Baltic states are looking to synchronise their electricity grids with Nordic countries, away from Russia, in a move that has angered the Kremlin and could cost hundreds of millions of euros, government and energy officials said.
More than 20 years after splitting from the former Soviet Union and joining the European Union in 2004, Lithuania, Latvia and Estonia still depend on Russian power grid operators.
They have begun reducing their dependence on Russian gas imports after Lithuania opened a floating liquefied natural gas (LNG) terminal last year, but ending the Soviet legacy in the power system has proved more complicated.
Russia's annexation of Crimea and its backing of pro-Moscow separatists in eastern Ukraine, however, have brought a sense of urgency towards ending this dependence as well.
Members of a common, synchronised power area have the same electricity frequency and manage its fluctuations jointly by boosting or lowering generation. Under the current arrangement, Russia is primarily responsible for frequency management since its power system dwarfs those of the Baltic states.
Referring to the interdependency of countries in such an area, Latvian Energy Minister Dana Reizniece-Ozola told Reuters: "It's like being in a single (blood) circulatory system ... If something falls down, then the whole system is traumatised."
The original plan was to synchronise with the grid of the continental European system via Poland, but Warsaw's reluctance to build more power lines through protected areas prompted the search for alternatives.
"We should also consider other scenarios, such as the Baltic power system operating in isolation and potential synchronisation with the Nordic system," Taavi Veskimagi, chief executive of Estonia's grid operator Elering, told Reuters.
Estonia is already linked with Finland by two subsea power cables across the Gulf of Finland, but extra cables will have to be built to synchronize the grids.
Baltic states' plans, however, have angered Russia.
Russian President Vladimir Putin told U.S. television network CBS in September that he was "perplexed and disappointed" about Baltic plans to leave the common power system with Russia and Belarus
Putin said Russia would have to spend "billions of dollars" to build new power lines to transmit electricity that is now routed via the Baltic states.
These so-called loop flows of Russian energy, however, are reducing transmission capacity between the Baltic states, leading to higher power prices, grid operators said.
Moscow is also concerned that its highly militarised Kaliningrad exclave, home to Russia's Baltic fleet and sandwiched between Poland and Lithuania, will be cut out from mainland power supply if the Baltic states leave
It fears that Ukraine could follow the Baltic states.
Synchronising with the Nordic grids also faces another big challenge: it will require pioneering technology to build subsea links with capacity of up to 1,000 megawatts to transfer alternating current (AC) for 70-150 km (40-90 miles) across the Gulf of Finland.
So far, the world's most powerful subsea AC cable is a 15-km, 540-MW link across the Little Belt strait in Denmark, built by Swiss engineering group ABB.
ABB has also won a tender to build the world's longest subsea AC cable to power the Martin Linge oil and gas platform offshore Norway. The 162-km cable will have a capacity of only 55 MW.
Subsea AC cable technologies, however, are developing fast thanks to the development of larger offshore wind farms.
The length and capacity of AC cables so far have been limited by physics rather than product development, the company said in an email to Reuters, adding that longer cables could be built. It declined to provide a cost estimate.
A study in 2013 by Swedish consultancy Gothia Power said it was technically possible for the Baltic states to synchronise with continental Europe by 2025, but costs overweighed the benefits.
Baltic officials put the costs at between 435 million and 1 billion euros.
(By David Mardiste and Gederts Gelzis, Additional reporting by Andrius Sytas in Vilnius, Barbara Lewis in Brussels and Anastasia Lyrchikova in Moscow)