Is your battery losing charge overnight? Do you suspect that the solar panel is draining the battery’s power?
There are several possible devices on a solar system that may be draining the battery – from a faulty battery that cannot hold charge, inverter, connected appliances, charge controller, and including a solar panel.
While it is possible for a solar panel drains the battery, it is not as common an issue more recently as charge controllers are used more and solar panels have blocking diodes.
So in this guide, I share information on signs that the solar panel is draining the battery, tests you can do to confirm battery drain by the solar panel, and how you can stop a solar panel from draining your battery’s power.
Do Solar Panels Drain the Battery
Good quality solar panels manufactured recently have inbuilt blocking diodes that stop the flow of power from the battery into the solar panel so do not drain batteries.
This used to be a problem several years ago with selected solar panels but is not an issue with recently manufactured solar panels with inbuilt blocking diodes.
Signs a Solar Panel is Draining the Battery
Note: These signs do not necessarily confirm that the solar panel is the reason that the battery is draining. There might be other causes. Therefore additional tests need to be done to confirm the actual cause of the battery drain.
- If a fully charged or partially charged battery charged directly by a solar panel looses power overnight or when shaded then it is possible that the solar panel is draining the battery.
Some solar phone chargers connected to and charging mobile phones have this problem.
Also, solar systems where the solar panel is directly connected to the battery with no charge controller in between may have it too.
You may want to read the article: Can you charge a battery by connecting a solar panel directly?
What Causes a Solar Panel to Drain the Battery?
The solar panel can drain the battery if the battery voltage is higher than the solar panel output voltage usually during the night or when the solar panel is shaded.
When this happens current flows from the battery to the solar panel if there is nothing blocking it like a blocking diode stopping the reverse flow of current.
The higher the voltage difference, the higher the current that will flow in the reverse direction if there is nothing stopping it.
How to Stop a Solar Panel from Draining the Battery
Here are a few tips to stop the solar panel from draining the battery:
#1. Only purchase solar panels that have inbuilt blocking diodes.
Check that solar panels have blocking diodes installed especially the small capacity solar panels that are connected directly to car batteries to keep them charged.
#2. Use a charge controller between the solar panel and battery. The charge controller blocks the flow of current from the battery to the solar panel.
Should You Unplug or Disconnect a Solar Panel Overnight (to Prevent Battery Drain)
You do not have to unplug the solar panel overnight to prevent the solar panel from draining the battery if using a charge controller or if the solar panel has blocking diodes and you are connecting the solar panel directly to the battery.
Consult the solar panel documentation or the supplier if the solar panel has inbuilt blocking diodes
How to Test if a Solar Panel Is Draining the Battery
To test if a solar panel is draining the battery, measure the current flow between the solar panel and battery terminals with the solar panel covered (with a blanket) so that it is not able to generate any power from the available light.
If there is a current flowing then the solar panel is draining the battery.
Final Word
A solar panel can drain the battery during the night or when shaded if it is directly connected to the battery and has no blocking diodes.
Connecting a charge controller between the solar panel and the battery also helps stop the reverse flow of current from the higher voltage battery to the low voltage solar panel during the night.
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