Solar Generator for freezer question

[Bearclaw]

Smart move is to fill all empty space in your freezer with frozen water bottles. That will help it maintain frozen food for a long time, as a cooler.

Don't open the door much to check. I don't even begin to worry about mine until it's been without power well over 12 hours.


.

Yep! Already do that!

 

[cosermann]

Finished up a DIY solar generator setup this week. Tested it with my freezer over the last 24 hours. Then I was reminded of this thread and thought I'd post up some real-world results as a data point for folks to illustrate performance in practical terms.

Test components:
Freezer - Whirlpool 16 cu. ft. chest freezer, model WZC5216LWO, 120 v, 3.5 amps.
Battery – LiFePO4 (lithium iron phosphate), 200 Ah, 12.8 v nominal, 2560 watt hrs. Charged to 100%.
Inverter – Giandel PS-1200JCR, 1200 w pure sine wave (2400 peak/surge), approx.. 90% efficient, no load draw 0.7 A
Battery monitor – Renogy RBM500-G1, ver 2.0, working dissipation 10-15 mA (standby 1-2mA), accuracy +/- 1%, backlight 500 mA.

Test conditions:
Turned on inverter and plugged freezer in for 24 hours.
Lid opened a time or 2 to start the freezer, and one of the kids opened it once to look for something.

Results as measured by battery monitor:
Battery down from 100% to 78% capacity (22% used).
Battery down from 200 Ah to 154 Ah (46 Ah used).

 

[cosermann]

Commentary:

Based on these results, this setup could run this freezer for approx. 4.3 ish days or approx. 103 ish hours hours without charge, to 0% battery capacity (possible with LiFePO4 in a pinch, not adviseable with lead acid).

Time could be extended if the freezer was only plugged in to cool every X hrs, freezer covered with a blanket, lid kept shut, etc.

Running the battery to 40% SOC (to be kind to your cells and extend its life) this setup could run this freezer for approx. 2.6 ish days or 62 hrs. (the numbers are slightly different depending on if the calc is run using the reported percentage capacity or Ah used).

I never observed the DC watt draw of the freezer being above 65 ish watts, and the freezer ran along at closer to 35 watts. Could be the sampling rate of the battery monitor isn’t fast enough to catch the initial surge when it starts up.

I haven't tested the solar panel input side yet as to how many watts of panels would be needed to keep this going indefinitely.

YMMV!

 

[ditcherman]

Wow great real world test!

 

[cosermann]

Pics of the setup for those who may be interested. This is version 1.0. It needs some tweaking (most notably a way to quickly disconnect the shore charger and solar controller when not in use to minimize parasitic loads on the battery).



(On the right, one might notice the high tech solution of using an old feta cheese container to cover/protect the terminals of the battery monitor shunt.)

 

[cosermann]

The whole thing is a chunk, weighing in at approximately 75 lbs, so it's permanently mounted to it's own hand truck.

 

[cosermann]

I've been asked how much solar generation capacity would be needed to keep this kind of thing going indefinitely. Not having tested it (yet), I'm going to recklessly make a number of assumptions and rip off a back-of-the-napkin calculation that may be of some benefit to someone.

During the test, 46 Ah were used, or 552 watts (46 Ah at 12 v). If we shoot for replacing that over a 6 hour solar charge window, that's would be 92 watts per hour. So, you might think a 100 watt solar panel would do the trick, but they're maybe more like 70% efficient in practice, so one could go with 3x50 watt panels (150 w total), or 2x100 watt panels (200 w total). To account for some less than ideal sun conditions, a rainy day here and there, losses, inefficiencies, etc. doubling that to 400 total watts of panels wouldn't be unreasonable, imho. This is all for LiFePO4 batteries. Lead acid batteries may require more as they are happiest when kept more regularly fully charged.

Those with further interest might like the following resources:

DIY Solar Power Forum

Love building DIY solar electric projects? Come hang out :D

diysolarforum.com

Mobile Solar Power: Made Easy! DIY Off-grid Solar Power!

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

Will's channel on YT -

https://www.youtube.com/c/WillProwse

 

[bwframe]

What a great rundown cosermann!

Got a ballpark figure of the investment on this system?


.

 

[churchmouse]

Commentary:

Based on these results, this setup could run this freezer for approx. 4.3 ish days or approx. 103 ish hours hours without charge, to 0% battery capacity (possible with LiFePO4 in a pinch, not adviseable with lead acid).

Time could be extended if the freezer was only plugged in to cool every X hrs, freezer covered with a blanket, lid kept shut, etc.

Running the battery to 40% SOC (to be kind to your cells and extend its life) this setup could run this freezer for approx. 2.6 ish days or 62 hrs. (the numbers are slightly different depending on if the calc is run using the reported percentage capacity or Ah used).

I never observed the DC watt draw of the freezer being above 65 ish watts, and the freezer ran along at closer to 35 watts. Could be the sampling rate of the battery monitor isn’t fast enough to catch the initial surge when it starts up.

I haven't tested the solar panel input side yet as to how many watts of panels would be needed to keep this going indefinitely.

YMMV!

