A refrigerator that runs on heat, from 1930, and a solar version on paper
On 11 November 1930 the United States granted patent 1,781,541, “Refrigeration”, to Albert Einstein and Leo Szilard. It was filed in December 1927 (and in Germany a year before) and assigned to the Electrolux Servel Corporation. It is a patent that has long since expired, so anyone may read it and build on it.
How it works. It is an absorption refrigerator. A cold liquid, butane in the patent’s example, evaporates in the presence of another gas, ammonia. The mixture passes to a chamber where water soaks up the ammonia and leaves the butane to turn back into a liquid. Heat then drives the ammonia out of the water so the cycle can start again, and the liquids flow by gravity. The point is that cold comes from heat. It does not need a compressor.
Why we care. Heat is easy to get from the sun. Cold storage that needs very little electricity would help food keep at outdoor gatherings and in places without a reliable power supply.
Our paper design. We drew a solar version in an AI hardware design tool and shared it there under the name Solar Einstein Cooler. As drawn, it is a sealed copper circuit fed by gravity, with evacuated-tube solar collectors supplying heat to the generator. A small ESP32 microcontroller reads two thermocouples and runs a fan. The tool lists 12 parts at an estimated US$262 and an overall size of about 3.0 by 1.6 by 0.6 metres. It lists uses such as off-grid refrigeration, farm storage and remote clinics.
What this is not. It has not been built, tested or checked by a refrigeration engineer. The cost is the tool’s own estimate. A system like this holds ammonia under pressure, and ammonia is toxic. Please do not build anything from this page. If you want to try, work with a qualified refrigeration technician.
Sources. US patent 1,781,541 (Einstein and Szilard, 1930). Our design page on the Blueprint tool.