Where is the power go ???

[monogram]

Does anyone know what is the AH or kWh for the Sams Club GC2 battery?

To prolong the life of battery, from CC, I set the cutoff voltage at 24V which mean when battery reach the level of 24V then the inverter will shutdown.


I'm in Southern California, the panels faced South at the angle of around 35-40 degrees
During this time, sun rise at around 6:00AM and set at 8:00PM. I have about 11 hours of sun


As you can see from the screenshot below that I just took from my phone at 6:39PM, the panels still produced 52W with today total of 4150Wh as of 6:39PM. This reading is from CC which has the same reading as my Current Clamp meter and Fluke 87 Volt Meter.

I have Clamp Meter and volt meter connected to solar input of CC. The reading on those 2 external devices are the same as CC display.
I also have clamp meter and volt meter connected to the inverter input. The Kill-a-Watt meter connected to the output of inverter. The reading on those 2 external devices is about 10W higher than the reading from Kill-a-Watt. (I assumed that 10W loss is from the inverter)

The graph below show today reading for the last 6 hours.

Capture.JPG

[SunEagle]

There are a number of Ah ratings for a Sams Club GC2 battery. It should be either written right on the battery or on the specification sheet that came with the batteries.

If you scroll down to the bottom of that advertisement you posted it shows a 20hr rating at 215Ah

[Raul]

I have made a calculation of my own system, using shunt battery monitor, energy meter for AC power and all victron gear, integrated with a CCGX hub.
For every 1kwh AC consumed, I have to harvest 1.5kwh DC to split even and not run in deficiency.
So, if I use 3kwh AC , I need to put back 4.5kwh DC.
That diference accounts for:
-charging and discharging round trip
-inverter eficiency and stand by load of inverter. These are two different things.
No load consuption 20w; partial load 90%; half load 93%; full load 95% eficiency.
The most inefficient is at partial/ small loads.
- solar charger eficiency (what the charger harvests and what goes in the battery is not the same. If you would have a shunt and look what energy goes in the battery is less to what the CC is producing, even if you add the load at that time.
- system overall losses in cables fuses etc
- battery state of health:
the more tired a battery is, the more energy is required to keep in float due to increased internal resistance. That energy will not come back to you in form of discharge.
i use rolls S480 from new. They are 3 years in service, and never struggled to keep the sg at 1.28.
Reason: I over panelled( double the amount needed), and over sized the bank to 6 day reserve. I never discharge more than 20%.

[Sunking]

Capture.JPG

Only thing your printout is showing is you are in deficit charging. You are using 115 watts and your panels are only generating 52 watts.

As for the missing power goes, is not missing. You just have not accounted for inefficiency. As Raul eluded too, and battery system at best is only 66 to 70% efficient. You have not accounted for system losses like battery charge efficiency, wiring losses, and inverter efficiency.

One problem I see is is your batteries are way undersized and your math is way off. A pair of GC batteries assuming they are 225 AH @ 12 volts has a total of 2700 wh, and you are discharging roughly 100% each day. That being said you need 4 to 5 times more battery capacity. That is why your battery voltage is so low in the morning and with that kind of abuse you can expect the batteries to be replaced inside a year or less.

[monogram]

Hi SunEagle,

Yes, I do see the 215Ah on the SC website. If that is the case then the batteries should have 5160Wh (215Ah x 24v). To prolong the battery, it's recommended to discharge DOD to 50% which is 2580Wh for 24V bank, right?

i have batteries (1 year old) to fully charged during the date via solar, the batteries also entered the floats condition. For 12 hours at night, the device only used 1380Wh (115W x 12 hrs)

From above assumption, I should have 1200Wh (2580Wh - 1380Wh) left or 70% by the next morning, but it not.

Hi Sunking,
Correct me if I am wrong as I think my math is correct: My batteries is 24V bank and I only discharge about 1380Wh at night (the device use 1380Wh directly from Solar during the day)
On my CC, I set it to charge the batteries to 29.2v (100%) and discharge to 24V (0%)

what you you see on the screenshot above is the device using 115W while solar only generating 56W because it is close to the evening, at 6:39PM therefore the inverter have to take 2.33A @ 25.7V out of the batteries.

