# Calculating refrigerator AH correctly

Posts: 111Registered Users ✭✭

So after years of design work, much of which involving numerous threads on this forum, we finally put our off grid solar system together along with all the loads it will be running at our cottage in northern Ontario. The system consists of 6 310 watt Rensola panels(1860 watts total) which get used to fill our 24V 430 AH bank of 8 batteries. The loads that the system is powering are an electric submersible water pump, an electric refrigerator, an electric front load washer and propane dryer, three LED light fixtures and cell phone and laptop charging for 8-10 people.

So far the system has been working great. We reach float at around noon or 1 PM. The lights flicker a bit when the water pump comes on but I think that is due more to the bulb than excessive amps. The thing that worries me is that the charge controller is saying that we are using about 15-20% of our battery storage while in resting mode during the night. Since this is July, which I should state is the only time of year we ever spend at this cottage, the resting mode usually only lasts from 9-10 at night to 6-7 in the morning. So the 15-20% of 430AH or 65-86 AH of use in 8-10 hrs would mean the fridge uses 8-8.5 AH per hour. All the formulas I have used to calculate required AH of battery storage, require at least 2 days of storage. That would be 384-408 AH for the fridge alone. Does this sound like the correct way to go about calculating this?

1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N

• Posts: 2,840Registered Users ✭✭✭✭✭
A reasonably efficient fridge/freezer, not a water-through-the-door, ice-maker, etc, but basic modern fridge might use ~1500 wh per day. That would be roughly 1500/25v =~60ah/day.

If it's using that or more just overnight, I'd suspect either very warm ambient, being left open, filled at night with lots of warm beer for the morning, etc which would cause more cycling, or a more solar specific issue. Some might include; electronics in the fridge or other loads preventing the inverter from going into sleep mode between cycles, or the sleep mode messing up the defrost cycle.
Off-grid.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
• Posts: 5,090Solar Expert ✭✭✭✭
1. I will bet that period at the fridge is defrosting, in the 'overnight'.. .norm is about 11.5 hrs between .5 hr defrost
2.  I have about 2 X your battery and almost the same PV and use about 7% with overnight loads, TV , reading, reharging |Smart phones , Tabs and laptop....
3.  But we do not have a water pump...
4. what is the Inverter draw?
5 how big is the fridge, Age?  We have a 3 year old,  plain Jane, 17 cu. ft G E that uses ~1.5 - 2.0 kWh per day
hth

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Posts: 111Registered Users ✭✭

Westbranch, if you’re using 7% of your battery storage with twice the AH and I’m using 15% with half the AH, then we are pretty close to the same. I was only able to really monitor my loads for a week and a half before we had to evacuate due to an approaching forest fire. During that period, the Classic 150 showed the batteries at about 86% most mornings but once or twice at around 82%. The fridge is a brand new LG 20.2 Cu. Ft. LTNS20220W which, according to it’s Energy Star sticker, uses 387 KWH per year. It has an inverter compressor which I was told was best for solar use.

My fear is that if the fridge eats up 15% of my battery storage in 10 hours, then I would go below 50% in 33 hours and that’s just on the fridge alone. Using the water pump which was not contributing to that 15% battery usage, would deplete them even faster.

I do have 4 more batteries that I was going to add to the system but decided not to at the last minute. I guess I will have to add them after all.

1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N
• Posts: 5,090Solar Expert ✭✭✭✭
edited July 25 #5
our fridge rated out at 319 kWh and it is  a different compressor than the old ones but not an inverter but very close as it will peak at ~40 Amps ad then down to 1 amp before it shuts off, runs about 50% of the time....
Do you have a WBjr? a real must ,  'knowing; how much is used and put back in to the batts.
Yes to adding batts....   just heading back to town, will check when there...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Posts: 111Registered Users ✭✭
Yes, we put in a Wiz bang but really didn't have enough time to look at any of the info it was giving us. This year was a big remodel year as well so the solar was just a small part on our project list. We are gone now for the season so maybe next year we can do more diagnostic work.
1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N
• Posts: 4,705Solar Expert ✭✭✭✭
Your sun may set at 9pm, but if you have a fixed array, you likely are running a net negative once you don't have direct sunlight on the panels. Do you check the battery capacity at 9pm?
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
• Posts: 111Registered Users ✭✭
edited July 25 #8
Sun sets at around 10 so even at 9 the panels are still generating power. Batteries at 100% and float before going to resting but since cocktails start at 5:30, my numbers could be a bit off. Again, I hope to pay more attention next season.
1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N
• Posts: 214Solar Expert ✭✭✭
I have a fridge rated 311 Kw=hr/ year. It uses just over 1 Kw=hr per 24 hour day so it seems to be similar to what you have. Unless you have a tracker, your panel output is going to vary over the day. Morning and evening output will be minimal.
Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. My 25th year.
• Posts: 2,211Solar Expert ✭✭✭✭✭
One piece of the puzzle is missing, the inverter self consumption which may account for a large portion of overall drain on the battery, perhaps up to 30%. of the total. Using a Kill-a-watt device one could see what the refrigerator itself uses over  24 hours as opposed to the net load, but the 1.5KW per day seems about right, 1Kw for the refrigerator 0.5 Kw Tare load.
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank

• Posts: 5,090Solar Expert ✭✭✭✭
To add, a WBjr can provide the same data, Inverter draw in all modes, especially 'Sleep'.  just turn on the system without the Inverter on, and then look at the consumption 'Page' or plot Battery amps as well as PV Amps.easy peasy...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep