From
<https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>

Tidal electricity generation is among the ideas listed by Boris Johnson as
a way of avoiding reliance on Putin’s Russia. It is an even stronger
candidate than he might have realised, holding out the promise not only of
increasing our energy independence but also levelling up. A group of
scientists and engineers has shown how we could generate electricity using
tidal energy that does not require the building of a costly lagoon, like
the cancelled scheme for Swansea Bay.

Schemes based on using tidal river basins would increase energy security,
reduce reliance on authoritarian dictatorships, increase "levelling up",
and (unlike other renewables) require no government subsidy. Moreover,
unlike wind and solar, there is no intermittency problem and electricity is
generated round the clock every day of the year.

A considerable amount of electricity could be generated on derelict,
brownfield sites that lie adjacent to the major industrial rivers in the
UK. They are former shipyards, chemical works, salt pans, wharves and
ironworks that have been abandoned.

In essence the plan involves taking over a derelict riverside site, near
the sea (to use the full tidal range) but far enough inland to avoid sea
storms. A simple concrete and steel construction, like a dry dock, is all
that’s required. Turbines work between the river and the excavated basin,
which is subdivided into chambers with turbines in the dividing walls. When
the tide comes in, through the turbines, it makes electricity and when it
goes out, it also passes through turbines to make electricity. Some water
is held back in the chambers to keep generating while the tide is turning.

Housing could be built on the roof of the basin and sold to help recover
capital costs. The sites could also be used as a base for frozen food
factories. The frozen food industry is a very heavy user of electricity but
siting a large operating plant over a tidal basin would enable the turnover
of cold tidal water to act as the cooling reservoir and take a considerable
load off the grid.

An even heavier user of electricity is the data storage industry. The
amount of power used to cool enormous memory banks is huge. Google,
Microsoft, Amazon, and Facebook, as well as the NHS, are all concerned
about the cost of keeping vast computer facilities cool. This burden could
be taken off the grid by transferring it to the cold water circulating in
the tidal basin. Green hydrogen could also be manufactured by electrolysis
using on-site electricity when not required by the national grid.

About 40 potential sites have been identified. The most promising are on
the Tyne (former dry docks), at the Forth (former salt pans), the Tees
(former ICI works), the Orwell (another former ICI site), and Swansea (a
former BP chemical works and a former steelworks). Each would be capable of
generating around 400MW.

The opportunity for inward investment is huge and no government subsidy is
required, unlike schemes for large-scale nuclear plants. Reliable income
streams would come from selling the electricity, using the water for
cooling, and selling green hydrogen.

If we want both energy independence and levelling-up, then generating
electricity in tidal river basins looks like the next big idea.

———————

Nice idea, but i suspect that the individual tidal plants would have quite
a low capacity, and I'm not convinced they could be built without subsidy.
But at least the green energy would be predictable.

Recliner <recliner.usenet@gmail.com> wrote:
> From
> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>
> Tidal electricity generation is among the ideas listed by Boris Johnson as
> a way of avoiding reliance on Putin’s Russia. It is an even stronger
> candidate than he might have realised, holding out the promise not only of
> increasing our energy independence but also levelling up. A group of
> scientists and engineers has shown how we could generate electricity using
> tidal energy that does not require the building of a costly lagoon, like
> the cancelled scheme for Swansea Bay.

I have wondered if you could do small scale tidal power generation using
gravity , weights and tide.

Have a large series of weights hanging on cables from a very large
flotation platform , the cables turn generators via gearing in the same
ways weights drive some clocks.
At Low tide the weights are on the sea bed and the cable slack wound in ,
floating platform rises on tide lifting weights off and when high enough
weights released to start their descent and power generators.
In practise to build a network that covered all states of the tide with
generating platforms would probably be too complicated for it to be worth
it and there are few places with a suitably large tidal range. But it would
save building dams that eventually cause silting and a floating something
bigger than a VLCC would not be affected by the waves that have broken
smaller wave power experiments.

