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Can You Charge Solar Lights Without Sun?

Can You Charge Solar Lights Without Sun?

Like many folks, you may be using solar power to provide electricity for your outdoor porch lights, your smartphone, or even your home. For a great number of homeowners, all of their exterior lights are powered by the sun.

The benefits are numerous — reduced electricity bills, lower reliance on coal, and it’s just plain cool.

But what happens when clouds decide to come out and the solar light power source is nowhere to be found? Is that device just dead until the sun comes back out?

Luckily, there’s a solution. You can charge solar lights without the power of the sun. However, you’re going to have to burn additional electricity to do it. Additionally, it’s extremely inefficient!

How to Charge Solar Lights Without the Sun

There are many reasons why you’d want to charge a solar light without the sun. Perhaps it’s cloudy, or at nighttime. Perhaps you’re indoors and don’t want to drag your light outside to point it up at the sun. Or maybe you’re just in a place with low light!

Whatever the reason, a technique exists to get that solar light charged up. We’ll explore each use case below.

Outdoors During Nighttime

Can you really charge solar lights at night?

It depends entirely on whether or not you have an additional light available and what kind of light it is. Most of the time, you can simply place an external light to the photovoltaic cells on your solar light. Then, stand back and let the photon magic do its work!

However, be aware that different types of artificial lights emit different areas of the light spectrum. As long as the external light source generates the same area of the spectrum as your solar light, it will charge!

An astute reader might be wondering which areas of the light spectrum charge solar cells. The site “Sciencing” has a great description of it, that I’ll reference here:

…solar cells do not respond to all forms of light. Wavelengths in the infrared spectrum have too little of the energy needed to jostle electrons loose in the solar cell’s silicon, the effect that produces electric current. Ultraviolet wavelengths have too much energy. These wavelengths simply create heat, which can reduce a cell’s efficiency.


So, there you have it. As long as your external light doesn’t fall into the infrared or Ultraviolet wavelengths, your external light will charge your solar light. Incandescent, fluorescent, and LED bulbs should all work fine.

On Cloudy Days

It’s a myth that solar panels don’t work on cloudy days — they do. They simply don’t work as well. Instead of the power generation of full sun, solar panels only produce 10% – 25% of their output when it’s cloudy.

This is plenty to charge your solar lights.

However, you can give your solar lights a small nudge to charge a bit more efficiently. The technique is well studied and simple to implement for something as small as a solar light. Yes, I’m talking about solar tracking.

Solar tracking is the process of orienting your solar cells toward the sun. During cloudy days this can make all the difference in the world.

Solar tracking setups can be as complicated or as simple as you want them to be. For a solar light, I’d simply adjust the panels to hit the sun more directly during the time of day you need to charge. I prefer simple solutions to short-lived problems.

If you’re interested in the more complicated option (or want to power something a bit beefier than a solar light), you could install your solar cells on a servo and set up a DIY solar tracker.


If you want to charge your solar light indoors, you can simply use the external light technique I covered above. Take the photovoltaic cells and place them next to a light source not powered by solar energy.

Consider using the lights that are already on inside the dwelling to avoid burning more electricity!

Keep Replacement Batteries

One of the easiest ways of “charging” a solar light without the sun is to simply switch out their batteries. If your light runs off battery power, you could store a replacement battery in a cool, dry place to use when the sun is taking a nap.

Be sure to only use appropriate, rechargeable batteries suitable for your model of light. Typically these are lithium. Using a lead-cell battery can damage your unit and even cause fires! I personally would not take any chances at all with this.

Plug Into an External Power Source

If you don’t have a battery and your system is standalone, you may consider plugging into an external power source. Hooking your solar light up the grid or a battery may seem counter-productive, but it’s the only way to guarantee light 24 hours per day.

Unless you’re comfortable with electricity (and even if you are), I would advise hiring an electrician to do this for you.

Tips to Avoid Solar Power Loss

Often, an ounce of preparation is worth a pound of cure. In the case of solar lights, you might solve your need to charge without the sun simply by avoiding solar power loss. Here are some helpful tips to ensure that your solar cells stay healthy and work for years to come.

  1. Regularly clean your solar cells of dust, bird poop, and other debris. Once per season should be enough!
  2. While it may sound counter-intuitive, shade your solar panels on especially bright, hot days. While solar energy will be strongest during this time, the heat reduces the panel’s effectiveness and can permanently damage the cells.
  3. Make sure to use low energy replacement bulbs when necessary and high-quality replacement batteries. Both of these are integral to maintaining a smoothly working solar light system.

Final Thoughts

Solar lights are great, energy-saving inventions. However, I completely understand the need to revert back to grid-power when the solar panels lack energy.

After all, the time when the solar panels will lack energy is precisely when you’ll need to use them!

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