Load management, also known as demand side management, is the process of
balancing the supply of electricity on the network with the electrical load by
adjusting or controlling the load rather than the power station output. This can
be achieved by direct intervention of the utility in real time, by the use of
frequency sensitive relays triggering the circuit breakers, by time clocks, or
by using special tariffs to influence consumer behavior. Load management
allows utilities to reduce demand for electricity during peak usage times,
which can, in turn, reduce costs by eliminating the need for peaking power
plants. In addition, peaking power plants also often require hours to bring
on-line, presenting challenges should a plant go off-line unexpectedly. Load
management can also help reduce harmful emissions, since peaking plants or
backup generators are often dirtier and less efficient than base load power
plants. New load-management technologies are constantly under development — both
by private industry and public entities. Brief history
In 1972, Theodore George “Ted” Paraskevakos, while working for Boeing
in Huntsville, Alabama, developed a sensor monitoring system which used
digital transmission for security, fire, and medical alarm systems as well as
meter-reading capabilities for all utilities. This technology was a
spin-off of his patented automatic telephone line identification system,
now known as caller ID. In, 1974, Mr. Paraskevakos was awarded a U.S. Patent
for this technology. At the request of the Alabama Power
Company, Mr. Paraskevakos developed a load-management system along with
automatic meter-reading technology. In doing so, he utilized the ability of the
system to monitor the speed of the watt power meter disc and, consequently,
power consumption. This information, along with the time of day, gave the
power company the ability to instruct individual meters to manage water heater
and air conditioning consumption in order to prevent peaks in usage during
the high consumption portions of the day. For this approach, Mr. Paraskevakos
was awarded multiple patents. Advantages and operating principles
Since electrical energy is a form of energy that cannot be effectively stored
in bulk, it must be generated, distributed, and consumed immediately.
When the load on a system approaches the maximum generating capacity, network
operators must either find additional supplies of energy or find ways to
curtail the load, hence load management. If they are unsuccessful, the system
will become unstable and blackouts can occur.
Long-term load management planning may begin by building sophisticated models
to describe the physical properties of the distribution network, as well as the
load behavior. The analysis may include scenarios that account for weather
forecasts, the predicted impact of proposed load-shed commands, estimated
time-to-repair for off-line equipment, and other factors.
The utilization of load management can help a power plant achieve a higher
capacity factor, a measure of average capacity utilization. Capacity factor is
a measure of the output of a power plant compared to the maximum output it could
produce. Capacity factor is often defined as the ratio of average load to
capacity or the ratio of average load to peak load in a period of time. A higher
load factor is advantageous because a power plant may be less efficient at low
load factors, a high load factor means fixed costs are spread over more kWh of
output, and a higher load factor means greater total output. If the power load
factor is affected by non-availability of fuel, maintenance shut-down,
unplanned breakdown, or reduced demand, the generation has to be adjusted, since
grid energy storage is often prohibitively expensive.
Smaller utilities that buy power instead of generating their own find that they
can also benefit by installing a load control system. The penalties they must
pay to the energy provider for peak usage can be significantly reduced. Many
report that a load control system can pay for itself in a single season.
Comparisons to demand response When the decision is made to curtail
load, it is done so on the basis of system reliability. The utility in a
sense "owns the switch" and sheds loads only when the stability or reliability
of the electrical distribution system is threatened. The utility will not disrupt
their business process without due cause. Load management, when done
properly, is non-invasive, and imposes no hardship on the consumer. The load
should be shifted to off peak hours. Demand response places the "on-off
switch" in the hands of the consumer using devices such as a smart grid
controlled load control switch. While many residential consumers pay a flat
rate for electricity year-round, the utility's costs actually vary
constantly, depending on demand, the distribution network, and composition of
the company's electricity generation portfolio. In a free market, the
wholesale price of energy varies widely throughout the day. Demand response
programs such as those enabled by smart grids attempt to incentivize the
consumer to limit usage based upon cost concerns. As costs rise during the day,
a free market economy should allow the price to rise. A corresponding drop in
demand for the commodity should meet a fall in price. While this works for
predictable shortages, many crises develop within seconds due to unforeseen
equipment failures. They must be resolved in the same time-frame in order
to avoid a power blackout. Many utilities who are interested in demand
response have also expressed an interest in load control capability so that they
might be able to operate the "on-off switch" before price updates could be
published to the consumers. The application of load control
technology continues to grow today with the sale of both radio frequency and
powerline communication based systems. Certain types of smart meter systems can
also serve as load control systems. The largest residential load control
system in the world is found in Florida and is managed by Florida Power and
Light. It utilizes 800,000 load control transponders and controls 1,000 MW of
electrical power. FPL has been able to avoid the construction of numerous new
power plants due to their load management programs.
