Cargo ships don't have enough free surface area to mount the number of solar panels that would be needed for propulsion. Sails are already being used on a few ships but they only save a small percentage of fuel.
There could be could add battery storage to be used during the journey. They could include wind turbines to add further power generation.
Also ships can go slower. In my limited knowledge of boats every extra knot takes significantly extra fuel. If we were bringing multiple power sources 'slow' cargo may be viable. And the has to be other ways to increase this function.
And there is always hybrid. Not all power has to be renewable sources. A solution could start with supplementing diesel driven thrust with some lower cost green power. Given diesel is 70% of shipping operating cost that seems a potential option.
No one really wants to build cargo ships right now, shipping companies are barely staying afloat right now because there is a glut of cargo capacity.
This technology would need to be cheap enough that it would make sense to retrofit a ship with it... which would probably not be the case for a very long time.
I do think it's a very thought provoking idea however.
It's a type of 'tragedy of commons' situation, where every shipping company is making the right decisions from their individual perspective, but collectively they're driving themselves into the ground.
For me this explains the rise of slow-steaming. It makes a lot of sense in this market because it lowers the cost of shipping a container (less fuel), while simultaneously reducing the market capacity (# of containers / year).
Finally, very few shipping companies make money on the major lines (e.g. China to Europe), because it's pure price competition. They're much more likely to make money in places where they have a 'monopoly' on something: e.g. being the only ship that leaves in the next 3 days, or being the only shipper going to a specific location. For example inter-Africa shipping falls in this category.
However ironically though, these mega vessels are considered with quite a bit of disdain by many in the industry. This link can provide quite the rabbit hole of information. http://www.supplychain247.com/article/state_of_ocean_contain...
Further exacerbating the problem with the glut of cargo capacity.
https://www.theguardian.com/environment/2010/jul/25/slow-shi...
Drone ships won't be practical any time soon because of maintenance problems. Crews spend much of their time at sea performing preventative maintenance, painting, and fixing broken equipment. With a drone ship all of that work would have to be done at the pier which would be far more expensive than paying a crew.
"When the wind conditions are favourable, Norsepower Rotor Sails allow the main engines to be throttled back, saving fuel and reducing emissions while providing the power needed to maintain speed and voyage time. Rotor sails can be used with new vessels or they can be retrofitted to existing ships."
There have been cracks at putting "sails" of one form or another on ships but they've always been heavy, relatively ineffective and basically just not worth the hassle.
The speed of a ship is actually quite easy to work out. You find the time/value curve for the cargo and the cost/time for the ship and see where they cross - essentially. The long and short of it is that the lighter and more valuable your cargo is, the faster the ship goes. This is why container ships are much faster than oil tankers.
The problem is that safe disposal of nuclear fuel is nontrivial.
Every nuclear powered ship becomes a prime terrorist target, either to hijack it or destroy it in place and cause a radiological incident. So you also need constant armed security (also expensive).
A more practical way to have "nuclear powered" ships would be to use electric power from land based nuclear plants to manufacture synthetic hydrocarbon liquid fuels, then load that fuel on the ships. Nuclear plants on land are far more cost effective since they can be built much larger to achieve economies of scale on operations and security.
Seems like a natural fit. For almost everything in the military, IMO there should be some market in the private space that could use those skills.
See some resources:
- https://en.wikipedia.org/wiki/Energy_efficiency_in_transport...
- https://people.hofstra.edu/geotrans/eng/ch8en/conc8en/fuel_c...
You could probably even find some ingenious way to run the current through the containers stacked umderneath to route the power. They are made of metal.