Tide turns when costs are considered

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The article, “Pentland Firth tides ‘can power half of Scotland’” (20 January), failed to mention cost. We can all dream up schemes for making electricity, but cost is crucial to sorting out what is usable and what is not.

The cost of gaining energy from the Pentland Firth is unlikely to be less than that of offshore wind, which is three times as expensive as coal gas or nuclear, and maintenance costs are bound to be higher – much higher.

The Severn barrage, easy to imagine, finally failed on grounds of cost. The price of electricity is absolutely basic to everything economic; its activity, employment, its creative development, standards of health and education, communication and role in reducing winter death rates.

No politician with any degree of responsibility towards the electorate should even think of bothering with any form of energy other than the cheapest that satisfies all criteria of reliability and cost.

Forget about terms like “green” and “clean” until the rest of the world agrees to curb emissions.

There is nothing noble about sacrificing the economy and its people for a minority ideology.

It is well known that green organisations never cost their ambitions. Governments and politicians should not make the same mistake.

(Prof) Tony Trewavas FRS FRSE

Scientific Alliance 

North St David Street


Your article, “Pentland Firth tides ‘can power half of Scotland’”, is a fine example of how to take a piece of technically correct information and produce a totally misleading ­impression.

Aside from the obvious misuse of “can” rather than “could” and the illustration of a wave rather than a tidal power device, the article ignores the fundamental technical and economic disadvantages of tidal energy.

While it is true that the potential of the Pentland Firth tidal stream energy output is about 76 terawatt hours annually, around half of Scotland’s total consumption, there is not yet a single commercial tide-stream ­device operating in UK waters.

While tidal power, unlike wind, is predictable, it is also highly variable and of course uncontrollable.

It goes from zero to its maximum value twice a day, this maximum varying by a factor of three between spring and neap tides. No practical method exists for storing energy on the scale required to smooth this out to match the needs of electricity users.

Finally, the article makes no reference to the cost to the ­consumer of this unproven technology.

If and when tide-generated electricity starts flowing into the grid, the long-suffering consumer – already paying twice the market price for onshore wind and three times for offshore – will be forced to pay nearly six times the going rate for it, a price, like that of wind, presumably guaranteed to the developer for 25 years.

Jack W Ponton, FREng

Emeritus professor of 



No-one can cavil at the idea of deploying hundreds and hundreds of tidal- and wave-based electricity generators in the Pentland Firth’s “mill race” – except enterprises that would like to carry on sending their ships though the firth.

While it is ludicrous to think that, in the manner of Saudi Arabia oil, the Firth could generate enough watts to feed the ever-increasing global demand for electricity, it seems feasible that Scotland’s needs could be half-met, but at the cost of blocking the Firth’s entire width.

The electricity output would not quite match the steady consistency of that from nuclear, coal or gas power stations but would 
go far to satisfy renewable cravings.

Coupled with equally expensive but relatively more effective off-shore wind farms, there would be no need for any more onshore turbines – and existing ones could be got rid of.

The relevant bit of Scotland’s Future will have to be rewritten – or is this just a true-for-once example of our “abundant natural resources”?

Unlike oil, the marine systems can go on forever (with upgrading of course). Let’s have the lifetime costings.

Joe Darby