UK unveils plans for huge lagoon power plants stretching miles into the sea | Hacker News Reader

UK unveils plans for huge lagoon power plants stretching miles into the sea

independent.co.uk

61 pointsAndrewDucker40 comments

UK unveils plans to build tidal power plants. We've been planning things in the Severn Estuary my entire life and so far not lit a single lightbulb from it. As all the comments on the BBC story say: get on with it, build the thing, and tell us when it's done.

(There are a few tidal-power-through-undersea-turbines schemes in operation off Scotland, I believe)

There is a scheme just starting to be built in the Pentland Firth between Caithness and Orkney:

http://www.meygen.com/

I believe the first commercial tidal scheme of this type (effectively underwater windmills rather than a barrage) was in Northern Ireland:

http://www.marineturbines.com/3/news/article/7/seagen__the_w...

There's been one in Brittany since the mid-sixties: http://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

It works alright, but unless you have a very luckily shaped coastline, it doesn't scale all that well. It's also subject to silting in the long run, which isn't great for the yield, or the local eco-system.

That's a barrage - like the scheme discussed in the original article. The NI and Pendland Firth schemes don't rely on a barrage but on the very strong tidal streams naturally found in those areas.

Yes I know, I was responding to the OP mostly, since you'd already provided a reference to underwater turbine schemes.

Re silting. If you split the pool into two or three, when one was empty (at low tide) you could use the water from a full one to flush the silt out. There is a system similar to this where I live, they use a tidal pool to flush the harbor.

Thanks, we updated the title.

That's very little head. Does anybody have the engineering data on these projects? Have they built a smaller installation to prove the concept?

Head height is a major factor in hydro power installations.

Almost simultaneous discussion: https://news.ycombinator.com/item?id=9130893 (9 points, 3 hours ago, 2 comments)

The link is: http://www.bbc.com/news/science-environment-31682529

And chisb put a additional link to: http://www.tidallagoonswanseabay.com/proposal-overview-and-v...

They have a little more information.

There are some technical details about flow rates and head height in section 4.8 (p. 85/88) of this document:

http://tidallagoon.opendebate.co.uk/files/TidalLagoon/DCO_Ap...

One other thing I noticed upon briefly skimming is they're considering installing turbines which can also be used as pumps. I suppose in principle, at the cycle of the tide when the head is low and the plant isn't producing power, you could use the same facility as pumped storage.

There's also a rather florid promotional video here, if anyone's interested:

https://www.youtube.com/watch?v=mXEmHDQtXnw

> Have they built a smaller installation to prove the concept?

Tidal lagoon / barrage power generation is already a thing, so the concept is well proven.

> Does anybody have the engineering data on these projects?

This paper covers the maths: http://www.inference.phy.cam.ac.uk/sustainable/book/tex/Lago... (while also exploring ways to increase head above tidal range).

Here's the operating sequence: http://i.imgur.com/y9IJ5Ip.png

Looks like for most of the power generation phase the head will be about 5m. According to their paper generation is effective down to about 1.5m

The plant in Somerset will be on the Severn Estuary, which has a tidal range of 15m:

http://en.wikipedia.org/wiki/Severn_Estuary

Here's a very readable quantitative discussion about tidal power generation in the UK:

http://www.withouthotair.com/c14/page_81.shtml

Here's a proof of concept built around 620AD. Obviously a bit different but this type of technology has been around a long time. http://www.archaeology.co.uk/articles/features/harnessing-th...

What I don't understand about the idea is this. This stretch of water has one of the highest tidal ranges in the world, but this presumably is a matter of resonance, i.e the Bristol Channel and Severn Estuary just happen to be shaped in such a way that their natural resonant frequency is a close match with the driving force's twelve and a half hour odd period. But surely this means that the extra energy in the water, over and above places with lesser tides, is not something that can be tapped again and again each tide at any significant scale, it's a one time only bonus in its potential and kinetic energy which is gone after you extract its power through dampening. The ultimate non renewable energy, gone in half a day!

Anyway, I'll be giving serious consideration to dragging my family out early to see a five star Severn Bore the weekend after next, it could be the last one ever.

That would be true if it were a freely oscillating system, but since the tide is 'powered' by the moon I'd think the tidal cycle should keep going until the moon stops orbiting. (though I'm not 100% sure I understand how tides work)

He is arguing, probably correctly, that the damping caused by energy extraction will cancel out the natural resonance and therefore not be repeatable.

I don't see that. Surely if you have two swings hanging from a swaying tree and one of them is swinging wildly because it's the right length to resonate with the moving branch above, you can't say hey this x kg tyre is rising and falling y cm every s seconds, lets harness that. It only has the same renewable energy as the other swing, plus a one time build up of energy that its taken to get it up that extra height.

But the moon is providing an input. So, for your swing example, there is someone on one side giving it a push every pass.

No one's pushing my swings! I've already accounted for the input, it's the great mass of the swaying tree (and in turn the wind etc.), and like the tides' moon it's the same input to both swings, only one's them is swinging like the clappers whilst the other barely moves. Even though the former clearly has more energy at a given point in time most of that is a one off build up, and there can't be any more repeatedly extractable energy in the big swinger than the small.

Flip the oscillators, the sea is the tree branch, and the swing is the moon.

The tree branch is moved slightly each swing, and if I am to extract energy from the branch by forcing it to do work, I will damp the motion of the swing and it will eventually stop.

