Battery storage projects are connected locally, but their economics increasingly depend on regional electricity market integration, cross-border capacity, balancing platforms and liquidity across Southeast Europe.
At first sight, a battery energy storage system looks like a local asset. It is connected to a specific node, under a specific grid connection agreement, in a specific country, with a specific licence and a specific.
The next battery market will not be built only inside national borders
At first sight, a battery energy storage system looks like a local asset. It is connected to a specific node, under a specific grid connection agreement, in a specific country, with a specific licence and a specific metering configuration. For the developer, the project starts with land, an ATR, permits, EPC contracts, batteries, transformers, EMS and a route-to-market agreement.
But commercially, that is no longer the full story.
In an increasingly integrated European electricity market, a battery connected in Romania is not influenced only by Romania. Its revenues are shaped by Hungarian prices, Bulgarian solar peaks, Greek generation profiles, Serbian and Ukrainian flows, interconnector availability, regional scarcity hours, balancing activation and the behaviour of neighbouring transmission system operators.
This is why the next phase of BESS growth in Southeast Europe will depend not only on national laws and support schemes, but on regional cooperation.
The simple way to put it is this: BESS is connected locally, but monetised regionally.
Why regional cooperation matters for storage
Battery storage earns money from differences. Differences between low-price and high-price hours. Differences between forecast and actual production. Differences between scheduled and real consumption. Differences between congested and uncongested zones. Differences between surplus and scarcity.
As European electricity markets become more interconnected, those differences are increasingly regional. A solar-heavy day in Romania may coincide with similar solar production in Bulgaria and Greece. An evening scarcity period in Central Europe may affect prices across the region. A constraint on one interconnector can change spreads in several markets. A balancing need in one system may influence activation prices and reserve availability in another.
This is why cross-border coordination is not an abstract EU policy concept for storage investors. It directly affects the revenue model.
A Romanian BESS project may be physically located in Dobrogea, Banat, Oltenia or Moldova. But the price signals it responds to may be shaped by what happens in Budapest, Sofia, Athens, Belgrade, Vienna or Kyiv. The better the regional market integration, the larger and more reliable the revenue pool available to storage.
Day-ahead coupling: the first layer of integration
The first important layer is day-ahead market coupling. Romania is already part of the European price-coupling architecture. OPCOM notes that, as of 17 June 2021, the Romanian day-ahead market switched to operating in a European-level price-coupling mechanism through the Interim Coupling project.
The broader European objective is clear. ENTSO-E describes Single Day-Ahead Coupling as a mechanism designed to create a single pan-European cross-zonal day-ahead electricity market, allocating scarce cross-border transmission capacity efficiently through a common algorithm while taking into account transmission constraints.
For a battery, this matters because market coupling improves price discovery. If cross-border capacity is properly allocated and markets are coupled, electricity prices reflect regional scarcity and surplus more efficiently. This can support more realistic arbitrage signals and better investment modelling.
But day-ahead coupling is only the beginning. For BESS, the most valuable signals often come closer to real time.
Intraday liquidity: where batteries begin to matter more
A battery is a fast-response asset. Its value is not only in buying electricity at noon and selling it in the evening. Its value also comes from responding to short-term forecast errors, renewable ramps, congestion, intraday price changes and imbalance risks.
That makes intraday liquidity essential.
If intraday markets are shallow, fragmented or illiquid, a battery cannot fully monetise its technical capability. It may be able to move electricity across time, but the market may not give it enough opportunities to do so efficiently. In a region with rapidly increasing solar and wind capacity, intraday markets become the bridge between weather uncertainty and system flexibility.
This is especially relevant for Southeast Europe. The region has strong renewable potential, but also uneven market liquidity, different balancing rules and different levels of integration with the EU market architecture. For storage investors, that fragmentation becomes a pricing and financing issue.
The more liquid and integrated the intraday market becomes, the more valuable batteries become.
