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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 />

S<br />

E<br />

C<br />

T<br />

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O<br />

N<br />

3

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