Boring into a seabed 3,000m below means the drawworks onboard a drillship \u2013 those sizeable winch systems controlling the drill lines \u2013 will be responsible for handling thousands of tonnes. But while active heave compensation (AHC) is key to keeping the drill head stationary, \u201ceach lift of the string asks a couple of megawatts of the generator load\u201d explains Richard Verhoef of NOV.<\/p>\n
An energy storage system could smooth out the power peaks and pick up the wasted kinetic energy \u2013 but the question is, what kind of ESS could handle not only the scale, but also the frequency of these cycles?<\/p>\n
The more familiar solutions used in the industry weren\u2019t capable of meeting the demands. Firstly, \u201cas a rough rule of thumb, a battery can only absorb around half of its energy capacity in one go\u201d, says Verhoef. Secondly, even scaled to cope with this challenge, the work schedule of a drillship could result in a million AHC-driven cycles in a couple of years. \u201cThat\u2019s enough to destroy any battery,\u201d he points out, and it would also likely kill a supercapacitor.<\/p>\n
By contrast, there\u2019s nothing better than a flywheel if cycle life is the issue.<\/p>\n
However, these are not merely big lumps of metal as there are huge forces to contend with: take the 1,500mm, 3.5 tonne flywheel developed by NOV and set it spinning at 2,000 rpm, and there will be tremendous stresses at its perimeter. Therefore, the manufacturing must be tightly managed.<\/p>\n
But the mass is, after all, what makes it work. As Verhoef explains, NOV\u2019s flywheel \u201ccan absorb a lot of power – 1.75MW peak – and give out the same amount for around six to ten seconds\u201d.<\/p>\n
That may seem like a short period of time, but it has been tailored to tally with the length of demand from the active heave, \u201cwhich is basically the wave period,\u201d he points out. Admittedly, this differs a little from region to region and the response is affected by the vessel\u2019s shape, but he adds that \u201cgenerally, it\u2019s around eight seconds.\u201d This brevity also simplifies the technology by, for example, allowing the design to stick with spherical roller bearings instead of specialised magnetic varieties designed to \u2018spin out\u2019 the energy retention.<\/p>\n
However, there are longer spans of demand such as when raising the drill bit. While it\u2019s theoretically possible to scale up the flywheel to meet these operations, it would entail an unfeasible rise in diameter and motor size.<\/p>\n
Therefore, NOV has added a more conventional 450kWh lithium-ion battery system linked by two 1,100 hp motors to create the PowerBlade kinetic energy recovery system. The neat thing about this pairing is that the flywheel can push the power either back to the winch or to the battery where it also acts as a buffer, giving the cells an easier ride. The combination lends the PowerBlade a 3.25MW maximum charge absorption, while it can also belt out a sizeable 4.75MW at peak output.<\/p>\n
It is effective: the theoretical figures from a Norwegian vessel show up to 80% energy recovery during active heave compensation. Further, as with other ESS, if incorporated at build, the technology allows resizing the power plant instead of scaling it for peak demand.<\/p>\n
Most importantly, it promises to soften wear and tear for much of the onboard kit. \u201cThe endless ups and downs on the distribution bus aren\u2019t good for any of the components,\u201d comments Verhoef. This gives you a more stable system.\u201d<\/p>\n
The PowerBlade is to be offered as a fully boxed solution in a standard ISO container that can be dropped onto the deck. \u201cThe installation philosophy is that it can be fitted between jobs with the pre-wiring carried out during operations and just a day or two allocated for putting this onboard while offshore – so the ship doesn\u2019t have to come into port,\u201d says Verhoef.<\/p>\n
OTHER APPLICATIONS<\/strong><\/p>\n It will likely find a wider audience than the drillships. Guido Van den Bos, business development director for vessel designer GustoMSC, (a NOV subsidiary), has been considering other potential applications. For example, he sees advantages for \u201clarge jackups or other semi-submersible vessels.\u201d<\/p>\n While the active heave draw will still be linked to the wave period, Van den Bos points out that the installation would likely have to be sized for the lifting capacity. Therefore, massive crane vessels would likely require a scaled-up version as two cranes working in tandem can have a combined lifting capacity over 14,000 tonnes. Additional flywheels, (rather than a single, oversized mass) make a neater, more flexible package.<\/p>\n Further, Verhoef adds the energy storage capacity can be tailored to suit. If the system is only designed to accommodate the AHC for a few seconds, it could even be installed without the battery, significantly cutting costs.<\/p>\n SPIN<\/strong><\/p>\n Other developments utilise another aspect of the flywheel principle.