1. ENERGY Energy is the ability to do work and transfer heat.
Kinetic energy – energy in motion
heat, electromagnetic radiation
Potential energy – stored for possible use
batteries, fuels, glucose molecules
Energy Quality
measure of an energy source’s ability to do useful work
High quality (concentrated)
Low quality (dispersed)

2. Source of Energy Energy Tasks Relative Energy Quality (usefulness)
Electricity
Very high temperature heat
(greater than 2,500°C)
Nuclear fission (uranium)
Nuclear fusion (deuterium)
Concentrated sunlight
High-velocity wind
Very high-temperature heat (greater than 2,500°C) for industrial processes and producing electricity to run electrical devices (lights, motors)
High-temperature heat
(1,000–2,500°C)
Hydrogen gas
Natural gas
Gasoline
Coal
Food
Mechanical motion to move
vehicles and other things)
High-temperature heat
(1,000–2,500°C) for
industrial processes and
producing electricity
Normal sunlight
Moderate-velocity wind
High-velocity water flow
Concentrated geothermal energy
Moderate-temperature heat
(100–1,000°C)
Wood and crop wastes
Moderate-temperature heat
(100–1,000°C) for
industrial processes, cooking, producing
steam, electricity, and
hot water
Figure 2.13
Natural capital: categories of the qualities of different sources of energy. High-quality energy is concentrated and has great ability to perform useful work. Low-quality energy is dispersed and has little ability to do useful work. To avoid unnecessary energy waste, you should match the quality of an energy source with the quality of energy needed to perform a task.
Dispersed geothermal energy
Low-temperature heat
(100°C or lower)
Low-temperature heat
(100°C or less) for
space heating
Fig. 2-13, p. 44

3. U.S. Energy Flow
40.18
Source: Energy Information Administration / Annual Energy Review 2008 (in quadrillion Btu)

4. ENERGY LAWS: Two Rules We Cannot Break
First law of thermodynamics:
We cannot create or destroy energy.
We can change energy from one form to another.
Second law of thermodynamics:
Energy quality always decreases.
When energy changes from one form to another, it is always degraded to a more dispersed form.
Energy efficiency is a measure of how much useful work is accomplished before it changes to its next form.

5. Mechanical energy (moving, thinking, living)
Chemical
energy
(photosynthesis)
Chemical
energy
(food)
Solar
energy
Waste
Heat
Waste
Heat
Waste
Heat
Waste
Heat
Figure 2.14
The second law of thermodynamics in action in living systems. Each time energy changes from one form to another, some of the initial input of high-quality energy is degraded, usually to low-quality heat that is dispersed into the environment.
Fig. 2-14, p. 45

6. Energy Efficiency
“A measure of how much useful work is accomplished by a particular input of energy into a system.”
can be technologically improved in some systems
can be calculated

7. Environmental Impact and Energy Laws
High-Throughput Economies:
Convert energy and material in a manner that promotes waste and pollution.

8. Sustainable Low-Throughput Economies:
Matter-Recycling-and-Reuse Economies:
Mimics nature by recycling and reusing, thus reducing pollutants and waste.
Recycle
and
reuse
Low-quality
Energy
(heat)
Waste
pollution
Pollution
control
Sustainable
low-waste
economy
Matter
Feedback
Energy Feedback
Inputs
(from environment)
conservation
System
Throughputs
Outputs
(into environment)
Figure 2.16
Solutions: lessons from nature. A low-throughput economy, based on energy flow and matter recycling, works with nature to reduce the throughput of matter and energy resources (items shown in green). This is done by (1) reusing and recycling most nonrenewable matter resources, (2) using renewable resources no faster than they are replenished, (3) using matter and energy resources efficiently, (4) reducing unnecessary consumption, (5) emphasizing pollution prevention and waste reduction, and (6) controlling population growth.