Introducing my solar powered (chest) refrigerator. It sits in an off-grid community garden and gets filled with fresh veggies for the local food bank

[Leeds]

Hello everyone, Western Pennsylvanian here, I just stumbled upon this site and it seems there are a lot of solar enthusiasts out there! Thanks for letting me join, I'm sure I still have a lot to learn and I look forward to every minute of it.
As the title suggests, I have a 7 cubic foot chest freezer that I run as a refrigerator. I first designed and built the system over the winter of 2016-2017 and it's been running out in the field ever since.
Originally I had the system tethered to a shed with the solar panel on the roof, the electronics inside and the cooler outside on the North side of the shed for shade. That worked very well but the rain did take its toll on the cooler and it collected some on the inside after every large storm and it began to rust up a bit after 6 years of sitting outside.
This year I finally completed my vision of tying the whole system into a stand-alone structure. The fridge is now on its own platform blocked from 99% of the rain and always in the shade. The solar panel itself is the roof and the electronics are all squirreled away in the bottom right corner of the structure. It's been running in its new form for the past few months but there are always improvements to make (like a winterization package).
Specs- (I'm kind of a nut for efficiency so in a lot of ways this was my attempt to make the most efficient solar-powered refrigerator I could.)

160W Solar Panel
20A MPPT Charge Controller
100AH 12V LiFePo4 Battery
7 cubic foot 110V Fridge
12V Inkbird Thermostat to drive the AC
1.5KW Square wave inverter from Harbor Freight

The system has a common negative ground and that is attached to a grounding rod driven into the ground (the only not easily moved part of the system). All grounds are directly connected but all other wiring is fused, both power and signal wiring. Breakers exist on the main feeds including the positive from the solar panel and the positive running to the battery.
The fridge is un-modified but there are wires that run over the back of it, under the hinged top and then into the cooler itself. The package inside the cooler contains the fan apparatus as well as the inkbird thermistor which is bonded to an aluminum heatsink with fins.
The cooler is set to keep vegetables in good shape before they're sent to the food bank so I allow a fairly wide deadband in the control. I cannot allow the bottom to get below 32°F or the bottom layer of produce will be damaged. I also cannot allow the top of the cooler to get about about 50° or it won't be doing its job taking the field heat out of the veggies. As I mentioned, I've recently added the interior circulator fan but I'm still experimenting with that (thus the tiny additional panel you see in the second photo).
Anyway, I could talk on this topic for hours, I look forward to better exploring this site and all the knowledge you folks have cataloged here!

-Leeds

 

[Samsonite801]

That's awesome and very creative!

 

[hellosf]

Cool idea for the community garden!

 

[crossy]

Nice job and nice community spirit!

How's the freezer doing on that square-wave inverter? Our's makes an "interesting" noise even on modified-sine!

 

[Leeds]

Nice job and nice community spirit!

How's the freezer doing on that square-wave inverter? Our's makes an "interesting" noise even on modified-sine!

Well it might well have 4 fets and not 2 (making it "modified" but either way it's never tripped me up. And 6 years later it still runs it whenever it calls for it.

As for noise, out in that field it's hard to even hear it running, I have to put my ear to it to easily know.

 

[dgeist]

Very cool idea with very limited space requirements. Have you tracked the battery's state of charge during any peak-load (i.e. summer) days? Curious if the system ever has to "cut out" until the next sunny period due to available juice.

 

[Leeds]

Very cool idea with very limited space requirements. Have you tracked the battery's state of charge during any peak-load (i.e. summer) days? Curious if the system ever has to "cut out" until the next sunny period due to available juice.

Back when I first designed the system it had a couple problem days in late summer where it cut out. That was a deep cycle lead acid 100ah though and I had the cutout set pretty high. I also had a pwm charge controller and the roof was pitched west, not south!

Any one of those improvements would have solved the issue. But at this point with all those improvements it's working so well that it also powers the lights on the pavilion and charges the 20vmax DeWalt battery pack for the garden's weed whacker.

I should monitor it for a while though, it would be interesting how much beyond my initial design I really have gone.

 

[DC99]

Class! Love it

 

[Eric_Jensen]

This is really cool - thanks for sharing!

 

[Leeds]

I'm almost done with the third generation power sled for the fridge and I thought it worth an update.

I've added a better controller/brain and that has allowed me to make the whole operation much smoother.

• There are now 4 modes based on battery level- Full Power, Basic Power, Reduced Power and Emergency Power.
• Reduced power mode for example raises the setpoint up to several degrees to preserve power. It also increases the dead and and locks out superfluous outputs like the case fan and limits the duration of the interior circulator fan to the times when the compressor is on.
• The battery is now insulated and heated to maintain a minimum temp of 38° but there is a bistable relay that knocks the charge controller offline if the battery temp was to drop below 33 preventing damage. If the temp rises before the battery is 100% drained it can reverse the relay at 34° and above. A fully charged battery can run the battery heater for 8 or more days straight before recharging.
• The circulator fan in the fridge is now also considered a gentle heater with the 10w or so it takes to drive it. This fan is integral to maintaining the fridges temperature throughout the winter season.
• There is now a (wired) touchscreen interface to debug it, view any alarms, stroke the courtesy power outputs, etc. I'm not sure if I'll install this or just use it to do an annual checkup on it though.

Those are the highlights anyway

 

[Bud Martin]

Love it! Great work.
You must be living in a very safe community to be able to have something like that not not walking away when there is no one around.

 

[Leeds]

Nails, screws and wood keep the power sled out of sight. And trailcams are about but obviously they can only do so much. At some point you also have to hope people appreciate that feeding the needy is something worth leaving alone.

I do wonder about the touch screen though. Probably not needed day to day anyway.

 

[spuds]

Beautiful setup.

I love those chest freezer conversions to refer,3 family members all prepared for doing this,is there anything out there thats more efficient?I use the inkbirds to run them currently as freezers with oF to 3F temps making a cheap freezer as accurate as a very expensive freezer,my meat lasts years in em.Grid down shtf in winter in a forest,my small but largest system i can fit in available sun,1200 watts will still give me a refer,lights,security cams/lights and comms.

Gotta love this stuff!