My battey charges better in cloudy days, why?

[wdc]

Hello, I have 240W worth of solar panels, they are connected to my Epever PWM 30A charge controller (with thermal compensation) and then to my SLA truck 90AH battery (2 months old), the battery powers only my 12V led light bulbs, these are the night lights to my house.

I'm happy with my new battery, but oddly, I've noticed that on cloudy days the voltage after sunset is higher than on sunny days. I live in the southern hemisphere and it's summer here, very hot summer, 14 hours-a-day of scorching sun, my battery rises up to 35ºC every day and even today (a cloudy day) the temperature was high (32ºC max), the battery voltage goes up to 14,2V every morning (that's my conservative setting to avoid water loss) and then, after bulk and absorb stages, it floats at 13,7-13,5V depending on the CC thermal compensation. At sunset, in a sunny day, voltage remains at 12,7V and with the use of the lights goes down to 12,3V aprox. in a normal day, never goes below 12,2V. But today it was cloudy all day long, even a few drops of rain fell, temperature is not low (29ºC right now) and oddly the battery voltage remained at 13V after sunset, right now is on 12,9V. I have noticed the same behaviour on some other partially cloudy days but not as stronger than today that was cloudy all day long.

How come my battery seems to get "better" or "stronger" charge in cloudy days? any explanation? thank you in advance.

[bob-n]

It could be that the electronics itself has an intentional temperature coefficient. Batteries are supposed to be charged 3mV higher in voltage for every degree C colder, so if the electronics is cooler, it may expect that the battery is also colder and charge the battery to a higher voltage.

Another fact is that solar panels produce more when they are cold than when they are hot. The effect is roughly 0.4% more output for every degree C cooler. I doubt that would explain what you're seeing.

[wdc]

It could be that the electronics itself has an intentional temperature coefficient. Batteries are supposed to be charged 3mV higher in voltage for every degree C colder, so if the electronics is cooler, it may expect that the battery is also colder and charge the battery to a higher voltage.

Another fact is that solar panels produce more when they are cold than when they are hot. The effect is roughly 0.4% more output for every degree C cooler. I doubt that would explain what you're seeing.

Thanks! the strange thing is that my battery is almost new and, being summer here, every day gets enough solar power to be charged easily, that's why it seems to me that cloudy day's charging doesn't mean fuller charge but "stronger" charge, if such a thing ever existed. Odd.

[Mike90250]

What is your voltage reading in the mornings, predawn ?
I suspect on cloudy days, you may still be in Bulk or Absorb, which is a higher voltage than Float. For a short while after sun goes down, the higher voltage surface charge may be fooling you. What are your daily watt hours harvest total ?

[wdc]

What is your voltage reading in the mornings, predawn ?
I suspect on cloudy days, you may still be in Bulk or Absorb, which is a higher voltage than Float. For a short while after sun goes down, the higher voltage surface charge may be fooling you. What are your daily watt hours harvest total ?

thanks! predawn my voltage is 12,4 in average. I have no idea how to calculate my daily watt hours harvest total, sorry.

It could be surface charge because it's a small difference, today at 00:00 hour my voltage was 12,6V, on sunny days it's about 12,4V at 00:00 hour.

I thought maybe this could be a well known phenomenon, but it seems it's not.

[chrisski]

I can only think you’re not using something on a cloudy day like air conditioning and the loss of an extreme load let’s the panels charge quicker.

Lots of different types of cloudy days. On what I call a light overcast where I can almost see my shadow, I get 1/3 rd the amps I normally do. On a light overcast day like that, I may not need to fire my generator up to fully charge my batteries, but my system certainly does not charge better than a sunny day.

[SunEagle]

I can only think you’re not using something on a cloudy day like air conditioning and the loss of an extreme load let’s the panels charge quicker.

Lots of different types of cloudy days. On what I call a light overcast where I can almost see my shadow, I get 1/3 rd the amps I normally do. On a light overcast day like that, I may not need to fire my generator up to fully charge my batteries, but my system certainly does not charge better than a sunny day.

I will agree that the OP's electric load is less on cloudy days so the panels can direct more if their energy to charging the batteries instead of running some load.

[wdc]

I can only think you’re not using something on a cloudy day like air conditioning and the loss of an extreme load let’s the panels charge quicker.

Lots of different types of cloudy days. On what I call a light overcast where I can almost see my shadow, I get 1/3 rd the amps I normally do. On a light overcast day like that, I may not need to fire my generator up to fully charge my batteries, but my system certainly does not charge better than a sunny day.

I will agree that the OP's electric load is less on cloudy days so the panels can direct more if their energy to charging the batteries instead of running some load.

Like I said, I only use my battery to power the ceiling led lights in my house, nothing else.

[SunEagle]

Like I said, I only use my battery to power the ceiling led lights in my house, nothing else.

Well logic says a cloudy day will yield less in solar production then a full sunny day.

If your load is not affected by the sun being out or behind clouds I have no other suggestions as to why your batteries are charging faster.

[wdc]

Never mind, I'll just get used to it. Thanks!