A possible better use of supertankers?

Supertankers are a highly contentious matter. They are a highly visible, concentrated risk way of transporting a dangerous, environmentally damaging material. There are arguments that it is easier to manage the risks by having them in well designed place: maybe that is true, but when things go wrong (e.g. Exxon Valdiz), they go wrong in a big way.

Be that as it may, that's not the topic I wish to write about here.

The idea of a vessel's life cycle is (generically) that, when a vessel exceeds it's useful life, it is scrapped, and the materials reused. That's good from the point of view of conserving materials, but it involves a significant amount of energy, and, as I understand it, very considerable risk to some workers in places like Chittagong, India. If another use could be found for a vessel like a supertanker, one that delayed the need to scrap it, that would save quite a bit of energy consumption.

I have also seen pictures/documentaries at various times over the last few decades of large fleets of temporarily decommissioned ships, including supertankers. I think I first saw this in the 1970s, during the oil crisis then - it looked a bit like some of the aircraft boneyards, but with massive ships rather than planes. Are all tankers/supertankers currently being utilised, or are some idle, doing nothing but deteriorating and/or costing money? If so, could they possibly be put to use via other means?

The other comment that contributed to my thinking on this was a comment I heard on ABC's Radio National about renewable energy, when someone said a relatively small area of Australia (something like 50km x 50km) could be used to provide energy by solar means for Australia AND also enough to export to south east Asia.

(As an aside, because of the materials used in photovoltaic cells, I consider using solar heat a better way of getting energy from the sun, even if it is a lower efficiency.)

So ... what if some supertankers could be converted to large batteries? Would it make sense - from an energy balance point of view - to use the solar generation capability in parts of WA, and perhaps some of the shipping facilities associated with the iron ore and other mining industries there, to charge a supertanker, and then send it to wherever it was needed, to hook into the power grid and provide renewable energy?

The energy involved in moving the mass is obviously going to be a consideration, as are the ways that the ship would be converted to a battery. Can this be done efficiently (or efficiently enough) and without creating a different environmental risk, or a different set of damages to the environment (with respect to obtaining suitable materials)?

Most electrical power transmission is via grids using cables, which can be laid across ocean floors, but that is expensive, damaging to some extent to local environments, and prone to damage from earthquakes (and we are all now well aware of the potential for such damage from the Asian tsunami - actually, maybe this could be used for disaster relief, by providing a large source of power if power girds can be repaired enough).

Would a converted ship be safer?

I don't know. Would the charge make the ship more susceptible to lightning strikes? Would discharge of the charge if the vessel sank kill the crew and marine life for some distance?

The type of technology used would be crucial.

Car batteries are lead-acid batteries: they aren't going to be suitable. Gel batteries or similar involve less risk of spillage, but maybe they could potentially still be damaging if the ship sank.

Lithium ion batteries are, I understand, the most efficient form of battery in that the highest power density. However, they're mostly used for small applications: would they be impracticable (e.g. weight, cost, risk) for this sort of large application? I suspect so.

Maybe molten salt batteries are more appropriate.

Maybe new technology would have to be invented, possibly including the use of parasails as is starting to be the case on some large cargo vessels.

It's all just a thought :)