[Sunking]

Hi Sunking,
Correct me if I am wrong as I think my math is correct: My batteries is 24V bank and I only discharge about 1380Wh at night (the device use 1380Wh directly from Solar during the day)

No you have gone about it wrong. You start with your daily load. In your case 115 watts x 24 hours = 2760 wh. You size the batteries to 5 day reserve capacity with only 50% of the capacity is usable so as to give you 3 days run time without sun. So 5 days x 2760 wh = 13,800 wh battery capacity.

To find AH capacity you must know nominal battery voltage and yours is 24 volts. AH = Wh / Battery Voltage. 13800 wh / 24 volts = 575 AH. You have 215 AH.

FWIW batteries do not float at night, they are discharging.

[monogram]

Hi Sunking,

I am discussing here is for the batteries with 1 day use, NOT 5 days.

As mentioned from my previous posts, the device only use 1380Wh during the night (12 hours). The power usage for other 12 hrs during the day is coming directly from the solar. The solar generated about 4200Wh a day during this time of year.

Since DOD 50% of the batteries, which is 2580Wh and I only use 1380Wh then why the batteries get to zero percent or only have 24V by 6:00AM the next morning?

[Bala]

Looking at the spec sheet your batteries are listed for 215ah at the 20 hr rate,

but they are only listed at 157ah at the 5hr rate.

You are basing your math on the 20hr rate for capacity when you are discharging over 12hrs so you need to work out a rough battery capacity for a 12hr rate.

Also consider that the manufacturer specs are for brand new in a perfect world.

As we do not live in a perfect world I always take 10% of any manufacturer spec for anything when new, you could take a little more as the batteries are not new.

[monogram]

This is where my my confusion start between 20 hours rate vs 5 hours rate or other hours rate, can anyone please explain?

[paulcheung]

Looking at the spec sheet your batteries are listed for 215ah at the 20 hr rate,

but they are only listed at 157ah at the 5hr rate.

You are basing your math on the 20hr rate for capacity when you are discharging over 12hrs so you need to work out a rough battery capacity for a 12hr rate.

Also consider that the manufacturer specs are for brand new in a perfect world.

As we do not live in a perfect world I always take 10% of any manufacturer spec for anything when new, you could take a little more as the batteries are not new.

He is not discharge the battery at 12 hours rate. He discharge the battery bank at 50 hours rate.

[NochiLife]

This is where my my confusion start between 20 hours rate vs 5 hours rate or other hours rate, can anyone please explain?

At the very simplest, the faster you discharge the battery (i.e. 5 hour rate instead of a 20 hour rate), as a result of internal losses, the less power you will be able to use before the battery is empty. Which is why the faster discharge rates have less capacity (i.e. 157Ah @ 5hr discharge, and 215Ah @ 20hr discharge).

Batteries used on RC (radio controlled) devices often get discharged at very high rates, often past 1C (i.e. discharging a 5Ah battery at 5A; 2C is "discharging a 5Ah battery at 10A")...and they can often get warm or hot to the touch. All of that heat is power that didn't make it into the RC device. Big batteries like used in solar systems (i.e. your batteries) will not measurably get warmer with typical solar loading--but power is still getting lost internally.

[Sunking]

Hi Sunking,

I am discussing here is for the batteries with 1 day use, NOT 5 days.

As mentioned from my previous posts, the device only use 1380Wh during the night (12 hours). The power usage for other 12 hrs during the day is coming directly from the solar. The solar generated about 4200Wh a day during this time of year.

That is where you have gone wrong and destroying your batteries. All I can say is good luck with that.

[inetdog]

Instead of trying to calculate (or guess) where the power to the load is coming from at any given time of day, the calculations are much simpler if you just take the total load over 24 hours (2760Wh if my math is correct) and then subtract that from the total output power from the panels that is actually used (that is sent out the DC output of the charge controller.) If the batteries do not need charging and there is no load, there will be zero output from the CC regardless of what the panels are capable of producing.
Second, as described several time, the maximum panel output will only be there for a few hours on either side of solar noon (based on the panel's facing direction.) The result is that for a middle latitude site, such as the US Midwest, the effective output over the entire sunlight period will be the same as the maximum output for 4-5 hours.
For 620W of panels, that would be at best 3100 hours if the panels produce their full nominal power at full maximum insolation. I do not see how you can measure panel output to the CC using a KillAWatt meter. Please tell us more!
3100 Wh -2760 Wh is the amount of "extra" power you would have if the inverter, the CC and the charging/cycling chemistry of the battery bank were all at 100% efficiency. Which is not credible.