Ripple control Ripple control is the most common form
of load control, and is used in many countries around the world, including
Australia, New Zealand, the United Kingdom, Germany, the Netherlands, and
South Africa. Ripple control involves superimposing a higher-frequency signal
onto the standard 50–60 Hz of the main power signal. When receiver devices
attached to non-essential residential or industrial loads receive this signal,
they shut down the load until the signal is disabled or another frequency signal
is received. Early implementations of ripple control
occurred during World War II in various parts of the world using a system that
communicates over the electrical distribution system. Ripple control
systems are generally paired with a two- tiered pricing system, whereby
electricity is more expensive during peak times and cheaper during low-usage
times. Affected residential devices will vary
by region, but may include residential electric hot-water heaters, air
conditioners, pool pumps, or crop-irrigation pumps. In a distribution
network outfitted with load control, these devices are outfitted with
communicating controllers that can run a program that limits the duty cycle of
the equipment under control. Consumers are usually rewarded for participating
in the load control program by paying a reduced rate for energy. Proper load
management by the utility allows them to practice load shedding to avoid rolling
blackouts and reduce costs. Examples of schemes
In many countries, including United States, United Kingdom and France, the
power grids routinely use privately held, emergency diesel generators in
load management schemes = New Zealand =
Since the 1950s, New Zealand has had a system of load management based on
ripple control, allowing the electricity supply for domestic and commercial water
storage heaters to be switched off and on, as well as allowing remote control
of nightstore heaters and street lights. Ripple injection equipment located
within each local distribution network signals to ripple control receivers at
the customer's premises. Control may either done manually by the local
distribution network company in response to local outages or requests to reduce
demand from the transmission system operator, or automatically when
injection equipment detects mains frequency falling below 49.2 Hz. Ripple
control receivers are assigned to one of several ripple channels to allow the
network company to only turn off supply on part of the network, and to allow
staged restoration of supply to reduce the impact of a surge in demand when
power is restored to water heaters after a period of time off.
Depending on the area, the consumer may have two electricity meters, one for
normal supply and one for the load-managed supply, with Controlled
supply billed at a lower rate per kilowatt-hour than Anytime supply. For
those with load-managed supply but only a single meter, electricity is billed at
the "Composite" rate, priced between Anytime and Controlled.
= France = France has an EJP tariff, which allows
it to disconnect certain loads and to encourage consumers to disconnect
certain loads. This tariff is no longer available for new clients. The Tempo
tariff also includes different types of days with different prices, but has been
discontinued for new clients as well. Reduced prices during nighttime are
available for customers for a higher monthly fee.
= United Kingdom = Rltec in the UK in 2009 reported that
domestic refrigerators are being sold fitted with their dynamic load response
systems. In 2011 it was announced that the Sainsbury supermarket chain will use
dynamic demand technology on their heating and ventilation equipment.
In the UK, night storage heaters are used to increase the load by about 5 GW
to accommodate the nuclear programme. There is also a programme that allows
industrial loads to be disconnected using circuit breakers triggered
automatically by frequency sensitive relays fitted on site. This operates in
conjunction with Standing Reserve, a programme using diesel generators.
These can also be remotely switched using BBC Radio 4 Longwave Radio
teleswitch. = Germany =
Existing storage heaters in Germany are charged up with a lower tariff
electricity, mainly during night and afternoon hours. The switch and the
two-tariff electricity meter are remotely controlled, using either ripple
control through the powerline or the European radio teleswitching system
based on longwave radio signals. See also
Energy management system National Grid: Estimating costs per kWh
of transmission Calculating the cost of back up: See
spark spread Energy in the United Kingdom
National Grid Reserve Service Cost of electricity by source
Diesel-electric transmission Motor–generator
Three-phase electric power Load bank
Wet stacking References
^ Example of largest load management system developed by private industry
^ US Dept. Of Energy, Office of Electricity Delivery and Electricity
Reliability ^ Analysis of current US DOE Projects
Archived July 17, 2011 at the Wayback Machine
^ U.S. Patent #3,842,208 ^ U.S. Patents 4,241,237, 4,455,453 and
7,940,901 as well as Canadian Patent 1,155,243
^ N. A. Sinitsyn. S. Kundu, S. Backhaus. "Safe Protocols for Generating Power
Pulses with Heterogeneous Populations of Thermostatically Controlled Loads".
Energy Conversion and Management 67: 297–308. arXiv:1211.0248.
doi:10.1016/j.enconman.2012.11.021. ^ Michael Andreolas. "Mega Load
Management System Pays Dividends". Retrieved 21 June 2011.
^ "FPL Files Proposal to Enhance Energy Conservation Programs". May 2006.
Retrieved 21 June 2011. ^ Jean Marie Polard. "The Remote Control
Frequencies". Retrieved 21 June 2011. ^ Claverton Energy experts library
Archived February 17, 2010 at the Wayback Machine
^ Claverton Energy Experts Archived July 8, 2011 at the Wayback Machine
^ EDF EPJ ^ EDF Tempo
^ EDF Price grid ^ Newsdownloads | Dynamic Demand, Smart
Grid solutions, energy balancing ^ Commercial Opportunities for Back-Up
Generation and Load Reduction via National Grid, the National Electricity
Transmission System Operator for England, Scotland, Wales and Offshore.
^ EFR - Energy management via radio Archived July 20, 2011 at the Wayback
Machine External links
Load Manager for automotive applications Distributed Energy Resources Customer
Adoption Model Center for Energy and innovative
Technologies All about ripple control in the
Netherlands. Ales over Toonfrequent in Nederland