Why not tidal power?

[IsleofRum]

We have wind turbines and they are good at generating electricity when the wind blows, but the tide comes in and out twice(three times in some parts) a day. In some areas (pentland firth, north channel, Western isles) the tide stream is calculable, known to mariners and anyone who understands charts.
Why do we not exploit this to generate wave and tidal power?

But it is just as variable as wind, tides do not flow all the time and they vary massively over the course of a Luna cycle and even the year.

Ten years ago Siemens poured millions of pounds into developing tidal energy, it wasn't commercially feasible, and they are now one of the biggest wind energy companies.

Currently renewable energy does create excess energy and even when the planned 500% increase in offshore wind is installed excess energy will be converted into hydrogen to power future vehicles and aircraft, or stored in batteries or pumped hydro.

@ErrolTheDragon there is a company planning to use disused mine shafts as energy storage, basically huge blocks of concrete are wound up using excess energy then slowly dropped down driving a generator. Genius!

I've seen another (in the US) building towers for the same sort of thing, but mine shafts seem like a much better idea, if you've already got deep vertical holes.

Predictable

Yes variable
But predictable

But yes I think that excess wind being used for hydrogen production would be something people should be doing a lot more of

@midgetastic I've actually done some of the studies I refer to and I really couldn't make it feasible. If you Google "low head hydro electric" you'll find literally thousands of studies that conclude it's not viable. The number of sites where it is remotely feasible are incredibly few which means that tidal turbine production will never reach the economies of scale to be competitive with wind and solar.

It's also not a new concept, the Romans built tide mills and there was one in use up to the 19th century on the river Itchen, I believe it's been restored as a working museum.

The French built a tidal lagoon hydro dam but are decommissioning it in favour of wind.

Tidal power definitely has its place but it will always be incredibly niche. I wish it were otherwise.

Thank you. Yes I did mean Electric Mountain. I maybe should have paid more attention on the tour but that makes sense, I did think it must use a lot of power to pump the water up. 😁

Oops, Currently renewable energy does not create excess energy.

Orbital Marine looks quite interesting too, operating off Orkney right now with plans for two more sites. I'm not sure it's really cost effective though or scaleable.

I really like the Orbital concept, it's gets away from difficult to maintain seabed mounted turbines, but the number of suitable sites are incredibly few and very discreet, 10s of square km rather than 10000s for wind. A lot of people seem to forget that generating electricity is only a part of the challenge, connecting it to the grid is still significant. Connecting 1000 wind turbines is vastly more cost effective than 10 tidal turbines.

the tide comes in and out twice(three times in some parts) a day.

OT and possibly slightly pedantic, but surely only twice per day, 12 hrs25min apart. Or are there really some places where there is a quirk of geography that means they have three tides? I just can’t figure out how that could possibly happen. (Genuine question).

tethys.pnnl.gov/project-sites/la-rance-tidal-barrage

The tidal range in the Bristol channel is the second highest in the world at 12.00 metres.

@iwishiwasafish strictly speaking nowhere gets three tides a day, tides are driven by the spin and orbit of the earth, moon and sun, and there are roughly two a day, but the period varies massively. Depending on location the period can drop down so that a few times a year there can be three high, or low, tides a day. Equally the same location might only have one tide a day at others periods.

Generally the rise and fall of the tides follow a sine wave pattern but there are some locations where geography interferes. The Solent is notorious for this in that there is a bump in the curve caused by the progression of flood and ebb and the way this spills into both the Eastern and Western Solent.

Not everywhere gets high tide at the same time. In the Solent a mid day high will be a spring, in North Devon early morning or evening high will be a spring.

On two days a year.

Tides are not constant.

I know this isn't a particularly active thread, but I have been very keen on the concept of tidal power gen for a long time, and have been really interested by @Daftasabroom 's considered input on the practical aspects of making it work. Clearly, there are difficulties on the civil engineering/steel making/sheer strength and resilience of making assemblies to function in open water/bad weather zones... but I sort of thought (that's my tech level) that if you were working at sea-bed level then tide function would still work, but the weather/wave would be less of an influence.

@EffortlessDesmond There are indeed tidal turbines that sit on the seabed. There are plans to install some around the Channel Islands which have strong tides over a relatively large area. They do make sense in niche applications but I believe they will always be niche unfortunately. People have been trying to make them work for decades but just aren't the economies of scale that you see with wind and solar and maintenance is another league (under the sea 🙄).

I would guess the Channel Islands are prime candidates for tidal turbines just based on sailing through the Alderney Race. Someone I know participated in the Orkney and Cornwall Wave Hub projects a few years ago, but their plan was to apply what they learned in the Caribbean and they failed to get any govt funding.

What about tidal lagoons? I know a rich inventor who lives local to me who has come up with a power generation idea which a university was studying and he is trying to commercialise. I really hope he gets there. Its a brilliant idea. I'd be interested in hearing the challenges but I knew already that sea water must make it very difficult to maintain. I wonder if its possible to use parts that don't corrode / degrade but are still tough enough.

Birds and wildlife

The wave hub has been shut down and sold to a Scandinavian company who intend to use the infrastructure for floating wind demonstrator trials.

If you look at the tidal energy map of the UK there are actually very few sites, and if you sail you'll know for example, that the Portland race only covers a relatively small area and is relatively shallow.

Oil and gas rigs operate in inhospitable places too, i.e. salt water, pressure when well heads on the sea bed, gases/chemicals etc down well holes. The technology/materials are definitely available to make the machinery/equipment to place in the sea or on the sea bed.

I used to work in a firm that designed/manufactured electrical connectors for rigs, wellheads, "downhole" equipment, submersible ROVs, etc. Our firm designed products exactly for inhospitable locations, capable of withstanding very high pressures, and not being damaged by sea water and other chemicals/gases found on or under the sea bed. Our customers included Exxon, Shell, Ferranti, Kvaerner, and we had our products in rigs all over the World.

It's been done since the Roman times! There is one in France and a good discussion here. The environmental damage would be massive.

I came across tidalpower24.com/ recently it could overcome many of the issues faced by tide stream turbines and barrages.

It's essentially a near shore barrage with a series of buffer tanks. But it's massively ambitious.

They've been working on solutions for tidal fro more than 20 years now in large scale trials, not just small proof of concept tests. The problem is the environment is so harsh - salt water corrodes lots of metals, wind and weather causes waves as well as their own impacts, it's equipment that needs to move around and is also not easily accessed to fix breakages unlike wind turbines on land etc.

If someone does get a product far enough to be commercially viable, it will be a game changer here in the UK, Ireland, Norway etc. But also hugely important for many coastal countries and particularly the much smaller island nations globally which are much poorer and have far less opportunities for generating renewable energy.

https://www.offshore-energy.biz/uk-supports-11-tidal-energy-projects-with-record-capacity-of-50mw-in-latest-cfd-scheme/