GC: n

CT: Energy density and the cost, weight, and size of onboard energy storage are important characteristics of fuels for transportation. Fuels that require large, heavy or expensive storage can reduce the space available to convey people and freight, weigh down a vehicle (making it operate less efficiently), or make it too costly to operate, even after taking account of cheaper fuels. Compared to gasoline and diesel, other options may have more energy per unit weight, but none have more energy per unit volume.
On an equivalent energy basis, motor gasoline (which contains up to 10% ethanol) was estimated to account for 99% of light-duty vehicle fuel consumption in 2012. Over half of the remaining 1% was from diesel; all other fuels combined for less than half of 1%. The widespread use of these fuels is largely explained by their energy density and ease of onboard storage, as no other fuels provide more energy within a given unit of volume.

S: http://www.eia.gov/todayinenergy/detail.cfm?id=9991 (last access: 26 December 2014)

N: 1. energy (n): 1590s, “force of expression,” from Middle French énergie (16c.), from Late Latin energia, from Greek energeia “activity, action, operation,” from energos “active, working,” from en “at” + ergon “work, that which is wrought; business; action”.
Used by Aristotle with a sense of “actuality, reality, existence” (opposed to “potential”) but this was misunderstood in Late Latin and afterward as “force of expression,” as the power which calls up realistic mental pictures. Broader meaning of “power” in English is first recorded 1660s. Scientific use is from 1807. Energy crisis first attested 1970.
density (n): c.1600, from French densité (16c.), from Old French dempsité (13c.), from Latin densitas “thickness,” from densus “thick, dense”.
2. Energy > Energy conversion: The amount of energy contained in a unit weight, or unit volume of an energy carrier or energy storage medium.
It is most often used when reference is made to storage cells. For instance, it has been said that electric-powered road vehicles will not come into their own until high energy density batteries can be readily and economically produced.
3. In the field of electricity, “energy density” is synonym of “gravimetric energy”.

S: 1. OED – http://www.etymonline.com/index.php?allowed_in_frame=0&search=energy&searchmode=none; http://www.etymonline.com/index.php?allowed_in_frame=0&search=density&searchmode=none (last access: 26 December 2014). 2 & 3. GDT (last access: 26 December 2014).

SYN:
S:

CR: electrical energy, energy.