GH

GH

On 24/03/2022 22:27, Recliner wrote:
> From
> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>
> Tidal electricity generation is among the ideas listed by Boris Johnson as
> a way of avoiding reliance on Putin’s Russia. It is an even stronger
> candidate than he might have realised, holding out the promise not only of
> increasing our energy independence but also levelling up. A group of
> scientists and engineers has shown how we could generate electricity using
> tidal energy that does not require the building of a costly lagoon, like
> the cancelled scheme for Swansea Bay.
>
> Schemes based on using tidal river basins would increase energy security,
> reduce reliance on authoritarian dictatorships, increase "levelling up",
> and (unlike other renewables) require no government subsidy. Moreover,
> unlike wind and solar, there is no intermittency problem and electricity is
> generated round the clock every day of the year.
>
> A considerable amount of electricity could be generated on derelict,
> brownfield sites that lie adjacent to the major industrial rivers in the
> UK. They are former shipyards, chemical works, salt pans, wharves an
> ironworks that have been abandoned.
>
> In essence the plan involves taking over a derelict riverside site, near
> the sea (to use the full tidal range) but far enough inland to avoid sea
> storms. A simple concrete and steel construction, like a dry dock, is all
> that’s required. Turbines work between the river and the excavated basin,
> which is subdivided into chambers with turbines in the dividing walls. When
> the tide comes in, through the turbines, it makes electricity and when it
> goes out, it also passes through turbines to make electricity. Some water
> is held back in the chambers to keep generating while the tide is turning.

And there's the weasel words right there. How big do those chambers have
to be? Size of the tidal lagoons required for the Swansea and Cardiff
schemes perhaps?

--
Graeme Wall
This account not read.

Graeme Wall <rail@greywall.demon.co.uk> wrote:
> On 24/03/2022 22:27, Recliner wrote:
>> From
>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>>
>> Tidal electricity generation is among the ideas listed by Boris Johnson as
>> a way of avoiding reliance on Putin’s Russia. It is an even stronger
>> candidate than he might have realised, holding out the promise not only of
>> increasing our energy independence but also levelling up. A group of
>> scientists and engineers has shown how we could generate electricity using
>> tidal energy that does not require the building of a costly lagoon, like
>> the cancelled scheme for Swansea Bay.
>>
>> Schemes based on using tidal river basins would increase energy security,
>> reduce reliance on authoritarian dictatorships, increase "levelling up",
>> and (unlike other renewables) require no government subsidy. Moreover,
>> unlike wind and solar, there is no intermittency problem and electricity is
>> generated round the clock every day of the year.
>>
>> A considerable amount of electricity could be generated on derelict,
>> brownfield sites that lie adjacent to the major industrial rivers in the
>> UK. They are former shipyards, chemical works, salt pans, wharves an
>> ironworks that have been abandoned.
>>
>> In essence the plan involves taking over a derelict riverside site, near
>> the sea (to use the full tidal range) but far enough inland to avoid sea
>> storms. A simple concrete and steel construction, like a dry dock, is all
>> that’s required. Turbines work between the river and the excavated basin,
>> which is subdivided into chambers with turbines in the dividing walls. When
>> the tide comes in, through the turbines, it makes electricity and when it
>> goes out, it also passes through turbines to make electricity. Some water
>> is held back in the chambers to keep generating while the tide is turning.
>
> And there's the weasel words right there. How big do those chambers have
> to be? Size of the tidal lagoons required for the Swansea and Cardiff
> schemes perhaps?
>
>
>

If I’ve done my sums correctly raising 100x100 metres of water by 1 metre
gives 100M joules of stored potential energy.

Raising 1 kg by 1 metre requires 10 Joules
A cubic metre of water is 1000kg. So raising that cubic metre requires 1000
x 10 Joules.
A 100 x 100 metre area would require 100 x 100 x 1000 x 10 Joules

A Megawatt hour is 3600 Mega Joules.

So you would have to have quite a surface area and quite a high tidal range
to get just this 1 MWhr of energy. The sums don’t seem to add up to me.

