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Seems counterintuitive, but solar energy can be harnessed to make ice cubes. An electricity-free alternative to refrigeration and air-conditioning, solar icemakers use the sun's heat during the day to drive a chemical reaction that separates a liquid refrigerant from a solid absorbent. The solid absorbent stays in the solar collector, while the liquid refrigerant is driven away and stored in a separate component called the evaporator. At night, the chemical reaction runs in reverse; the solid absorbent sucks the liquid refrigerant back into the collector. The movement happens through natural convection - without pumps, valves or any mechanical components. In the process, the liquid refrigerant evaporates and gets very cold. Any water touching the outside of the evaporator is frozen to ice, in an intermittent absorption refrigeration cycle. Basically, the two materials (absorbent and refrigerant) create a chemical reaction that becomes so cold that anything near the chemical reaction freezes - like water. To create ice continuously, the chemical reaction is produced over and over again by separating the two chemicals, using the heat of the sun, and then combining them again, at night. Once the icemaker is constructed, it has a zero carbon footprint. Greenhouse gases are not emitted during its operation nor are there any chemicals emitted that would deplete the ozone layer. (scroll to bottom for additional resources)
Three Types of Solar Ice Makers
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.
How They Work
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.
Self-Cooling Beer Kegs
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.
Solar Ice Maker: No Moving Parts, No Electricity
by Doug Gunzelmann, September 17, 2008
Intended for disaster relief situations, refugee camps, and developing nations the bright minds at San Jose State University have created an ice making machine that uses the heat from sunlight to power a chemical reaction. What happens is the tubing (or heat exchanger) is filled with a liquid refrigerant material. The convex reflective panel focuses light and heat energy from the sun onto the piping which vaporizes the refrigerant. So far, no ice. When the sun goes down however the vapor goes through massive heat loss due to pressure differences and roughly 14 pounds of ice are produced depending on the design.
The refrigerant rapidly cools once it hits 104 degrees Fahrenheit, due to its unique properties making, it perfect for typical temperature ranges in warm climates. The system is completely closed, there are no moving parts to wear out, and overall little maintenance should be required so long as the piping doesn’t crack or leak. The implications for this device are astounding. It can produce ice off the grid, can completely sustain itself, and offers a form of food storage through the production of often hard to find ice in places that need it most.
ISAAC Solar Ice Maker
By Energy Concepts
The ISAAC Solar Icemaker is an Intermittent Solar Ammonia-water Absorption Cycle. The ISAAC uses a parabolic trough solar collector and a compact and efficient design to produce ice with no fuel or electric input, and with no moving parts.
The ISAAC Solar Icemaker operates in two modes. During the day, solar energy is used to generate liquid ammonia refrigerant. During the night, the generator is cooled by a thermosyphon and ice is formed in the evaporator compartment as ammonia is reabsorbed to the generator.
The daily ice production of the ISAAC is about 5 kg per square meter of collector, per sunny day. The construction of the ISAAC Solar Icemaker involves only welding, piping and sheet metal work, and there are no expensive materials. It is estimated that, when produced in-country where wages are low and transportation costs can be minimized, the 11 square meter ISAAC can be produced for less than $7,000. When produced in-country, the creation of urban employment is an additional advantage of ISAAC technology.
The characteristics of the ISAAC which make it particularly well suited to provide refrigeration to unelectrified rural communities are:
• It is solar thermally powered, avoiding expensive diesel fuel or photovoltaics
• Low cost construction requires only welding, piping and sheet metal work
• Very low maintenance
• The quantity of ice is sufficient to support small scale businesses while maintaining sustainability in fragile environments, or provide low cost household refrigeration
The ISAAC design was developed by Energy Concepts Company. Over forty systems have been built and twenty installed in seven countries. The ISAAC is on display in Annapolis, Maryland and at Sandia National Lab, Albuquerque, New Mexico. ISAAC is now being distributed and commercialized by Solar Ice Co.
Providing Jobs to Remote Communities – By Providing Ice
The ISAAC Solar Icemaker makes enough ice at low cost to support many small scale businesses in rural unelectrified areas. Enterprises using ISAAC will be environmentally sustainable because no fuel is required. They will be economically sustainable because the cost of producing the ice by the ISAAC is sufficiently less than the value of the ice that it can easily be recovered by a micro-enterprise.
Ice is of major economic importance. In rural communities of developing countries, there is frequently a shortage of ice to support business activities. The result is loss of revenue, jobs, and substantial food spoilage.
Three important community needs for electricity are:
• communications and entertainment
Lights, communication and entertainment require modest amounts of electricity and are affordable even at the high cost of
electricity from emergency generators, diesel mini-grids or photovoltaics.
When refrigeration is needed also, the amount of electricity required from the power system increases drastically. Thus it is usually omitted to keep costs down. An ISAAC Solar Icemaker supplies refrigeration without the intermediary step of electricity and at a much lower cost. Thus ISAAC Solar Icemakers, in combination with mini-grids and/or photovoltaics, are a good method of supplying remote community needs.
For example, ISAAC can provide domestic refrigeration. An ISAAC produces six blocks of ice each day, weighing ten kilograms each. If an icebox requires five kilograms of ice per day to stay cool, then one ISAAC will be able to supply domestic refrigeration to twelve households. The cost of a standard electric refrigerator, plus the constant requirement of expensive electricity, would be much higher.