Page 178 - Solar Power in Building Design The Engineer's Complete Design Resource

148 ENERGY CONSERVATION

In large commercial or industrial complexes where large amounts of electric power
are used for fluorescent lighting or heavy machinery, the efficiency of incoming
power, which is dependent upon the maintenance of the smallest possible phase angle
between the current and voltage, is usually widened, thus resulting in a significant
waste of energy. The cosine of the phase angle between the current and voltage
referred to as the power factor, is the multiplier that determines whether the electric
energy is used at its maximum to deliver lighting or mechanical energy or is wasted
as heat. Power (P) in electrical engineering is defined as the product of the voltage (V)
and current (I) times the cosine of the phase angle, or P × V × I × cosine phase angle.
When the phase angle between the current and voltage is zero, the cosine equals 1 and
therefore P = V × I, which represents the maximum power conversion or delivery.
The principal components of motors, transformers, and lighting ballasts are wound-
copper coils referred to as inductance elements. A significant characteristic of induc-
tors is that they have a tendency to shift the current and voltage phase angles, which
results in power factors that are less than 1 and, hence, in reduced power efficiency.
The performance of power usage, which is defined as the ratio of the output power to
the maximum power, is therefore used as the figure of merit. The reduction of electric
power efficiency resulting from reactive power is wasted energy that is lost as heat. In
a reactive circuit, the phase angle between current and voltage shifts, thus, giving rise
to reactive power that is manifested as unused power, which dissipates as heat.
Mitigation measures that can be used to minimize inductive power loss include the
installation of phase-shifting capacitor devices that negate the phase angle created by
induction coils. As a rule, the maximum power affordable for efficient use of electric
power should be above 93 percent. In situations where the power factor measurements
indicate a value of less than 87 percent, power losses can be minimized by the use of
capacitor reactance.

A Few Words about Power Generation
and Distribution Efficiency

It is interesting to observe that most of us, when using electric energy, are oblivious to
the fact that the electric energy provided to our household, office, or workplace is mostly
generated by extremely low efficiency conversion of fossil fuels such as coal, natural
gas, and crude oils. In addition to producing substantial amounts of pollutants, electric
plants when generating electric power operate with meager efficiency and deliver elec-
tricity to the end user with great loss. To illustrate the point let us review the energy pro-
duction and delivery of a typical electric-generating station that uses fossil fuel.
By setting an arbitrary unit of 100 percent for the fossil fuel energy input into the
boilers, we see that due to losses resulting from power plant machinery, such as tur-
bines, generators, high-voltage transformers, transmission lines, and substations, the
efficiency of delivered electric energy at the destination is no more than 20 to 25 percent.
The efficiency of energy use is further reduced when the electric energy is used by
motors, pumps, and a variety of equipment and appliances that have their own specific