On 2022-03-24 22:58:08 +0000, Marland said:

> Recliner <recliner.usenet@gmail.com> wrote:
>> From
>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>>
>>
>> Tidal electricity generation is among the ideas listed by Boris Johnson as
>> a way of avoiding reliance on Putin’s Russia. It is an even stronger
>> candidate than he might have realised, holding out the promise not only of
>> increasing our energy independence but also levelling up. A group of
>> scientists and engineers has shown how we could generate electricity using
>> tidal energy that does not require the building of a costly lagoon, like
>> the cancelled scheme for Swansea Bay.
>
> I have wondered if you could do small scale tidal power generation using
> gravity , weights and tide.
>
> Have a large series of weights hanging on cables from a very large
> flotation platform , the cables turn generators via gearing in the same
> ways weights drive some clocks.
> At Low tide the weights are on the sea bed and the cable slack wound in ,
> floating platform rises on tide lifting weights off and when high enough
> weights released to start their descent and power generators.
> In practise to build a network that covered all states of the tide with
> generating platforms would probably be too complicated for it to be worth
> it and there are few places with a suitably large tidal range. But it would
> save building dams that eventually cause silting and a floating something
> bigger than a VLCC would not be affected by the waves that have broken
> smaller wave power experiments.

The energy available from such a scheme will be the weight times the
tidal range, times 2 because 2 tides per day. If you want to get, say,
1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
per tide. A typical tidal range is around about 3 m, so that gives an
object of about 75 tonnes (in round numbers). To make a dent in the UK
power supply, you'll need GW scale, so you're looking at 75,000 tonnes
for your weight. In broad terms, you're looking at something about 50%
larger than a Panamx ship. A Panamx ship draws somethign in the range
of 12 m, so 50% larger will draw 18 m. In a 3 m tide, that means about
66% of the weight will still be supported by the buoyancy of the bit
that's still in the water, and the lower you drop it the greater this
proportion grows. You'll therefore need something like 6 objects of
this size, or alternatively 9 Panamax-sized objects for ~1 GW. The
current UK demand is somewhere in the ballpark of 35 GW, so if you
wanted to make up 10% of demand, you are looking at something like 35
such objects. You'd need these distributed around the coastline at
places with different times of high and low tide to smooth out the
unevenness of the power supply.

Robin

Bob <email@domain.com> wrote:
> On 2022-03-24 22:58:08 +0000, Marland said:
>
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> From
>>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>>>
>>>
>>>
>>> Tidal electricity generation is among the ideas listed by Boris Johnson as
>>> a way of avoiding reliance on Putin’s Russia. It is an even stronger
>>> candidate than he might have realised, holding out the promise not only of
>>> increasing our energy independence but also levelling up. A group of
>>> scientists and engineers has shown how we could generate electricity using
>>> tidal energy that does not require the building of a costly lagoon, like
>>> the cancelled scheme for Swansea Bay.
>>
>> I have wondered if you could do small scale tidal power generation using
>> gravity , weights and tide.
>>
>> Have a large series of weights hanging on cables from a very large
>> flotation platform , the cables turn generators via gearing in the same
>> ways weights drive some clocks.
>> At Low tide the weights are on the sea bed and the cable slack wound in ,
>> floating platform rises on tide lifting weights off and when high enough
>> weights released to start their descent and power generators.
>> In practise to build a network that covered all states of the tide with
>> generating platforms would probably be too complicated for it to be worth
>> it and there are few places with a suitably large tidal range. But it would
>> save building dams that eventually cause silting and a floating something
>> bigger than a VLCC would not be affected by the waves that have broken
>> smaller wave power experiments.
>
> The energy available from such a scheme will be the weight times the
> tidal range, times 2 because 2 tides per day. If you want to get, say,
> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
> per tide. A typical tidal range is around about 3 m, so that gives an
> object of about 75 tonnes (in round numbers). To make a dent in the UK
> power supply, you'll need GW scale, so you're looking at 75,000 tonnes
> for your weight. In broad terms, you're looking at something about 50%
> larger than a Panamx ship. A Panamx ship draws somethign in the range
> of 12 m, so 50% larger will draw 18 m. In a 3 m tide, that means about
> 66% of the weight will still be supported by the buoyancy of the bit
> that's still in the water, and the lower you drop it the greater this
> proportion grows. You'll therefore need something like 6 objects of
> this size, or alternatively 9 Panamax-sized objects for ~1 GW. The
> current UK demand is somewhere in the ballpark of 35 GW, so if you
> wanted to make up 10% of demand, you are looking at something like 35
> such objects. You'd need these distributed around the coastline at
> places with different times of high and low tide to smooth out the
> unevenness of the power supply.
>
> Robin
>
>