So, this is totally on the battery/inverter no solar back up then....????
We had a battery backup system for the house with 4 deep cycle marine battery's and it eventually grew to 8 total with 2 4 battery marine (bass boat style) chargers on shore power to keep it topped off. 2 inverters to split the load. Never ran it to the bottom but it would keep the lights on. Both refrigerators running and the furnace from Friday night until Monday morning. Voltage was not quit critical yet but close.
1 TV and sound bar.
Of course we had to monitor our usage which drove CKW crazy. Never could train her to shut off a light when she leaves the room... I put duct tape on the fridge doors so if you wanted in it had to be necessary. Dont just fan the doors to be looking. Its amazing how spoiled folks have become.

That is a very nice set up. Have you considered adding battery's?

 

[cosermann]

So, this is totally on the battery/inverter no solar back up then....???? ... That is a very nice set up. Have you considered adding battery's?

There's a Renogy 40A MPPT solar controller on the board, just haven't tested that aspect yet. So yes, there's solar recharge capability as well. Heven't considered adding more batteries yet. The number of batteries that can be added are limited only by one's budget!

 

[churchmouse]

There's a Renogy 40A MPPT solar controller on the board, just haven't tested that aspect yet. So yes, there's solar recharge capability as well. Heven't considered adding more batteries yet. The number of batteries that can be added are limited only by one's budget!

Understand. It took a while for mine to grow as the batteries were not cheap.
No idea what yours cost as I can only imagine.

 

[wsmith1indy]

I have a small 5.1 freezer that I would like to be able to run off of some sort of solar generator. The only electricalspecs I can find on it are 115v, 60hz &1.7 amps. Any suggestions on what the minimum size of generator could be used? As you can tell I don’t know much about electrical stuff, but just wanting a small plug and play option if the power goes out fir some time. Thanks

Amps times volts equal wattage. 1.7X115=195.5 watts

 

[cosermann]

Got a ballpark figure of the investment on this system?

Well, let's see, I'd say $2700 ish. That's for a capacity of 2560 Wh, so about $1.05 / Wh.

This includes 4x100 watt solar panels, and a 6 port USB charger not shown in the pics. (Also includes a couple of crimpers I now have for other projects, and misc connectors, wires, and other hardware of which I have enough leftovers to put together another unit.)

Ended up with 2 AC outlets (1200w/2400w), 7 USB charge ports (1 on the inverter), 2 lighter sockets, and a fuse panel to connect any desired 12 volt loads/appliances. Solar and AC recharge capability. Approx. 10 year battery life with proper maintenance (> 5,000 cycles at 1 C charge/discharge).

When one factors in that this includes the solar panels, it comes out cheaper than a commercial unit and the battery chemistry life is about double that of the commercial units. OTOH, it's not nearly as portable and it takes some fiddling to set it all up. OTOH, the components can be swapped out as needed if something fails, or to upgrade whereas with a commercial unit, you get what you get. Just kind of depends what one is looking for.

 

[bwframe]

Understand. It took a while for mine to grow as the batteries were not cheap.
No idea what yours cost as I can only imagine.

What is the lifetime of those batteries?


.

 

[cosermann]

...Results as measured by battery monitor:
Battery down from 100% to 78% capacity (22% used).
Battery down from 200 Ah to 154 Ah (46 Ah used).

Did this for another 24 sample. Similar results with a little variation. 48 Ah used this time (vs. 46 Ah), and a 25% draw down on the battery (vs 22% - 78 to 53%).

This time, I did observe a power spike when the freezer first kicked on (which I expected, but wasn't around to see last time), of about 2.89x the amp rating of the freezer. In the past, I've sized generators for other inductive loads at 3 to 3.5x the rated power. These results support this as a conservative sizing factor.

 

[Bearclaw]

Wow Cosermann! Great write ups! Thanks for posting.: I have learned a lot. At this time, I went with a WEN duel fuel 4000 genny. But I’m still going to start putting the pieces together for something like you have. I can run it in my shed for tools till I ever need it at the house.

 

[churchmouse]

What is the lifetime of those batteries?


.

Just saw this.
I do not know. Never ran it until the battery’s needed replacement. That system was sold to a friend with an off the grid remote hunting cabin west of Rockville Ind. it’s been a few years (5 maybe) and I believe it is still on the original battery’s. I will ask him when I see him next.

 

[Leo]

Cool conversion, and nice write up.

In other times, one would think that there is no way that would pay off, you couldn't put $2700 plus dollars in a freezer. Even if you lost 1/2 a beef, it would be cheaper to replace it than your system.

Now that the wicked men, (I mean politicians), are planning, (I mean predicting) a food shortage, that freezer full of beef may not be an economic convenience, but a life saving expense.

 

[Somemedic]

This is step by step and would get you through some difficult scenarios. It's also very scalable so a fella could make a small version but add onto as funds become available.

 

[inxs]

I have a small 5.1 freezer that I would like to be able to run off of some sort of solar generator. The only electricalspecs I can find on it are 115v, 60hz &1.7 amps. Any suggestions on what the minimum size of generator could be used? As you can tell I don’t know much about electrical stuff, but just wanting a small plug and play option if the power goes out fir some time. Thanks

Just a suggestion - research solar refrigeration. Around 1900 there were several places with such equipment. Most notable a large packing house in St Louis. Ammonia based same as RV type currently in use.... Why convert energy back and forth and no compressor start load....