Some people find that their solar batteries are discharged during the night and suspect that their solar panels drain the battery during the night. Is this really the case? In this article, we will explore what is really happening.
Your battery will not be drained overnight by solar panels. If your battery is flat, it could be due to a faulty charge controller/regulator or a problem with the battery itself. Charge controllers include built-in blocking circuits that should keep any back current to a minimum. Solar batteries have a lifespan of 5 to 10 years before needing to be replaced.
There are a couple of simple steps you can take to figure out what’s causing your flat battery:
Check the current flowing from your solar panel
During the day, you can monitor the current flowing from your solar panel to your battery. This will vary depending on the battery’s state of charge, but you’ll get a good idea of how much power your solar panel is producing.
You can use a multimeter to check this, and the reading will obviously vary depending on the size of the solar panel. A 100-watt solar panel should generate approximately 18 volts.
Check if there is current flowing from your battery after dark
After the sun has set and your solar panel is no longer producing energy, repeat the previous test in reverse. This time, you should look for any current flowing from the battery to the solar panel.
If there is a current present, the culprit is the charge controller/regulator, which is faulty and must be replaced.
Wire the regulator out of the circuit
Another way to check if the regulator/charge controller is at fault is to wire it out of the circuit. If, after doing this, your battery is still charged, you will know the charge controller is at fault. As it must remain active, albeit in “standby,” the regulator will always draw a small residual current. The residual current drain, on the other hand, is of mA order and thus nominal.
One of the main reasons for a charge controller to get faulty is when it is underrated for your solar panel’s power. It is always a good idea to get a bigger charge controller to have some leeway regarding its current amount.
Your battery is dead
If you discover that your charge controller or regulator is working properly after going through all of these steps, the main culprit will be the battery itself. Batteries have a set lifetime, ranging from 5 to 10 years, depending on the conditions under which they were used. The battery will then need to be replaced.
What is a blocking diode for a solar panel?
A blocking diode allows current to flow from a solar panel to a battery but prevents/blocks current from the battery to the solar panel, preventing the battery from discharging.
This works in theory, but it is not worth installing a blocking diode between your solar panel and battery, as a blocking diode will cause a voltage drop when charging the battery.
Should you install a blocking diode?
Many older books and articles advise blocking diodes to prevent reverse current flow back through the panel at night, while many others do not. It depends on the circumstances, but in general, in 12 volt systems, you will lose more power from diode losses than from leakage back into the panel at night.
The problem is that a diode will cause a voltage drop when the solar panel is charging the battery, and this loss of power is greater than the small amount of back current that it will block. It is thus not a good idea to install a diode in your solar panel system.
Installing a blocking diode is pointless if you use a charge controller because all charge controllers have built-in blocking circuits.
What is a bypass-diode?
It’s also worth noting the distinction between a blocking diode and a bypass diode. A bypass diode differs in that it is used to improve the performance of a solar panel if some of the cells are damaged or shaded. The bypass diode directs power flow around the damaged or shaded cell, preventing performance loss. Most modern solar panels have built-in bypass diodes.
How long should solar batteries last?
Solar batteries should last between 5 and 10 years, depending on the type, how they were treated, and the conditions in which they were stored. Lithium-ion batteries typically outlast lead-acid batteries, whose lifespan is reduced if a 50% DoD is exceeded.
How do you test a solar battery?
By Making Use of a Voltmeter or a Multimeter.
- Set the meter to a reading of 15-20 volts (Or a voltage higher than your battery voltage rating).
- Connect the meter’s negative terminal to the battery’s negative terminal.
- Connect the meter’s positive terminal to the positive terminal of your battery.
You will then be able to see the voltage that the battery is producing. If it is much lower than the manufacturer’s claimed rating, the battery is faulty.