Thanks for doing the figures. If the rafts were made big enough then you
could put a number of wind turbines on top or even cover the spaces in
between them with Solar panels as well though the latter would soon get
covered in a film of salt which would lower output till the next heavy
shower to wash them off.
It was a bit of a whimsical idea but if the world turns away from oil there
will be plenty of tankers to melt down and rebuild into large floating
rafts.

GH

On Fri, 25 Mar 2022 10:56:14 +0100, Bob wrote:

> On 2022-03-24 22:58:08 +0000, Marland said:
>
>> Recliner <recliner.usenet@gmail.com> wrote:
>>> From
>>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-
tidal-energy-superpower/>
>>>
>>>
>>> Tidal electricity generation is among the ideas listed by Boris
>>> Johnson as a way of avoiding reliance on Putin’s Russia. It is an even
>>> stronger candidate than he might have realised, holding out the
>>> promise not only of increasing our energy independence but also
>>> levelling up. A group of scientists and engineers has shown how we
>>> could generate electricity using tidal energy that does not require
>>> the building of a costly lagoon, like the cancelled scheme for Swansea
>>> Bay.
>>
>> I have wondered if you could do small scale tidal power generation
>> using gravity , weights and tide.
>>
>> Have a large series of weights hanging on cables from a very large
>> flotation platform , the cables turn generators via gearing in the same
>> ways weights drive some clocks.
>> At Low tide the weights are on the sea bed and the cable slack wound in
>> , floating platform rises on tide lifting weights off and when high
>> enough weights released to start their descent and power generators.
>> In practise to build a network that covered all states of the tide with
>> generating platforms would probably be too complicated for it to be
>> worth it and there are few places with a suitably large tidal range.
>> But it would save building dams that eventually cause silting and a
>> floating something bigger than a VLCC would not be affected by the
>> waves that have broken smaller wave power experiments.
>
> The energy available from such a scheme will be the weight times the
> tidal range, times 2 because 2 tides per day. If you want to get, say,
> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
> per tide. A typical tidal range is around about 3 m, so that gives an
> object of about 75 tonnes (in round numbers).
....
Is that right? 75 tonnes is 75,000 kg or about 750,000 N weight. For a 3m
height that's 2.2 MJ (or less than 1 kWh)? Are you a factor of 1000 out?

