These definitions come from Environmental Accounting: Energy and Environmental Decision Making by Howard T. Odum, pg. 288.
Available Energy: Energy with the potential to do work (exergy).
[If one has firewood they can cook with it because the potential of the wood
to be burnt is still there; after cooking, the same amount of energy exists
in the form of heat released into the air, but the wood can no longer be used
to do what we wanted it for. Energy must be in an available, or usable form
for it to be of worth to us.]
Transformity: The emergy of one type required to make a unit of energy of
another type. For example, since 3 coal emjoules (cej) of coal and 1 cej of
services are required to generate 1 J of electricity, the coal transformity
of electricity is 4 cej/J. [If our dinosaur blood spooner
sweats for 100 hours to dig up a barrel, we would want to know the available
energy in that 1 barrel, how many hours of sweating could be replaced through
the utilization of that fuel to power machinery to do work. Using the solar
emergy transformity values for dinosaur blood and liquid motor fuel and knowing
the efficiency of fuel-to-work conversion of internal combustion engines we
can answer about 4000 sweat hours per barrel for the fuel. But the work when
finally done, would also include the spooning to get that fuel, and so be at
least with a sweat value of 4100 hours.]
Emergy: (spelled with an "m")—all the available energy that was used in
the work of making a product and expressed in units of one type of energy.
[When you have your transformities worked out so that you know how much one
kind of energy is worth in terms of every other, you can sum up in terms of
one type of energy all the available energies used directly or indirectly to
create something or to offer a service. That total is the emergy.]
Net Emergy: The emergy yield from a resource after all the emergy used to process it has been subtracted. [First, we take into consideration all the emergy that it has taken to get our spooner online, fed, clothed, sheltered, and with spoon, in terms of dinosaur blood, even if the energy required was and is of many different kinds. Then, if he comes up with more blood than what it takes to put and keep him on the treadmill, that is an emergy gain, a net emergy that will allow society to go around. It depends, of course, upon taking the primary source of energy for granted, such as the dinosaur blood in this case.]
Emergy Yield Ratio: The ratio of the emergy yield to that required for processing. [This
is the number of spoonfuls that society has left over for every spoonful of
energy required directly and indirectly by our spooner as he spoons.]
Solar transformity: solar emergy per unit of energy, expressed in solar
emjoules per joule. [Because sunlight is the great and only
form of energy that continually comes from outside the Earth, and because it
is the basis of all plant life and thus animal life, the challenge is to calculate
the emergy worth of something in terms of present sunlight. The only other energy
source affecting us that is not somehow related to sunlight, is a result of
the process that gathered together bits of matter from the stars to form the
planet Earth and its moon, the energies that are contained in the surface elements
of the planet, the uplifting of the continents and the restless tides, the volcanoes
and earthquakes.]
Sustainable use: the resource use that can be continued by society in the
long run because the use level and system design allow resources to be renewed
by natural or human-aided processes. [When we use natural
resources at a speed and in a manner which does not diminish them, or use them
to create a way of living that can last so that we are not threatened with catastrophe
as they do run out, that use can be said to be sustainable. If we do not, then
we will be forced to adapt to the condition of less, either by there being less
to spread around or by becoming a lesser number of people, or both.]