VOA慢速英语 Development Report - Making a Solar Water Heater（在线收听）

This is the VOA Special English Development Report.

Solar water heaters are devices that use energy from the sun to heat water. Solar water heating is used around the world.
　
An example of a rooftop solar water heater being built in South Africa

The solar water heater described here is based on a design developed some years ago in Afghanistan. Since then, it has been built and used in many countries. It can heat seventy liters of water to sixty degrees Celsius. It can do this between sunrise and noon on a clear day with an average outside temperature of thirty-two degrees Celsius.

There are two parts to the solar water heater. One part is made of a sheet of metal painted black. This metal surface, placed in contact with the water, will heat the water. Black-painted surfaces that receive the sun's heat become hotter than surfaces of any other color.

The black metal plate is called a collector. There are several kinds of metal sheets that can be used for the collector. Metal sheets that have raised sections will work very well. These corrugated sheets often are used to make the roofs of houses.

Once the water is heated, it is kept hot with material called insulation. This allows the water to stay warm for a long time.

The second part of the solar water heater holds the water for the system. This storage tank can be a container that holds about one hundred liters. Two rubber pipes are attached to the water storage tank. One pipe lets water flow into the system. The other lets water flow out.

When the water heater is working correctly, water will flow from the storage tank to the collector and back again. You can use the hot water at the top of the tank for washing and cleaning. You can change the flow of water so that the temperature is hot or warm as desired.

This solar water heater is easy to build and operate. It will last about two years before the rubber pipes need to be replaced.

There is also something else you will need to make the solar water heater work -- the sun. As you might expect, the heater will heat water only on sunny days.

You can get more information about projects like solar water heaters from EnterpriseWorks/VITA. This nonprofit group works to fights poverty in many countries. The Web site is enterpriseworks.org. Choose the link for News & Resources, then Publications.

Transcripts, MP3s and podcasts of our reports are at voaspecialenglish.com.

And that's the VOA Special English Development Report. I'm Steve Ember.