La Rance is a barrage across a river mouth on the coast at 48.6180N 2.0233W.

The turbine is deployed off the Île-de-Bréhat, near Paimpol in Côtes-d’Armor, on the seabed at a depth of 35 meters. The island is at 48.8461N 3.0047W butI don’t know exactly where the turbine is located.

There are some very strong currents on this coast, some peaking at over 6 knots, but the tidal flow will depend on the turbine’s location.

As for assumptions, I would bet on 30+ year life once the bugs are worked out. First generation wind turbines lasted for ~30 years before maintenance costs started being a major problem. Wind turbines are subject to a lot more stress with rapidly changing wind speeds where these underwater turbines will undergo fewer and more gradual changes in speed.

And because the speed range of tidal flow will be smaller than the conditions in which wind turbines operate it will probably be easier to build them without gear trains, the weakest part of wind turbines. Also, blades can be shorter (but fatter) which may also reduce stress.

And they are not going to get beat up by storms, sitting in deeper water. They are not going to experience much thermal stress.

I’d guess closer to 90% up time with mature tech. Not much to go wrong, alternator/generator hooked to a set of blades. A few bearings, a few water seals.

I’m thinking that tidal is going to be BFD….

If I look at the wind info page I see

“The cost of electricity generated from wind is now at record lows: several projects in high resource areas (US, Brazil, Sweden, Mexico) display a levelised cost of energy – excluding the impact of subsidies but after including the cost of capital and maintenance – below EUR 50/MWh ($68/MWh). This compares to current estimated average costs of $67 per MWh for coal-fired power and $56 per MWh for gas-fired power.” (In $/kWh, the figures would thus be less than $0.068/kWh for wind, $0.067/kWh for coal, and $0.056/kWh for gas-fired power.)”

How do I guess the approx number for these tidal turbine.
Not sure I read the number right but looks like $55millionUS/(4*2MW turbine) = $6.875M/MW
Is the about MWh for one year? 365*24 is 8790hours a year
$784.82/MWh in one year (assume up 100%)

Or do the numbers on the wind page assume a life span for the plant.
If I assume X% up time? Cost MWh over N years with (X% up time), round to nearest dollar
$78(100%), $87(90%), $112(70%), $157(50%) — 10 year life
$39(100%), $44(90%), $56(70%), $78(50%) — 20 year life
$26(100%), $29(90%), $37(70%), $52(50%) — 30 year life

I know it the first large scale grid connected, so cost will come down; and no one really know how long they will last or how much down time they will have. But just wondering where current engineering WAG (will ass guess) puts them now compared to wind/solar/coal. These are NOT put together in someones back yard; there must be number which back up investing $55m.

Should I be thinking good first baby step, or best dream ever.

With constant flow streams like the Gulf Stream or rivers the flow might not be as fast as peak tide flow, but it’s constant. Four knots of stream flow might produce the same amount or more power as a tidal flow that peaked at eight knots.

Larger blades will likely harvest that power once the technology matures a bit more.

Off the coast of Florida we have the very abundant Gulf Stream which flows 24/365 at 4 knots. We have hundreds of miles of available real estate for flow harvesting.

Or move down to the Keys to the Straights of Florida where the end of the state and Cuba force the flow into a narrower channel and the flow is more like six knots.