solar panel discharging battery

The most absurd work of a solar panel-discharging a battery

If you own a solar setup or if you are a outdoor person who carries around  a solar charger for your outdoor trips, it’s most likely that you would have seen the solar panel go bonkers sometime or the other.

Imagine a situation when the mobile phone battery shows up to be 30% charged, you want to be the nice guy to your phone, you connect the device to the solar charger. After a couple of minutes being connected to the solar charger it shows up to be 25% charged and you start blaming the phone for it.

The similar situation in case of a solar setup in your house, the battery connected to a solar panel has lower voltage in the morning compared to previous day night.

Sound little too familiar?

The answer is YES in either case the solar panel/ solar charger is most likely discharging the battery (There is a possibility that your smartphone is acting equally weird). I’ll get back to why it’s possible in the case of solar charger in a minute, now let us dive into solar panel.

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Can a solar panel discharge a battery?

If you found out the problem by yourself, here is a virtual high-5 to you for your observation skill. Trust me, most of them never figure it out the fact that solar panel can leach energy from the battery.

In solar home setups there are namely 2 common types of setups-Grid-tie setup and off-grid setup. In either cases this problem can occur. In one case it’s clearly visible and in other, not much.

If you own a grid-tie setup, you’ll be able to figure out the decrease in battery voltage and you’ll find out that the solar panel has been up to something.

The fishy part about off-grid setup is that, you may not even find out that the solar panel is leaching the battery. The reason being when you are completely off-grid you will use the battery’s energy in the night, say for air conditioning.

Hence the loss in energy(leaching) from the battery due to the solar panel will be masked, like a green bug on a leaf. When you get up in the morning and check out the voltage of the battery, it will seem perfectly normal but only the poor battery would know that the helper guy called solar panel is not helpful after all.

What is the reason for the leaching of the battery?

When you look into this issue you can find that, in the morning when your solar panel is connected to the battery, everything works as expected.

When the solar panel is exposed to sunlight, the photon of sunlight knocks out the electron(-ve charge) of the solar cell and hence it acts as a source of electron and hence source of current.

Due to this release of electron, the solar panel system is at a higher potential than the battery. This difference in potential between the solar panel and the battery leads to flow of current from the solar panel to the battery. Nice and clean.

But in the night or even in the morning when the solar panel is shaded due to a tree or due to clouds, the battery will eventually have a higher potential than the connected solar panel(no flow of electrons for the solar panel). Hence the solar panel will start draining the battery, the amount of draining depends on the extent and duration of shading.

Now, how to prevent the draining of battery?

If you have already bought a solar panel and you found out that it has the problem, the good news is that there are 2 solutions to this problem.

  • Using a series diode
  • Using a LED

Before you start hunting for a diode, I got to warn you that this is not recommended DIY thingy. The diode is better off when it’s pre-installed in the solar panel.

Most of the solar panels produced today have a series diode to block the discharge of the battery. Sometimes a LED is also used to block the self-discharge. LEDs allow small forward currents and very low reverse voltages.

That’s the reason why panel array should have built-in diode. If not there would be significant drain from the battery through the panels under low/medium sunlight conditions.  The diode will maintain the panel’s voltage above the battery and thus prevent the back-flow.

There is one last solution to this problem, it’s more of a quick fix than a solution and it would require work from your side everyday!. Yup everyday.

The solution is you would have to disconnect the cables connecting the solar panel to the battery everyday before you go to sleep. This solution is not recommended until you know which cables to disconnect and only if you know your way(precautions) to handle with electrical equipments.

If you are yet to buy a solar charger/panel then all you need to do is just apply the geeky tip below.

Geeky tip: Next time when you buy a solar panel or a solar charger, try asking the manufacturer whether their products have “Reverse flow protected circuitry”. That’s the technical term these kids use for connecting an extra diode to the panel.

Can a solar charger discharge my phone’s battery?

The case with the solar charger is exactly same as with the solar panel. The only difference being in the case of solar panels it was a battery which was connected, here it’s a device namely an iPhone or an iPod. The solar charger drains the phone’s battery when it’s shaded. The solution here is also the same- add a series diode or a LED.

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Did the leaching of battery energy happen to you. I would love to hear from you in the comment section below. Also don’t forget to SHARE and LIKE the article.

  • Ash45

    Interesting, this must be why my car’s battery kept dying when I plugged a solar trickle charger into it. While it probably worked fine during the day, I worked 2nd shift, so whenever the sun went down it must have been draining the battery.

    I had one die on me, and replaced it because it was about 4 years old and due for a replacement. Then the new battery kept dying too, and when I stopped using the solar charger, it went back to normal.

    I hope that future solar chargers have something like this implemented in them to prevent the solar panels from draining batteries, especially as solar panel batteries become more affordable and commonplace for home energy storage.

    • Brian Robert

      Yes Ash, in your case the solar charger could have been the problem, it sounds too familiar.
      More number of solar chargers which are being released these days have this feature. If it’s not too much ask can you tell me the trickle charger you had been using previously?

      • Ash45

        It was a cheap Sunforce solar 12v battery maintainer I bought at Home Depot for like $15. I think I bought it back in 2011. Says up to 1.8 atts/125 mAmp under ideal conditions, but that’s all I can remember from it.

        • Brian Robert

          Thanks for the reply Ash :)

  • Harley Kiener

    Yes. it happened. I bought a NOCO battery life plus solar charger. Hooked it up to a battery in my van that is only responsible for interior lights and is isolated from the starter battery. This panel supposedly has protection against a drainage, but by the end of night two my battery is completely dead.

    • Brian Robert

      Yes, the panel could be the reason in your case.

  • Zephod Beeblebrox

    Hah. I put a 5W solar panel and a charge controller on my bus batteries. That’s two batteries at 1300CCA. The battery read 12.3V when I started and 12.29V after a day in the sun. I have a feeling this solar panel stuff is a load of garbage. And yes, I have a charge controller.

    I have two 10W panels, each powering a single CPU fan. That’s all the power I can get from them and those fans do not shift much air at all. I’d have been better saving the $60 on solar crap and just buying a pile of D cells or installing another 12V battery and charging it from the alternator.

  • Tom Kilheeney

    I have 6 35 amp batteries in series, morning star pwm 15 amp, two 45 w harbour frieght panels and using 6 Guage wire. What should I do to better the system understand I just started only know little.

  • JR Thompson

    Hi Brian, great article. I’ve been living entirely off grid for 3 years now, the past few months I have noticed a slight drain in my batteries (2 type 27 Nautilus 12v). I have nerrowed it down to the very panel (stupid Coleman crap) causing the issue by simply waiting until dark and placing my trusty meter on the panel side of the blocking diode. The panel is out of the equation now, but my question to you is, can a unit be installed at the junction of all my panels to act as a primary blocking diode, thus leaving the diodes in the individual panels as back up? If so, does such a module exist or can you point me in the direction of one who can make me one (with the right info on my system of course)?
    Cheers and thanks.

  • Anthony Nicdao

    Sir, may I ask how to connect the diode or led in the solar panel with battery? or circuit diagram. Thanks for the answer..