Greece is producing more low-cost power during solar-heavy hours, while Bulgaria has moved faster to build large-scale batteries. That difference is changing the economics of cross-border trading, even if the power does not simply travel north at noon and return south at night.
On sunny afternoons, wholesale power prices in Greece can fall close to zero. A few hours later, after solar production fades, prices across Southeast Europe can become much higher.
At the same time, Bulgaria has rapidly expanded its battery-storage capacity.
Those two developments have encouraged a simple explanation for what is happening across the border: Bulgaria buys cheap Greek power during the day, stores it, and then sells electricity back to Greece after sunset at a higher price.
There is a real economic mechanism behind that claim. Bulgarian batteries can absorb power when regional prices are low, including imports from Greece, and discharge later when energy is more valuable.
The broader picture is more complicated. Greece has recently been exporting power to Bulgaria across much of the day, including well into the evening, while Bulgaria has developed considerably more battery capacity for shifting energy from one part of the day to another.
Cheap at noon, expensive after sunset
Solar power has changed the daily rhythm of the Greek electricity market.
Photovoltaic production rises through the morning and is strongest around midday. On days with abundant sunshine and moderate demand, the supply of inexpensive power can become so large that wholesale prices fall toward zero.
Several hours later, solar production declines while evening demand can remain high. The system must rely more heavily on hydroelectric plants, natural gas generation, imports and other flexible resources.
This creates large differences between what power is worth in the afternoon and what it can be worth later in the same day.
The European Union Agency for the Cooperation of Energy Regulators reached a similar conclusion after examining the severe electricity price spikes that hit Southeast Europe in 2024. ACER’s 2026 assessment found that the spikes were driven mainly by a shortage of flexible resources capable of replacing solar generation quickly during high-demand evening hours. It identified storage, demand response, and other flexible generation as part of the solution.
Batteries address part of that problem by charging when power is cheap and releasing energy later when prices rise.
Bulgaria has moved faster on batteries
The European Commission’s 2026 country report for Bulgaria recorded 1,181 MW of battery storage already operating, alongside contracts for 1,120 MW of batteries paired with renewable projects and close to 14,000 MWh of grid-scale battery storage. The Commission said the expansion was supporting greater flexibility as solar generation grows.
Bulgaria has also indicated substantially more deployment. Under the European Commission’s June 2026 energy-storage agreement, the country’s expected additions include 2,900 MW with 9,700 MWh of storage in 2026, followed by 1,150 MW with 4,000 MWh in 2027 and further capacity in 2028. These figures form part of the commitments associated with the agreement rather than binding national targets.
Bulgaria also has pumped-storage hydropower, which uses electricity to pump water uphill and releases it through turbines when power is needed.
The important Chaira pumped-storage plant is gradually returning after years of outages. Bulgaria’s National Electricity Company reported in April that a second restored unit had returned to service, bringing the plant’s available capacity across two operating units to 420 MW.
Greece starts from a different position.
It already has roughly 0.7 GW of pumped-storage capacity, including the Sfikia and Thisavros plants. PPC identifies both as Greece’s existing pumped-storage facilities.
Modern grid-scale batteries, however, entered the Greek system much later.
According to Greece’s Environment and Energy Ministry, the country’s first two grid-connected battery projects, totaling 32 MW, entered operation on April 1, 2026. By July, operating battery capacity was approaching 200 MW. Energy Minister Stavros Papastavrou said Greece was expected to reach roughly 700 to 800 MW by the end of the year.
For now, Bulgaria has significantly more short-duration battery capacity available to respond to price changes within the day.
How a battery profits from the price gap
A particularly clear example came on April 29.
Shortly before 4 p.m., Bulgaria was generating about 4.82 GW of electricity while consuming approximately 4.09 GW. Domestic generation was already above domestic demand, yet the country was still importing power.
Its batteries were charging at roughly 1.67 GW, absorbing both domestic production and electricity entering from neighboring systems, according to data from Bulgaria’s Electricity System Operator reported by Balkan Green Energy News.
At the same time, the price difference across the Greek border was unusually large. For the relevant 15-minute interval, the Bulgarian day-ahead price was €44.34 per MWh. In Greece, it was just €0.01 per MWh. The scheduled flow from Greece to Bulgaria was 879 MW.
For a storage operator, the opportunity is straightforward. A battery can charge while power is inexpensive and discharge several hours later when it is worth more.
The difference between those prices, after efficiency losses, fees and other costs, is the basis of energy arbitrage.
April 29 shows how Bulgarian storage can take advantage of cheap power flowing from Greece. It should not be treated as the normal daily pattern between the two countries.
The stored energy does not have to be exported back to Greece for the battery operator to profit. It can be discharged into Bulgaria’s own market, reduce the need for another generator to run, participate in balancing services or support exports elsewhere in the region.
