Live Simple Live Free: Solar ice maker

While at first glance it seems odd to use heat to make ice but most RV refrigerators use heat to keep them cold. The cooling is provided by an ammonia adsorption system. The heat is provided by propane or an electric heater. With the solar ice maker, the heat is supplied by the sun using a collector. These intermittent solar absorption cycle ice makers are heated during  the day by the sun and then at night they cool off forming ice. They have no moving parts and require only solar power and water to freeze.

Solar ice makers use one of 3 different methods: Zeolite/water - vacuum, CaCl /ammonia, or carbon/methanol. The zeolite/water under a vacuum is the easiest to implement since it doesn't include a hazardous chemical like methanol or ammonia. The carbon/methanol needs 1 square meter of collecting area to generate around 20 lbs of ice. While the ice is generated over night with these intermittent refrigeration cycles, you can cover the solar collector after a few hours to start the process.

The plumbing of the ice maker can be divided into three parts: a generator for heating the salt-ammonia mixture, a condenser coil, and an evaporator, where the distilled ammonia collects during generation. Ammonia needs to flow back and forth between the generator and evaporator.These ice makers operate in a day/night cycle, generating distilled ammonia during the daytime and then re-absorbing it at night. The gas condenses in the condenser coil and drips down into the storage tank where, ideally, 3/4 of the absorbed ammonia collects by the end of the day.

As the generator cools, the night cycle begins. The calcium chloride re-absorbs ammonia gas, pulling it back through the condenser coil as it evaporates out of the tank in the insulated box. The evaporation of the ammonia removes large quantities of heat from the collector tank and the water surrounding it. Water in bags around the tank turns to ice. In the morning the ice is removed and replaced with new water for the next cycle.

An example of a Zeolite ice maker has been incorporated into the Self Cooling Beer Keg. The self-cooling keg contains three chambers. A reservoir of water in an evacuated chamber surrounds the inner chamber containing the beer.. This water reservoir is connected by a tube to the outer chamber containing Zeolite. Since this tube is also evacuated it contains water vapor. By opening a valve the water vapor flows to the Zeolite where it will be absorbed. As this happens, the Zeolite warms up, absorbing heat from the water reservoir as it does so. The reaction is sufficiently intense to cool the water in the reservoir enough so that it freezes. After 30 minutes, a cold glass of beer can be tapped and the keg will keep a perfect drinking temperature for at least 12 hours.

There aren't any commercially available models of these ice makers yet that aren't rather large and cost $1000 or more. The first viable product is the beer keg($35) but soon will we see other products. If you can chill 5 gallons for 8 hours with no power, they would be perfect for chilled drinks while camping or boondocking.