MOSCOW (Reuters) - The Kremlin is trying to reassure residents of Crimea, left in the dark after electricity supplies from Ukraine were cut off, that it is coming to their rescue by installing a power link with Russia.

A customer visits a grocery lit with candles due to a power cut, in Simferopol, Crimea, in this November 22, 2015 file photo. REUTERS/Pavel Rebrov/Files

But the reality is that it will take many months of complex engineering before Russia can provide Crimea with a secure electricity supply, while Western sanctions over the peninsula’s annexation have made it more difficult to buy the best equipment for the job.

The electricity problems are a stark reminder that when Vladimir Putin last year decided to make Crimea part of Russia he was not just courting international outcry but also taking on huge practical problems about how to sustain a peninsula that is physically cut off from Russia.

Crimea was plunged into darkness around three weeks ago after electricity pylons in southern Ukraine that carry the four lines that supply Crimea with the bulk of its power were blown up by unidentified people.

The authorities in Ukraine, where anger over the annexation last year is still raw, have shown little urgency in restoring the power supplies.

Russia has flown in emergency generators that cover some of Crimea’s power needs, and Ukraine has partially restored power. But until Crimea is fully hooked up to the Russian grid, it will be vulnerable to power disruptions.

Moscow’s response has been to speed up work on a so-called “energy bridge” - a series of cables along the seabed - it is building across the Kerch Strait that separates Russia from Crimea.

That project was launched by Putin on a visit to Crimea on Dec. 2, but its transmission capacity remains limited and Russian officials have largely glossed over the huge engineering challenges the remaining work will entail.

“The issue is really pressured. The energy bridge is not just an underwater cable, you see,” said Sergei Pikin, director of Russian consultancy Energy Development Fund. “It’s difficult work that normally takes years to complete.”

ENERGY BRIDGE

Russia has hired a Chinese firm, Hengtong, to supply the power cables to be laid across the Kerch Strait, a source at a Western electrical corporation said. Russia’s Kommersant newspaper also reported the Chinese firm was supplying the cables. The Western source also noted, however, that Chinese companies have much less experience in this field than those cut off from the project due to sanctions.

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The previous time Russia laid an undersea cable for such a project, in 2011 between the Pacific port of Vladivostok and the island of Russky, it contracted a Japanese firm to supply the cable. A French company supplied the cable for a link under Lake Baikal in Siberia, completed in 2005.

Hengtong did not respond to questions submitted by Reuters about its role in the project. Russia’s Energy Ministry declined to say who was supplying the cables.

If everything goes to plan, by June next year all the cables planned for the energy bridge will be laid.

“850 Megawatts is what it will be possible to send via the energy bridge from May 2016, without any risk to the energy system of the south of Russia,” Deputy Energy Minister Andrei Cherezov told Reuters.

That should allow Crimea to plug its electricity deficit with supplies from Russia, according to Vladimir Sklyar, director for utilities research at Renaissance Capital.

But the challenges don’t end with the undersea cables.

Russia must also build electricity substations and lay new transmission lines on either side of the Kerch Strait to connect the new cables to the existing networks.

Analysts say that because Crimea’s power has always come from the north, via a neighboring Ukrainian region, its grid is set up to handle north-to-south flows, and now will have to be re-configured to take in power from the east.

Work must be done too on the Russian side of the bridge to ensure there is sufficient spare capacity in the southern portion of Russia’s grid to supply power to Crimea.

E.ON Russia EONR.MM, controlled by German firm E.ON EONGn.DE, said on Thursday it was interested in building generating capacity in the Krasnodar region, which Russian authorities have said could be used to send power to Crimea.

Maxim Shirokov, E.ON Russia’s head, told journalists: “It will supply electricity to the wholesale market. ... The same thing that we’re doing at the moment. Therefore I don’t see any risks linked to this.”

ENDURING SOLUTION

Experts say power stations in Crimea itself offer a more enduring solution to the peninsula’s energy needs.

Russia plans to build these near Crimea’s capital Simferopol and Sevastopol, home to its Black Sea fleet.

The first blocks at those stations are due to come online in September 2017, and their generating capacity is to be doubled to around 940 Megawatts the following year.

That will ensure Crimea is self-sufficient and can use the bridge as backup or during times of peak consumption, when around 1.3 Gigawatts of electricity are needed.

But the power plants are some way from being completed, and sourcing machinery could present problems.

With a few exceptions Russian firms do not produce the powerful gas turbines often installed in Russian power stations. Such turbines are usually bought from Germany's Siemens SIEGn.DE, France's Alstom ALSO.PA and General Electric GE.N of the United States.

Alstom said it had received no requests to supply equipment to Crimea and declined to comment on whether it was prepared to deliver supplies there. Siemens did not respond to a request for comment, and GE declined comment.

If those suppliers were to sign contracts to provide equipment for power stations in Crimea, they run the risk of violating sanctions. Finding an alternative solution is liable to be time-consuming and expensive.

On top of that would be the challenges of upgrading a power network that was already creaking after years of under-investment from Kiev.

“There is several years’ work to bring the system into a good, stable condition,” a source in Russia’s utilities sector said. “No one has managed such a task over the past 50-60 years. Of course it won’t be easy.”