Solar Absorption Refrigerator
Small Power Systems has developed a non-electric solar refrigerator-freezer. The refrigerator uses an aqua-ammonia absorption system similar to that used in propane refrigerators. The refrigerator consists of two separate units; the solar collector-generator and the refrigerator box.
The collector-generator consists of a thermal solar collector and most of the refrigeration works. It measures about 5' x 4'x 1' and weighs over 100 lbs. It needs to be mounted in a sunny location, the same as any solar collector.
The refrigerator box is the refrigerator per se and can be placed wherever is convenient, presumably the kitchen.
When the sun shines, the collector-generator produces ammonia refrigerant which is stored until night when the actual cooling takes place. To keep the refrigerator cold through the day and during cloudy weather, there is built-in storage sufficient for five days. There are no moving parts.
In use, our solar refrigerator is little different from any other refrigerator. It even has automatic defrost. Currently, the drawbacks are slightly higher freezer temperatures and a greater temperature variation since there is only one cycle per day.
We are currently building a very limited number of these refrigerators for customers who are willing to work with us on the design and put up with the idiosyncrasies of our current work. We do not currently have a date when we might have refrigerators in quantity. The interest in these refrigerators has exceeded our expectations and we are wondering on what scale to proceed. The cost is also an unknown, but roughly the cost of a Sunfrost not counting installation is an estimate.
The current plan is to build units 30" wide and 48" and 70" tall. We are also prototyping a very small unit where the refrigerator box is under the solar collector so it is all one unit that is left outside. This is meant to be used for vaccines and to be as low cost and simple as possible. We do not plan to include a freezer except limited ice-making capacity, as this simplifies the design. This may be the first model to be generally available.
Since there has been a lot of interest in North America which wasn't our original design area, we have been looking seriously at auxiliary cooling for prolonged cloudy spells. We are trying an external heat pipe for colder locations and thermoelectric cooling for warmer locations. These have the advantage of being relatively inexpensive and can be offered as add-ons instead of requiring extensive redesigning. Even though propane is a natural, it seems too difficult to implement at present.
We are also considering two technologies which would add to the expense but make a better product. Even though Owens Corning has canceled their Aura vacuum panel insulation production, others are working on similar products. The advantage is better insulation and thinner walls, resulting in a smaller cabinet. The disadvantages are higher cost and no guarantees that the product will be able to hold its vacuum for extended time. Guarantees with most products are under 5 years at present.
The other technology we are considering is keeping the cold storage outside at the solar collector and using a pump to circulate the cold into the refrigerator. This would add significantly to the expense and require electricity, but would simplify installation and keep ammonia out of the living space.
We feel that safety, particularly in transportation and installation is a significant issue that needs to be thoroughly looked into before we can offer these refrigerators to the general public, and this will take time.
We would appreciate any comments as we would like to know what you want. Please indicate if you would like to be put on our mailing list of future updates if you write.