The renewable energy expansion in Spain opened up new commercial opportunities for storage, but it also introduced a contradiction in the financial models of the projects: the same price differentials that favored electricity arbitrage could not be guaranteed for the 15 or 20 years considered in BESS investments .
According to data provided by AleaSoft Energy Forecasting , the one-hour intraday spread averaged approximately €114/MWh during 2026 up to August , with an increase to €148/MWh in July and levels close to €193/MWh in August.
The magnitude of these differences reinforced the economic appeal of batteries, although their future profitability remained linked to the evolution of the renewable energy sector, demand, and the incorporation of new storage systems.
The energy context also reflected a growing need for flexibility.
According to Red Eléctrica , renewables contributed 53.6% of Spain's electricity generation in August , with 13,640 GWh and an 11% year-on-year increase. During that month, the system integrated 954 GWh through battery storage and pumped hydro storage , while electricity demand accumulated a 2.8% increase during the first eight months of the year.
The evolution of the market thus opened up an opportunity that went beyond the buying and selling of electricity between different time slots. In a dialogue with Energía Estratégica , Antonio Delgado Rigal, CEO of AleaSoft Energy Forecasting , identified four revenue streams for BESS (Buyer Energy Service Companies): arbitrage in day-ahead and intraday markets, balancing services, the capacity market, and contracts capable of stabilizing part of the billing .
"The volatility that we consider a problem today is also the economic signal that will allow us to develop the flexibility that the electricity system of the future needs," the executive said.
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The growth of energy storage introduced new demands for developers. In addition to identifying energy trading opportunities, projects had to assess their participation in services related to system balancing, the terms of remuneration for available capacity, and the possibility of securing revenue through commercial agreements.
Adjustment services became especially important in a system that needed to manage a growing share of variable generation. According to figures released by Red Eléctrica, between January and September 2026, generators received €3.906 billion for adjustment and regulation services , a figure corresponding to all participating technologies and not exclusively to storage.
For BESS, effective access to these markets depends on the technical requirements of each service and the operators' ability to adapt their strategies to the system's needs. This diversification also introduced economic decisions about where to use stored energy, how long to commit capacity, and which opportunities to prioritize each day.
In that scenario, Delgado Rigal highlighted a fundamental difference with respect to conventional renewable technologies:
"A battery has a huge advantage: it can continuously modify its strategy and seek the market that best rewards its flexibility. But precisely this optionality makes its modeling considerably more complex than that of a photovoltaic or wind power plant," he explained.
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The optimization of these assets incorporated technical variables that could substantially alter the financial results.
Degradation, efficiency, number of cycles, and operating strategy had to be analyzed together with price and remuneration expectations, since greater utilization did not necessarily imply a proportional improvement in economic performance.
Added to this was the future competition among battery storage solutions. According to figures presented by AleaSoft, Spain had around 260 MW of operational electrochemical storage capacity in August 2026 , compared to more than 40 GW of projects with access and connection permits granted or in process . Although this portfolio did not represent capacity that would necessarily be built, its size anticipated a scenario where commercial strategies would have to consider the gradual entry of new competitors.
The evolution of spreads also depended on this deployment. Greater storage capacity would allow for the absorption of renewable surpluses and the shifting of generation towards peak demand hours, but this same process could reduce some of the price differences exploited by arbitrage.
"The challenge is not to prove that a battery can make money. The challenge is to prove that it can generate sufficient revenue in different scenarios throughout the life of the project," Delgado Rigal warned.
The capacity market and contracts complete the financial equation
The need to sustain long-term revenues gained a new regulatory instrument with the approval of Order TED/966/2026 , which created the Spanish capacity market in September. The mechanism incorporated auctions to remunerate firm capacity and opened participation to generation, storage, and demand, through a competitive pay-as-bid scheme.
For new investments, the regulations stipulated service periods of up to 15 years , while remuneration was linked to the recognized MW of firm capacity and the price awarded in each tender. The design allowed for the incorporation of a revenue stream other than electricity sales, although its economic value depended on the specific conditions of each auction.
One of the elements yet to be defined was the firmness coefficient, or derating , used to determine what proportion of each installation's nominal power could be recognized as an effective contribution to security of supply. This parameter proved especially important for BESS systems, as it would determine the amount of power they could offer and, consequently, their potential revenue from capacity.
Regarding the incorporation of this mechanism into the financial model, Delgado Rigal noted: "For a battery company, this is especially interesting because it introduces a different source of income that is less correlated with arbitrage."
However, regulatory approval alone did not resolve the commercial uncertainties. The final coefficients, the schedule for the first auctions, and the award prices remained necessary variables to determine the mechanism's contribution to financing new facilities.
In parallel, long-term contracts, including agreed-upon remuneration schemes for the use or availability of storage, offered another alternative for reducing exposure to market fluctuations. Their implementation could provide greater predictability to cash flows, although it also entailed negotiating the allocation of risks and opportunities among owners, operators, and commercial counterparties.
The combination of these tools altered the financing requirements. Developers needed to construct scenarios that considered changes in electricity prices, ancillary service conditions, allocated capacity revenues, and the technical performance of batteries throughout their lifespan.
Consequently, the competitiveness of Spanish storage began to depend as much on the initial investment as on the commercial structure designed to recover that capital . Volatility offered immediate opportunities, but the possibility of turning them into bankable projects was contingent on revenue diversification, market evolution, and the ability to sustain results in less favorable scenarios.