One of the key efficiency factors was being able to pull and hold a vacuum. And obviously the more efficient the engine that pulls the vacuum the better.
If it's a modern high efficiency unit, it probably already pulls a vacuum. If not, it may be worth physically hacking.
That being said since the system doesn't use batteries to store energy it might make sense to use any leftover energy to pump the air out of the fridge even if you don't reach a full vacuum.
Or maybe just build up the vacuum externally throughout the day until a certain time, then use it to pull the air out of the fridge for the night when it won't be opened and won't have power.
But you do make a really good point. In cruising, people who choose to have a fridge have systems for this.
It is usually to get saltwater really really cold or frozen in some kind of containers: it is popular to use PVC pipe, capped off of course, filled with seawater (or a mix of fresh and sea).
You store your food in the freezer and charge up these pipes, cycling them on to the top of your food in your cooler (not powered) once every 3-4 days.
This: "1 kilowatt of solar panels has managed to cool the fridge down close to standard fridge temperatures."
Is kind of silly to me though... because that's an "incredible" amount of power.
Pessimistically that means 3kWh/day, which if you're storing it efficiently (in a battery or as thermal mass like OP) gives you a nominal 125W supply
The relevant part from scuttlebutt:
@IBob on temp probe placement, I think I know why it was seeing such sharp swings when outside the water. I had the wire coming down along the inner fridge wall corner, touching it for a foot, and then the probe was pulled out an inch from the corner. So, it was both very close to the walls, and wire's contact would suck more heat away when the wall cooled down.
The spring thermometer I have mounted in there to measure the air temp now avoids this problem, and has been staying just above freezing during long compressor runs despite frost buildup on the walls
> (Numbers in this graph are running higher than the actual temps of food in the fridge, for reasons explained in the scuttlebutt thread.)
Instead of smarter software, the focus should be on insulation and adding mass to hold the heat. For example, I put a foam insulating board over my 22 cu. Chest Freezer to improve it's efficiency.
 https://news.ycombinator.com/item?id=17107254  https://news.ycombinator.com/item?id=17107439
Anyone know a good insolation forecast API?
During the summer I don't need to run the generator at all and I only have 350w of solar panels. This is mainly because I run almost entirely 12v appliances.
Engineering sometimes is so wrong, people before tech had a lot of simple an nice hacks!
Mr. Hess might want to consider adding additional insulation to the outside of his unit, especially as temperatures rise in summertime.
A good quality camping coldbox (e.g. made of fibreglass or thick polyethylene plastic) can keep ice solid for days even in an Australian summer.
Also, "patented crystal technology" what?!
Resistor based water heaters and space heaters, heat pump / compressor based air conditioners and water and space heaters, fridge and freezer cooling compressors, work air compressors etc all could be used to increase grid stability instead of now decreasing it. Or, if you have your own generation or are off grid, to reduce the electricity trading or storage needs
Wildly my first thought from from this is that you theoretically could use a peltier in reverse to generate energy. It wouldn’t be efficient but possible.
At a different level, you can also think about your interactions with the fridge. You could segment the fridge such that it had different insulated sections that you use.
Bread, eggs, etc.
Maybe curdle the milk!
That looks like a big fridge, maybe then it can be smaller.
Although smaller doesn't necessarily mean more efficient you may want to check the star energy rating.
It copes with keeping a number of phones, radios, tablets and a small laptop charged, some moderate use of lights, an occasional run of a webasto diesel air heater, and continously powering a compressor driven fridge box.
I think the batteries are one of the cheapest thing in my system.
My 1.5kw solar panels and electronics cost $2k (self-installed) and will last 20+ years.
To run the fridge on demand from batteries during the night and rainy days, I'd need something approaching the capacity of a powerwall, $6.6k every 10 years.
Or would this simply just cause spikes in electricity usage to compensate for the down-cycle along with increased mechanical wear?!
> Glycerol sadly has the tendency to supercool,so once all of your solution melts you will lose all of your seed crystals and then you have to drop down to a really low temperature before it will get back to a solid.
Add sand to the water tanks?