nib

On 25/03/2022 10:18, Marland wrote:
> Bob <email@domain.com> wrote:
>> On 2022-03-24 22:58:08 +0000, Marland said:
>>
>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>> From
>>>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>>>>
>>>>
>>>>
>>>> Tidal electricity generation is among the ideas listed by Boris Johnson as
>>>> a way of avoiding reliance on Putin’s Russia. It is an even stronger
>>>> candidate than he might have realised, holding out the promise not only of
>>>> increasing our energy independence but also levelling up. A group of
>>>> scientists and engineers has shown how we could generate electricity using
>>>> tidal energy that does not require the building of a costly lagoon, like
>>>> the cancelled scheme for Swansea Bay.
>>>
>>> I have wondered if you could do small scale tidal power generation using
>>> gravity , weights and tide.
>>>
>>> Have a large series of weights hanging on cables from a very large
>>> flotation platform , the cables turn generators via gearing in the same
>>> ways weights drive some clocks.
>>> At Low tide the weights are on the sea bed and the cable slack wound in ,
>>> floating platform rises on tide lifting weights off and when high enough
>>> weights released to start their descent and power generators.
>>> In practise to build a network that covered all states of the tide with
>>> generating platforms would probably be too complicated for it to be worth
>>> it and there are few places with a suitably large tidal range. But it would
>>> save building dams that eventually cause silting and a floating something
>>> bigger than a VLCC would not be affected by the waves that have broken
>>> smaller wave power experiments.
>>
>> The energy available from such a scheme will be the weight times the
>> tidal range, times 2 because 2 tides per day. If you want to get, say,
>> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
>> per tide. A typical tidal range is around about 3 m, so that gives an
>> object of about 75 tonnes (in round numbers). To make a dent in the UK
>> power supply, you'll need GW scale, so you're looking at 75,000 tonnes
>> for your weight. In broad terms, you're looking at something about 50%
>> larger than a Panamx ship. A Panamx ship draws somethign in the range
>> of 12 m, so 50% larger will draw 18 m. In a 3 m tide, that means about
>> 66% of the weight will still be supported by the buoyancy of the bit
>> that's still in the water, and the lower you drop it the greater this
>> proportion grows. You'll therefore need something like 6 objects of
>> this size, or alternatively 9 Panamax-sized objects for ~1 GW. The
>> current UK demand is somewhere in the ballpark of 35 GW, so if you
>> wanted to make up 10% of demand, you are looking at something like 35
>> such objects. You'd need these distributed around the coastline at
>> places with different times of high and low tide to smooth out the
>> unevenness of the power supply.
>>
>> Robin
>>
>>
>
> Thanks for doing the figures. If the rafts were made big enough then you
> could put a number of wind turbines on top or even cover the spaces in
> between them with Solar panels as well though the latter would soon get
> covered in a film of salt which would lower output till the next heavy
> shower to wash them off.
> It was a bit of a whimsical idea but if the world turns away from oil there
> will be plenty of tankers to melt down and rebuild into large floating
> rafts.
>
> GH
>

The tidal range in the Seven Estuary is about 15 metres which is why we
have another new scheme being proposed.

On 2022-03-25 10:46:39 +0000, nib said:

> On Fri, 25 Mar 2022 10:56:14 +0100, Bob wrote:
>
>> On 2022-03-24 22:58:08 +0000, Marland said:
>>
>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>> From
>>>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-
> tidal-energy-superpower/>
>>>>
>>>>
>>>> Tidal electricity generation is among the ideas listed by Boris
>>>> Johnson as a way of avoiding reliance on Putin’s Russia. It is an even
>>>> stronger candidate than he might have realised, holding out the
>>>> promise not only of increasing our energy independence but also
>>>> levelling up. A group of scientists and engineers has shown how we
>>>> could generate electricity using tidal energy that does not require
>>>> the building of a costly lagoon, like the cancelled scheme for Swansea
>>>> Bay.
>>>
>>> I have wondered if you could do small scale tidal power generation
>>> using gravity , weights and tide.
>>>
>>> Have a large series of weights hanging on cables from a very large
>>> flotation platform , the cables turn generators via gearing in the same
>>> ways weights drive some clocks.
>>> At Low tide the weights are on the sea bed and the cable slack wound in
>>> , floating platform rises on tide lifting weights off and when high
>>> enough weights released to start their descent and power generators.
>>> In practise to build a network that covered all states of the tide with
>>> generating platforms would probably be too complicated for it to be
>>> worth it and there are few places with a suitably large tidal range.
>>> But it would save building dams that eventually cause silting and a
>>> floating something bigger than a VLCC would not be affected by the
>>> waves that have broken smaller wave power experiments.
>>
>> The energy available from such a scheme will be the weight times the
>> tidal range, times 2 because 2 tides per day. If you want to get, say,
>> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
>> per tide. A typical tidal range is around about 3 m, so that gives an
>> object of about 75 tonnes (in round numbers).
> ...
> Is that right? 75 tonnes is 75,000 kg or about 750,000 N weight. For a 3m
> height that's 2.2 MJ (or less than 1 kWh)? Are you a factor of 1000 out?

Looks like you're right, so that would imply 35,000 ships rather than 35.

