Energy Metrics and Analysis Tools
There are several types of energy quantities that come up frequently. How do you decide which of these quantities is relevant to your estimation and decision?
Here is a list of types of quantities and their uses
- Density
- converts volumes to masses
- Energy Density
- calculates the volume or mass required to generate an amount of energy
- A gravimetric energy density relates energy and mass
- A volumetric energy density relates energy and volume
- Efficiency
- determine how much of one type of energy can be converted to another
- Carbon Intensity
- calculates the carbon released from a given amount of energy
- Be aware that the number may be for the mass of carbon dioxide or the mass of carbon.
- Power and Energy Density per Unit Area
- Often used for renewable energy
- Power available per area of land or rooftop
- Energy available per area of land or rooftop (in a given time period)
- Others
- MPGe the equivalent miles per gallon
- “charging velocity” miles of range added per hour
- Equivalent cost of gasoline
Mass Density
A density converts a mass to a volume or a volume to a mass.
| Material | Density(g/cubic centimeter) |
|---|---|
| Crude Oil | ~0.9 |
| Water | 1.0 |
| Air | 0.0012 |
| Gasoline | 0.740 |
Gravimetric Energy Density
This is the quantity of energy is released by the conversion (often combustion) of a given mass of the material. Here is a table of the gravimetric (mass) energy densities for a few popular energy storage sources.
| Material | Energy Density (MJ/kg) |
|---|---|
| Gasoline | 45 |
| Crude oil | 42–44 |
| Natural gas | 33–37 |
| Coal | 12–31 |
| Wood | 14–16 |
| Lithium Battery | 0.5 |
An energy density has different dimensions and different units on the top and bottom. The dimensions of a mass energy density are energy over mass.
This means multiplying by an energy density changes the dimension of a quantity unlike a unit conversion.
Volumetric Energy Density
This is the quantity of energy that is released by a given volume of the material.
Efficiencies
Carbon Intensity
Carbon intensity is defined as the carbon released divided by the amount of services provided. This could be mass of CO2 per mile driven, or mass of CO2 per unit of electricity generated.
These are averages for the carbon intensity of electricity for some power plants.
| Fuel Source | Carbon Intensity |
|---|---|
| Coal | 1001 gram CO2/kWh |
| Natural Gas | 469 gram CO2/kWh |
| Biomass | 230 gram CO2/kWh |
| Solar PV | 46 gram CO2/kWh |
| Geothermal | 45 gram CO2/kWh |
| Nuclear | 16 gram CO2/kWh |
| Wind | 12 gram CO2/kWh |
| Hydroelectric | 4 gram CO2/kWh |
Median intensity from IPCC 2011 Annex II.
Carbon Intensity of Electricity
These are averages for electricity power plants.
| Fuel Source | Carbon Intensity |
|---|---|
| Coal | 2249 lb CO2/MWh |
| Natural Gas | 1135 lb CO2/MWh |
| Proposed EPA Limit | ~ 1100 lb CO2/MWh |
Power Per Unit Area
something about the DOE use of this metric
Miles Per Gallon Equivalent
is this a unit conversion between electricity and gas?
Equivalent Cost of Gasoline for EV
If we set the cost per mile of an EV and an internal combustion engine vehicle (ICEV) equal, we can solve for cost of gasoline and create an “equivalent” cost of gasoline.
The equation answers the question, at what price of gasoline is the cost per mile of the ICEV the same as that of an EV?