Balancing-market integration: the real prize for BESS
If day-ahead and intraday markets are important, balancing-market integration may be even more important.
Battery storage is particularly well suited to balancing and ancillary services because it can respond quickly, accurately and repeatedly. It can provide fast flexibility, help manage frequency restoration needs, support system stability and reduce the cost of balancing a renewable-heavy system.
At EU level, the direction is toward integrated balancing platforms. ENTSO-E describes MARI as the European implementation project for the creation, future development and operation of the European mFRR platform. The corresponding European architecture also includes PICASSO for aFRR, with European balancing platforms designed to enable more efficient cross-border exchange of balancing energy.
This is not technical bureaucracy. It is future revenue infrastructure.
When balancing markets remain purely national, the revenue pool for batteries is smaller and more volatile. When balancing markets integrate, batteries can participate in deeper and more efficient markets, subject to prequalification, TSO rules and cross-zonal capacity availability.
For Romania, this is one of the most important regional topics. A Romanian BESS project may initially monetise local balancing opportunities, but its long-term value will increasingly be influenced by European balancing integration, harmonised products, TSO accession to platforms and the degree to which cross-border balancing energy can be activated efficiently.
A good investor will not ask only whether Romania has a balancing market. It will ask how that market connects to the European balancing architecture.
Cross-border capacity: not just transmission infrastructure, but revenue infrastructure
Interconnectors are usually discussed in the language of security of supply, system adequacy and market integration. For BESS, they should also be understood as revenue infrastructure.
A battery earns from price spreads and system needs. If cross-border capacity is constrained, some price signals remain trapped locally. If cross-border capacity is increased and efficiently allocated, regional price signals become more meaningful. That improves market liquidity, reduces inefficiencies and supports better optimisation.
ACER’s 2025 electricity-market integration report identifies increasing cross-border capacity as a key driver of integration and efficiency. For storage, that means cross-border capacity is not only a transmission-policy issue. It affects the size, quality and reliability of the revenue stack.
This is particularly relevant for Romania because of its geographic position. Romania sits between Central Europe, the Balkans, the Black Sea region and increasingly relevant flows connected to Moldova and Ukraine. That position can become a strategic advantage if interconnection, market coupling and balancing integration continue to improve.
Romania could become a regional flexibility hub. But that will not happen through national regulation alone. It requires coordination between TSOs, regulators, market operators and neighbouring countries.
Curtailment is also becoming regional
Renewable curtailment is often discussed as a local grid issue. But in Southeast Europe, it is becoming a regional problem.
Romania, Bulgaria and Greece all have strong solar ambitions. Solar generation peaks broadly during similar hours. If each country builds large volumes of PV without enough interconnection, storage, demand response and balancing coordination, the region risks simultaneous low-price or negative-price intervals, local congestion and inefficient curtailment.
Batteries can reduce this problem, but they cannot solve it alone. A battery can absorb excess production locally, shift energy into later hours and reduce pressure at a specific node. But if the broader regional system remains fragmented, flexibility is not used efficiently.
This is why regional planning matters. Storage should not be planned only as a private asset behind a grid connection. It should be understood as part of a regional flexibility architecture. That includes interconnectors, grid reinforcement, market coupling, reserve sharing, congestion management and cross-border balancing.
The smartest countries in the region will not only ask how many batteries they can subsidise. They will ask where batteries should be located, how they interact with the grid, and how they support regional flows.
Bankability: why regional integration matters to investors
For investors and lenders, regional cooperation is important because it improves bankability.
A small, fragmented, illiquid market creates modelling risk. A deeper regional market creates better price discovery, more liquidity, more robust balancing signals and more credible revenue assumptions. That does not eliminate merchant risk, but it makes merchant risk easier to understand and price.
This matters especially for Romania. Romania has real volatility, solar growth, grid congestion and balancing needs. These are good fundamentals for BESS. But compared with more structured markets, Romania still lacks long-term revenue certainty for storage. Regional integration can help improve the quality of the revenue environment by expanding the practical opportunity set for batteries.
