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One approach many electrical utilities have taken to ensure the electrical load is less than what can be generated is to exercise some form of load control. In this case, certain applications are identified as “deferrable” -- to run later in the day, after the peak. These applications will vary by region, but common loads include residential electric hot-water heaters, air conditioners, pool pumps, crop-irrigation pumps, etc. 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. The utility only exercises the equipment when necessary. The consumer is usually rewarded for participating in the optional load control program by paying a reduced rate for energy. Proper Load management by the utility allows them to practice Load shedding on a less drastic scale to avoid Rolling blackouts and penalties by the Public Utility Commission.


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 load only when the stability or reliability of the electrical distribution system is threatened. The utility (being in the business of generating, transporting, and delivering electricity) will not disrupt their business process without due cause. Load Control, when done properly, is non-invasive, and imposes no hardship on the consumer.

Demand response on the other hand 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 are anything but flat. In a free market, the wholesale price of energy varies widely throughout the day, every day. Demand Response programs such as those enabled by smart grids attempt to incentivise the consumer to limit usage based upon cost concerns. As cost rises during the day in the supply of electricity as the system reaches peak capacity and more expensive "peaking" power generation is used, a free market economy should allow the price to rise. A corresponding drop in demand for the commodity should meet a rise 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 timeframe 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.

Implementations of Load Control systems

Early implementations occurred in WWII in various parts of the world using a system that communicates over the powerline (known as the "Ripple Control" system). 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 AMI systems can also serve as load control systems.

The largest residential load control system in the world is found in the United States, in Florida at FPL[1]. It utilizes 800,000 Load Control Transponders (LCT’s) and controls 1,000 MW of electrical power (2,000 MW in an emergency). FPL has been able to avoid the construction of numerous new power plants due to their demand side management programs. [2] Smaller utilities which 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.

Plant load factor

A plant load factor is a measure of average capacity utilization. If the PLF is affected by non-availability of fuel, maintenance shut-down, unplanned break down and no offtake (as consumption pattern fluctuates lower in nights), the generation has to be adjusted. A power (electricity) storage is not feasible. A generation of power is controlled to match the offtake. For any duration, a power plant generates below its full capacity. To that extent it is a capacity loss.

Ripple control for many years in New Zealand

Ripple control can be used to manage electric water heaters, allowing energy tariffs to be switched from daytime to evening, or hot water power supply to be turned off during daytime. Most electricity lines companies set 7:00am–11:00pm for a more costly daytime tariff, and 11:00pm–7:00am for a discounted evening tariff, which favours dairy farmers that complete milking soon after 7:00am. However, some electricity lines companies set 6:00am as the start of the more expensive daytime tariff, which is somewhat less favourable to dairy farmers - the option being to complete morning milking before 6:00am.

Local lines companies benefit from spreading energy demand throughout the evening as well as the daytime. This improves the utilisation of the electricity network and can be used to defer investment in electricity transmission and distribution lines. However, ripple control is often not utilised by the lines company to control water heating, unless periods of peak demand or power shortages occur.

Depending on the difference between day and night tariffs, significant savings may be achieved through simply installing a timer switch with suitably rated contactors to control electric water heaters. The cost of this is estimated in the area of $500 installed.

See also




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