Environmental Engineering Reference
In-Depth Information
Table 1.2
Prefixes
Prefix
Symbol
Value
Prefix
Symbol
Value
Kilo
k
10
3
(thousand)
Milli
m
10
-3
(thousandth)
Mega
M
10
6
(million)
Micro
µ
10
-6
(millionth)
Giga
G
10
9
(billion)
Nano
n
10
-9
(billionth)
Tera
T
10
12
(trillion)
Pico
p
10
-12
(trillionth)
Peta
P
10
15
(quadrillion)
Femto
f
10
-15
(quadrillionth)
Exa
E
10
18
(quintillion)
Atto
a
10
-18
(quintillionth)
Note:
Words in parentheses according to US numbering system
kW. It concluded that the compensation of
0.087 to be paid per kW for
feeding into the public grid was very low. Indeed, such a subsidy would be
very low: it would have been 2.2 kW
•
€
0.19 in total because it
was stated as a subsidy for installed power (unit of power = kW). Although
subsidies to be paid for solar electricity were quite low at that time, no owner
of a photovoltaic system in Germany got as little as a total of 20 Eurocents.
The author should have quoted that the payment per kilowatt
hour
(kW
h
) for
electricity fed into the grid was
€
0.087/kW =
€
0.087. Assuming that the system would feed
1650 kWh per year into the grid, the system owner would get
€
143.55 per
year. This is 750 times more than the compensation on the power basis. This
example demonstrates clearly that a missing 'h' can cause significant
differences.
Physical laws state that energy can neither be produced nor destroyed or
lost. Nevertheless, many people talk about energy losses or energy gains,
although the
law of energy conservation
states:
€
The energy content of an isolated system remains constant.
Energy can neither be destroyed nor be created from nothing;
energy can transform to other types of energy or can be
exchanged between different parts of the system.
Consider petrol used for moving a car: petrol is a type of stored chemical
energy that is converted in a combustion engine to thermal energy, which is
transformed by the pistons into kinetic energy for the acceleration of the car.
Stopping the car will not destroy this energy. It will be converted to potential
energy if the car climbed a hill, or to ambient heat in the form of waste heat
from the engine or frictional heat from tyres, brakes and air stream. Normally,
this ambient heat cannot be used anymore. Thus, driving a car converts the
usable chemical energy of petrol into worthless ambient heat energy. This
energy is lost as useful energy but is not destroyed. This is often paraphrased
as energy loss. Hence, 'energy loss' means converting a high quality usable
type of energy to a low quality non-usable type of energy.
An example illustrating the opposite is a photovoltaic system that converts
sunlight to electricity. This is often described as producing energy, which,
according to the law of energy conservation, is not possible. Strictly speaking,
