2MW wave power generator in Spain

[Moxi]

i'm recalling the planet mechanic version where they had spray rising through the unit as it wasn't sufficiently submerged - presumably a possible event on other schemes if not designed for all tidal eventualities ?

Moxi

[AE-NMidlands]

Where is this spray? The oscillating water and air are inside the structure. The water simply rises and falls when operating, so while suitable materials would obviously need to be specified, the construction seems to pose few problems.

With a wave smacking into the hole at the bottom of the shaft and blasting the air upwards I can't imagine there will only be a gentle to-and-fro current of air...
I'm sure it will vent at the top (or it would get blown up) so that is a route for water to get carried with the air - unless you think it will be sealed off in stormy conditions.

[Oliver90owner]

You clearly don’t understand much about design - I suspect you a a very much junior member on the forum and don’t have the experience of life, like some of us?

Ever seen how a cattle watering trough? Ever noticed how they work? Clearly not, or you would not be making such (seemingly to me) crass comments such as ‘a wave smacking into the hole at the bottom of a shaft and blasting air upwards’.

I’ve actually observed the phenomenon of cavities filling with sea water (while walking the coastline near Camerinös in Spain). Have you?

A Wells turbine (clearly?) uses an oscillating air column. These sites are obviously on the coastline, so salt water conditions will always apply. Engineers routinely deal with conditions such as those. It is not a problem to an engineer, simply one issue of many.

[AE-NMidlands]

You clearly don’t understand much about design - I suspect you a a very much junior member on the forum and don’t have the experience of life, like some of us?

Ever seen how a cattle watering trough? Ever noticed how they work? Clearly not, or you would not be making such (seemingly to me) crass comments such as ‘a wave smacking into the hole at the bottom of a shaft and blasting air upwards’.

I’ve actually observed the phenomenon of cavities filling with sea water (while walking the coastline near Camerinös in Spain). Have you?

A Wells turbine (clearly?) uses an oscillating air column. These sites are obviously on the coastline, so salt water conditions will always apply. Engineers routinely deal with conditions such as those. It is not a problem to an engineer, simply one issue of many.

Actually I'm about 70 and was in the other place for about 15 years, and have been here since a fortnight before you! (and I have 2 graduate engineer sons, one Chartered doing highly responsible work in the infrastructure field.)

I worked as an industrial scientist sitting with corrosion chemists (among other very good specialists, like coatings people, optics specialists, cleaning chemists, etc.) A lot of our work was with engineers who came to us after designing and building something which fell over quite quickly - and we would be taken right through it to spot what was causing it to fail, then point them at (hopefully a selection of) solutions for them to choose from. Throughout my life I have also taken to bits and repaired things, often ending up with stuff more robust and much longer-lived than the manufacturers intended... My sons say I should have been an engineer, but in the late 1960s (remember them?) you had to be really good at maths to get onto an engineering degree course, so I did a joint honours science degree instead.

Do you think I haven't enjoyed watching the raw power of big waves hitting rocks? or marvelled at how even quite honeycombed rock withstands the compression and blowing - and seen the spume that erupts out when the compressed air gets released? I have also been sailing (in a big old wooden boat) in pretty rough weather and am very aware how much raw power has to be withstood (or accommodated) by things in a marine environment.

So I do understand a bit - more than a bit - about design, and had wondered whether a coalescer of some sort - maybe just a sheet of expanded metal - would prevent spray getting to the turbine, but soon realised that in storm conditions it would be pointless, so why bother at all? (One spell of my time was on filter research and testing, so I know more than a bit about the theory and practise of that too.)
Keep up the good work.

[Joeboy]

We used aluminum for the ROV frames, pressure vessels and also prop shafts. It works very well in a salt water environment up to and including the temp changes and repeated wetting/drying cycles of the middle east. Used magnesium anodes for galvanic corrosion. Aluminum is an excellent material to work with, just a shame about the pollution and energy use to manufacture.

On first viewing of the floater video I didn't think much, then looking a little further I was taken by the idea that each unit is essentially a bellows for fluid, quite simple as are some of the best ideas.

[Moxi]

https://file.scirp.org/pdf/OJFD_2013072417112487.pdf

A very interesting read and clears up some of my questions at least as to why we don't see more of these Wells turbines.

The main issues seem to stem from noise, high speed of rotation and inertia upon reverse air flow, this latter issue struck a chord with me as it was one of the problems they had on the planet mechanics episode where i think they used a non return valve and possibly a second turbine so that each unit saw flow in one direction only to eliminate wear and overcome electrical losses from the inertia encountered at flow reversal.

Probably doesn't help that the Wells turbine only manages 15% either.

With regard to the water droplet entrainment there are a coupe of documents floating around (pun intended) to suggest a relationship between partial pressures in the air column as the flow reverses giving rise to droplet formation and also something to do with the standpipe diameter and depth of submergence relative to mass transition height as well as fiction losses (K) from the standpipe material so it seems clear that theres a trade off to be had for efficiency vs stability of the water column.

Moxi

[smegal]

Not the planet mechanic one but actually commercially operating system in two locations.

I wonder why we don’t see more of these around the British isles ?

Moxi

I'd like to see more, but was told when doing my renewable energy MSc that they weren't cost effective, they even did a nifty demo of the Wells turbine showing that it can accept flows from either direction. Unfortunately, this is probably still the case that civil costs vs output don't stack up.

[ecogeorge]

I suspect with current energy prices the cost analysis may be different ?
George