Energy density is the quantity of energy that can be held in a given system, material, or region of space. In other words, Energy Density can be defined as the total amount of energy in a system per unit volume.
Different materials have varying degrees of energy density, which may be assessed in terms of equivalent energy released after burning.
Hydrogen has the highest energy density of any fuel and is also the simplest chemical component known to man.
| Term | Energy density |
| Definition | The amount of energy stored in a given system or region of space per unit volume. It may also be used for energy per unit mass |
| Unit | J/m3 |
| Symbol | u or η (eta) or ε (epsilon) |
Table of Contents
Fuel Energy Density
Different fuels (i.e. LNG, LPG) have varying amounts of energy, which may be measured in kilocalories. Energy density refers to the amount of energy released by a given mass or volume of fuel. Energy density may be measured in two ways: gravimetrically (per unit of mass) or volumetrically (per unit of volume) (per unit of volume).
The gravimetric energy density of a fuel is a measure of how much energy a battery carries in contrast to its weight, and it is usually stated in watt-hours per kilogram (W-hr/kg).
The volumetric energy density of a fuel is a measure of how much energy a battery carries in relation to its volume, and it is usually stated in Watt-hours/liter (W-hr/l).
Energy Density Examples
- The number of calories per gram of food.
- The energy is stored in the electric fields of the capacitor per unit volume.
- The energy density of a magnetic field. The total magnetic energy can be obtained by integrating the energy density over all space.
Energy Density Formula
| Case | Formula | Symbol |
| Electric field or capacitor | U = 0.5 ε0 E2 | ε0 = Permittivity E = Electric field |
| Magnetic field or inductor | U = 0.5 μ0 B2 | μ0 = magneti permeability B = Magnetic field |
Energy Density vs Power Density
Power density is commonly given in Watts/L or Watts/Kg and should not be confused with energy density, which is expressed in Watt-hours per kilogram (W-hr/kg). To put it another way, energy density refers to how much energy a battery can store. The higher the energy density, the shorter the battery’s run duration. Li-ion batterie is one example. Power density, on the other hand, denotes how much power a battery can give on-demand.
In simple words, the power density of a device refers to how quickly it can discharge its energy, whereas the energy density of a device refers to how much energy it contains. Batteries have a low power density but a high energy density, which means they hold a lot of energy that is slowly discharged.
Summary
Energy density is defined as the total amount of energy in a system per unit volume. Total energy density includes both capacitive and inductive energy density.
The total energy density formula of an electromagnetic wave is U = 0.5 ε0 E2 + 0.5 μ0 B2.
The energy density of a system or material is related to the amount of energy it can store. Different materials have different energy densities, which may be measured in equivalent energy released after burning.
Related Links
Light Energy| Definition, and Properties
Work-Energy Theorem
Thermal Energy Equation- Simple Overview
Conduction in Physics| Easy Examples
Surface Charge density
Current Density| Definition, and Formula
Can Kinetic Energy be Negative?| 6 Examples
Frequently Asked Questions
1. What is magnetic energy density?
A magnetic field can be created by a permanent magnet or an electromagnet. Both magnetic fields store energy in some form. The magnetic flux produced by a permanent magnet is constant and unaffected by other external factors. However, an electromagnet generates changing magnetic fields dependent on the amount of electricity it carries.
2. What is the formula for the density of a gas?
The original ideal gas law uses the formula PV = nRT, the density version of the ideal gas law is PM = dRT, where P is pressure measured in atmospheres (atm), d is density in g/L, T is temperature measured in kelvin (K), R is the ideal gas law constant 0.0821 atm(L)/mol(K), M, in this case, is the molar mass (g/mol). Check the full article “Ideal gas law” for details.
3. What is the energy density of LPG?
The energy density of natural gas lies in the range of 900–2200 Btu/ft3or 33.4–82.7 MJ/m3 [Reference].
4. Why is energy density important in fuels?
Energy stored in a given amount of fuel — a higher volume-energy density indicates that less room is required to store the fuel in the vehicle, which can result in less space required for a fuel storage facility on the vehicle.
5. What is the energy density of LNG?
LNG has an energy content ranging from 24 MJ/L to 21 MJ/L. LNG has an energy density of 0.41 kg/L to 0.5 kg/L, depending on temperature and pressure. LNG has 2.4 times higher energy density than CNG. This makes transportation more cost-effective.
6. What is the difference between specific energy and energy density?
Specific energy, often referred to as massic energy, is defined as energy per unit mass, whereas “energy density” is defined as energy per unit volume.
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