Acciona Energía tests hybrid battery-ultracapacitor storage in Spain

Acciona Energía is advancing a hybrid energy storage pilot in Navarra, Spain, combining UCAP with lithium-ion batteries to validate new grid stability services for renewable energy facilities.

The project aims to demonstrate that solar and wind plants can provide functions traditionally delivered by conventional thermal power plants, including fast frequency response, virtual inertia, and voltage support during short-duration disturbances.

Ultracapacitors are an electrochemical storage technology positioned between conventional capacitors and batteries. They can absorb and deliver high levels of power almost instantly, although they store less energy than battery systems.

In renewable energy applications, ultracapacitors can complement lithium-ion batteries by handling rapid power fluctuations and short-duration peaks, reducing battery stress and potentially extending system lifetime.

Acciona Energía began testing the hybrid system at its Barásoain wind farm, where ultracapacitors and batteries were integrated to divide storage functions. The batteries manage longer-duration energy delivery, while ultracapacitors respond to rapid power variations.

The first phase operated at 250 kW. After completing initial tests, the company increased system power to 1.25 MW in 2025 to expand the scope of trials and evaluate grid-forming capabilities.

The company also moved the original 250 kW system to its Tudela solar facility, where it is testing the combination of solar generation, batteries, and ultracapacitors in a photovoltaic environment.

Acciona Energía said the technology could help renewable plants provide advanced grid support services as power systems integrate higher shares of variable renewable generation and rely less on synchronous generators.

From pv magazine España