From the threat of natural disasters to climate change, there are many good reasons behind today’s calls to step up use of renewable energy. But power generated by the sun and wind is volatile, intermittent and variable over time. One promising approach is to harness the potential of energy storage technologies. We will take a look at some of those technologies and how they can accelerate the use of renewable power.
By its nature, electricity moves so fast that it reaches consumers as soon as it is generated.
Ampère’s circuital law explains how electricity flows and the relationship between an electric current and a magnetic field. An electricity flow is the propagation of electromagnetic waves made up of electric and magnetic fields. The movement of an electric charge generates a magnetic field(*1), and they are alternately propagated due to changes in the strength or direction of electric fields. Magnetic and electric fields are thus alternately propagated as an electromagnetic wave.
(*1) A magnetic field refers to the space around a magnet or similar object that is experiencing magnetism. An electric field refers to the space where voltage is applied.
Schematic of electromagnetic waves
The different types of electromagnetic waves include light, x-rays and electricity. In a vacuum, electromagnetic waves propagate at the speed of light, 300,000km per second.
In a power plant, an electromagnetic rotor is turned inside a series of coils, the stator, and the rotation induces electric current that is sent to us along power lines instantaneously.
Power plants produce electric power.
Today, technologies for storing electric energy in various forms are being studied and developed. The aim is to prevent power outages and to contribute to the utilization of renewable energy. We focus on two of them.
There are a wide variety of electrical energy storage methods.
There are a wide variety of electric energy storage methods. One is pumped hydroelectric energy storage (PHES). While it generates electric power, it also serves as a full-fledged power storage technology.It does this by storing water in an upper reservoir, as mechanical potential energy that can be used to meet high electricity demand. Released into a pipe, a penstock, it flows downhill to a lower reservoir with enough force to drive water turbines and power generators. During low electricity demand, surplus energy is used to pump the water from the lower reservoir back to the upper reservoir. For example, if a PHES power plant with four 400-megawatt turbines operates for eight consecutive hours, it can generate electricity equivalent to the daily energy consumption of nearly 1.6 million households(*2).
(*2) Source; Federation of Electric Power Companies of Japan in 2015
Mechanism of pumped hydroelectric energy storage
Toshiba is a long-established leader in PHES technologies, and the originator of one of the sector’s most important technology advances, the world’s first adjustable-speed PHES system. Adjustable speed means that, during both generation and pumping operation, electric power from and to a PHES system can be controlled in response to the change of grid frequency, the latter achieved by rotational speed adjustment of the generator motor of the PHES system. Adjustable-speed PHES systems contribute to more efficient operation and improved power grid stability.
Adjustable-speed generator motor No. 4 at the Kazunogawa Power Station, Japan
Another technology is rechargeable batteries. You may be familiar with these as storage batteries for smartphones.
Reachargable batteries are an electrochemical energy storage solution. They do not store electricity such as —when the anode material in the positive electrode and the cathode material in the negative electrode are immersed in electrolyte, an electrochemical reaction occurs that discharges electric energy. A reverse electrochemical reaction, charging, occurs when electricity is applied from an external source. This restores the anode and cathode materials to their respective states before discharge and allows repeated use.
Toshiba’s SCiB™ rechargeable battery
Apart from these two technologies, research and development efforts are underway for many different energy storage technologies, including hydrogen energy storage system using fuel cells that chemically convert hydrogen and oxygen energy into electric energy.
These innovations are creating a broad range of energy storage technologies that support our lifestyles by mitigating disruptions in the demand-supply balance that can cause power outages. Energy storage brings more flexibility to the power grid by helping grid operators to manage variable energy resources such as wind and solar.