<\/p>\n As kinetic energy is proportional to mass times velocity squared, doubling the mass doubles energy storage… but doubling the rotational speed quadruples it. So, increasing the spin speed yields a far more compact unit explains Tim Rumney of Inetic.<\/p>\n Imagine a package \u201cless than a 50cm cube with a mass of around just 100kg\u201d, says Rumney, who was involved in a development project exploring flywheels for naval vessels. He added: \u201cThe brief included getting it through any doorway on the ship.\u201d<\/p>\n The focus wasn\u2019t so much about regenerating energy, but using the technology for a typical ESS application: peak shaving the onboard load, with motors \u2018charging up\u2019 the flywheel.<\/p>\n The advantages also align neatly with commercial vessels\u2019 challenges, especially since, like battery cells, flywheels lend themselves to a modular approach. As a result, \u201cyou can pick the amount of energy and power you need and arrange the units in a series or parallel configuration\u201d, Rumney explains, so they can act in concert, or take up the load sequentially.<\/p>\n A typical naval application would see half-a-dozen of these modular packages distributed around the ship, making it suitable for managing \u201cshort, but large bursts of power inside a particular area\u201d he says, without recourse to huge capacitors or main grid cabling. Further, this makes it\u2019s possible to shunt the energy between nearby consumers \u2013 enabling zonal power management.<\/p>\n However, reducing the size in this way requires spinning the flywheel at up to 40,000 or 50,000rpm. Therefore, friction is the enemy: \u201cAt that rate, the air drag resistance alone can lose tens of kilowatts of energy if not managed,\u201d explains Rumney. As a result, all high-speed flywheels need to be enclosed in a vacuum.<\/p>\n There\u2019s also another challenge for developers: the spin creates a considerable gyroscopic effect. As a ship will experience pitch and roll movement, there\u2019s a need for \u201cfairly robust bearings\u201d to deal with these generated forces says Rumney, potentially entailing magnetic or low-friction precision systems, though some recent automotive developments have put gimbals beneath their installations.<\/p>\n Construction is likewise evolving.<\/p>\n While steel versions generally tend toward utilising a separate motor to convert spin into electrical energy, others neatly double up the flywheel\u2019s role, turning it into a motor-generator\u2019s rotor. These use permanent magnets rather than coil windings for strength and higher power density.<\/p>\n Because a high moment of inertia (that is, mass times radius) is no longer the most important feature at very high rotational speeds \u2013 seen in the land based and automotive market units \u2013 these flywheels can take advantage of either part or full composite construction, embedding the magnetic material evenly around the perimeter. Balancing these systems is essential; since, as Rumney underlines, \u201ccentripetal acceleration at these flywheel speeds can be 10,000G or more\u201d.<\/p>\n Further, fully composite designs can be completely integrated; high tensile strength carbon fibre rotor\/flywheel being a single assembly. It\u2019s lighter, and, not to put too fine a point on it, potential failures are better contained.<\/p>\n It makes for a much more complex system than the PowerBlade \u2013 but getting all these elements right yields a longer energy storage window, with significantly reduced envelope and mass. \u201cTypically this sort of flywheel has an energy storage half-life of several tens of minutes,\u201d explains Rumney: that\u2019s a big enough window for a range of \u2018peaky\u2019 consumers.<\/p>\n It might not be long before both types of technology start putting their own spin on short-term regeneration and peak shaving applications.<\/p>\n","protected":false},"excerpt":{"rendered":" Energy storage solutions (ESS) are turning up onboard an ever-increasing range of vessels, but batteries are not the only, or even the most suitable, solution for peak shaving a supersized demand. Flywheels might do better, writes Stevie Knight<\/p>\n","protected":false},"author":8,"featured_media":693,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[39],"tags":[],"sponsor":[],"class_list":["post-692","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-battery-hybrids-full-electric-vessels"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/posts\/692","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/comments?post=692"}],"version-history":[{"count":0,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/posts\/692\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/media\/693"}],"wp:attachment":[{"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/media?parent=692"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/categories?post=692"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/tags?post=692"},{"taxonomy":"sponsor","embeddable":true,"href":"https:\/\/www.motorship.com\/propulsion-and-future-fuels-conference\/wp-json\/wp\/v2\/sponsor?post=692"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}