Understanding the Energy Storage Solutions and the Technologies Used Today 

We live in a day and age where we are generating the electricity we need to power our daily lives from the Sun, wind, water, and other renewable sources.  

These technologies are cool, but they are intermittent in nature, meaning they are not available all the time. What do we do at night when there is no sun to power our solar panels, or there is not enough wind to spin the wind turbines? Or if we have excess energy and need to store it for later use? 

That is where Energy Storage comes into play, working behind the scenes to ensure that we get clean power whenever we need it. 

Uses and Benefits of Energy Storage Systems (ESS) 

1. ESS can help balance electricity supply and demand on many time scales (by the second, minute, or hour). 

2. Charging an ESS during periods of lower electricity demand and discharging an ESS and using or selling the electricity during higher demand periods can help to flatten the daily load. 

3. Localized pockets of increasing electricity demand sometimes require electric utilities to upgrade existing or build new, expensive substations, and power transmission and distribution lines. ESSs at strategic locations on the grid can help utilities manage growing electricity demand at a lower cost than upgrading or expanding electric grid infrastructure. 

Different types of ESS are deployed around the world. Let’s take a look at some of the technologies used today.

Batteries 

These come under electrochemical energy storage solutions, meaning it is the conversion of chemical energy into electrical energy. There are various forms of batteries, including lithium-ion, flow, lead acid, sodium, and others designed to meet specific power and duration requirements with lithium-based solutions being the most popular. 

Initially used for consumer products, lithium-ion batteries now have a range of applications, including smaller residential systems and larger systems that can store multiple megawatt hours (MWh) and support the entire electric grid. Due to the growing popularity of electric vehicles, lithium-ion batteries have received a lot of press for their rapidly declining costs.  

In another article, we examined the Battery Energy Storage System (BESS) in detail. In this article, let’s examine some of its advantages and disadvantages. 

Advantages 

1. The technology has a high energy density (amount of energy stored) and longer cycle life (the number of times a battery can be charged and discharged before it reaches the end of its life) compared to other battery solutions. 

2. The technology is widely deployed and commercially available. 

3. Lithium-ion batteries can charge and discharge rapidly, minimizing downtime. 

Disadvantages 

1. While prices have fallen significantly, Li-ion batteries remain relatively expensive, especially in large-scale applications. 

2. Lithium and cobalt, essential materials for these batteries, are finite and pose environmental and ethical concerns related to mining. 

Mechanical Energy Storage 

These systems store mechanical energy in the form of kinetic energy (either through linear or rotational motion), potential energy (by elevating water for later use in power generation), or compressed air (in compressed air energy storage). During periods of surplus energy, the excess power is converted into a mechanical form for storage, and this stored energy is then released during times of energy shortage. 

Let’s take a look at some mechanical energy storage technologies deployed today –  

1. Pumped Storage Hydropower (PSH) 

This technology is widely used around the world and is similar in principle to hydroelectric power produced from dams. PSH is a configuration of two water reservoirs at different heights that can generate power as water moves down from one to the other (discharge), passing through a turbine. The system also requires power as it pumps water back into the upper reservoir (recharge). PSH acts similarly to a giant battery because it can store power and then release it when needed.  

PSH can be characterized as open-loop or closed-loop. Open-loop PSH connects a reservoir to a naturally flowing water feature via a tunnel, using a turbine/pump and generator/motor to move water and create electricity. Closed-loop PSH connects two reservoirs without flowing water features via a tunnel, using a turbine/pump and generator/motor to move water and create electricity.  

Source: US DOE 

Advantages 

1. This technology can store vast amounts of energy, making it ideal for balancing grid demand over long periods. 

2. PSH has a long-life time and is a mature technology. 

3. It is renewable and sustainable. 

Disadvantages 

1. Long Construction Time 

2. PSH requires specific topographical conditions, including a suitable elevation difference and access to water. 

3. Large-scale PSH projects can have significant environmental impacts, including habitat disruption and water use concerns. 

2. Flywheel Energy Storage 

 Flywheel systems are kinetic energy storage devices that react instantly when needed. When excess electricity is available, the flywheel spins faster, storing the energy as rotational kinetic energy. During the peak hours when grid electricity is expensive or when the energy demand is greater than the production, the motor is rotated as a generator. Flywheels are capable of providing rapid bursts of power, making them ideal for stabilizing grid fluctuations and providing backup power.  

Source: Beacon Power  

A recent project in China, claimed as the world's largest flywheel energy storage system, has been successfully connected to the grid. The system boasts a total installed capacity of 30 MW, featuring 120 high-speed magnetic levitation flywheel units. The first flywheel unit of the Dinglun Flywheel Energy Storage Power Station, located in Changzhi City, Shanxi Province, was recently connected by the project’s developer, Shenzhen Energy Group.  

Advantages 

1. Flywheels can operate for many cycles without significant degradation. 

2. The technology has a short construction time 

3. Flywheels can discharge energy within milliseconds, making them good for stabilizing grid when needed. 

Disadvantages 

1. Flywheels have a lower energy density compared to chemical storage systems like batteries, meaning they are better suited for short-duration rather than long-duration storage. 

2. Unexpected dynamic loads or external shocks can lead to failure 

Thermal Energy Storage 

Thermal energy storage (TES) is a technology that stocks thermal energy by heating or cooling a storage medium so that the stored energy can be used at a later time for heating and cooling applications and power generation. TES systems can store energy from hours to weeks before converting it back to electrical energy or discharging the thermal energy directly. TES systems can provide 10s or even 100s of hours of electricity or heat at rated capacity.  

TES has improved safety relative to traditional electrochemical and mechanical storage technologies. There are mainly two types of TES technologies that companies are working on currently.   

1. Sensible heat 

Sensible thermal storage includes storing heat in liquids such as molten salts and in solids such as concrete blocks, rocks, or sand-like particles. Sensible storage relies on a temperature difference within the storage medium to enable useful work to be performed, such as using hot molten salt to heat water and generate steam to spin a turbine for electricity production. 

2. Latent heat 

Latent heat storage technology is a method of storing energy in thermal storage materials that undergo a phase change when energy is stored and released.  

In order to generate latent heat storage, phase change materials (PCMs) are commonly used. These materials can absorb or release significant amounts of heat during a phase transition (such as from solid to liquid or liquid to gas), allowing for efficient energy storage and release. Common PCM materials include paraffin wax, salt hydrates, and various organic compounds.