Elektra: the power behind the innovation

Siemens ties battery information together on the touchscreens mounted in both the bridge and power control room
Siemens ties battery information together on the touchscreens mounted in both the bridge and power control room
Engine room on 'Elektra'
Engine room on 'Elektra'
'Elektra' has 1MW of power, split into two banks
'Elektra' has 1MW of power, split into two banks
It’s important that with any new technology that it’s working from day one
It’s important that with any new technology that it’s working from day one
Industry Database

New tech comes with a price, but there’s a lot resting on it - all the more so when it concerns commercial, battery-driven ro-ro that promises to clean up the market in more ways than one.

New tech comes with a price, but there’s a lot resting on it - all the more so when it concerns commercial, battery-driven ro-ro that promises to clean up the market in more ways than one.

Siemens’ Odd Moen outlined the issue: “It’s important that with any new technology that it’s working from day one. There’s always a lot of scepticism so if something fails... you go two steps back and the industry won’t trust it.”

And so it is with the power for Finland’s battery ro-ro, Elektra. This has 1MW of power, split into two banks, powering a pair of 900kW, Z-drive, azimuthing thrusters from Rolls-Royce: “These mean Elektra can actually move sideways, so it’s easy to manoeuvre,” said Mats Rosin, FinFerries’ CEO.

There are recharging points at both the Parainen and Nauvo turnarounds; a Cavotec vacuum mooring system and recharging tower combo holds Elektra in place while allowing a plug to descend from above to mate with Elektra.

Rosin explained that 20kV of power is delivered to a transformer some 150m from the charging tower which reduces it to 690V AC for transfer to the ship. “We were lucky because the grid had been recently strengthened nearby, and so it was able to deliver the necessary charge,” explained Rosin. Moen added the only other commercial electric ferry, Ampere, had to compensate for a weak grid by using battery banks on shore to collect the charge before delivering it; a more costly exercise.

Grant Brown of PBES, Elektra’s battery supplier, said that 160 of its 6.5kWh power batteries have been lined up for an installed total of 1,040kWh at 1,000V on the DC bus. He explained: “In fact, Elektra uses roughly 125kWh from shore every 30 minutes.” However, he added that these batteries could absorb power at quite a rate as the banks “can comfortably charge at 3C, so they could, theoretically, fully charge from empty in 20 minutes”. This is partly because the batteries are liquid cooled; after all, putting a bolt of energy through even capacious batteries can shorten the cell’s lifetime.

It’s not seawater from outside but rather a closed loop of tightly temperature-controlled tap water (the region’s domestic supply being incredibly pure and uncontaminated). Elektra’s chief engineer added: “We have a guarantee from Siemens that we’ll get a ten-year life from these batteries – but only if we keep within a fraction of a degree away from 18C. That’s up or down.”

More, as depth of discharge also affects the cells’ lifetime, these too are being rigorously bracketed, with the top rising to no more than 80% and the bottom sinking no lower than 60% of the total capacity. Of course, Siemens’ will be watching, monitoring all this and more via a Cloud link.

It’s nice that while Siemens ties battery information together on the touchscreens mounted in both the bridge and power control room, PBES has also installed easy-to-read data displays on each case, showing heat, loading rate, state of charge, state of health and so on, not just for that battery alone but for the whole bank.

Solar panels high on the superstructure also bring in another small energy stream, the power from them varies, depending on weather condition but around 4kW to 8kW, not enough to make a meaningful contribution to the propulsion, “but it’s useful to see what they can add,” said Rosin, even if it’s just enough to provide the aircon in summer, warmth and hot drinks in winter.

But, despite being labelled an electric ferry, Jansson explained that the ro-ro does have a set of three, Lindenburg - Angalen diesels paired with Stamford motor generators yielding 450kW each. This is partly because although the banks are sized to do as many as five journeys without a charge, that would damage the carefully controlled parameters. The problem is largely the weather which can knock out the charging infrastructure: indeed, just four months from start of operations, the grid connection failed for several hours, underlining the need for the onboard gensets.

More, “the ice is, as you say, “the joker in the pack”, said Rosin. It could be that if the vessel encounters ice the diesel gensets will have to play their part, not just to boost the power but also to top up the charge from the grid: “Ice could put us behind schedule, and that means even less time charging,” he explained.

But he added, in these circumstances, the real challenge came from tying together more than one power source in an acceptable balance: “We still wanted to take as much as we could from the grid and optimise what we took from the diesel.” Not an easy demand, but despite that, Siemens has delivered.

Despite the hefty investment costs (20mEuro for the total project including infrastructure), benefits are significant. Operating costs should be minimal, concluded Odd Moen. Ampere, for example, takes just 5Eur to recharge – and even given the slightly higher price of electricity in Finland “it really is nothing, a couple of cups of coffee maybe”.

Finally, it should be noted Siemens is now taking on manufacturing of the batteries themselves: it’s also making sure the batteries will be liquid cooled, following a similar path to the technology originally developed by PBES.

By Stevie Knight

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