Robin

On Fri, 25 Mar 2022 12:50:16 +0100, Bob wrote:

> On 2022-03-25 10:46:39 +0000, nib said:
>
>> On Fri, 25 Mar 2022 10:56:14 +0100, Bob wrote:
>>
>>> On 2022-03-24 22:58:08 +0000, Marland said:
>>>
>>>> Recliner <recliner.usenet@gmail.com> wrote:
>>>>> From
>>>>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-
>> tidal-energy-superpower/>
>>>>>
>>>>>
>>>>> Tidal electricity generation is among the ideas listed by Boris
>>>>> Johnson as a way of avoiding reliance on Putin’s Russia. It is an
>>>>> even stronger candidate than he might have realised, holding out the
>>>>> promise not only of increasing our energy independence but also
>>>>> levelling up. A group of scientists and engineers has shown how we
>>>>> could generate electricity using tidal energy that does not require
>>>>> the building of a costly lagoon, like the cancelled scheme for
>>>>> Swansea Bay.
>>>>
>>>> I have wondered if you could do small scale tidal power generation
>>>> using gravity , weights and tide.
>>>>
>>>> Have a large series of weights hanging on cables from a very large
>>>> flotation platform , the cables turn generators via gearing in the
>>>> same ways weights drive some clocks.
>>>> At Low tide the weights are on the sea bed and the cable slack wound
>>>> in , floating platform rises on tide lifting weights off and when
>>>> high enough weights released to start their descent and power
>>>> generators. In practise to build a network that covered all states of
>>>> the tide with generating platforms would probably be too complicated
>>>> for it to be worth it and there are few places with a suitably large
>>>> tidal range. But it would save building dams that eventually cause
>>>> silting and a floating something bigger than a VLCC would not be
>>>> affected by the waves that have broken smaller wave power
>>>> experiments.
>>>
>>> The energy available from such a scheme will be the weight times the
>>> tidal range, times 2 because 2 tides per day. If you want to get,
>>> say,
>>> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or
>>> 2.16 per tide. A typical tidal range is around about 3 m, so that
>>> gives an object of about 75 tonnes (in round numbers).
>> ...
>> Is that right? 75 tonnes is 75,000 kg or about 750,000 N weight. For a
>> 3m height that's 2.2 MJ (or less than 1 kWh)? Are you a factor of 1000
>> out?
>
> Looks like you're right, so that would imply 35,000 ships rather than
> 35.
>
> Robin

Let's see if I can get any closer!

I'm imagining 1 hectare of pound, 100m by 100m or about 2.5 acres, and 3m
depth. That's 30,000 tonnes of water, 30,000,000 kg or 300,000,000 = 300
MN. The average head for generation will be about 1.5m, so 450 MJ or
about 125 kWh.

So say allowing for losses 100 kWh per hectare.

So now a wild guess.

I assume you get 4 goes per tide, 2 filling and 2 emptying.

A figure from Google suggests that the UK uses 280TWh of electricity per
year, which I make about 192 GWh per fill/empty. On that basis, our
hectare will supply a little more than one half of a millionth of the
total UK requirement.

2 million hectares is about the area of Wales.

Where are my errors!

nib

On Fri, 25 Mar 2022 09:41:29 -0000 (UTC), Tweed <usenet.tweed@gmail.com> wrote:

