Solar, Batteries and Fridges...oh my

[Kropdad]

I have a dual fridge freezer combo, 80 litres running on 2 by 105 gel batteries, 50 amp Mppt and 2 by 120 watt panels. I have the exact same solar battery set up for house and nav system plus a 3rd bank of a single 90 amp crank battery. Rarely see house and fridge bank under 90%. I also run the fridge from the load output on the Mppt, it holds a solid 13.8 v, and I believe that this uses power off the panels during the day then over to batteries at night. Could be wrong but I've had the system for over a year no probs.

[Sunstone]

Originally Posted by jackjb53

I can't help you with the solar info...just starting to look at solar myself. I do have a suggestion about leaving your food in the fridge/freezer. A delivery captain advised me to leave a cup of ice cubes in the freezer portion of the fridge. If on your return to the boat the cup is filled with a solid mass of frozen water and not cubes, you can surmise that the power to the fridge was off long enough for the cubes to melt and the food to spoil.

Well now jackjb53, that is a sublime and simple answer to the problem of unattended food spoilage if away for a time.

Thanks for the heads-up.

- JB

[CarolM13]

We have a C& C 110 and put in a 100 watt solar panel which charges the two house batteries which runs the frig. Summer of 2019 we were on Block Island and we did not need to run the engine for the three days while we were there. I also try to put Block Ice in the bottom of the frig. to keep it cold. Although We do not keep the frig on when we are not on the boat. We only use the frig when we are away for more then one night. My husband put the panel and controller in with technical input from a fellow boat club member. If you want additional technical info let me know (beyond my pay grade and will have my husband reply).

[wesevans]

If it was me I would have separate battery battery banks for house and engine start.

[dmkkeng]

Originally Posted by gusdog

I upgraded to a Block Island 40 this past fall and it will be moored in Midcoast Maine. It has an installed and working Norcold de0051 refrigerator, but I don't have the juice on my 12V system to run it on battery. The label on the fridge says nominal DC 12/24V 3.0/1.5A
I was thinking of setting up a 3 bank battery system: start, house and fridge. I would like to have the fridge always on so that I can leave a few things behind and not have to always drag everything to the boat for every trip. I was thinking of 2 50W panels, a Victron Cyrix battery combiner, and a Victron Charge controller and of course a few batteries. I did get recommendations from the folks at Victron NA, but that was before I had the idea of having a 3rd bank just for the fridge.
I know the fridge will not run 24/7, but how much it runs depends on many factors such as temp, how much is in the fridge, how many times my 4-year-old opens the fridge, etc.
So, my questions are 1.) has anyone set up a similar system? 2.) is having the fridge on its own bank a silly idea? I have pressurized water, a mix of different lights (LED and incandescent), circulation fan on new Airhead composter and I don't want to not have enough power to run everything. 3.) what size battery should I be putting in for the fridge and how many? 4.) is the dual 50w solar panel setup enough?

be easy on me, I am a noob to solar and am comfortable with electrical, just not super knowledgable.

Let the beatings begin

Fridge draw per day approximately 50 amp hours
Conservative output of a 100W panel per day 25 amp hours
Size of battery bank (Useable Flooded Lead Cell battery capacity is 35% of total capacity, that is based on not discharging the batteries below 50% and likely not being able to charge up the batteries much higher than 85% capacity) for 2-3 days of running the fridge (100-150 amp hours) with no sun equates to a battery bank size of approximately 300 -425 amp hours.

Recommend a minimum of 2 100W solar panels
Recommend a minimum of 2 12v 200+ah batteries or 4 6v 200+ah batteries

Having a separate battery bank for the fridge is not an efficient use of battery capacity, a house battery bank and separate start battery is the typical configuration. Make sure you have a low voltage disconnect on the house battery bank to prevent the batteries from discharging below 50%.

There are other battery technologies with increased useable capacity however they cost significantly more. I have 400W of solar and 660ah of battery capacity however, at times I run both a fridge and freezer and likely have higher daily amp hour bud. I also have a back-up portable generator that I use early/ late season.

Hope that helps!

[tomsnrg]

Originally Posted by Lost Horizons

Yes. Serves no purpose and makes things more complex.

Expect 300-350 watt-hours from two unshaded 50 W panels per day in a summer, 150-200 watt-hours in winter. Your refrigerator will need about 800 watt-hours a day if 3 A is the average current, or approximately 400 watt-hours if it is a maximum current with 1/2 duty cycle.

This production seems optimistic. Try it out. You can go for a bigger MPPT charge regulator and add panels, this opens a can of worms of problem with shading and is generally not a good idea, or put more panel-controller combinations in parallel.

[skipgundlach]

Originally Posted by jackjb53

I can't help you with the solar info...just starting to look at solar myself. I do have a suggestion about leaving your food in the fridge/freezer. A delivery captain advised me to leave a cup of ice cubes in the freezer portion of the fridge. If on your return to the boat the cup is filled with a solid mass of frozen water and not cubes, you can surmise that the power to the fridge was off long enough for the cubes to melt and the food to spoil.

Another is to freeze a small cup of water and then put a quarter on the top.

If you return to it on the bottom, you know it thawed the entirety before refreezing...

[lmxr]

Originally Posted by gusdog

I upgraded to a Block Island 40 this past fall and it will be moored in Midcoast Maine. It has an installed and working Norcold de0051 refrigerator, but I don't have the juice on my 12V system to run it on battery. The label on the fridge says nominal DC 12/24V 3.0/1.5A
[...]
I know the fridge will not run 24/7, but how much it runs depends on many factors such as temp, how much is in the fridge, how many times my 4-year-old opens the fridge, etc.

