Having worked in the marineenergy sector for almost 24 years may I offer the following:
1. Tidal power subdivides into two categories
a. tidal range - such as the proposed tidal lagoons in Swansea Bay or a barrage such as is being developed for the Mersey in Liverpool. In these the change in water level within the lagoon or upstream of the barrage is used to power turbine to produce power.
b. Tidal stream whereby the flow of the tide is used to power a turbine immersed in the flow like a windmill under water.

2. The Government have not been supportive of tidal range technologies. They declined to contribute investment to the Swansea Bay lagoon which was deemed too small to be cost effective. That was something of a pity as the projected cost per unit of electricity generated was comparable to that of new nuclear and although small would have been an excellent deonstration from which a lot ofinformation would have been gathered. The Severn Barrage proposal was refused due to severe objections around loss of marine and bird life diversity arising from a net loss of inter-tidal area as well as the loss of the unique "Severn Bore" - tidal wave that occurs in the Severn. A larger lagoon solution was considered for Cardiff bay which would have caused limitations to shipping in/out of Cardiff Port. The lagoons carry less damaging environmental consequences than the barrages.

3. Tidal stream - a lot of which has been carried out in Orkney and Shetland - is a better contributor to the energy mix and can be developed from smaller starting scales. The Meygen facility (by Simec Atlantis in Caithness rather than Orkney); Orbital Marine Energy (Orkney) and Nova Innovation array (Shetland) are examples of the leading technologies that are progressing towards being commercial and will get closer to being competitive with offshore floating wind as more is deployed. Minesto are deploying a different tidal stream technology in the Faroe islands where the turbine "flies" through the water attached to a solid base on the seabed by a cable tether. Government is investing in these technologies through the bidding system series of auction rounds that offer a given "strike price" for the power produced.

4. The attraction of tidal stream is that the tides are absolutely predictable and so the power produced can be predicted well. The load factor (average output/peak output) for tidal stream is around 50% better than the 30%(ish) for wave and does not depend on the wind blowing. Investments in these technologies are less risk for the better developed versions as identified by the auction results, but are only suitable for a small proportion of anyone's portfolio at present .

5. Wave technology is more complex and only one or two companies are beginning to approach what may turn out to be closing in on a commercial situation which is still to be proven. Wave power is more intermittant but is a vast resource which makes it worth pursuing. MPS are combining a wave device with a floating wind facility - still to be demonstrated.

6. Wind power, due to intermittency, requires back up of "spinning" spare which is usually natural gas powered turbines which can start up quickly when there is too little wind. This aspect of wind is somewhat ignored in estimating the true cost of wind power and so to some extent for wave power.

It means exactly that the state should not be wasting money on dead end research...

But that requires unbiased assessment of a technology and the chances of it ever succeeding. But trying to find such people is quite hard, so politicians shrug and give grants out.

There are plenty of things that money was poured into that finally, after millions spent, quietly died a death.

A great example was magnetic levitation railways in the 70's.

Someone has to decide, and being like a model parent have the ability to say "no".

The classic current one (pun intended) is fusion. It's just a money pit of research money with zero chance of ever providing anything useful.

EV's have been going for what, ten years now? And they are still expensive and an ownership nightmare. Because despite weekly claims of "new battery tech" with xxx miles range and ten minute recharge (or whatever) it just doesn't and won't happen.

The government are almost getting the message. Insurance companies and fire brigades are in the know, but someone has to put their hands up and call it. Instead they just kick it down the road by five years (so far). That "pump priming" of subsidy just didn't work. Reality kicks in and the EV things is staggering towards the edge.

In the river Dart near where I live is an Archimedean screw. It generates power 24/7 and powers a large school and industrial estate.

Cost about £1mn I think.

That is another Archimedes screw further up river.

The Totnes one is over five times more powerful, still expensive, but it goes 24/7. It powers a lot of stuff and generates a lot of cash.

Have spoken to the guys who look after it.

I like this idea of micro generation. Any river with a race can do this.