Curtailment has become a core design constraint for solar projects in Iberia. With Spain and Portugal each recording hundreds of negative-price hours per quarter, developers can no longer size a plant on annual yield alone. They have to test how much output can actually reach the grid, and pair solar with storage, before a layout is locked.

Iberia has never lacked sun, and for solar developers that has long been the easy part. But the most productive hours on the irradiance chart can also be the least bankable in the market. To keep their models honest, developers have to stop sizing projects around the best-case solar day and start testing against the most congested hours. RatedPower lets you design a project to its grid connection point and compare how different layouts perform on energy yield and economics.

Iberia's solar paradox

There is plenty of yield to chase in this high-irradiance region. Spain's southern provinces offer some of Europe's strongest solar resource, and single-axis tracking with bifacial modules, now standard on utility-scale sites, pushes generation higher still. The country has built one of Europe's largest solar fleets: Red Eléctrica reported almost 50 gigawatts (GW) of installed solar photovoltaic (PV) capacity by the end of 2025, after adding 8.8 GW that year, and PV set a record 18.4 percent share of national electricity generation.

A growing slice of peak-hour output now has nowhere to go, however. In the first quarter of 2026, European Union day-ahead markets cleared 1,223 hours below zero. Iberia was the epicenter of the glut: Spain accounted for 347 of those hours and Portugal for 294.

Curtailment is now the norm

Given these capture-rate pressures, Iberian projects should assume curtailment will happen often enough to eat into saleable output. 

Uncompensated PV curtailment in Spain is expected to stay high for at least the next two years. Analysts still expect 3.05 terawatt-hours (TWh) to be clipped in 2026, rising to 3.38 TWh in 2027, as grid reinforcements play catch-up. If 2025's curtailment patterns become the new baseline, the summer months will be especially bruising.

These national averages hide high-pressure congestion pockets that only appear once you zoom in. In Badajoz, one node might lose just 3.55 percent of its output to the grid's ceiling while a neighbor stuck behind a congested substation sees 22.5 percent discarded. Regional forecasts can make a site look bankable while node-level constraints quietly upend the revenue case. The underlying grid fragility is not hypothetical either: the grid collapse that hit the peninsula is worth understanding in detail.

Curtailment should be treated as a design constraint

Relief may come after 2028 if planned grid upgrades land on schedule, but projects being designed now cannot bank on that timing. Solar plants in Iberia can no longer be judged only on how much power they generate in a year. The question is how much of that output can realistically become revenue once export limits start to bite.

Rethink the DC/AC ratio trap

A higher direct current to alternating current (DC/AC) ratio only helps if the project can export or store the extra output. Adding more DC capacity when peak-hour export is already constrained is like pouring a gallon into a pint glass: the surplus just gets curtailed or sold for scraps. The DC/AC ratio should be set against the site's real export limit, not chased for its own sake.

A dense layout will not always improve revenue

Tighter layouts flatter the internal rate of return (IRR) on paper, but if that extra energy surges during the hours the grid is already overloaded, it is effectively ghost production doing little for revenue. It shows up as clipping and other conversion losses rather than saleable energy. Stress-test for curtailment before breaking ground so the design matches the site's export limits, because once the ink is dry, changes get harder and slower.

BESS can give stranded solar value somewhere to go

Spain has built so much renewable capacity that gas now sets the power price less often than before, which has helped push wholesale prices down. Good for consumers, but a revenue problem for solar developers.

Photovoltaic projects tend to produce in lockstep, saturating the same daylight hours, so peak solar output can be worth very little for merchant projects. For power purchase agreement (PPA) backed solar, that concentration erodes the capture price, making it harder to sell energy at the expected value when production clusters in low-price hours.

More RatedPower users are now running hybrid PV and battery energy storage system (BESS) simulations. Rather than treating storage as a separate add-on, developers are testing solar and storage together, much earlier, because batteries affect both revenue and technical design. Comparing AC-coupled and DC-coupled BESS options now belongs in the layout decision itself.

Storage is not a cure-all: it cannot remove local congestion or fix a poor grid connection point. But it gives a project more control over timing, protecting more generation from becoming low-value output. Battery arbitrage lets a project hold some output and discharge when prices are stronger or when the grid can accept the power.

Designing without full export

Iberia, along with the rest of Europe, has entered what the International Energy Agency (IEA) calls the Age of Electricity. New loads from data centers and green hydrogen are connecting faster than network capacity can comfortably absorb.

To avoid designing around an export capacity that may not exist, developers need to test the plant under realistic export limits before committing to a layout, and to assess PV and storage together, because storage can change which layout makes sense. RatedPower helps teams compare those layout and storage choices at the design stage. Use it to:

●      Design for constrained export: what happens if the plant cannot export at full capacity during peak solar hours? Compare how alternative layouts turn generation into saleable energy and returns, so return on investment (ROI) is not left dying on the vine during peak sun.

●      Test PV and BESS configurations together: how much output should the battery absorb, and how does that change the layout? Compare hybrid configurations while there is still room to reconfigure.

●      Compare curtailment-aware layouts early: two sites with similar irradiance can behave very differently once local grid constraints are taken into account. Put their energy yield and economics side by side to find the layout that holds up best.

There is plenty of equity flooding Iberia's solar market, but to thrive here a plant needs curtailment-aware design grounded in real export constraints. Our Iberia curtailment and hybrid design playbook walks through the full workflow, from establishing the injection cap to comparing PV-only and hybrid economics. Download it to put the logic to work, or request a demo to see RatedPower design and compare storage-backed hybrid projects first-hand.

Frequently asked questions

What is solar curtailment in Spain?

Curtailment is generation a solar plant could produce but cannot deliver, because the grid cannot accept it or prices have turned negative. In Spain it now occurs for hundreds of hours a year, concentrated in high-output midday periods, and it is expected to affect around 3 terawatt-hours of PV output annually through 2027.

Why are Spanish electricity prices going negative?

When solar and wind flood the market during sunny, windy hours, supply outstrips both demand and export capacity, pushing day-ahead prices below zero. In the first quarter of 2026, Spain recorded 347 negative-price hours and Portugal 294.

How does battery storage reduce curtailment risk?

A battery lets a project store output that would otherwise be curtailed or sold at very low prices, then discharge it when prices recover or the grid can accept it. It does not fix a congested connection, but it gives the project control over timing and protects more of its energy value.

Should storage be designed in from the start?

Yes. Because a battery changes both the revenue profile and the technical layout, testing PV and storage together at the design stage produces better decisions than adding storage later, when changes are costly and slow.

Key takeaways

RatedPower lets teams hybridize a PV plant and engineer the battery in one place, comparing design cases without rebuilding the model each time an assumption moves. Schedule a demo to see how it handles export-constrained, storage-backed projects in Iberia.