>Graeme Wall <rail@greywall.demon.co.uk> wrote:
>> On 24/03/2022 22:27, Recliner wrote:
>>> From
>>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>>>
>>> Tidal electricity generation is among the ideas listed by Boris Johnson as
>>> a way of avoiding reliance on Putin’s Russia. It is an even stronger
>>> candidate than he might have realised, holding out the promise not only of
>>> increasing our energy independence but also levelling up. A group of
>>> scientists and engineers has shown how we could generate electricity using
>>> tidal energy that does not require the building of a costly lagoon, like
>>> the cancelled scheme for Swansea Bay.
>>>
>>> Schemes based on using tidal river basins would increase energy security,
>>> reduce reliance on authoritarian dictatorships, increase "levelling up",
>>> and (unlike other renewables) require no government subsidy. Moreover,
>>> unlike wind and solar, there is no intermittency problem and electricity is
>>> generated round the clock every day of the year.
>>>
>>> A considerable amount of electricity could be generated on derelict,
>>> brownfield sites that lie adjacent to the major industrial rivers in the
>>> UK. They are former shipyards, chemical works, salt pans, wharves an
>>> ironworks that have been abandoned.
>>>
>>> In essence the plan involves taking over a derelict riverside site, near
>>> the sea (to use the full tidal range) but far enough inland to avoid sea
>>> storms. A simple concrete and steel construction, like a dry dock, is all
>>> that’s required. Turbines work between the river and the excavated basin,
>>> which is subdivided into chambers with turbines in the dividing walls. When
>>> the tide comes in, through the turbines, it makes electricity and when it
>>> goes out, it also passes through turbines to make electricity. Some water
>>> is held back in the chambers to keep generating while the tide is turning.
>>
>> And there's the weasel words right there. How big do those chambers have
>> to be? Size of the tidal lagoons required for the Swansea and Cardiff
>> schemes perhaps?
>>
>>
>>
>
>If I’ve done my sums correctly raising 100x100 metres of water by 1 metre
>gives 100M joules of stored potential energy.
>
>Raising 1 kg by 1 metre requires 10 Joules
>A cubic metre of water is 1000kg. So raising that cubic metre requires 1000
>x 10 Joules.
>A 100 x 100 metre area would require 100 x 100 x 1000 x 10 Joules
>
>A Megawatt hour is 3600 Mega Joules.
>
>So you would have to have quite a surface area and quite a high tidal range
>to get just this 1 MWhr of energy. The sums don’t seem to add up to me.
>

Yes, without doing the sums, that was my instinct. Given the fairly small height difference, the surface area would have
to be huge to produce meaningful amounts of energy. Using old brownfield industrial sites for such reservoirs is a good
idea, but they're unlikely to be nearly large enough to be worthwhile. And the cost of the steel and concrete to create
them is likely to be disproportionately high.

Bob <email@domain.com> wrote:
> On 2022-03-25 10:46:39 +0000, nib said:
>
>> On Fri, 25 Mar 2022 10:56:14 +0100, Bob wrote:
>>
>>> On 2022-03-24 22:58:08 +0000, Marland said:

>>>>
>>>> I have wondered if you could do small scale tidal power generation
>>>> using gravity , weights and tide.
>>>>
>>>> Have a large series of weights hanging on cables from a very large
>>>> flotation platform , the cables turn generators via gearing in the same
>>>> ways weights drive some clocks.
>>>> At Low tide the weights are on the sea bed and the cable slack wound in
>>>> , floating platform rises on tide lifting weights off and when high
>>>> enough weights released to start their descent and power generators.

>>> The energy available from such a scheme will be the weight times the
>>> tidal range, times 2 because 2 tides per day. If you want to get, say,
>>> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
>>> per tide. A typical tidal range is around about 3 m, so that gives an
>>> object of about 75 tonnes (in round numbers).
>> ...
>> Is that right? 75 tonnes is 75,000 kg or about 750,000 N weight. For a 3m
>> height that's 2.2 MJ (or less than 1 kWh)? Are you a factor of 1000 out?
>
> Looks like you're right, so that would imply 35,000 ships rather than 35.
>
> Robin
>
>

I did think that my crazy idea had turned out better than expected,
Now feel like I did when I was about six and excitedly showed Dad the new
type of engine I had just invented by blowing into the tube of my bicycle
pump upon which he explained how pneumatic
drills worked and what a compressor was.

GH

On 2022-03-25 14:20:11 +0000, Marland said:

