Iberia's BESS price curve explained: What 2026 means for developers

In Iberia, batteries are no longer a nice-to-have. Because of wider electricity price swings and rising curtailment, a solar project without storage is increasingly exposed to hours when the power it generates is worth very little, or even nothing. Battery energy storage systems (BESS) have become the tool developers use to manage that risk. But building one profitably takes more than knowing prices are volatile. It takes getting the design right before any money is committed.

RatedPower gives your team the ability to model battery systems based on your actual site and project constraints, rather than industry averages, so the cost and output estimates you use in financing conversations more accurately reflect what you are building.

Inside Iberia's battery-backed solar buildout

Spain and Portugal have both experienced rapid growth in solar capacity. That growth is now running ahead of the grid's ability to absorb it at all hours, which is creating real problems for developers who built projects without factoring in storage. Batteries are the fix, and investors and developers across both markets are responding.

The price problem is getting harder to ignore

Hourly electricity prices in Spain have become far more volatile. Spreads between cheap midday hours and expensive morning and evening periods widened by almost 25% between 2024 and 2025. Around 10% of hours now clear at zero or negative prices. That means generators receive nothing and, in some cases, pay to stay connected.

It is not a fringe problem. In May last year, 21% of solar output failed to clear the market despite bids already being close to zero. Those hours are direct revenue losses. A battery changes the situation: instead of selling into a zero-price market, the system holds that energy and releases it when prices recover, typically within the same day.

Utilities are already committing to storage at scale

The largest players in Spain have been paying attention. Naturgy has committed to building 160 MW of battery capacity across 10 sites, retrofitting storage onto some of its existing solar plants and pairing others with new batteries from the start. Nine of the 10 sites will be co-located with solar. One will be a standalone battery project.

Portugal is moving in the same direction. French developer Akuo is building an 80 MW battery system integrated into its 181 MW Santas solar plant in Borba, with support from Portugal's EU recovery funding. Portugal awarded around €100 million to storage projects in early 2025 and is preparing another storage auction. These are not speculative developments. They are utility-scale investments by experienced operators who have run the numbers and decided that storage is worth building now.

In Spain, regulation has also moved to support this trend. Following the April 2025 Iberian grid blackout, Spain passed legislation specifically designed to make it easier to add batteries to existing solar plants. Developer FRV has announced plans for 1.2 GW of battery projects across Spain, most of them co-located with its existing solar portfolio, and is targeting construction starts in 2026 and 2027.

New ownership and revenue models are making projects more accessible

One barrier for solar developers has been the upfront cost of adding a battery. As a result new deal structures are emerging to lower it. BESS developer Lunas Energy has pioneered a model in Spain where it finances and operates the battery independently, paying the solar owner for land use and a share of battery revenues. The solar developer takes on none of the capital cost or trading risk.

On the revenue side, structured contracts are becoming available that were previously uncommon in this market. In July 2025, Zelestra and EDP signed what is claimed to be the first power purchase agreement in Europe to cover both solar and battery dispatch together. Rather than selling solar on one contract and managing the battery separately, the deal packages both into a single offtake arrangement. That gives the developer a more predictable revenue base and gives the offtaker guaranteed energy delivery at specific times of the day.

Developer Grenergy has gone further, signing a 12-year capacity contract for the 680 MWh battery portion of its Escuderos hybrid project in Castilla-La Mancha. Under this kind of arrangement, a counterparty pays for access to the battery's capacity over a fixed term, regardless of day-to-day price movements. For investors, that is a meaningfully different risk profile than a purely merchant battery.

The hardware is no longer the hard part

Battery technology has matured quickly. The physical systems developers are buying today are largely standardized: containerized units that connect to the grid through a power conversion system, with well-understood performance characteristics. What that means in practice is that the risks and cost variables have shifted away from the battery hardware itself.

The complexity now lies in how a battery integrates with a specific site: the distance from the grid connection, the cost of trenching and cabling, the capacity of the local substation, and whether the project needs to provide additional grid services beyond basic energy storage. Engie's recent acquisition of two battery projects in Andalusia totaling 1.1 GWh, both paired with additional equipment to provide grid stability services, is a good illustration of how project scope is expanding. The cells are standard. Everything around them depends on the site.

Lower prices have not removed the risk of getting costs wrong

Battery costs have fallen in recent years, largely driven by increased manufacturing output in China. But those prices are not guaranteed to stay low with an uptick in early 2026. They remain sensitive to raw material markets, factory output rates, and shipping conditions, all of which are harder to predict than they were two years ago.

More fundamentally, a project that looks viable at today's equipment prices can still fail if the upfront cost estimates are not grounded in the actual design. A rough cost-per-kilowatt-hour figure is not enough to take into a lender conversation or a board approval process. The number that matters is the installed cost of this battery, on this site, with this interconnection scope. Getting there requires modeling the project in enough detail to know what you are actually committing to.

The cost of getting it wrong comes in at the feasibility stage

Most cost overruns on BESS projects do not come from unexpected hardware prices. They stem from underestimating what it takes to install a battery at a specific site: the civil works, grid connection upgrades, cabling, and site-specific compliance requirements. Those costs are highly variable and very difficult to estimate accurately without a real design.

To produce numbers that hold up through development, developers need to work from site-specific assumptions at the feasibility stage. That means:

• Choosing equipment configurations early (battery size, inverter rating, and site layout) based on the actual site rather than default assumptions.

• Estimating how much energy the system will produce and when, based on the real interconnection terms and site design.

• Understanding how the choice between a shorter-duration and longer-duration battery affects both cost and what the battery can realistically earn.

• Including the full scope of site works (cable runs, trenching, grid connection) in cost estimates, not just the equipment.

• Using current cost data for the region, not global averages or figures from two procurement cycles ago.

• Testing how the numbers change if procurement timing shifts or a key supplier changes.

• Designing hybrid solar and battery systems as a single integrated project, not two separate systems added together.

Model true BESS costs from the feasibility stage, with layout-specific accuracy

RatedPower gives BESS developers in Iberia the tools to estimate costs more accurately and earlier in the project timeline, using up-to-date cost benchmarks and site-specific design outputs rather than rough averages. It can:

• Generate early-stage CAPEX estimates based on design configuration and cost databases.

• Generate a detailed bill of materials tied to the system configuration and site layout.

• Model the physical layout of battery components against real site constraints.

• Iterate with different battery sizing configurations to understand trade-offs in cost and performance between shorter- and longer-duration systems.

• Estimate energy dispatch and performance of hybrid PV+BESS systems based on the modeled design.

• Compare costs across different design approaches and equipment topologies.

• Assess how decisions about cable routes and equipment placement impact system performance and installed cost.

• Export single-line diagrams and technical reports to support financing or permitting processes.

RatedPower works for both standalone battery projects and hybrid solar and storage plants.