BESS turns into the region’s new balancing layer: how arbitrage, ancillary services and financing shape returns in South-East Europe

Battery storage in South-East Europe is increasingly being treated as a structural part of the power system rather than a standalone add-on. In South-East Europe, where renewable output is rising and congestion can intensify, batteries are being positioned between generation and transmission—changing both how prices move through the day and how investors underwrite project economics.

From volatility to bankable cash flows

The core driver is the region’s evolving price profile. Across trading venues including Greece (HEnEx), Romania (OPCOM), Bulgaria (IBEX) and Hungary (HUPX), intraday spreads have widened materially. In Greece, linked to LNG-linked marginal pricing and solar saturation, the gap between midday lows and evening peaks often reaches €60–100/MWh, with extreme days pushing beyond €120/MWh. Bulgaria and Romania show narrower—but still meaningful—spreads that typically sit in the €30–70/MWh band during periods of high renewable output or constrained interconnection.

Those spreads translate directly into what batteries can earn through time-shifting electricity. A common utility-scale configuration discussed for the region pairs 50–100 MW of power capacity with 2–4 hours of duration, corresponding to roughly 100–400 MWh of storage volume. With reported cost levels of €400–600/kWh, total CAPEX for a 100 MWh system can range from €40 million, while a 400 MWh installation may reach €160–240 million. Adding balance-of-plant, grid connection and EPC costs increases total project costs by another 10–20%, placing overall investment into a broader €50–280 million range depending on size and configuration.

The revenue stack: arbitrage first, reserves second

Batteries monetize flexibility through multiple layers. Energy arbitrage remains central: buying electricity during low-price intervals and selling during peak-price windows. For example, in Greece a 200 MWh system cycling 250–300 times per year can capture spreads of about €50–80/MWh, producing gross annual arbitrage revenues estimated at €15–30 million. In Bulgaria and Romania, where spreads are lower but persistent, similar systems are described as generating roughly €10–20 million per year, depending on utilisation and market conditions.

An additional stream comes from ancillary services. As regulatory frameworks evolve, storage assets are increasingly able to access products such as frequency containment reserve (FCR) as well as automatic frequency restoration reserve (aFRR) and manual reserves. The article notes that in Romania and Greece ancillary revenues can contribute around €20–40/MW/year, adding approximately €1–4 million annually for mid-sized systems. While smaller than arbitrage income, these services are presented as important for smoothing earnings volatility—supporting bankability.

How returns are forming—and why financing terms matter

The combination of these streams is shaping targeted return profiles for investors considering BESS projects across South-East Europe. Under base-case assumptions, equity IRRs are described at 12–16%, with upside scenarios reaching 18–20% in high-volatility environments such as Greece.

The financing picture also reflects the transition from early-stage experimentation toward more repeatable structures. Debt financing is increasingly available with leverage levels of about 50–65% and tenors of roughly 8–12 years. The underlying implication is that lenders view battery revenue models as sufficiently defined to support longer-term capital stacks—though they remain less mature than those tied to traditional generation.

Hybrid plants shift value toward evening peaks

The economics improve further when storage is integrated with renewables rather than operated purely as an independent merchant asset. Hybrid projects—pairing solar or wind with co-located batteries—are highlighted as central to development strategies in Serbia, Bulgaria and Greece.

A representative structure cited is a pairing of a 100 MW solar plant with a 200 MWh battery. By shifting output away from low-value midday periods toward higher-value evening peaks, realised prices can increase by about €8–20/MWh. That uplift is associated with additional annual revenues estimated at roughly €10–25 million, which could raise project IRRs by approximately 2–4 percentage points.

Navigating competition for spreads as deployment accelerates

The expansion of BESS brings its own risks for monetisation strategy. As more capacity enters the market, competition for arbitrage opportunities may intensify—potentially compressing spreads over time. The article points out early signs in Greece that extreme spread levels could moderate if storage smooths intraday price curves.

This potential evolution increases the relative importance of ancillary services and multi-market participation as sources of revenue stability rather than relying solely on energy arbitrage timing.

Tenders, regulation gaps and regional differences in readiness

The pace of deployment varies across countries but follows similar logic: where policy support exists alongside volatile price conditions, batteries move faster from planning into contracting. Greece stands out as the most advanced market in the region due to government-backed tenders and regulatory support. Projects cluster around high-volatility nodes including Thessaly, Central Greece and the Peloponnese. The interaction between storage activity and Greece’s reported 7–8 GW solar fleet is already described as reshaping intraday price curves—reducing extreme midday collapses while preserving enough spread for arbitrage operations.

Romania is said to be following a similar trajectory driven by renewable expansion together with grid constraints in areas such as Dobrogea. Storage development there runs alongside wind and solar projects supported by both private capital and institutions including the EBRD. Bulgaria’s pipeline is characterised as smaller but growing—particularly in southern regions where interaction with Greek price dynamics creates strong arbitrage opportunities.

The article also flags that regulatory clarity remains decisive elsewhere. Clear rules covering market participation mechanics, access to ancillary services and treatment within grid tariffs are described as essential for sustaining investment momentum. While progress has been made in Greece and Romania, frameworks in markets including Serbia and North Macedonia are still developing enough not to fully recognise storage value yet.

A trading-and-optimisation ecosystem emerges around BESS dispatching needs

Batteries’ performance depends heavily on operational timing—which helps explain why traders play an expanding role across the region’s storage build-out. Firms such as Axpo (Axpo listed alongside MET Group), MET Group (MET Group appears explicitly), PPC Trading (PPC Trading appears explicitly)) are described not only providing market access but also acting as optimisation partners using advanced algorithms and real-time data to maximise battery revenues.

The article also highlights platforms such as Electricity.Trade being integrated into these operations by supplying information on price spreads along with ATC utilisation signals and congestion patterns that inform dispatch decisions.

BESS changes transmission stress—and adds new temporal value opportunities

beyond trading economics, storage affects physical network behaviour. By absorbing excess generation during periods of peak renewable output while releasing it during demand peaks, batteries reduce stress on interconnections and improve utilisation of existing capacity. This has implications for congestion pricing dynamics—including flow patterns—and may moderate extreme price differentials even while creating fresh temporal arbitrage opportunities tied to when flexibility is deployed.

A scale-up plan signals system-critical status by 2030s targets

The direction of travel is clear from deployment expectations cited for the region overall: discussion now includes building up toward roughly <3–5 GW across South-East Europe by 2030 , alongside country-specific ambition such as Greece targeting more than <1 GW via near-term tenders . Taken together with hybrid structuring trends—from curtailment-risk management models referenced in Serbia (where curtailment risk exceeds <stronqg>10–15%?? –> </stronqg>) ) —the message is that BESS is moving toward becoming grid-layer infrastructure rather than experimental capacity.