Online version: PDF - DTIE
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Online version: PDF - DTIE
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180<br />
UNIT 5: THE SUSTAINABLE SITING, DESIGN AND CONSTRUCTION OF TOURISM FACILITIES<br />
Experience in Australia, the Mediterranean and the Caribbean show that the<br />
payback period for solar water heaters is usually 2-5 years. An important<br />
consideration is the price of the fuel-powered backup water heaters. Solar water<br />
heating systems are generally guaranteed for 10 years.<br />
2<br />
Other types of<br />
semiconductor<br />
materials such as<br />
amorphous silicon<br />
and cadmium<br />
telluride may also<br />
be used.<br />
Examples of Good Practice<br />
A solar thermal water-heating system provides St. Rose Hospital in San Antonio,<br />
Texas with up to 90% of its hot water needs, by using 5,000 square feet of flatplate<br />
solar collectors. The system can hold 9,000 gallons of heated water at<br />
once. It is estimated to save the hospital close to $17,000 a year compared to<br />
the alternative of using a steam boiler fired by fuel oil.<br />
The residents of a 20-storey condominium in Honolulu, Hawaii opted in 1984<br />
to use solar energy to provide hot water because of the high price of oil. The<br />
system uses some fifty 48-square-inch flat-plate collectors to meet 70% of the<br />
hot water needs of the building.<br />
At the Youth Club in Hilo, Hawaii, 54 flat-plate 4-by-10-inch collectors covering<br />
the south roof of the building maintain the water in the swimming pool at 80°F.<br />
This is the largest system of its kind on the island. The system also supplies hot<br />
water to the locker-room showers.<br />
Photovoltaics (PV)<br />
As the name suggests, photovoltaic cells convert light into electricity. They are<br />
made of a semi-conductor material, typically crystalline silicon 2 , formed into thin<br />
wafers or ribbons. One side of the cell has a positive charge, the other side a<br />
negative. When sunlight hits the cell, the electrons on the positive side activate<br />
those on the negative side to produce an electric current.<br />
PV cells are electrically connected to each other, packaged in a transparent cover<br />
(usually glass or plastic), and encased in a watertight seal to form a panel or<br />
module. The panels are wired together to form a larger array, the size of which will<br />
depend on the power requirements of the user.<br />
PV can be used as a stand-alone system or a grid interface system. A stand-alone<br />
system consists of:<br />
• PV array;<br />
• Structure to mount the array;<br />
• Batteries to store power;<br />
• Converter to turn the stored direct current (DC) into alternating current<br />
(AC) - most household appliances work on AC;<br />
• Electric cables that enable electricity to move between cells, batteries<br />
and usage points;<br />
• Backup diesel generators to ensure a reliable supply of energy when<br />
there is no sunlight.<br />
Grid interface systems do not store energy. Instead they supply PV-generated<br />
power to the grid when excess power is being produced (i.e. when the sun is<br />
shining), and use power from the grid when no energy is being produced. The<br />
interface between the PV system and the grid can be metered in such a way that<br />
when power is being supplied to the grid the meter will run backwards. When<br />
power is drawn from the grid, the meter will move forward in the usual manner.<br />
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