Metrics
There are several metrics by which we quantify the benefits of a proposed energy technology.
Economics
Economics is often the deciding factor for many energy decisions.
Central questions
How much does something cost per unit of use?
What does your car cost per mile?
What does your phone cost per minute of use?
Which is cheaper, buying a more efficient product or paying the extra energy?
How does this answer change if we add a carbon tax?
Life-cycle assessment
The analysis of all costs, benefits, and impacts over the entire lifetime of a product.
Cost of conserved energy
How much does it cost to save energy?
You can purchase energy
You can purchase a device that "buys" you that energy
Conserved Cost of Energy
Has dimensions of cost per unit of energy
Simple definition
Conserved Cost of Energy
For long term investments, we do this for a year at a time
$$ CCE = \frac{\textrm{Annual Investment}}{\textrm{Annual Energy Savings}}
Lifetime Energy
Most energy devices (lights, cars) have both recurring energy costs
and initial energy costs
Recurring energy: electricity to emit light or gasoline to drive
Initial energy: energy to manufacture the bulb or the car
Levelized energy use
We can estimate the energy per unit of light or mile driven by
Adding energy over the life of the device
Dividing the energy by the amount of use over the device
Dimensions of energy per unit of use (hours light, miles driven)
Energy Return on Investment (EROI)
This is the ratio of the energy out for a product divided by the energy in to get that energy.
It should be greater than one to be useful.
Payback Time
How long will it take for an investment to pay back the initial cost in energy savings?
Further Reading
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