lifespan of a lithium-ion battery typical in a solar garden light is around 2 years although may be longer in many cases. Some such as the these from Litom come with an 18-month warranty, so the batteries will at least last that long.
How do I know the batteries are dead in my solar lights?
To test if your solar garden lights batteries have died, wait until you have some sunny days with little cloud and leave them out in direct sunlight all day, for at least 6 hours. Following this take them into a dark room, or wait till night time and see if they function at full brightness and for how long.
What you are most likely to find, is that they will still work but they will lose their charge more quickly and might not last all the way through the night.
Can I replace the batteries in solar lights myself?
Yes, you can replace the batteries yourself in most cases. This wouldn’t be much of an environmental website if I told you to simply throw the lights away every two years and buy new ones!
Annoyingly you will see many manufacturers telling you not to try and replace the batteries yourself because you may damage the circuitry or get water in the device! And yes getting water inside would be bad news for the performance of the battery, but as long as you do the replacement in a dry place, such as inside, you should be fine.
How to replace the batteries in a solar garden light
If you are using larger lights which have backup mains power, always ensure you are disconnected from any power source before trying to change any batteries.
For smaller garden lights, they will often state on the base which batteries are inside, or you can check the specifications on guidance or on the website where you originally bought them.
When you unscrew the unit check that you don’t have any obvious water damage (a common problem in solar garden lights).
Replace the battery with a new battery and try to ensure the battery is the same type as the one you are replacing (if possible) to ensure it works correctly. You can replace a NiCad battery with NiMH batteries which are actually slightly better for the environment, just ensure you check the voltage and mAH values are the same if possible.
Are batteries provided with the solar lights?
In pretty much every case, solar powered garden lights will come with batteries included. Just like with any other rechargeable gadgets, you buy these days you are not expected to provide the battery yourself.
So in conclusion, yes solar garden lights do require batteries to function. They use solar energy to create electricity but this needs to be stored somewhere so the lights can work when most need, and that is at night.
But as I say, you shouldn’t need to worry about finding batteries yourself as they are included in most cases, and when it comes to replacing them after a few years just find a like-for-like replacement and your lights should last you a long time.