years, utility power outages have made headline news, and not only caused
inconveniences but loss of business, revenue and hardships for many. Whether these outages are caused
by hurricanes, ice storms, power shortages or other utility disturbances, our way of life is significantly
disrupted without electrical power.
In the aftermath of major storms and the expected damage to
local electrical distribution systems, it is not uncommon for
utility power to be out for several days, if not for weeks or even
over a month in some cases, and the longer the power remains
out, the greater the problems that result. As a solution, many
businesses and homeowners are looking into alternative
sources of electrical power to mitigate potential and
probable utility outages.
The high availability and low cost of energy is something
Americans have taken for granted for some time, and our
entire economy and way of life are predicated on this
seemingly inexhaustible supply of energy. While we are
accustomed to this panacea, most do not consider the value of energy until supplies become limited or
unavailable, like during extended utility outages. In these cases, people are often willing to pay several
times what it normally costs to have energy available when we need it.
For example, consider the cost of energy from common alkaline batteries, which we seem to use more and
more of over time. A typical D cell stores about 4 amp-hours at 1.5 volts, equating to about 0.006 kWh of
electrical energy. At a cost of about one dollar apiece, the cost of energy from a D cell amounts to about
$167 per kWh up to 2,000 times what most pay for utility-supplied electricity ($0.08-0.10/kWh)! So the cost
of energy is relative to availability and convenience, and most of us are willing to pay much more for energy
when its not readily available.
Several backup power options are available to businesses and homeowners, with each having limitations on
their application as well as operational issues. This article describes three typical back-up power
alternatives: uninterruptible power supplies, engine generators and battery-based solar photovoltaic (PV)
systems.
Photovoltaic arrays may serve as temporary, stand-
alone power sources in a disaster area.
(
Photo: Robin Flynn
) Uninterruptible Power Supplies
Uninterruptible power supplies (UPS) have become increasingly used by homeowners and businesses to
back up computers, security systems, office equipment and other critical electrical loads in the event of
utility outages or disturbances. UPS systems are available in a variety of sizes ranging from very small units
designed to power small loads for short periods of time, to much larger systems designed to power much
larger equipment and even entire facilities for extended periods of time.
A typical UPS system includes a battery, charger, inverter and automatic transfer switch, where the battery
is used to store electrical energy. While some UPS systems are designed to power critical loads directly
from the battery to isolate these loads from the utility service and potential surges at all times, most UPS
systems operate in standby mode, while the batteries are kept at full state of charge from utility power.
When a utility disturbance occurs, the automatic transfer circuit isolates critical loads from the utility, and
connects them directly to the inverter which converts DC power from the battery to AC power at utility
service voltages. At this point, there is a limited supply of energy in the battery, which dictates the
magnitude and duration of the critical loads that can be operated from these systems.
UPS systems with small batteries may only be able to sustain loads of a few hundred watts like computers
for only a few minutes, to allow time to backup work and properly shut down equipment. Larger UPS
systems include larger battery banks and inverters capable of sustaining much larger loads for longer
periods of time. Ultimately, most UPS systems rely on utility power to recharge the batteries, and without an
alternative source to recharge the batteries, these systems are unable to sustain backup of electrical loads
for long-term operation.
Engine Generators
Many homeowners and small businesses are purchasing engine generators as a solution to power outages.
Generators are available in a variety of sizes from a few hundred watts to hundreds of kilowatts, and can be
portable or permanently installed in service, making them very versatile in meeting a variety of electrical
loads in many applications. Prime duty machines are generators designed to operate in continual service,
while stand-by machines are designed for backup power applications of limited duration. While generators
may be the least initial cost option for back-up power, they can present a number of operational and
maintenance issues for users, as well as potential electrical and fire safety hazards if they are not installed
and operated properly.
First of all, engine-generators need a fuel source. Smaller portable units are
typically fueled by gasoline, while larger and stationary units are typically fueled
by diesel, propane (LP gas) or natural gas. During natural disasters, gasoline
supplies are often disrupted, there is high demand for product, and many gas
stations are closed or operating at reduced capacity due to loss of power or
delays in fuel deliveries. Long lines at the few open stations are the norm under
these circumstances. To mitigate these supply problems, some opt to store
large quantities of gasoline on site in portable containers for stand-by
generators, which can be unsafe to transport in vehicles, and hazardous to
store in quantities anywhere, particularly interior to buildings. Due to the limited
fuel tank size on many small generators and their rate of fuel consumption,
users are often required to refuel generators many times a day, which increases
the chance for fuel spills, and the risk of fire, personal injury and property
damage. All it takes is some gasoline spilled on a hot exhaust manifold and a stray spark or ignition source
to ruin someones life. Permanent generator installations done by professionals often include means to store
fuel as well as a means to deliver fuel automatically to the engine, with diesel or propane being the fuel of
"While generators
may be the least
initial cost option
for back-up power,
they can present a
number of
operational and
maintenance issues
for users ." choice for these systems. As opposed to gasoline, large quantities of diesel and propane can be stored
safely on site in approved containers, and degrade much less over time than gasoline. Diesel fuel is also
less flammable than gasoline, and less hazardous when spilled. Incidentally, propane and natural gas can
also be used to directly power a number of non-electric appliances, including water and space heating,
cooking equipment such as gas ranges, ovens, and outdoor grills, and even refrigerators and freezers.
However, some of these appliances may incorporate ignition systems or valves that may require electric
power to operate. Clothes dryers and certain air conditioning equipment can also be powered by propane or
natural gas, although this equipment also requires electrical
power to operate motors and fans.
In addition to a requiring a readily available fuel source,
generators present a number of other operational and safety
issues. For one, generators operated in the open can be quite
loud, and many can agree this incessant noise is quite
bothersome and even unnerving to some in close proximity to
the generating equipment. While improved muffler systems
and certain generator designs produce less noise, complaints
from neighbors are common where large numbers of
generators are used after a storm in high density residential
areas. Like other internal combustion engines, generators also
produce large quantities of deadly carbon monoxide gas in
their exhaust. In fact, carbon monoxide poisoning and deaths
are quite common in the aftermath of disasters, as folks are
operating generators within buildings to prevent theft of the
generator or to minimize noise for neighbors, and otherwise
not making proper provisions for ventilation of exhaust gases. Many install generators on porches, adjacent
to bedroom windows or entrances that may be opened, increasing the potential for carbon monoxide
poisoning.
Generators also require regular maintenance and exercise to ensure that they will operate properly and
safely when needed. This required maintenance typically includes oil and filter changes after a number of
hours of service or storage period, replacement of spark plugs, and regular inspections of fuel systems for
leaks, servicing of starting battery, etc. While smaller units are typically air cooled, larger units are typically
water cooled, requiring proper maintenance of antifreeze/coolant levels, and periodic flushing of the entire
cooling system. Like any automobile engine, generators must also be routinely exercised to ensure reliable
and safe operation. Fouled fuel and carburetors are a common problem for any internal combustion engine
that is not routinely and properly operated and maintained. Many automated generator systems incorporate
a weekly exercise cycle for 10-15 minutes to ensure they will start and operate when needed. Automatic
start generators depend on a starting battery, which when not charged for extended periods will slowly lose
capacity to the point where it will no longer start