Battling the Oil BarrelFortunately, steps are now being taken to promote energy independence in the islands. Among the options being studied are geothermal energy, ocean thermal energy conversion (utilizing the temperature gradients in Atlantic and Caribbean waters to produce electricity), wind energy (capturing the northeast trade winds that consistently blow over the area), biomass applications (such as the use of bagasse, a combustible by-product of sugar cane) and — of course — harnessing the region's abundant solar radiation.
Now, because of the Caribbean's mild climate year round (the average air temperature varies only from about 78 degrees Fahrenheit in February to 83 degrees Fahrenheit in September), there's little need for space heating. The most practical way to use solar energy, then, would seem to be to heat water with it. However, recent experiments have indicated that solar-powered air systems could have far-reaching implications, as well.
Solar Cooling in the CaribbeanThe Government Analyst Laboratory in the St. Michael parish of Barbados has been conducting studies on solar thermal-powered air conditioning and has an operational absorption chilling system that cools its research building. Water is heated by 240 roof-mounted flat-plate, copper-coil collectors and is then pumped into a 25-ton absorption chiller unit. The hot liquid serves the same purpose as did propane in the gas-powered absorption refrigerators that were fairly common a few decades back (and are still used in some areas).
Another experimental solar-powered air conditioning installation is located at the Frenchman's Reef Hotel in St. Thomas. The system was federally funded — through NASA — in association with the SunMaster Corporation of Corning, New York, the company that executed the design and installation.
The operation consists of 13,384 square feet of specially designed evacuated-tube solar collectors mounted on the roof of the luxury hotel complex. Five thousand gallons of water circulating through the system are heated to boiling temperatures and then piped into a SAM 120 solar absorption cooler specifically manufactured by the Carrier Corporation for Frenchman's Reef. The cooling system — which is quite similar to that used by the Barbados laboratory — provides air conditioning to the public areas of the hotel, including bars and restaurants, night clubs, a ballroom, the lobby and a number of shops.
Today the system has few flaws, but several modifications have had to be made since the experiment began in 1979, including substituting the SAM unit for the original Carrier 16JB 200-ton absorption chiller, replacing the original mechanical tracking system with one that makes use of parabolic concentrators and redesigning the chiller.
The entire process from start-up to shutdown is run by a time clock, and its function isn't dependent upon the collectors' receiving a minimum amount of sunshine. At 8 a.m. the system starts up, and water is released into the rooftop collector arrays. If the liquid in the return lines doesn't reach the required temperature within 15 minutes after the collectors are filled, the pumps shut off. After the water heats up to about 205 degrees Fahrenheit, however long that might take, the pumps will automatically turn on. Then, at the end of the day, the arrays are drained by de-energizing a series of spring-return motorized valves. The collectors will also drain automatically in the event of a power failure or if the temperature within any component of the system exceeds a set limit.
Generally, the solar installation must operate until 11:00 a.m. every day in order to achieve temperatures hot enough to power the absorption chiller, so — since the sunshine starts dwindling around 5:00 p.m. — the hotel receives only about six hours of solar-powered cooling daily. Because of this limitation, the arrangement includes a steam heat exchanger, which supplies supplemental steam to run the system at night or on cloudy days.
A digital microcomputer called the Sun-Logger — designed by Andover Controls in Andover, Massachusetts — monitors the entire process and oversees all functions of the system. The computer collects data every 15 seconds, recording exactly how much energy is being captured and how much is being lost.
Solar Crop DryingAcross town from the Barbados Government Analyst Lab in St. Michael stands the Animal Nutrition Unit and Veterinary Services Center, a research station funded by that country's Ministry of Agriculture.
Roy Millington, a spokesman for the center, showed our group two prototypes that are currently being used to study practical methods of employing solar energy to dry crops and process livestock feeds.
The first project is a solar food dryer that was designed by an Australian professor at the University of West Sydney. The dehydration unit incorporates a long chimney which sets up a convection current, circulating the heated air over the to-be-dried matter — a method that greatly speeds up the processing of edibles.
Simple and Functional Way to Dry Animal Feed
The second experiment under study at the research station is a drying shed for animal feeds. Mr. Millington noted that although the structure is little more than a crude shack with a fiberglass roof, the simple design has performed remarkably well. Galvanized sheeting is attached on three sides of the shed to keep rain from blowing in and to reflect — and thus intensify — the sun's rays, which enter the box by way of its glazed roof. Grasses, grains, and such — when spread over the concrete floor and turned occasionally — will dry satisfactorily in two to three days. (Eventually the research crew intends to replace the metal on the east side with fiberglass in order to capture the sun's morning heat.)
Small drying sheds of this type could prove practical for folks interested in preparing small batches of various livestock feeds. What's more, the ministry's staff members are also working on ways to apply similar methods to large-scale commercial feed production.
A Sunny FutureAlthough many governments and universities throughout the Caribbean islands are making real efforts to move toward meeting energy demands through natural resources, a great deal of work is still left to be done. And convincing the huge Caribbean tourism industry — which currently consumes approximately 60 percent of all the electricity used on the islands — that alternative sources of power will benefit both it and the region's economy would be an important step. We hope that by planning tours that highlight energy and cultural alternatives, we car help promote that understanding.