You're right in that it's not renewable, the energy is being extracted from the kinetic energy of the moon, and it will slow the moon to some minute degree.

The high tidal range is due to water being 'dragged' into a confined space by tidal forces and its kinetic energy becoming focussed as a result.

Could be missing something but I don't see resonance as the right model. In my mind the high tides are as a result of a large body of water being pushed into a confined space by a the geometry and currents of the area. That seems like it'd happen regardless of whether some energy had been tapped from a previous tide.

I agree that tidal power isn't "renewable" though, but for different reasons, as it (making a semi-educated guess) decreases our gravitational pull on the Moon, letting it drift away slightly faster than it might naturally, but the effect would be microscopic.

(My disclaimer is that I wrote a Newtonian model of the Solar System and its effects on tides as part of a Physics degree. Doesn't mean I know what I'm talking about, just that I thought a bit about it 15 years ago)

It has nothing to do with resonance. It's much the same principle as a pulley where you focus little force over a long distance into a lot of force over a smaller distance.

Picture a single wave entering a V shaped harbor. http://en.wikipedia.org/wiki/Bay_of_Fundy Now realize you can think of the tide is a very low frequency wave.

It's an oscillating system with a dramatically greater amplitude than its neighbours sharing the same driver. I'm having a hard time believing it has nothing to do with resonance.

Edit: Resonance may pay a tiny role, but it's a long way from the star of the show.

It also works with normal waves, storm surges, and Tsunamis which are non-oscillating systems. It's due to the large amount of kinetic energy in moving water which allows a much wider range of waves to benefit than you get with a resonance effect. Picture a large rock in a fast moving stream, the water bunches up in front of it and in some cases you can see a bump the water over some obstruction. http://ak.picdn.net/shutterstock/videos/6538901/preview/stoc...

PS: Because the land slopes up the water nearing the shore can have a slightly lower angel over a long distance which adds up. Thus, the total height at the end might be 20+ feet, but at the edge of the bay it's only vary slightly above sea level. However, the reverse at low tide does not work nearly as well because the slope dampens the effect vs reinforcing it. Resonance effects require both the height and trough of each wave to reinforce each other.

FYI tidal power plants are slowing down Earth's rotation. http://physics.stackexchange.com/questions/6400/are-tidal-po...

The movement of the oceans, and flexing in the earth crust, also slows down earth's rotation. But we are talking milliseconds per century. [1] So, tidal power plants are going to have a very small effect overall.

http://en.wikipedia.org/wiki/Tidal_acceleration

This article reads like it was written by an 11 year old. Or someone who does not speak English natively.

Either that or, knowing how these things have been rolling aroud the planning and NIMBY protest camps for years, perhaps the author gave it precisely the right amount of effort and attention to detail it deserved.

"Tidal Lagoon Swansea Bay is thought to be seeking a guaranteed subsidised price of about £168 for every megawatt-hour (MWh) of electricity it generates over a 35-year period – almost four times the current market price of power." http://www.telegraph.co.uk/finance/newsbysector/energy/11426...

I'd assume that 35 years of inflation needs to be factored in as well, at 2% that would half subsidy by that point. Also, there is an inherent cost to green power, if it was cheap power companies would flock to build them of their own accord, but of course they dont, so the government has to subside them.

If something has negative externalities, the solution is to tax the externality. E.g. a carbon tax will raise the price of fossil-fuel energy, which will make some green energy projects worth building. That's it -- job done.

Subsidising "good" projects is instead of taxing bad projects is the wrong way to do it, because the government has to evaluate every project proposal to figure out which projects should be subsidised. Whereas a carbon tax does it for you; all the government needs to figure out is the cost of carbon, and the market takes care of the rest.

Timestamp this and come back in three years because we are basically sitting on the tipping point of some clean energy sources (not the one in this article!) becoming cost competitive. Solar and wind are at grid parity in an increasing number of places (Deutsche Bank says 47 of 50 states by 2016) and innovations in financing will be able to pick up the slack if/when subsidies expire.

Presumably the barrages will last >100 year and be able to generate power the entire time. In the long run it could be much cheaper.

It likely won't, because it will be heavily silted before then, and dredging a lagoon that size is really quite expensive.

At GBP1bn for 320MW, this doesn't look too good. If the numbers on wikipedia for the Sihwa Lake Tidal Power Station [0] are right (254MW for GBP180m), this is prohibitively expensive, even for the technology.

[0] http://en.wikipedia.org/wiki/Sihwa_Lake_Tidal_Power_Station

That's for the first plant, the other 7 are expected to cost the same as the recent nuclear power deal for Hinckley C. That's in the BBC article.

I actually think that's pretty amazing as a first off price. By contrast, solar panels have only got to where they are today because governments (principally but not exclusively in Germany) subsidized them for decades at two to three times that level. God know how many billions of subsidies have gone in nuclear, and the strike price is still high. Or, for that matter, into traditional energy technology and infrastructure.

Many new technologies do require up front subsidies in order to develop, and that's sensible as long as there is a credible path to reducing the cost. Solar panels are just now starting to become competitive, if this technology could do it second or third time out, that is something to be lauded.

How are they going to stop the lagoon from silting up and becoming shallower, short of dredging it regularly?

Multiple pools. When the silted one is empty at low tide, use the water from the other pools to wash the silt out.

Reply on news.ycombinator.com