Off-grid Refrigeration – a cheap and effective way

Okay. I have finally decided to develop an improved refrigeration system. Here’s what I’ve been using up until now.

Basically, it’s just a stock pot with a wet t-shirt thrown over it for evaporative cooling. And filled with well water, which is actually between 48 – 50 degrees. So it keeps it pretty decent for vegetables but it’s not good enough for long-term storage of perishables. I need to get the temperature down to about 40. Or lower

Since I want it to be off grid I’m going to have to make it 12 volts so I don’t have to run my inverter.

And using a regular compressor driven refrigeration unit just uses too much power for the solar panels I have .

So I’m going to use thermoelectric cooling devices. Peltier chips. What they do is when you apply voltage one side gets hot and the other side gets cold. They can lower the ambient temperature by anywhere from 15 to 30 degrees. So since I’m only needing to go 10 to 20 degrees, I should be able to accomplish this. I could buy thermoelectric coolers pre-made but they won’t fit what I want to do. Because they only lower the ambient temperature, if it’s 90 degrees out it will only go down to maybe 60 degrees. But if I can submerse it in my well water, and change the well water regularly, the ambient temperature would effectively be 50 degrees. Which means I could get down to 40 with no problem anytime of the year. And also during the winter I could still use the storage system and just use the temperature outside to refrigerate like I have been doing. So I have two peltier chips on order. They’re not that expensive. About six bucks a piece. One is just for backup. I’m only going to use one and I’m going to put it on top of that stock pot so the cold is on the inside and the heat dissipation is on the outside and then a fan blows the cold around inside and I will insulate the pot outside.

The basic parts. An old peltier chips is shown on the right.

I could have used just a store bought cooler and cut holes in it to put the peltier unit inside but I like the idea of the metal container. I think that it will hold the cold longer when it’s not running if it’s insulated from the outside. And also I will submerse the bottom into the cold water. I may just get a round cooler and put put the pot inside the round cooler. And have the benefits of both.

In addition I plan on something that almost all of the inexpensive thermoelectric coolers for sale, don’t do. I ordered a cheap $5 temperature control module, that runs on 12 volts and very low power usage, that can sense the temperature inside and turn on the thermoelectric unit when it needs to be and turn it off when it doesn’t need to be on.

Most of the $50 – $70 thermoelectric coolers don’t have thermostat control. They just get cold or if your reverse the voltage they get hot to warm things up. They don’t get real hot, but you can keep food warm in them too. So my unit will actually be able to do that too if I want to heat it up, but I can’t imagine why I want to do that. But here’s the unit that I ordered.

Temperature Control Module

It’ll be here tomorrow. So I’ll update this post as I complete it. I have to cut a small square hole in the top of the lid of my stock pot. Mount the heat sinks on either side of the chip. Mount fans on top of that.

The fan on the bottom is to circulate the cold air. The fan on the top is to dissipate the heat and if it works out, I may just develop a way to circulate water through the heat part. So I don’t have to run the fan and just use a gravity-fed water to circulate through and cool the top heat sink. The better the heat is is disappated the colder the other side gets.

I always have to try to limit the amount of electricity I use, otherwise I’m going to have to go buy more batteries and more solar panels.

Because of my years doing computer repair, I have plenty of heat sinks and fans from old computers. So I don’t have to purchase those.

The drawback? Peltier chips are not very efficient. (ie. power in for result produced). But since they use such little power the amount of power lost doesn’t matter. And a large compressor does much more than I need, so I wouldn’t be saving anything.

Oh, and by the way. Those peltier chips that take electricity and make heat and cold? They also work the other way around. If you make one side hot and the other side cold they produce electricity. Not very efficient but they make a product which is a pot with a peltier chip mounted on the bottom. When you put cool water into the pot and put it on a campfire it can charge a cell phone. I think the ones I saw were called PowerPots.

UPDATE:. He is the nearly complete refrigerator with the insulation out side. The insulation is not permanently attached yet. A little more testing but so far it works pretty good.