> Bob <email@domain.com> wrote:
>> On 2022-03-25 10:46:39 +0000, nib said:
>>
>>> On Fri, 25 Mar 2022 10:56:14 +0100, Bob wrote:
>>>
>>>> On 2022-03-24 22:58:08 +0000, Marland said:
>
>>>>>
>>>>> I have wondered if you could do small scale tidal power generation
>>>>> using gravity , weights and tide.
>>>>>
>>>>> Have a large series of weights hanging on cables from a very large
>>>>> flotation platform , the cables turn generators via gearing in the same
>>>>> ways weights drive some clocks.
>>>>> At Low tide the weights are on the sea bed and the cable slack wound in
>>>>> , floating platform rises on tide lifting weights off and when high
>>>>> enough weights released to start their descent and power generators.
>
>>>> The energy available from such a scheme will be the weight times the
>>>> tidal range, times 2 because 2 tides per day. If you want to get, say,
>>>> 1 MW over 12 hours, that's 4.32 GJ of energy you need to store, or 2.16
>>>> per tide. A typical tidal range is around about 3 m, so that gives an
>>>> object of about 75 tonnes (in round numbers).
>>> ...
>>> Is that right? 75 tonnes is 75,000 kg or about 750,000 N weight. For a 3m
>>> height that's 2.2 MJ (or less than 1 kWh)? Are you a factor of 1000 out?
>>
>> Looks like you're right, so that would imply 35,000 ships rather than 35.
>>
>> Robin
>>
>>
>
> I did think that my crazy idea had turned out better than expected,
> Now feel like I did when I was about six and excitedly showed Dad the new
> type of engine I had just invented by blowing into the tube of my bicycle
> pump upon which he explained how pneumatic
> drills worked and what a compressor was.

Nothing wrong with coming up with novel ideas, and even if a novel idea
isn't useful in the way you first expect it, that doesn't mean its not
useful ever. It is sometimes the case that people trying to solve one
sepcific problem, but find their idea is actually not suitable for that
application, then find out there is some other niche application they
didn't initially consider, where their solution fits well. An example
of this is the PEM fuel cell. The initial intention was to develop a
lighter weight conventional battery. While this didn't work, the
technology developed in the process proved to provide the means of
making a room temperture fuel cell that did not rely on expensive
matierals like platinum, making possible portable fuel cells for
vehicle applications at an affordable price.

Robin

Graeme Wall <rail@greywall.demon.co.uk> wrote:
> On 24/03/2022 22:27, Recliner wrote:
>> From
>> <https://www.telegraph.co.uk/news/2022/03/24/britain-could-become-tidal-energy-superpower/>
>>
>> Tidal electricity generation is among the ideas listed by Boris Johnson as
>> a way of avoiding reliance on Putin’s Russia. It is an even stronger
>> candidate than he might have realised, holding out the promise not only of
>> increasing our energy independence but also levelling up. A group of
>> scientists and engineers has shown how we could generate electricity using
>> tidal energy that does not require the building of a costly lagoon, like
>> the cancelled scheme for Swansea Bay.
>>
>> Schemes based on using tidal river basins would increase energy security,
>> reduce reliance on authoritarian dictatorships, increase "levelling up",
>> and (unlike other renewables) require no government subsidy. Moreover,
>> unlike wind and solar, there is no intermittency problem and electricity is
>> generated round the clock every day of the year.
>>
>> A considerable amount of electricity could be generated on derelict,
>> brownfield sites that lie adjacent to the major industrial rivers in the
>> UK. They are former shipyards, chemical works, salt pans, wharves an
>> ironworks that have been abandoned.
>>
>> In essence the plan involves taking over a derelict riverside site, near
>> the sea (to use the full tidal range) but far enough inland to avoid sea
>> storms. A simple concrete and steel construction, like a dry dock, is all
>> that’s required. Turbines work between the river and the excavated basin,
>> which is subdivided into chambers with turbines in the dividing walls. When
>> the tide comes in, through the turbines, it makes electricity and when it
>> goes out, it also passes through turbines to make electricity. Some water
>> is held back in the chambers to keep generating while the tide is turning.
>
> And there's the weasel words right there. How big do those chambers have
> to be? Size of the tidal lagoons required for the Swansea and Cardiff
> schemes perhaps?

It’s easy to do calculations on this.

The maximum possible energy you can get at 100% efficiency (in Joules) is
the mass of water in kg multiplied by the vertical drop in metres
multiplied by 9.8 m/s^2.

A couple of conversions are useful:
1 m^3 of water is 1000 kg and
1 kWh is 3 600 000 J.

--
Jeremy Double