Energy Services

Energy Services

I claim that you have absolutely no interest in your energy source. What you ultimately care about is what the energy is used for.

Here is a short list of services that are provided by energy.

• Hot water

• Cooking

• Transportation

• Refrigeration

• Lighting

Note that hot water could be provided using natural gas or the sun. Most consumers are indifferent to the energy source used to provide the service.

In this chapter we'll discuss the difference between energy services and sources. We will also discuss the conversion of energy from the sources to the services and their efficiencies.

Primary Energy

Primary energy is a form of energy as it is found in nature.

Examples include:

• Coal

• Sunlight

• Oil

• Wind

Secondary Energy

Secondary energy is an energy source that is created from the primary energy source. This secondary source usually has some advantage or convenience over the primary source.

Here are a couple of secondary energy sources

• Oil is converted to gasoline

• Coal is converted to electricity

Energy Efficiency

Efficiency

• Whenever we convert energy, we are not able to convert all of it

• A measure of how well a resource is converted

• Defined as useful energy out divided by total energy in

$\eta = \frac{E_{out}}{E_{in}}$

Example Efficiencies

• Electrical generators (70--99%)

• Electric motors (50--90%)

• Gas furnace (70--95%)

• Wind turbine (35--50%)

• Fossil fuel power plant (30--40%)

• Nuclear power plant (30--35%)

• Automobile engine (20--30%)

• Solar cell (5--28%)

• Fuel cell (40--60%)

Multiplication of efficiencies

• When we want to know the efficiency of a process with many steps, we

  multiply the efficiencies at each step to get the total.

$\eta_{total} = \eta_1 \cdot \eta_2 \cdot \eta_3 \cdots$

Energy Efficacy

Efficiencies are usually expressing energy to energy conversions and are dimensionless. Sometimes, we want to express a quantity like the miles traveled per gallon of fuel or the amount of light provided per unit of electrical power. These are called efficacies.

Usually they are a fraction with the quantity of service provided on the top and the amount of energy, power, or fuel input on the bottom.