Energy Conversion Efficiency

When energy is converted from one form to another, the conversion efficiency is always less than 100%. In other words, some of the energy will be lost as waste heat during the conversion process. Energy conversion efficiencies are limited by rules in thermodynamics and material properties. They are generally less than 50%. For example, when heat is converted into electricity, the conversion efficiency is about 40% in most of power stations. Motor vehicles have efficiencies of only 20%. Solar energy conversion is typically below 10% even when the most sophisticated technologies are used.

Thus, the waste heat from the power stations, motor vehicles and solar cells are 60%, 80%, and 90% of the input energy respectively. Invariably, this waste heat will have a negative impact on our environment and health. For example, waste heat from power plants discharged into water streams can have harmful effects on aquatic life. Almost half of all water withdrawn in the United States each year is for cooling electric power plants. The cheapest method is to withdraw water from a nearby body of surface water, pass it through the plant and return the heated waste water to the same body of water. Warmer temperatures lower the oxygen content of water, and increase the susceptibility of aquatic organisms to disease, parasites and toxic chemicals. This is called thermal pollution.

For more information, check these sites:
Thermal Pollution
The Environment Site
What Is Energy?
Energy Basics
Changing Energy
Energy Conversion Efficiency



Go to Topic 2. Renewable Energy Sources