Understanding the value of pumped storage.
Mark Griffith is a senior vice president at Ventyx Energy and leader of its asset valuation practice. He can be reached at Mark.R.Griffith@Ventyx.com.
The key value driver for electric power is time; that is, the exact clock time at which it is produced. Time determines the demand for electricity, the resources competing to supply the power and the state of congestion in the delivery system.
Benjamin Franklin once said that “lost time is never found again.” While there is much truth to this, the time value of electric energy can, in a way, be deferred and “found again” by storing energy in some form and then retrieving it later.
This is the key factor in understanding the value of energy storage. Storage allows one to conquer time, as it were, and deliver power when it is needed, not just when it is generated.
Various schemes exist to store energy, with the most common being chemical energy (e.g., batteries) and hydroelectric pumped storage. The concept of pumped storage is deceptively simple. When its value is low during off-peak periods, electricity is used to pump water from a lower reservoir to a higher reservoir (see Figure 1). Later, when the value of the electricity is much greater (on-peak periods), the water is allowed to flow from the upper to lower reservoir, and this movement is used to generate electricity. The pump and generator often constitute the same device, just operating in an opposite direction. Either reservoir can be a natural body of water or a man-made lake.