I don't have the specific number, but maybe another way to describe the scenario is to compare the difference between net-pen and land-based systems. In net pen, the industry is operating in water. They've got cages in there, and they rely on the natural flow of the currents and tides to move water through the systems. They will often have a barge there with a generator to support the requirements of people living and working on-site. Other than that, there are very limited power requirements for net-pen culture.
If you contrast that with a land-based system, you've got buildings with tanks. You need to be pumping water, depending on the system you're looking at, from the ocean into or around the system. As well, you have the costs for light and heating the water, etc.
So the big difference between a net-pen system and a closed system is in the physical infrastructure, and in maintaining that infrastructure in order to maintain the living conditions for your fish. A closed system requires much, much more power than a net-pen situation.