Overview

One form of energy can be converted into another form with a certain loss of efficiency. The various forms of energy currently available and the methods to generate them appear below. Some of these energy forms are renewable, and others are nonrenewable, as outlined in Fig. 7.1. The nonrenewable energy forms have been practiced traditionally for several hundreds of years and are currently expected to disappear completely in a few hundred years or less.

• Heat

  • by burning fossil fuels

  • solar radiation

  • warm air, water, subsurface water, and ocean

  • nuclear energy

  • earth's core (hot springs)

  • electricity passing through wires

• Light

  • sun

  • fluorescent and incandescent lightbulbs

  • LED

  • laser

  • burning fuels

• Electricity

  • photovoltaic

  • dynamo generators

  • batteries

  • hydrogen fuel cells

  • static (friction, lightning)

• Radio waves

  • radio transmitters

• Mechanical

  • hydroelectric facilities

• Sound

  • vibrating surfaces (microwave)

Figure 7.1: Energy sources

The two most common forms of energy used by humans are heat and electricity.

Greenhouse Gases

When sunlight strikes the earth's surface, some of it is reflected toward space as infrared radiation (heat). Many chemical compounds found in the earth's atmosphere allow sunlight to enter the atmosphere freely, while certain gases and vapors absorb this infrared radiation and trap the heat in the atmosphere (these are known as greenhouse gases). Over a period of time, the cumulative effect of these greenhouse gases is a slow increase in the earth's surface temperature. Some of the gases found in nature, such as water vapor, carbon dioxide, methane, and nitrous oxide, and others, which are exclusively human...