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Solar Icemaker in a Mexican Fishing Village

by K Sheinkopf, the CADDET US National Team

INTRODUCTION

While ice is an essential component of income-generating activities in many parts of the world, it is often difficult and expensive to produce.

The development of a solar-powered ammonia absorption refrigerator has given many remote areas the opportunity to produce up to 450 kg of ice per day reliably and at low cost.

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The demonstration project in Mexico has seven ISAAC units

THE ISAAC SYSYEM

The Intermittent Solar Ammonia Absorption Cycle (ISAAC) is based on a technology developed in the 19th century and still in use today in a number of industrial applications. Energy Concepts Co. of Annapolis, Maryland has adapted this technology, resulting in a low-cost and reliable method of making significant quantities of ice in areas that do not have electricity.

The intermittent cycle is used instead of a continuous cycle because of the much lower cost. The intermittent cycle does not need a pump and a single pipe serves as the generator and the absorber.

During the day, the system's solar collector focuses the sun's energy onto the ammonia generator in the collector trough. Solar heat distills ammonia vapour from the water-ammonia solution in the generator. This vapour then condenses in the cooling coils and collects as liquid ammonia in the receiving tank in the evaporator.

At the end of the day, water is loaded into the evaporator according to the amount of ammonia which was generated during the day, and the unit is switched to 'night' mode. In the night mode, a passive thermosyphon is activated to remove heat from the generator which is now referred to as the absorber. As the absorber cools, its pressure decreases allowing the ammonia in the evaporator to evaporate and be reabsorbed into the absorber. As the water in the evaporator is the source of heat to evaporate the ammonia, it freezes during the night.

The next morning, the operator harvests the ice from the evaporator and resets the unit back to 'day' mode to begin the next cycle.

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Schematic of the system

THE MEXICO PROJECT

The small fishing village of Maruata is located in an isolated area on the Pacific coastline of Mexico. Selling their fish in cities about three hours away provides the only significant source of outside income for the 750 villagers. The hot, dry, sunny climate gives average temperatures ranging from 25 C to 38 C, making ice essential to preserving the marketability of the fish. There are about 50 fishermen in the local cooperative, which has one refrigerated truck to take the catch to market. The truck is expensive to operate and even more expensive to repair. And it is not practical to use unless there is a reasonable-sized catch to take to the nearby towns. The lack of ice and refrigeration keeps the village at a subsistence-level economy. And thousands of other remote villages need ice and refrigeration for vaccine storage, food preservation, and other functions vital to the health and well-being of their citizens.

In 1991, the Mexican programme for community development, PRONASOL, initiated a solar icemaking project in the village to improve the profitability of the co-operative. Technical assistance was provided by Mexican engineering firm, CIEDAC. After evaluating the cost and performance figures of the prototype ISAAC, they selected it for use in the Maruata project.

Energy Concepts Co. already had more than 30 of their icemakers in use in seven countries, but this project gave them the opportunity to field test seven units in one installation and in an accessible setting with a well-defined economic purpose.

The need for ice in the village was clear. Unrefrigerated fish had to be consumed the same day, but fish kept in a cold storeroom would retain premium quality for up to eight days. Refrigeration would let the fishermen go to market once each week, greatly reducing transportation costs. They would also be in a better bargaining position with the local wholesaler since they could store the fish instead of needing to sell it that day. And they would be able to use a standard pick-up truck instead of a refrigerated truck to transport the fish, greatly reducing their costs.

FURTHER DEVELOPMENTS

In July 1993, Hurricane Calvin passed very close to Maruata, exposing the ISAACs to 161 km/h winds. Several of the collectors were damaged, but one of the ground unit collectors was completely undamaged. This experience has been turned to positive use; the collectors were subsequently strengthened to withstand winds up to 161 km/h provided they are securely anchored to the ground.

A second important lesson learned was the elimination of the float valve. The float valve was not able to control the ammonia level properly and resulted in poor performance. The evaporator was modified to work without a float valve significantly increasing the reliability and decreasing the cost.

In autumn 1993, the National Renewable Energy Laboratory funded the installation of new
strengthened collectors and a new evaporator.

Energy Concepts has closely monitored the performance of these systems, and technicians have made several visits to Maruata to repair and maintain the systems as well as monitor their performance. They have been able to respond to requests for help from the fishermen.

ECONOMICS

The main goal of this programme has been to increase the profits of the fishermen. Previous
expenses included $100 per trip (where $ is the US dollar) to take their catch to market each day. Making this trip daily for 40 weeks means the transportation costs alone were $20,000 annually. Now with only weekly trips needed, this cost has dropped to only $4,000 per year.

The bargaining power of refrigeration in selling the catch to a wholesaler has netted them an
additional 3 pesos per kg of fish and 10 pesos per kg of lobster. Based on their annual catch, this has equated to about $16,000 per year extra.

Energy Concepts estimates that four of the new units two for icemaking and two for cooling the cold room would be adequate for their needs at a cost of $48,000. This yields a payback of three years, not counting any tax incentives.

However, these objectives have not yet been achieved, primarily because of problems with the early equipment requiring redesigns, and rough sea conditions in 1993 and 1994 which limited the catch. The viability of the technology has been proven though, and design changes should help the fishermen reach their economic goals.
The amount of ice produced by the ISAAC depends on the amount of sunshine and the ambient temperature. On a good sunny day, with a daytime high of 32 C and a night-time low of 21 C, the double ISSAC, which has a 12 m2 collector, will produce about 64 kg of ice/day. But, if the daytime high is 27 C and the night-time low is 16 C, the double ISAAC will produce up to 73 kg of ice. Other factors affecting ice production are wind, humidity, haze and the initial temperature of the water to be frozen.

Sixty-four kilograms of ice is enough to keep up to 130 kg of fish, milk or fruit cool for several days in a well-insulated icebox. Every three days, up to 390 kg of fresh food could be taken to market. Four double ISAACs at a single location would be able to supply refrigeration for up to a tonne of fresh food per week. Such quantities of fresh food sold at a market would repay the cost of the complete ISAAC system within three years.

CONCLUSION

The ISAAC icemaker is a totally new appliance that is supplying a vitally needed product for the people of Maruata. Further modifications and improvements will make it even more efficient and effective in meeting this critical need.

For more information contact the CADDET US National Team at Golden, Colorado.

The CADDET Renewable Energy Newsletter is a quarterly magazine published by the CADDET Centre for Renewable Energy at ETSU, UK.

The articles published in the Newsletter reflect the opinions of the authors. They do not necessarily reflect the official view of CADDET.

Enquiries concerning the Newsletter should be addressed to
Pauline Toole, Editor, CADDET Centre for Renewable Energy, ETSU, Harwell, Oxfordshire OX11 0RA, United Kingdom. Tel: +44 1235 432968, Fax: +44 1235 433595.