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Do Solar Panels Drain Batteries at Night?

By Benjamin Strusnik February 14, 2022

Do Solar Panels Drain Batteries at Night

With many views on how to best prevent solar panels from draining batteries at night, discerning the forest from the trees can be challenging. 

The solutions are, however, more straightforward than they might appear. So whether you are still weighing up the pros and cons of utilizing solar panels or are an owner of solar panels, we’re here to show you all about solar panels potentially causing the draining of batteries and what to do to prevent it. 

Below, we list what we think is a helpful summary of the critical aspects you must understand to make an informed decision to prevent draining of batteries during nighttime.

Solar Panels and Nighttime Electricity 

Solar panels generate electricity through a process called solar energy conversion. That means solar panels convert sunlight into electrical energy during the day and store the converted solar energy in batteries.   

Does solar panel drain batteries at night

In general terms and with exceptions, the conversion of nighttime light energy (e.g., Moonlight, etc.) into electrical energy occurs at such a low scale that it is scarcely worth mentioning. However, the implication is that solar energy panels would, as a general rule, not generate enough energy to charge batteries at night.

It is a solar panel fact that when panels are not storing electrical energy in the batteries at night, the panels can draw power from the batteries causing a reverse flow. So, effectively it means that the panels are potentially “draining” the batteries at night. 

The Compatibility of Solar Panel Voltage and Battery Voltage 

The first point of departure to ensure that panels do not drain batteries (during the daytime or the nighttime) is to ensure that your solar panel voltage output is compatible with your battery voltage.

Suppose your solar panel voltage is not compatible with your battery. In that case, the battery will overcharge, or the battery will not work at all (e.g., charging a 12-volt battery with a 24-volt solar panel or charging a 24-volt battery with a 12-volt solar panel). A 12-volt battery requires a 12-volt solar panel, and similarly, a 48-volt battery needs a 48-volt solar panel.

The Importance of Solar Charge Controllers 

In addition to the panels and battery voltage compatibility, it is essential to ensure that a Solar Charge Controller connects to your solar power system.  

Do solar panels drain batteries at night or not

A Solar Charge Controller (Solar Charge Regulator or Voltage Regulator) is an important component of your solar system found between the solar panels and the batteries. It regulates the voltage from your panel going into your battery to make sure the voltage of the two devices matches up, increasing energy efficiency.

The function of the Solar Charge Controller is threefold in that it:

(i) ensures that the battery doesn’t overcharge during the daytime;

(ii) ensures that reverse flow does not take place during the nighttime (i.e., blocks a reverse current from going back into the solar panels);  

(iii) protects the batteries from electrical overload when the panels produce more voltage than the battery can endure.

In terms of nighttime drainage, the Solar Charge Controller prevents the panel from draining the battery by way of the power reversing from the battery into the panels.

PWM and MPPT Solar Charge Controllers 

There are two types of Solar Charge Controllers that ensure current flows only one way (from the panel to the battery) and that the solar panel and battery voltages align, namely a PWM or an MPPT type Controller.

A PWM (Pulse Width Modulation) Controller lowers the panel voltage to match the battery voltage.

PWM Controllers require the voltage of the solar panel and the battery’s voltage to match (e.g., using a 12-volt panel that has a potential higher volt output) with a 12-volt battery. Therefore, the Controller will lower the 12-volt panel, whose actual voltage output is higher than 12 volts, back to 12 volts to match the 12-volt battery it is charging.

An MPPT (Maximum Power Point Tracking ) Controller is more sophisticated. It can handle higher voltage solar panels without the panel or the battery voltage 100% compatible.

However, PWM Solar Charge Controllers are more popular due to the high cost associated with MPPT Solar Charge Controllers.

The Relevance of Blocking Diodes 

A Blocking Diode or Isolation Diode serves the same purpose as a Solar Charge Controller, effectively “blocking” electricity flow from the battery to the solar panel while admitting electrical charge from the solar panel to the battery. 

If you don’t have a Solar Charge Controller, the next best thing is to make sure that the solar panel comes with a Blocking Diode component, which will ensure that the panel does not discharge the battery due to reverse flow.             

Troubleshooting 

Do you find that the battery still discharges at night, even after ensuring that the panel and the battery are compatible? The following might be avenues you can pursue to resolve the issue:

Check Solar Controller for damage or programming reset                                                                                              

If the battery still drains at night, regardless of having inserted a Solar Charge Controller, chances are that the Solar Charge Controller is not working correctly. That will mean that the power from the battery will flow back to the panel, as the Controller is not stopping the reverse flow.

Do solar panels drain batteries after sunset

You can also check that your Controller is correctly programmed to ensure that it operates functionally, as incorrect programming could also cause the battery to drain.  

Drained Battery 

Generally, it helps if you recharged your batteries when their charge is below 50%. In addition, batteries should never be allowed to deplete their charge all the way to 0% before recharge, as this could damage the battery and cause spontaneous battery discharge. You can use a multimeter to confirm whether the battery carries a charge. 

Power Draw Even After the System Shuts Down

Although a Solar Charge Controller prevents the solar panels from draining the battery, household appliances can still drain a battery even when your system seems to shut down (e.g., a computer in sleep mode can still draw power).  

You should check whether your household appliances continue to draw power from the battery at night, even though the devices are in off-mode.

Extreme weather 

what if Solar Panels drain batteries at night

Very hot or freezing weather can also affect the functioning of the battery's circuits.

However, you can mitigate this risk by ensuring that your batteries are not degraded or old. Most modern solar batteries should be able to cope with extreme weather conditions.   

Conclusion

It helps if you understood the potential draining of batteries at night by solar panels in the context of the Solar Charge Controller and Blocking Diodes. 

Draining batteries are not always related to solar panels or a faulty Controller. However, they could also indicate other issues you need to attend to (e.g., battery maintenance, weather circumstances, household appliances draining the battery at night, etc.) 

Solar panels are massively beneficial to the environment, but that benefit is going to be diminished if your batteries are constantly discharging and wasting the energy your panels have collected. 

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