Energy Efficiency: How can it be achieved at all levels of the power system?

A recent ENBALAtalks blog entry discusses energy efficiency, providing background and context on how it is traditionally viewed and how industry perspective on energy efficiency needs to be expanded. A more holistic approach to grid operation that utilizes state-of-the-art smart grid technologies would allow for further efficiency improvements to the overall power system – not just at the end user. Let’s look at more details on how intelligently managing the power usage of large electricity users can improve both generation and delivery efficiencies.

Energy Efficiency at Generation

On the generation side, decades of research and development have led to more efficient power plants. Like the internal combustion engine in a typical car, the turbines, boilers and reactors in power plants have been optimized as much as possible, resulting in efficiencies that are essentially maxed out. Some plants utilize waste heat to create steam in order to meet heating demands. This is a technique called Combined Heat and Power and can significantly increase the overall system efficiency.

power plantAlthough the designs of power plants have been optimized to maximize efficiency, they are always designed for a particular rated power output. But in order to balance the supply of power with the demand for power, not all generators can be operated at their rated capacity. By partially loading these units, their efficiencies decrease and the additional losses can be significant. Typically, generators are operated and dispatched in order to maximize the total system efficiency. By utilizing a different, demand-side approach to generator dispatch, utilities can improve generator efficiency. Real-time, demand management technology continuously connects a network of demand-side loads (energy-consuming equipment), which is viewed by the utility as an “ungenerator.” This single, dispatchable resource has inherent flexibility that allows utilities to minimize the time spent away from the optimal efficiency points of the generation fleet.

A study from the Electric Power Research Institute (EPRI)[1] found that three hydro plants could improve their plant efficiencies by 0.4 – 2.5% by optimizing the plant demand schedule. In order to fully realize these savings, the most efficient plants must be utilized as much as possible and continuously operated at their high efficiency operating points. By controlling demand-side resources through intelligent load management technology, this can be made possible.

Energy Efficiency in Delivery

The second application of energy efficiency in the power system is in the delivery from the generation source to the end user. In transmission and distribution, energy is lost as heat due to the resistance against electron flow in the wires. These losses are proportional to the square of the current in the conductor and can therefore increase significantly when the wires are highly loaded. Inductive loads make the problem worse because they create a phase difference between the voltage and current sinusoids. The result is that some of the power in the wires does not do any useful work. This is called reactive power and it must still be generated even though it will be wasted. Compounding the problem is the fact that reactive power still must flow in the wires and will have resistive losses of its own.

Transmission and distribution losses can be reduced using methods of reactive power compensation. Capacitors shift the phase difference between voltage and current in the opposite direction to inductors. Therefore, capacitor banks are often installed along transmission lines or at highly inductive load sites in order to keep voltage and current in phase. Often these capacitor banks will supply a constant capacitance even though the optimal value is constantly changing with the line loading. Others are designed to switch depending on a local measurement such as the voltage.

There are two potential opportunities for real-time demand management to reduce delivery losses. The first is through peak management. Because the losses are proportional to the square of the current, a smoother demand profile means fewer losses. The second is through reactive power control and optimization. This could include control of reactive loads as well as switches for capacitor banks.

Energy Efficiency at the End User

lightbulbsAs mentioned earlier, this is likely the most well-known form of new energy efficiency measures. More appliances and technologies are being designed with efficiency in mind than ever before. Prospective car buyers are fully aware of fuel economy when making their decisions. LED and CFL light bulbs are becoming increasingly more popular. Washers, dryers, you name it – there is probably a high-efficiency version of it on the market. Even commercial and office buildings are starting to be built from the ground up with energy efficiency in mind. Alternatively, for large industrial electricity users, new controls and automation techniques can increase efficiency as well.

So improving efficiency at the end user level is one way to cut back on energy consumption. And if you consider the total lifetime cost of many products, they are economical as well. Nevertheless, they do cost money and the cost is all up front. The payback period can be ten or more years, which is unacceptable for many small businesses or residential customers. These products require the end user to “buy in” and so government programs must often help subsidize the cost.

Although the “smart” energy usage of technology, devices and equipment at the end user is the typical way we think of energy efficiency, there are other opportunities available to improve the overall efficiency of the grid. End users can participate in energy initiatives offered by their electric utility; these initiatives help utilities manage a reliable and efficient power system – while benefitting the end user as well. Consider taking all aspects of today’s modern grid into consideration, and you might gain a new perspective on energy efficiency.

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