In other words, regional cooperation does not replace good national regulation. But it makes national BESS projects more investable.
A lender looking at a Romanian battery will want to understand not only the ATR, the licence and the local route-to-market agreement. It will also want to understand the depth of the intraday market, the direction of balancing integration, the liquidity of regional markets, the stability of cross-border rules and the ability of the project to access multiple revenue streams.
Regional integration turns storage from a local volatility bet into a more credible flexibility investment.
The Southeast Europe challenge: opportunity and fragmentation
Southeast Europe has the ingredients for significant BESS growth: renewable resources, growing solar pipelines, coal phase-out pressure, system adequacy concerns, grid constraints and increasing price volatility.
But the region is still fragmented. Countries differ in licensing rules, grid connection practices, TSO prequalification requirements, balancing products, settlement rules, aggregation frameworks, tariff treatment, support schemes and permitting procedures. EU Member States follow the internal electricity market framework, while Energy Community countries are still aligning at different speeds.
This fragmentation slows capital deployment. An investor active in Romania, Bulgaria, Greece, Hungary and Serbia cannot simply replicate one storage model across all markets. Each country has different legal, technical and commercial assumptions.
That is why convergence matters. Not because every country must have identical rules, but because storage investors need enough alignment to scale platforms regionally. Harmonised balancing products, transparent prequalification, predictable settlement, compatible metering standards and coordinated grid planning would materially reduce transaction costs and investment uncertainty.
Romania’s position: a potential flexibility hub
Romania has a potentially strong position in this regional story. It has a large domestic market, strong renewable resources, increasing solar deployment, meaningful grid challenges and interconnections with relevant neighbouring markets. It also has a developing legal framework for storage, aggregation and grid-capacity allocation.
But Romania will not unlock the full BESS opportunity if it looks only inward.
The country needs national reforms — clearer ATR treatment, better permitting, bankable route-to-market contracts and predictable balancing access. But it also needs regional integration: stronger interconnector use, TSO coordination, participation in European balancing platforms, cross-border intraday liquidity and better alignment with neighbouring markets.
For Romania, regional cooperation is not a diplomatic accessory. It is part of the storage business case.
What should happen next
The next phase should focus on practical coordination.
TSOs should coordinate grid planning more transparently, especially in renewable-heavy zones where battery placement can reduce congestion or defer reinforcement. Regulators should align on the treatment of storage, aggregation, balancing responsibility and metering. Market operators should support deeper intraday liquidity and more efficient cross-border trading. Balancing platforms should be implemented in a way that allows storage to compete fairly and transparently.
At the same time, non-EU neighbours matter. Serbia, Moldova and Ukraine will increasingly influence regional flows, adequacy and price formation. Their gradual alignment with EU electricity-market rules will become important for the long-term value of storage in the region.
If Southeast Europe wants to attract serious storage capital, it must avoid building five or six isolated national BESS markets. It needs to build a regional flexibility market.
Conclusion: the battery is local, the value is regional
The next wave of BESS investment will not be unlocked only by cheaper batteries or more generous subsidies. It will be unlocked by market design.
A battery may sit behind one grid connection, in one country, under one licence. But its value is shaped by regional volatility, cross-border capacity, balancing markets, interconnectors and neighbouring systems. That is especially true in Southeast Europe, where renewable growth, coal phase-out and market integration are happening at the same time.
Romania has the opportunity to become one of the important BESS markets in the region. But to do that, it must think beyond national regulation. It must see storage as part of a regional flexibility architecture.
The best summary is simple:
BESS will be built project by project, but its full value will be unlocked region by region.
Related reading and services
For Romanian investors, regional BESS strategy connects directly with our Energy Law in Romania work, renewable energy services and Romanian renewable projects map.
Related reading: Romania's battery storage market in 2026, hybrid renewable and storage projects, day-ahead and intraday markets in Romania and PRE, BRP and aggregation in Romania.