Off Grid Solar Powered Fridge

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Our off-grid project at Rally Creek has been growing organically over the past 9 months. The first big upgrade was the pre-built sheds that look like cabins that we got from WestWood Sheds, a huge upgrade from pitching a tent then breaking it down and cleaning it every weekend we visited the property. Soon after we added a composting toilet, then a foam bed and bed frame. Last month the upgrade as to add a small electric cooler so we can stop running to the store to get ice very day. This article dives into that journey, what we got, and what it looks like now.

A Solar Powered Fridge

We started out with a standard mid-sized cooler. Nothing fancy, just your typical molded plastic insulated cooler. Throw ice in it, stack some beverages and snacks and head up to the property. The problem with that system is you need to empty the water the next day and replenish the ice every day or two. With some 3-day weekends coming up, that was going to be a pain. Not to mention the cooler doesn’t stay super cold for things which means frozen or well-refrigerated meats were really not an option.

Since we know we want to move to a solar-centric system the choice was made to look for an electric powered solution that worked on DC. We also had an initial basic solar setup that is built around a basic 12-volt configuration. This is also an experiment so we don’t want to spend a fortune as we want to see how this works before going “all in”. The initial search criteria for a fridge:

  • Low cost (well under $1k, preferably < $500)
  • DC Powered, 12V preferred
  • Large enough for 2 days of drinks and basic cold groceries (meats, fruits/veggies) for 2 people

It didn’t take long to learn that there are a lot of good 12V DC options on the market these days. It also didn’t take long to learn that a true small fridge/freezer combo or any larger cooler boxes that are meant for camping, RV life, “Jeep Life” or other such rugged outdoor scenarios can quickly run well over the $1,000 mark. We are not ready for that.

After some research we found a cooler that runs on 12V DC for under $500 that would could get in less than a month — the Alpicool CF55 as outlined in our Portable 12V Refrigerator article.

We got the cooler and using the included 120V to 12V power adapter we plugged it in the first weekend to our fully “on grid” 110V service on site. It worked well keeping drinks and some cold cuts cool. Not ice cold, but the cooler was also set to 32-degrees , which in reality seems like it only cooled to something closer to 42 degrees. Even at 27-degrees nothing really froze, though it was a lot closer to freezing at that setting. Temp inaccuracies aside, it looks like this solution will be adequate for now.

Time to power it up with 12V solar.

Powering The Fridge

Now that we know the cooler works well enough for our needs, time to power it up. We have a pre-existing solar setup, but it is the “baby trial run” configuration from a kit we got off Amazon from Expert Power. You can read about that in our “A Compete Small Solar Power Kit” article.

Let’s break that down as our starting point.

Solar Powered Fridge Starting Point

Here are the items we started with, the solar kit is not large enough to power both the fridge and other DC items on the circuit, so the fridge is on 120V for now.

The solar power setup will not run the fridge on it’s own. From our prior real-world testing we know this solar panel setup will generate an AVERAGE of 2.5A @ 12V an a maximum of 4A @ 12V under perfect conditions. This one solar panel won’t be able to keep up when the fridge is running.

Calculating The Solar Upgrades

With the solar panel pushing 2.5A average over 8 hours we can get 20Ah max output.

The weekend the fridge was plugged in it cycled on for about 5 minutes every 15 minutes it sat during the day; a bit less at night. Over an hour that is about 20m of run-time @ 5A = 5A every 3H or 40Ah in a day. About twice what our single panel can produce. Remember this is solar and there is a large margin of variability here, however even in great conditions we are likely to come up at least 10Ah under what we need in a day.

Time to boost our system.

Upgrading The Power

To keep up with the fridge we need to double (at least) our solar power generation. We will add another 100W solar panel, a Y-combiner for MC4 connections to get both panels to send power to the controller, and a larger 100Ah battery. A deep cycle AGM to keep costs down since weight is less of an issue and we don’t expect rapid charge/discharge and should be able to keep the battery at/near 50% most of the time.

With (2) 100W panels behaving in a similar fashion we should be able to easily push 5A (sometimes more) for 8h/day. 40Ah/day which is at/above the cooler needs. In colder fall & winter months the cooler will run far less often so the panels should be able to add to the battery and fill it up over time. Not quickly, but it should get there — real world testing will tell use more over the next few months.

For now, let’s add a 100W panel, the Y combiner cable, and the battery bank.

Considering The Cabin Upgrades

In addition to upgrades need to the power system, the electrical system of the cabin needs some upgrading. Currently there is a single 120V power inlet that brings our “on grid” power into the cabin, mostly to run our AC unit on 90-degree humid summer nights. On cooler fall nights it was used for a weekend to power the cooler for a test run. However we want to move away from that and this solar upgrade is an opportunity to move in that direction.

In addition to the 120V service, we have the starter solar kit noted above. This kit has the controller, battery, and solar panel inside the cabin to power a fan in the bathroom composting toilet. That means every visit we drag the solar. panel, battery, and controller outside during the day to charge it up, then plug everything in inside during the night. On our last visit we kept things wired up, and with some new walls built hung the panel on the wall, but that is a stop-gap as it only generates 1A (or less) from sun coming in a window for 4-5 hours per day.

Now that we are upgrading the solar array and battery storage it is time for a more permanent solar solution. The plan is to house the controller (and eventually an inverter) inside the cabin to protect those sensitive electronics. The panels need to be outside to collect sunlight and we are going to store our battery array outside to avoid any leaks, fire hazards, and other issues that may come up with the most volatile part of this configuration.

Lastly a 12V cigarette lighter outlet is part of the configuration as many 12V appliances from our electric cooler to our water kettle come with a standard “car cigarette lighter” cable. This will prevent us from having to craft our own custom 12V cables as many consumer devices use this as a standard despite better options like SAE or even MC4 connectors being on the market for years.

The Solar Connection

To do this we need some connectors to keep outside things out — bugs, rain, etc. — while getting power routed into the cabin. We opted to use MC4 connectors as they have become the defacto standard for solar panel connectors and support high voltage DC. It will be overkill for now, but will grow as the system grows. This means we need a couple of MC4 Glands for the cabin. For wiring we will re-use the 12AWG 10′ cables from our kit for panels => solar entry gland. That gland has 10′ 10AWG pair of wires that will connect to the controller.

The Battery Connection

The controller will use another entry gland with a 10′ 10AWG pair to lead back out to the battery array. Outside the shed a 15′ 10AWG MC4 extension cable will lead to a MC4 to M8 o-ring adapter which will attach to the batteries. Our panels and batteries will now be outside with the controller and our DC loads inside the shed.

Our Shopping List

Supporting Cast — items to check our work and caffeinate the crew:

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