Have I set up my system correctly?

WillAK

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Joined
Nov 17, 2021
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Hey Guys,

I'm wondering whether I've set up my Solar System correctly, I've done some research into what I need and I thought I could put this together myself, but it's just not putting as much power into the batteries as I thought it would...

I live in Spain (Malaga, Costa Del Sol) so we get a lot of sun.
During the day the inverter itself cuts the power because the batteries always read 100% but at night even the slightest discharge (80W to power my off grid fridge, charging points and lighting) almost empties the batteries and the next morning the batteries are down to 60%. I'm wondering if the batteries are faulty or whether I've done something wrong.

My set up:
4x 100w Ecoworthy Mono Panels
2x 250Ah TAB MOTION 250/12v Batteries
30A TRIRON Epever Modular MPPT Charge Controller
2000W/4000W Green Cell Pro, Pure Sine Wave DC Power Inverter
ANFIL 4mm² / 12AWG Solar Panel Cables

With this set up (500Ah @ 12v) I'm expecting 6000w / 50% = 3000w which if I'm correct should mean my 80w power output should run without charge for 36 hours before the batteries get to 50%. Considering we get 10 hours of sun per day and the charge controller says it's putting in 340w of power during the day, this should run seamlessly forever right?
So why at night, 10 hours x 80w empties the batteries by almost half?

Any help/advice is much appreciated!
Will
 

rmaddy

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Your math is basically correct. 12V 250Ah batteries gives you 6000Wh. 50% is of course 3000Wh. So an 80W load should last 37 hours.

However, assuming your inverter is running it uses a lot of power just being turned on. Look in the specifications for something about idle power usage.

And your solar is probably not giving you 340W for the full 10 hours. You might get 340W in the middle of the day but early and late you will get less.

When you say "during the day the inverter itself cuts the power" do you actually mean the charge controller and not the inverter?

More math: since you state you have 10 hours of sun you have 14 hours of dark. So assuming your 80W load uses 40% of the battery in 14 hours, you have 14 hours x 80W = 1120Wh / 0.4 = 2800Wh instead of 6000Wh. But this doesn't take into account the inverter's power usage.

I would double check the settings for the charge controller and make sure the charge settings are correct for the batteries you have. You might also want to add a battery shunt so you know what's really being used and the real state of charge of the batteries.
 

Rednecktek

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Are those batteries Lith or Lead? If they're any form of lead acid (FLA, AGM, GEL) then you're only going to get half the available power which cuts your battery bank down to 250Ah. Recalculate if needed but that might be an issue as well.
 

WillAK

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Nov 17, 2021
Messages
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Yes, my typo, that's what I meant, the charge controller stops the input for most of the day, because the batteries say 100%. But if I was to disconnect the solar, the batteries drop down to about 80% with no input.
I don't find the solar has any problems in filling the batteries with power, I think the problem lies with the batteries themselves discharging too quickly, which would mean I need more batteries not solar panels?

Yeah its a minimum 2000w inverter, I'll try and find the idle power usage but I imagine It's quite high.

Could you explain this math please:
14 hours x 80W = 1120Wh / 0.4 = 2800Wh
( What's the / 0.4? )

The way I thought it would be if I have 100% battery power, I could run 80w (not including the inverter's power usage) for a straight 37 hours without having any input at all. So why would it run down to 60% after just 14 hours? This would mean the inverter pulls the remainder of the power?
 

WillAK

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Nov 17, 2021
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Are those batteries Lith or Lead? If they're any form of lead acid (FLA, AGM, GEL) then you're only going to get half the available power which cuts your battery bank down to 250Ah. Recalculate if needed but that might be an issue as well.
Yeah, they are Lead Acid. But I've already divided my battery output by half because I wouldn't want to run the batteries below 50%.

Or do you mean divide the Ah by 50% and then only use 50% of the remaining power to preserve the longevity of the batteries?
 

rmaddy

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The division by 0.4 is account for that being 40% usage. The result of 2800Wh instead of 6000Wh either means you are using a lot more than 80W all night (which is true because the 80W doesn't account for the inverter's own power draw) and/or your battery isn't really full when the charge controller cuts off.
 

rmaddy

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Yeah, they are Lead Acid. But I've already divided my battery output by half because I wouldn't want to run the batteries below 50%.

Or do you mean divide the Ah by 50% and then only use 50% of the remaining power to preserve the longevity of the batteries?
Your calculations are already properly taking into account that you can only use 50% of your battery capacity.
 

Rednecktek

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Sep 8, 2021
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775
Yup, I missed that. You've already calculated for that. What do the batteries read voltage-wise when the SCC shuts off? You may have a bad battery as well, the easiest way to check that is to take a battery out of the loop for a night, math the run hours, swap batteries and repeat. If you get drastically different numbers you probably have a bad battery that's dragging the other battery down significantly.

Yes, you'll have half your capacity for the test but with the loads you posted you should still have plenty to make it through the night.

Another thought, have you checked the water levels?
 

WillAK

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Nov 17, 2021
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Yup, I missed that. You've already calculated for that. What do the batteries read voltage-wise when the SCC shuts off? You may have a bad battery as well, the easiest way to check that is to take a battery out of the loop for a night, math the run hours, swap batteries and repeat. If you get drastically different numbers you probably have a bad battery that's dragging the other battery down significantly.

Yes, you'll have half your capacity for the test but with the loads you posted you should still have plenty to make it through the night.

Another thought, have you checked the water levels?

My first thought was bad batteries. But I only bought them 10 months ago so I've never checked the water levels.
I have tested them both separately and they both read a correct voltage (as far as im aware). But I will do another test.

Luckily I have mains power too so when the batteries run dry I can just switch the plug over to the mains whilst the solar charges the batteries up, which doesn't take long at all. Weirdly it charges quickly and reads 100% until night when the power just drops dramatically.

So considering I have 3000wh to use at night, what power output could I comfortably use to maintain the batteries?
 

Rednecktek

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Sep 8, 2021
Messages
775
Another check that doesn't risk going dark is to let the SCC stop charging, disconnect a battery and check the voltage. When it starts getting dark re-measure the voltage and make sure it hasn't self discharged while it was sitting there disconnected (a sign of a bad battery) and then repeat with the other battery the next day.
 
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