Implementing energy storage for peak-load shifting

Engineers should offer building owners the ability to reduce energy load by shifting it from peak to off-peak hours.

Learning objectives

Understand the basics of peak load shifting using energy storage systems.

Identify the benefits of implementing energy storage systems with respect to mitigating generation requirements, energy demand, and usage costs.

Understand the basic concept of implementing energy storage systems with renewable energy storage.

Peak-load shifting is the process of mitigating the effects of large energy load blocks during a period of time by advancing or

delaying their effects until the power supply system can readily accept additional load. The traditional intent behind this process

is to minimize generation capacity requirements by regulating load flow. If the loads themselves cannot be regulated, this must

be accomplished by implementing energy storage systems (ESSs) to shift the load profile as seen by the generators (see Figure 1).

Depending on the application, peak-load shifting can be referred to as "peak shaving" or "peak smoothing."

The ESS is charged while the electrical supply system is powering minimal load and the cost of electric usage is reduced, such as at night. It is then discharged to provide additional power during periods of increased loading, while costs for using electricity are increased. This technique can be employed to mitigate utility bills. It also effectively shifts the impact of the load on the system, minimizing the generation capacity required.

Load shifting is not a new concept and has been implemented successfully by end users in numerous industrial and large-scale commercial facilities in the past to decrease electrical peak demand and associated energy costs. With the rapid expansion of renewable energy plants in recent years, peak-load shifting has received noteworthy attention, and for different reasons than in the past. Renewable energy sources-specifically wind and photovoltaics (PV), which have seen exponential growth recently-provide irregular power due to meteorological and atmospheric conditions (see Figure 2). As these power sources come to provide an increasingly significant contribution to the load flow in the electrical grid, their effects become more pronounced on the power quality of that grid. The erratic fluctuations in power generated by these renewables can be detrimental to maintaining transient and dynamic stability within the system.

Power quality concerns generally associated with renewable energy sources include voltage transients, frequency deviation, and harmonics.

However, by implementing an energy storage system, it is possible to turn the

intermittent source into one with a relatively uniform and consistent output. As such, the large-scale deployment of renewable energy sources coupled with the Smart Grid relies greatly on energy storage systems for maximum effectiveness and optimization.