Does the electricity actually come back to Greece?
The broader cross-border data do not support a regular pattern of Greece exporting at noon and importing the same electricity back after sunset.
An analysis by The Green Tank using hourly ENTSO-E data found that, through June 27, 2026, Greece was a net exporter to Bulgaria during 3,601 hours, or about 84% of all hours examined.
The pattern was not confined to the solar peak. Average net exports to Bulgaria were about 386 MW between noon and 3 p.m., but approximately 398 MW between 9 p.m. and midnight.
Greece, in other words, was often still sending power north well into the evening.
Flows do reverse at times. Prices, generation, demand and transmission availability are constantly changing. But the first-half 2026 data do not resemble a simple cycle of cheap Greek electricity moving north in the afternoon and expensive Bulgarian electricity returning south at night.
There is another important distinction. Greece’s exports to Bulgaria should not be described as if they were predominantly solar power.
The Green Tank calculated that during the hours when Greece was a net exporter to Bulgaria, the energy-weighted Greek generation mix consisted of 37.4% natural gas, 24.8% wind, 17.7% solar, 15.1% hydropower, and 5.1% lignite.
Solar generation is a major reason Greek prices can collapse during the middle of the day, but Greece’s wider export position in 2026 extended far beyond those hours.
The midday solar-price collapse and Greece’s wider rise as an electricity exporter are related, but they are not the same phenomenon.
The border is part of a larger market
Greece and Bulgaria do not trade electricity as two isolated national systems.
Their day-ahead markets have been coupled since May 2021. IPTO explained at the launch that the common European algorithm simultaneously calculates prices and cross-border flows while taking available transmission capacity into account.
The Greek-Bulgarian border was also incorporated into Europe’s Single Intraday Coupling at the end of 2022.
When power is cheaper in Greece and there is room on the interconnection, there is an economic incentive for it to move north. If relative prices change, that incentive can change with them.
The physical connection has strengthened as well. A second 400-kV line between Greece and Bulgaria entered operation in June 2023, increasing transfer capability at the border to about 1.7 GW, according to IPTO.
That gives both countries greater access to generation and flexibility on the other side of the border.
Bulgarian batteries are therefore part of a wider regional balancing system. When they absorb power during periods of low prices, they can create additional demand when renewable-heavy systems have excess generation available.
Why Greece exports electricity when prices collapse
When renewable generation exceeds what the Greek system can use at that moment, some of the excess can be absorbed by domestic demand or storage, while the rest can be exported through Greece’s interconnectors.
If those outlets are insufficient, renewable production may have to be curtailed.
Greece has already faced increasing pressure from renewable-energy curtailments. The Environment and Energy Ministry has linked the accelerated development of storage with efforts to integrate more renewable generation and manage curtailments.
Exports are not evidence that Greece is simply giving electricity away. If the alternative is curtailing generation that cannot be used domestically, selling power into a neighboring market can make both economic and operational sense, even when wholesale prices are very low.
The question for Greece is how much of that low-cost energy could instead be stored domestically and made available later, when the system needs it more.
More Greek batteries could change the economics
More storage would allow a larger share of power produced during solar-heavy hours to remain available inside the Greek system until later in the day. Part of the generation that might otherwise be exported or curtailed could instead be discharged during evening demand.
All else equal, that should absorb some of the surplus that contributes to extremely low midday prices while adding supply during more expensive evening hours.
The actual effect on wholesale prices will still depend on demand, fuel costs, hydroelectric availability, transmission constraints and generation conditions elsewhere in Southeast Europe.
As Greece adds batteries, some of the short-term price differences that currently create attractive arbitrage opportunities may narrow.
Electricity is increasingly about when
The shift extends beyond Greece and Bulgaria.
Southeast Europe is adding large amounts of solar generation, and much of that power becomes available across the region at roughly the same time.
The challenge is no longer only whether enough electricity can be produced over the course of a day. It is whether enough power is available during the hours when consumers need it most.
Interconnections move electricity between countries. Storage moves it between hours.
That combination is central to ACER’s recommendations for Southeast Europe. Better use of cross-border networks can move power geographically, while batteries, demand response and flexible generation can help replace renewable output as conditions change.
Bulgaria has moved particularly quickly on batteries. Greece is now accelerating its own rollout.
The familiar claim that Bulgaria buys cheap Greek electricity during the day and sells it back at night captures one possibility created by battery storage, but not the broader trading pattern. During the first half of 2026 through June 27, Greece was exporting power north during most hours, including well into the evening.
What is increasing is the value of flexibility. Greece has rapidly expanded renewable generation, while Bulgaria moved earlier on grid-scale batteries. As Greece adds more storage of its own, the economics of that relationship are likely to change again.
Electricity increasingly has very different values from one hour to the next. Storage determines who is best positioned to capture that difference.