Hybridizing Europe's Hydro With Wind and Solar Could Bypass Grid Constraints, Ember Finds

How Copying Wind and Solar Onto Hydro Connections Could Ease Europe's Grid Crunch

A new report from the think tank Ember argues that Europe can ease its renewable grid bottleneck without waiting for new transmission lines. The proposal: add wind and solar capacity behind the meter of existing hydropower plants, using the same grid connection for multiple generating technologies.

Ember assessed hydropower assets in Austria, Bulgaria, France, Italy, Portugal, Romania and Spain — countries that together hold 93GW of the EU's 131GW hydro fleet. The report finds that the eligible hydro plants operate at just 19% of their maximum output on average, leaving significant unused capacity in their grid connections. Adding wind and solar could raise utilization to 36% and 31% respectively, and in some cases could triple the productive use of the same connection.

According to Ember, 25GW of new wind and solar could be integrated behind the meter without disrupting typical hydro dispatch behavior. That equals about 18% of the renewable capacity Europe expects to add in the coming years — capacity that could come online without grid reinforcements or lengthy connection queues. The report arrives as European leaders push electrification for industrial competitiveness, but at least 120GW of grid capacity shortfall is projected against renewable growth by 2030.

Only Spain and Portugal currently have rules covering hybrid projects, Ember says. The report calls for new legislation to streamline hybrid connections, including simplified procedures and provisions allowing temporary overcapacity, so existing infrastructure is used far more intensively.

The Utilization Math Behind Ember's 25GW Estimate

Why 19% Utilization Is a Large Untapped Resource

The central insight of Ember's report is not that wind and solar are cheap — it is that existing hydro grid connections are severely underused. A plant operating at 19% of its maximum output leaves most of its connection capacity idle for the rest of the year. Hybridization stacks variable renewables onto that idle capacity, turning a stranded asset into a higher-utilization one.

The mechanism, called cable pooling, has two commercial forms: fixed export limits for each generation source, or a single overall export limit managed by one entity. The latter is more flexible because it lets the combined wind, solar and hydro output smooth variability, giving the grid a more stable power profile. Ember's estimate that 25GW can be added without altering typical hydro dispatch is important because it implies no new grid intervention is needed for that tranche of capacity.

Spain and Portugal: The Only Rulebooks, and What They Permit

Regulatory asymmetry is the real story behind the numbers. Ember's report covers seven countries, but only Spain and Portugal have adopted rules for hybrid projects. That means most of the eligible hydro fleet sits in markets where developers cannot easily combine generation sources behind one meter.

Without legislation defining export limits, grid charges and connection rights for hybrids, utilities have little legal certainty to invest. Ember's recommendations — accelerated connection procedures, simplified permitting and legal room for overcapacity — are aimed directly at closing that gap. The countries that act first on hybrid rules are likely to unlock renewable capacity faster and at lower network cost than those that wait for full grid build-out.

What the Tâmega and Lazer Projects Demonstrate

Two projects show the models in practice. The Tâmega wind farm in Portugal will share the same substation as the Tâmega hydroelectric system, creating a hybrid hydro-wind connection. In France, the Lazer floating solar plant — over 50,000 panels with 20MWp of capacity, owned by EDF — pairs solar with a hydro scheme whose water is partly used for crop irrigation in summer. EDF says the solar plant helps keep electricity flowing during those months, when hydro output is constrained by irrigation demand.

Floating solar also requires no new land and reduces evaporation from reservoirs, making it a second viable path to hybridization. Together, the two projects illustrate that hybrid hydro can work in different hydrologies and market conditions — but scaling it across Europe depends on regulators catching up.

What Utilities and Governments Should Do With Ember's Findings

For European utilities and renewable developers:

• Audit hydro fleets in the seven countries Ember studied, prioritizing plants with low average utilization and existing substation capacity that can host additional generation.
• Evaluate cable pooling structures — fixed export limits versus a single managed export limit — early in project design, since the choice affects dispatch flexibility and revenue stability.
• Use the Tâmega and Lazer projects as reference cases for the two main hybrid models: shared hydro-wind substations and floating solar on reservoirs.

For policymakers and grid operators:

• Adopt hybrid project rules modeled on Spain and Portugal, which are currently the only EU countries with clear frameworks.
• Provide simplified, accelerated grid connection procedures for hybrids, as Ember recommends, since they have minor network impact and can relieve bottlenecks.
• Include legal provisions for temporary overcapacity during hybridization to maximize use of existing grid connections rather than forcing costly upgrades.