Usually fridges are designed to run for about 30 to 50 % of the time. Assume 50 % and a 12 V system, then it will consume around 50 % * 24 h * 3.0 A = 36 Ah. Or 12 V * 36 Ah = 432 Wh.

Worst case it runs full time and then it draws 72 Ah or 864 Wh (each 24 h).

So, my questions are 1.) has anyone set up a similar system? 2.) is having the fridge on its own bank a silly idea?

A silly idea? Perhaps, perhaps not. I do not immediately see an advantage while I do see disadvantages (increased complexity). Is there a particular reason why you want it to have a separate bank? If the concern is that the fridge should stop before the house battery is empty (such that more important loads keep running), then put the fridge on its own voltage sensitive relay that cuts out when, for example, the battery voltage drops below 12.4 V.

[...]
3.) what size battery should I be putting in for the fridge and how many?

Worst case the fridge draws 72 Ah/day. Assuming you generate your energy with solar panels, the battery is only discharged by the fridge during the night, and during the night (about 12 hours) the fridge cannot consume more than 72 Ah / 2 = 36 Ah.

This is not much and can be sustained by almost any fully charged house battery bank in decent condition. A good deep-cycle lead-acid of more than 100 Ah should do the job for a few years assuming it only has to power the fridge during the night.

If really necessary you can let the fridge run less during the night. The temperature will go up a few degrees during the night but it will stay sufficiently cold, especially if you put a few gallons of water in it to increase the heat capacity.

Be aware though that the overall energy consumption does not depend on when the fridge runs, so running it less during the night means that it will run more during the day.

4.) is the dual 50w solar panel setup enough?

This is always a bit of a guess, yet we can do some calculations to get a rough idea. Assume those two 50 W panels are unshaded and have an ideal slope of 40 °. We'll put Midcoast Maine in the PVGIS calculator (https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP). We assume a nice MPPT controller and thick cables such that the losses will be 10 % or less. Putting this in the calculator returns for the month of July 15 kWh or about 471 Wh/day. Somewhat less for the other months, although those are probably also cooler.

This 471 Wh/day is slightly more than the expected fridge consumption of 432 Wh/day. There does not appear much room for losses. One major cause of losses is the energy efficiency of the battery. For lead-acid this is around 80 % so 20 % is lost. Assume the panels put 235 Wh in the batteries (excess energy during the day), then 20 % * 235 Wh = 47 Wh is lost.

Taking above into account, I expect your setup will run below break-even, even if you have only the fridge running and even if your solar panels are unshaded and angled well. Therefore I think you need more energy sources. Perhaps more solar panels?

[Pete7]

Originally Posted by lmxr

Worst case the fridge draws 72 Ah/day. Assuming you generate your energy with solar panels, the battery is only discharged by the fridge during the night, and during the night (about 12 hours) the fridge cannot consume more than 72 Ah / 2 = 36 Ah.

This is always a bit of a guess, yet we can do some calculations to get a rough idea. Assume those two 50 W panels are unshaded and have an ideal slope of 40 °. We'll put Midcoast Maine in the PVGIS calculator (https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP). We assume a nice MPPT controller and thick cables such that the losses will be 10 % or less. Putting this in the calculator returns for the month of July 15 kWh or about 471 Wh/day. Somewhat less for the other months, although those are probably also cooler.

Taking above into account, I expect your setup will run below break-even, even if you have only the fridge running and even if your solar panels are unshaded and angled well. Therefore I think you need more energy sources. Perhaps more solar panels?

Actually, we find the fridge uses far less at night simply because no one is opening and closing the lid and the air is generally cooler.

Since this thread started before the Spring, be interested to hear how he got on.

Pete

[bensolomon]

I put a small battery operated fridge fan in this season. Major improvement in cycle time fir the fridge.

[goboatingnow]

Originally Posted by gusdog

I upgraded to a Block Island 40 this past fall and it will be moored in Midcoast Maine. It has an installed and working Norcold de0051 refrigerator, but I don't have the juice on my 12V system to run it on battery. The label on the fridge says nominal DC 12/24V 3.0/1.5A

I was thinking of setting up a 3 bank battery system: start, house and fridge. I would like to have the fridge always on so that I can leave a few things behind and not have to always drag everything to the boat for every trip. I was thinking of 2 50W panels, a Victron Cyrix battery combiner, and a Victron Charge controller and of course a few batteries. I did get recommendations from the folks at Victron NA, but that was before I had the idea of having a 3rd bank just for the fridge.

I know the fridge will not run 24/7, but how much it runs depends on many factors such as temp, how much is in the fridge, how many times my 4-year-old opens the fridge, etc.

So, my questions are 1.) has anyone set up a similar system? 2.) is having the fridge on its own bank a silly idea? I have pressurized water, a mix of different lights (LED and incandescent), circulation fan on new Airhead composter and I don't want to not have enough power to run everything. 3.) what size battery should I be putting in for the fridge and how many? 4.) is the dual 50w solar panel setup enough?



be easy on me, I am a noob to solar and am comfortable with electrical, just not super knowledgable.



Let the beatings begin

Bad idea. A single bigger bank is better then subdivided smaller banks.

[Adelie]

Single large bank or 2 banks that are normally connected but which you can cut part out for servicing.

Peukert effect, the faster you draw energy the less total a lead acid battery will provide. By having everything in one bank the load compared to the bank size is smaller and the bank will provide you with more power. Alternatively you get the same amount out but your depth of discharge is smaller and the battery has more cycle life.