RenewaFLEXNL, a three-year Dutch initiative led by TNO, aims to accelerate long-term energy storage (8-100 hours) to reduce grid congestion and better integrate renewable energy. pv magazine spoke with the project coordinator, Iraxte Gonzalez Aparicio, about various storage technologies, real-world applications, regulatory guidelines and tools for energy management systems to support the large-scale deployment of solar plus storage in the Netherlands and beyond.
A new initiative led by the Netherlands Organization for Applied Scientific Research (TNO) aims to increase the use of long-term energy storage solutions (LDES) to address the chronic problems on the country’s electricity grid.
The three-year project, called RenewaFLEXNL, involves 17 partners from across the energy sector to test and integrate storage solutions that can hold renewable energy for hours or even days, to better balance supply and demand.
“Expected solutions include a national strategy for LDES implementation, system-level scenarios and regulatory guidance to inform incentives, congestion management and the recognition of LDES in markets and permits – supporting faster adoption of solar plus storage in the Netherlands and serving as a model for other EU countries,” the project coordinator, Iraxte Gonzalez Aparicio, told IPS. pv magazine. “Key barriers include regulatory challenges such as unclear storage roles, ownership and market access; economic barriers such as capital expenditure, revenue and contract certainty; and technical issues including medium voltage (MV) and high voltage (HV) integration and standardized energy management and assurance.
“To address these, we provide legal recommendations, contract templates and rollout strategies at both Dutch and EU level,” she continued. “And although As momentum increases, our assessment shows that further steps are needed: clarify the legal status of storage, enable participation in multiple markets for LDES, align rates with congestion value, and support unique multi-day projects to reduce the risks of capital investments. Our products are designed to support exactly these policy steps.”
RenewaFLEXNL aims to fill these gaps by exploring technologies that can provide the flexibility needed for a fully renewable system. The project will conduct three pilot demonstrations that reflect real-world energy system challenges. In the port of Rotterdam, LDES will link offshore wind energy to industrial heat and electricity demand. In De Kwakel, greenhouses will use stored energy to reduce dependence on gas-fired cogeneration. And in Altena, sustainable generation will be linked to storage for charging electric trucks and local heat supply.
A range of storage technologies will be tested, from saltwater flow batteries and iron-air systems to hybrid thermal-electric solutions combining heat pumps and water-based storage. In addition to the hardware, the project will also evaluate system-level performance, economic feasibility and potential regulatory frameworks that could support broader adoption of long-term storage.
“We will use the 8-100 hour range that defines long-term storage because it covers both day-night shifts and multi-day weather breaks that short-term batteries cannot accommodate,” explains Gonzalez Aparicio. “This duration is most effective at reducing curtailment and improving reliability in systems with high penetration of wind and solar energy.”
The consortium will initially test three Dutch LDES solutions: Aquabattery, a storage technology that uses only salt water as a storage medium and is described as a flow battery capable of independently adjusting power (kW) and energy (kWh) capacity; Ore Energy, a 100-hour iron-air LDES solution; And BB1 Project BV hybrid thermal and electrical long-term energy storage system that combines heat pumps, water-based heat storage and sodium ion batteries with smart control to store sustainable electricity for longer periods as both heat and power.
“The selection of these technologies was based on their reliance on safe and abundant materials, suitable for a service period of 8 to 100 hours, and their integration potential with PV, wind energy and energy suppliers, as well as their financeability and assurance pathways,” said Gonzalez Aparicio. “For multi-day needs, iron-air is promising in terms of cost and lifespan, while flow batteries offer scalable, non-critical materials and long life; thermal storage combined with electrified heat can be very cost-effective where heat demand is high.”
“We also build a blueprint for an open energy management system (EMS) with modules for LDES control, hybrid operations and a network congestion model; it uses renewable energy generation forecasts and demand profiles to optimize when storage absorbs PV and wind surpluses and when it is sent to local loads or the gridshe added.The EMS integrates market signals and DSO/TSO constraints, co-optimizing behind-the-meter and before-the-meter operations to avoid congestion while maximizing value stacking. We also develop certainty methods to ensure safe, predictable behavior alongside BMS/converters.”
The consortium brings together utilities, network operators, technology developers, academic partners and industrial users, including Vattenfall, Stedin, TU/e, Aquabattery, Ore Energy, BB1 Project and Energy Storage NL.
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