Do Solar Panels Drain Batteries At Night?

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As someone who lives with off-grid power, I am in the habit of checking the batteries every night. I do this in order to ensure that there is adequate charge to get us through till morning when, hopefully, the sun will return to power our day.

Also, having a flock that needs to be released at first light, means that I am up at the crack of dawn every day where I, once again, check the batteries to see how we have fared.

Sometimes the loss of charge is significant, while other times it is negligible. But even when the only things in the house that have been drawing power are the modem and a nightlight, there will always be a loss of power – no matter what.

One could be excused for wondering if the panels themselves weren’t pulling power from the batteries.

But the fact is, if your solar panels are connected to a properly functioning charge controller then they will not drain your batteries at night.

How Solar Panels ‘Could’ Drain Your Batteries

As discussed in the article, ‘How Do Solar Panels Work?,’ solar panels are, for the most part, inert, until the photons present in sunlight strike the panels and gets things started. Once this process begins, an imbalance in electrons occurs (see electron holes) initiating electrical current as electrons flow back around in an attempt to re-established a proper balance.

So long as sunlight continues, the catalyst for electron imbalance persists. However, once the sun goes down, this catalyst becomes absent – in other words, there is nothing to trigger further electron imbalance.

Once this has occurred, all that is left is for the electron balance to be restored – at which point your solar panels will return to their static state.

And this is how batteries could be drained.

It is possible that electrons could be drawn from their place in storage – your batteries – and sent to the solar panels in order for electron balance to be restored.

However, there are a few things to consider.

  • First, the amount of electron charge pulled from your batteries would only be equal to the amount of charge necessary to achieve electron balance. Once this balance was achieved, there would be no reason for further electron flow.
  • Second, sunlight is rarely binary. In other words, there is a ramp up and a ramp down in the amount of sunshine that directly strikes your panel. For this reason, there shouldn’t be a ‘hard demand’ for electrons in order to achieve balance, but rather a gradual weaning off.
  • And the last reason is because of charge controllers. One of the main functions of a charge controller is to prevent back-flow from your batteries into the panels. For this reason, if your charge controller is performing properly, your panels will not drain your batteries at night.

Common Causes Of Nightly Battery Drain

This past winter, we had an issue with our backup generator. Because of this we were forced to shut the entire house down in order to make certain that there was no draw on the batteries.

Even with every breaker flipped off, ensuring that there was absolutely no electricity being consumed by the house, the charge on our whole house battery package regularly dropped overnight.


Because current battery technology does not retain its charge indefinitely. There is always some power loss. The reasons for this are plentiful such as ambient temperature, type of battery, age of battery, battery charge level, ect. But you can absolutely plan on some loss.

This is why it is so important to be familiar with the established behavior of your home-power system. Knowing what is normal power loss and what is not, can you help you in determining whether or not your have a serious problem.

Some common reasons for excessive battery drain are;

  • Phantom loads – Simply put, phantom loads are those unseen electrical demands that come from devices you didn’t realize were pulling power – sometimes even when they are supposedly turned off.

The best way I have found to deal with these little power vampires is to simply unplug them when not in use.

  • Bad Habits – Little things really can add up. One might think that leaving an outdoor light on every night or running a fan for noise doesn’t really do a lot. But I can assure you, as some one who lives on off-grid power, it really does make a difference to your batteries.
  • Accidents – Some summers back, I was up at first light and found that my whole house batteries were 82% charge. This is notable as they were reading at 97% when I had gone to bed.

Somehow, I had managed to use 15% of my available power overnight and this was concerning to me as this was not normal behavior.

Immediately, I went back into the house and starting looking for the problem.

A quick inspection found that the only thing running was the water pump. I thought this odd as no one was up yet, so there was no chance of the shower running.

Checking all the indoor water sources, I began to get frustrated as there was no sign of water being used. So why was the pump running?!

It was then, that I decided to walk around the house and check the outdoor faucets.

Sure enough, someone had decided to water her flowers late in the evening and had forgotten to turn the sprinkler off. Consequently, our water pump had been running the entire night (water pumps are notorious power hogs!).


If you find yourself in a situation where you are concerned about the power being drained from your batteries at night, then it would probably beneficial for you to ask yourself two things;

  • What is the normal nightly power drain?
  • What exactly is pulling power overnight?

It can be easy to blame the solar panels as solar power is still a new technology for most and consequently, there is still a lot most people don’t know about them. However, it would be a very rare situation for your solar panels to be the actual culprit.

Look for the basic common causes first and then if you still are challenged by a significant power loss, consult a qualified solar expert. It could be a faulty, or even power hungry, charge controller. Or it could be an electrical device in the house that is in the process of shorting out.

When it comes to solar power, it pays to be safe… which means proactive.

THANK YOU for sharing!