Like the link says, it’s true that natural friction is causing the spin to marginally slow. I believe the misconception lies in the fact that it assumes a tidal plant will not add additional resistance. (Actulally, the link does say this in its defence, and is mearly trying to state that it can be used as a long-term solution. “But even if we doubled the power ex-tracted from the earth–moon system, tidal energy would still last more than a billion years.”)

A barrage creates much greater friction comparatively by preventing the mass of water from naturally flowing back, the source of which we then harness the energy from. If the barrage does not exist, the mass of water is free to flow back with limited friction and little work is done. Of course, we are talking minute changes, so it’s neither here nor there in reality.

To understand this, you need to know the physics of how tides are formed. As I said, I’ll create a page later to explain this, but in basic terms it is to do with ‘something like’ the combined centre of gravity of both the earth and moon (which is just below the earth’s surface) that the earth pivots around. The centrifugal force around this pivot creates the tide in one direction when part way through rotation, and then the opposite tide occurs on the next part. Visualising on a much smaller scale; if we were to place a barrier to prevent the flow of water from continuing onto the second part, it would act as a break for that one cycle and will require greater force to keep the spin continuing. If the water is then released (like in a tidle plant), then the same forces can occur on the next cycle.

Hope this explains things. I’ll try and make it more acurate later

I’ve been looking into this for a few years as part of an OU degree, and it seems that a lot of the things to overcome can be achieved with relative ease, even the environmental impacts on wildlife which seems to be the main social resistance of the project.

An interesting factor of mine is what will be the long term effect resulting from the slowing of the earths spin? It’s not significant, but it will increase the length of the day by around 1/10th second every thousand years, and if other countries follow suite we will be in the realms of entering whole seconds. Whatever the consequences, this technology is greatly needed at least as a stepping stone to immediately reduce our carbon emissions until we can better our technology and understanding.

I really hope that such a project can be contracted soon, as it will greatly help curb our emissions, something which needs to be on all of our top priorities at this moment in time.