Energy Storage Systems: What They Are, Types and Benefits

At i-DE, this article explores the concept of energy storage what it is, how it works, and its main systems.

What Is Energy Storage and How Does It Work?

Energy storage is the process of capturing and preserving generated energy for use when consumption demand requires it.

This process balances energy supply and demand, especially in systems that integrate renewable sources.

There are various types of energy storage. The most commonly used are pumped storage and batteries. At large scale, pumped hydroelectric plants or grid-connected batteries are used; at medium and small scale, batteries are connected to the grid or to renewable generation plants.

For example, in solar installations, when panels generate more electricity than is consumed, the surplus can be stored in batteries for later use, ensuring a constant supply.

How Is Solar Energy Stored?

This process is mainly carried out using energy storage batteries, which convert and preserve electricity for later use, offering advantages beyond simple surplus management:
 

• Resource optimization: Enables the use of energy generated during production peaks, ensuring zero waste.
• Consumption efficiency: Stores surplus energy for use during high demand, resulting in more rational and economical energy use.
• Contribution to sustainability: Strengthens commitment to a clean energy matrix, reducing carbon footprint and promoting a sustainable transition.

Types of Energy Storage Systems

There are currently several energy storage systems adapted to different needs and scales, each with its own application area and characteristics.
Hydraulic pumping systems are massive energy reservoirs, but they can only be installed near rivers with adjacent mountainous areas to take advantage of natural elevation differences and to build reservoirs or pools for water storage. These are costly projects that take around ten years to build but have a very long lifespan.

Electrochemical battery storage can be implemented at any scale. Large systems are also costly but can be installed anywhere, and construction times are short (months).  As an electronic technology, their response time is much faster than hydraulic systems (milliseconds), offering greater versatility. Batteries can be used to create microgrids, electrical islands, adjust voltage on power lines, avoid laying lines in protected environmental areas, and more.

Pumped Hydroelectric Storage

This method is especially effective for managing large volumes of energy.

Pumped hydroelectric plants —also known as gigabatteries— are the most efficient storage system for very large installations.
Pumping works with two interconnected reservoirs in a closed circuit: during off-peak hours, water is pumped to the upper reservoir, storing potential energy, and during peak hours, it is released to generate electricity by descending through reversible turbines.

Iberdrola has become a leader in large-scale energy storage using pumped hydroelectric technologies.

Projects include the Tâmega Gigabattery, one of the largest hydroelectric projects in Europe, with a capacity of 207 MW and a hybrid battery system of 15 MW, integrating solar and wind energy.

Other notable projects include the Valdecañas plant, commissioned in February 2025, and the future Alcántara II reversible installation, projected with 440 MW of installed capacity.

Electrochemical Batteries

These systems convert electrical energy into chemical energy during charging in rechargeable batteries.

Advantages include high energy density and adaptability to different scales, though they also have limitations. Their lifespan ranges from 12 to 20 years, depending on usage.

While prices for other technologies continue to rise, battery costs have been decreasing for years. They are the most efficient solution for small, medium, and large sizes.

They are faster and more versatile, can be installed anywhere, and solve many problems beyond energy storage.

The Moss Landing installation in California, with 400 MW of capacity, is considered one of the largest, while the Edwards & Sanborn project in California, with 3,287 MWh of capacity, is currently recognized as the largest in the world.

 
Most common types:

• Lithium-ion batteries: Offer high energy density and considerable lifespan, though they require advanced protection systems to prevent overheating.
• Flow batteries: Allow scalability and a high number of charge/discharge cycles.
• Lead-acid batteries: A more economical technology, though slightly less efficient in comparison.

Battery Storage Systems for Grids

Battery storage systems for grids are installations used exclusively to improve electrical service to consumers. 

These solutions help regulate voltage delivered to homes, manage consumption peaks, supply electricity to remote towns during grid emergencies, and support renewable energy integration.

In this context, i-DE has launched Spain’s first battery storage system for grids, located in Caravaca de la Cruz. With a capacity of 3 MWh, this lithium-ion system can operate independently and supply electricity for up to five hours during grid outages. It can also create a microgrid with nearby solar plants, extending its duration to over 15 hours. A battery can respond so quickly to a grid fault (e.g., caused by a lightning strike on power lines) that it can maintain electrical service to nearby populations without users noticing the incident.

Its fast response also allows it to maintain constant frequency on a power line, enabling local generation plants to continue operating during a blackout if a battery controls the electrical island. This is the case in Valcarlos (Navarra), where i-DE has installed a battery that stores energy during low-demand periods and releases it when needed, keeping local mini-hydroelectric plants running, avoiding outages, and reinforcing supply reliability in a hard-to-access location, especially during heavy winter snowfalls.

Both initiatives demonstrate how battery energy storage systems help stabilize the electricity distribution grid and improve service quality in response to demand variations or adverse weather conditions.
 

Benefits of Energy Storage

Together, these infrastructures reflect Iberdrola’s commitment to energy storage, contributing to the integration of renewable energy and the strengthening of Spain’s electricity distribution grid. 

Implementing storage systems allows for:

• Balancing production and consumption.
• Strengthening grid stability.
• Maximizing renewable energy use.
• Reducing dependence on fossil fuels.
• Promoting self-consumption and energy efficiency.
• Contributing to a more resilient and sustainable system

Present and Future of Energy Storage in Spain

Spain’s current landscape is undergoing transformation driven by initiatives such as the Energy Storage Roadmap, Next Generation EU funds, and the 2030 Agenda.

With a long-term focus, storage systems will play a decisive role in renewable energy integration, grid optimization, and improved self-consumption.

At i-DE, we work to ensure these technological advances translate into real benefits for society.