Because building a power plant next to a power plant so the power plant can turn the waste of the power plant back into fuel for the power plant is lunacy. It's easier and cleaner to simply turn the coal power plant off.
Yes, it can be done. The question is if it can be done economically.
> ... we can do big oil rigs on the shelf than in fact we can do solar panels like this with a submerged oil rig as the under-structure.
An oil rig has all the equipment concentrated on a platform, tapping into a concentrated source of energy. The structure can be built tough to withstand heavy use and tough environmental conditions.
The floating solar platform needs to be spread out as wide as possible, and over-building the infrastructure will dramatically increase capital costs.
Overall, I'll be a little more interested in the idea when they've done a year-long trial at sea of at least a small-scale demo system.
Oh, wait, they haven't actually built the hardware yet, this is just a concept? Yeah, thought so.
From some notes: The long range vision is to create an industry that will provide a range of ecosystem services that would supply food, fuel, fertilizer, fiber, farmaceuticals (nutraceuticals). Not just along the coasts, but in the open ocean. Think of it as biorefinery management. An MPA would likely have a 3 month service interval, and 3 year overhaul schedule to deal with things like biofouling that are part of maritime activities.
A one sq kilometer MPA might generate $1 million a year in value from kelp, maybe another $1 million a year from fish. The fish part is an unknown.
The best way to ride out an ocean storm is to submerge, like whales do. They could adjust bouyancy of an MPA if satellites tell them a storm is coming.
They intend to use mesoscale ocean current eddy shear levels to move MPA's to different locations in a region (imagine using foils to tack across the difference in current layers speeds, or to keep them circling in a small area, and want to develop cheaper marine vessel navigation automation [This means they won't need to anchor or tether the arrays to the bottom of the ocean]
The sea brings with it storms and waves (as mentioned in the article) but it also brings: saltwater corrosion, barnacles and other sea life trying to live on your equipment, serviceability issues (harder to get to and work on), and more.
There's also the energy needed to extract the CO2 from the water. If you want CO2, we generate concentrated amounts of it on land (like from coal power plants). Why not get that at the source?
We have plenty of flat land in the deserts around the world, and solar farms there are easier to maintain than out on the ocean.