Hybrid projects |


Historically, assets were required to provide these services continuously for a week at a time. This implicitly favoured long-duration assets like pumped storage hydropower. But in recent years, these commitment periods have been reduced dramatically. In some countries, assets can participate for a single day, or even a single hour. This shift reduced the purchase cost on the grid operator side, but it also created a systemic vulnerability: the grid is increasingly relying on assets that cannot sustain flexibility beyond a few hours. During typical operations, deviations are short. During major events, they may not be. Goodenough highlights the recent Iberian blackout in which low levels of hydropower and inertia were among the contributing factors. The core flaw, she argues, is that “a battery which can deliver flexibility for two hours is treated the same in terms of revenue as a hydro pump storage plant which could deliver that flexibility for five months.” As long as market design values fast response but not duration, long-duration storage will not receive adequate investment. We don’t see the effects of this flaw in


today’s energy landscape, because a lot of the infrastructure live or in development has already sunk their capital investments. But without long- duration market signals, upgrades, reinvestment and new builds will stall. “By the time they go away, it will be too late to react.” To correct this imbalance, Goodenough says that markets need products that explicitly reward long-duration storage. This could come in two forms:


Longer auction windows for secondary and tertiary reserve-restoring weekly commitments for part of the market. New products focused on long-duration flexibility, potentially analogous to a fourth reserve category.


She emphasises that policymakers must make a clear decision: either maintain purely market- driven structures or introduce policy tools such as tax incentives or investment support. But something must change. Hydropower projects have long development cycles. A failure to incentivise them today means they will not exist in 2035. That timeline matches exactly when system-wide renewable penetration is expected to peak.


Without action, she warns, the industry could face a decade of curtailments or blackouts while waiting for long-duration storage to be built.


A practical hybrid scenario To illustrate hybrid potential, Goodenough


describes a solar-rich country with predictable midday production peaks. Installing enough pumped storage to absorb the entire peak would be costly and unnecessary. Instead, a combination of 2GW of pumped storage and 500MW of batteries could balance the system efficiently. Batteries would shave the highest part of the solar peak, shifting energy into


shoulder hours. Pumped storage would store the lower portion of the surplus. Across each 24-hour cycle, nearly the full solar oversupply could be stored. The battery serves the daily problem; the hydropower plant serves the seasonal one. This model also addresses extended periods of low renewable generation. Stored hydropower can support the grid during two or three weeks of low wind and solar-a capability batteries alone cannot provide. In short, battery storage delivers rapid frequency and voltage support, while pumped storage provides inertia and spinning reserve, therefore working together they ensure a resilient, stable grid.


Digitalisation as the enabling


layer in the energy transition Digitalisation is central to hybrid storage becoming viable. HYDROGRID plans to release an extension to its HYDROGRID Insight platform in 2026 to handle joint hydro-battery optimisation. Although often labelled as AI, Goodenough emphasises that the Insight platform uses a machine learning optimisation model that improves over time taking into account all physical and operational constraints. She differentiates this from large language models, stressing that grid operations require reliability, not probabilistic generation. Goodenough expands on this point,


explaining that the real challenge lies in the nature of the problem itself: “Optimally choosing between hydro and battery dispatch is a deterministic task, defined by clear physical boundaries. For most energy applications, security and dependability are non-negotiable. That’s why cutting-edge mathematical optimisation models often outperform AI or LLMs in the strict sense. Our system already acts as an agentic AI –it aggregates data from multiple sources and autonomously determines optimal decisions –but its strength lies in precision and robustness rather than generative capabilities.”


Investment signals and risk Goodenough says the industry has been


discussing hybrid hydro-battery projects for at least five years. There are now several concrete projects in development, though not yet at the stage of final investment decisions. Hybridisation is both “over and underestimated” because while the benefits are clear, uncertainty remains high. Small changes in grid-cost structures or reserve markets can dramatically affect profitability. Battery economics are especially sensitive. Investors therefore wait for policy stability before taking the final step. Beyond market design, Goodenough highlights permitting as a critical barrier. Hydropower permitting is often very slow, significantly limiting capacity expansion. Batteries face less complex permitting but are still affected. Clearer, faster processes would accelerate deployment. She also notes that advances in battery


16 | December 2025 | www.waterpowermagazine.com


technology could shift the landscape. Solid- state batteries, long discussed in the industry, have seen first commercial-scale production in China. If they deliver lower costs and higher storage capacity, they could accelerate battery deployment significantly. Goodenough expects most hybrid systems


to emerge at existing hydropower sites because grid connections and electrical infrastructure are already in place. Hydropower siting is geographically constrained, making retrofit logical. Batteries, by contrast, “you can just place behind the powerhouse in principle almost everywhere.”


Regional leaders


Asia is clearly leading in hybrid potential. China alone has roughly 90GW of pumped storage under construction –more than the rest of the world combined –and dominates global battery production. Centralised decision-making and less stringent permitting accelerate this trend. Goodenough expects Asia, and China in particular, to host the earliest large-scale hydro- battery hybrid systems.


On the other hand, she mentions that North America is emerging as an innovation hub, with a robust pipeline of hybrid projects and real- world success stories like Idaho Falls Power’s water-powered microgrid, which demonstrates black start capability and grid resilience. On top of that, federal and state incentives for grid modernisation, alongside research leadership from institutions such as Lawrence Berkeley National Lab, reinforce this trend. Nonetheless, Goodenough points out that


Europe still remains a global leader in pumped storage technology but faces a catch-up challenge in battery deployment. While policy frameworks and renewable integration goals are strong, permitting complexity and slower investment cycles have limited hybrid adoption. However, Europe’s expertise in pumped storage hydropower and commitment to decarbonisation position it as a key player in the next wave of hybrid solutions.


By 2035: hydro still dominates


stored energy By 2035, global battery storage capacity is expected to reach 135-200GW. Pumped storage hydropower is projected at around 225GW. But looking at storage volume, hydropower will still dominate: batteries will hold 350-2300GWh, while hydropower will hold around 13,000GWh, “dwarfing” batteries by at least a factor of five. Hydropower will therefore remain the backbone of global storage, even as batteries grow significantly. HYDROGRID expects to play a central role in this future, supporting both hydropower optimisation and hybrid systems. Goodenough describes hydropower as “the storage giant that orchestrates and enables moving towards a much more carbon-neutral form of energy generation,” with a role that will extend far beyond the next decade.


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