Batteries older, fridge more inefficient, deeper discharges: Here's my plan

SurfpathSurfpath Posts: 352Solar Expert ✭✭✭
My Trojan L16REB's are now 5.6 years old. They have been pretty good I think.  For 5 years we typically discharged to 70-80% SOC. However, our 11Cu Ft fridge has been getting more inefficient.

In 2012 it was drawing ~1.7 KWH/d, now it's about 2.4 KWH/d (it's also a bit leaky and it's getting a bit small for us). 

Subsequently, over the past 3 months we now discharge to 57%-67% SOC (Trojan's DOD/cycle life chart here).  I am pretty sure this is because of the fridge. I believe we may hasten the end of our Trojans a little if we continue this way, so....

We are looking at purchasing a new, more efficient, slightly larger fridge and have narrowed it down to either an LG or a Panasonic Inverter Fridge. The 2 models that are available to us [we live very remotely - we cannot simply go to Home Depot, everything is pretty expensive to ship in] draw an advertised ~25.6KWH/Month (LG) to 35 KWH/Month (Panasonic). So a little less or more than one KWH/d.

Seems like a good solution?  here are a couple of hesitations:

1) Search: It seems like the Outback "Search" function may not work so well with these new fridges.  Here's the link to that discussion:

2) Cost: They are around 50-70% more expensive than a conventional compressor fridge here. Roughly speaking the inverter fridge will cost me 1,850us and a similar feature conventional fridge will cost 1,100us.

The reason for an inverter model is the low start up surge (aside: we don't come close to the wattage max for our Outback, but perhaps this feature will be helpful in the future). They also seem to have less moving parts and therefore last longer than a conventional fridge.  All the conventional fridges here come with a 1 year warrantee, but the dealer has the inverter fridges on a 3 year warantee.

Anyway, wondering what you all thought of this plan. As I explained, I am a little limited in what I can purchase.  I am not keen on a chest freezer conversion at present. But I am keen on raising the SOC's a little.

Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.


  • mcgivormcgivor Posts: 1,899Solar Expert ✭✭✭✭
    The efficiency of the refrigerator probably hasn't changed, but the batteries have, as batteries age they have higher internal losses which reflect in the amount of energy required to change them, I'm assuming you're looking at daily solar input rather than a measure on the output of the inverter with a Kill-a-watt device.

    Inverter refrigerators are perfect for off grid reducing consumption considerably as well as not having surge, they do however have a problem with search settings, reference to my system. Price wise it seems in North America the inverter units are on the higher en models only, here in Thailand there are many, ranging in size from small apartment sizes to double door monsters, non inverter seems only available in smaller size these days.

    One way around the search mode would be to have a dedicated small low idle 300W inverter for the refrigerator to allow search mode enabled on the large inverter to function, or do a timed shut down overnight. Some ideas.

    Did a quick search at on retail outlet here for inverter refrigerators, they carry 50 different models, divide price by 32 to get an idea of US $ just to give an idea. Grid power costs reflect the demand and supply responds accordingly, North America has cheap energy costs and higher disposable incomes.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • SurfpathSurfpath Posts: 352Solar Expert ✭✭✭
    It's an interesting question (whether it's the batteries that are not holding charge, as opposed to the fridge incurring more of a draw at night).

    I do know for sure that the fridge is drawing more (I make regular and lengthy K-A-Watt measurements), especially over the last 3 months.

    But I have not done the math to see if it is proportional to the increase in daily battery discharge.
    Can this be done?

    I am sure there are inefficiencies involved at each step. But here's a very simplistic attempt:
    My Fridge's going from 1.7 to 2.4KWH/d is a increase of .7 KWH/d (but, this is not used all at night, right? hmm)
    My 370 Amp hr 48v bank (potential for 17,760 watt hours) is now cycling (say) 12.5% deeper (or 2,220 watt hours).

    Rats, not as easy as I thought. But doing the math makes me realize that it's likely both the fridge and the old batts that are at issue.

    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • BB.BB. Posts: 27,574Super Moderators admin
    Also make sure the fridge condenser coils on the outside are clean (no dust bunnies) and if the coils are in the refrigerator walls (no coils on back/under fridge), that the sides have good air circulation too.

    And look inside the fridge--Cold air vents clear. Door and gaskets are sealing well when closed. Not making lots of ice (or cooling warm/hot food) when making day to day energy measurements.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Posts: 1,825Solar Expert ✭✭✭✭
    edited June 30 #5
    Is the ambient air around the fridge warmer this year? More house guests? Change in diet preferences? Somebody turned down the settings on the fridge? Dirty coils? Heavier loads on the fridge circuit starving the fridge of the voltage that it grew accustomed to? 

    Random ideas....
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • westbranchwestbranch Posts: 5,046Solar Expert ✭✭✭✭
    edited June 30 #6
    well you can always get an off the floor in you local seller from GE
    the price is in Can $$1,149, so discount that MSRP heavily if you aren't North of the 49 th..

    Pulls  ~30 Amps at 25 V when starting,

    similar on in Home Depot US$ 849

    These models do have a non inverter compressor that reacts like  the inverter type without the cost  $$ and Watts per day!.

    PS your rough location would help us understand your local environment... :)

    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, Hughes1100 Sat Modem
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Posts: 27,574Super Moderators admin
    Surfpath may be roughly in the Miami Florida region...

    -Bill "guessing" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.