Tying it all together
Although people often seem to be looking for the next novel power source, it’s more likely that the offshore support market will see an increasingly complex set of combinations rather than a ‘one size fits all’ energy generator, says Stevie Knight.
This will mean one type of energy being matched with another so their characteristics complement each other explains Erik Ovrum of DNV.
He points out this could put fast take-up items right beside other elements which may be slower in getting into their stride but which are inherently longer lived; these might be rather different to what we expect, for example although batteries are an obvious element it’s also possible to see a future marrying slower-to-react hydrogen cells, whether these are the MCFC, SOFC or high-temperature proton exchange membrane (HTPEM) varieties with the immediacy of LNG or even methanol engines. This last option could be give a number of benefits - as after all, once you have methanol onboard to power a combustion engine it’s a very short step indeed to hive off an amount to power an HTPEM fuel cell.
The fact that these systems are going to be complex is a given: “As soon as you move away from the straight diesel engines and into multiple power sources you need something intelligent to tie together the energy input,” says Walter van der Pennen of Imtech Marine.
He adds: “Of course it has to be robust, otherwise there’s no way that it will get past the classification societies, who are all about ‘safety, safety, safety’, especially where the spinning reserve needed for Dynamic Positioning is concerned.”
However, Mr van der Pennen says that of all the sectors, it’s the offshore support industry that could probably benefit most from this approach simply because it has an extremely varied set of tasks which come into play at different points in the operational cycle. Mr Ovrum adds that it’s not just fuel savings that can gain from playing to the strength of each element, there’s emissions reductions sitting alongside this, something that the oil majors seem to be increasingly interested in.
However, marrying these energy generators together has not traditionally been that easy, only recently leading to developments like Imtech Marine’s smart energy system. This sits on top of the existing power management and Mr van der Pennen is careful to point out that while these power managers tackle the fairly limited job of sharing the load in such a way as to protect the structures beneath “they are a long way from realising anything more than that”.
He goes on to explain the variety of needs that the smart system is trying to answer: “Optimum can mean a number of different things depending on what you are doing,” says Mr van der Pennen: “The idea is that you can switch or combine a number of ‘optimals’, for example when you are in transit then it’s possible that what you want is fuel saving capability, when you are there you aren’t looking at fuel savings, you are looking at instant power.” But there’s another dimension to add – wear and tear. “Maintenance rounds are also on some operators minds with good reason,” he says. “Low loads, high loads, all can have an impact but it’s just not feasible to try to calculate this kind of parameter while underway, and it’s certainly not possible for someone to estimate how this balances out against the other issues.”
The good thing about such an arrangement is that if a vessel needs to respond to a different role the capacity is already in place to make further changes. In fact, there’s a lot more capability inherent in the system so frontiers can be explored, figuratively and literally, with a parameter adjustment.
However, back to the proven energy saving figures for a moment. One version of the system has been installed onto a hybrid Calmac ferry recently, and while the savings from having a battery bank charging overnight account for a 22% drop in fuel consumption, this is easily explainable. What is more impressive in its way is that you get an extra 6% saving from the intelligence with which the boat handles its demands, for example, using the engines’ low load periods to charge up the batteries.
None of this would be as attractive if the human interface left operators overlooking certain aspects of the energy management, or worse, confused. “The danger is hiding too much. You need to know what is going on with the whole system at a glance without it being distracting. And of course, we want the operators to be involved in ‘playing the efficiency game’, not just bypassed them by clever electronics. So while the system can run itself the operators are left with the choices, what to adjust, which parameters need a new focus and getting to a balance they are happy with.”
Although the Edda Ferd’s Siemens system runs on DC, you can still coax economy benefits from an AC generator set if an energy storage battery is added to the system, along with a rectifier. This is the path that Imtech Marine are taking for the moment, “especially as onboard AC systems are very mature, very robust technology”.
However, Mr van der Pennen doesn’t count out DC systems for the future. At the moment though, the DC part of the loop is limited to the variable speed drive which has to run from a DC supply. He adds: “This is the point at which we add the batteries in order to get the best out – or into them.”
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