Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Petrochemicals on 03/04/2021 23:15:59
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If we where to do an tidal barrier generation in the Irish Sea Belfast to Scotland and Pembrokeshire to County Wexford to , would these figures suffice? I now these are tedious to read, sorry.
Area(rough estimate) 100x300 km =30,000km2 or 30,000,000,000m2 or 30x10^9m2 o
Depth of tide 4 to 8 metres, so 5m for standard design height.
Volume 30x10^9 m2 x 5m= 150x10^9 m3
Mass 150x10^9m3 x 1000kg per m3=150x10^12kg
Average height of hydrostatic head 5÷2+2.5
MGH
150x10^12 x 10 x 2.5 = 3.75x10^15 joules of potentially harvestable energy per tide
4 tidal changes a day =15x10^15 joules per day
In Watt hours - - - - - 15x10^15÷3600=4.167x10^12 watt hours or 4.2 Terra watt hours per day.
The uk only uses 300twh per year
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I'd be curious about the power generation of current tidal generators. They also aren't without controversy, potentially creating a species barrier and impacting the life within the pools. And, of course, human activities including shipping.
A couple of fallacies may include time and distance.
Those Pembrokeshire tides are pretty extraordinary, but don't seem to represent the tides around the England, Scotland,and Ireland.
I get the feeling that tides within a restriction may not be as severe as those outside of the restriction. So you wouldn't necessarily be able to calculate the whole 5+m tides at the more distant sections of the estuary especially if you put a dam in the middle.
You can see that to some extent. The tides at Dublin are about 2 meters.
Every 6 hours you transition from high to low or low to high. This means you have to get all your tidal flow you wish within that time. You can't simply hold all the water out until high tide, then transport it all in instantly, then hold it in until low tide and instantly transport it out.
My guess is once you calculate in all of those factors, maximizing flow, you'll get a headspace of about 1 foot. Still not without power, but very different from what you would imagine.
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Logically, one would expect some pretty extreme underwater currents, and an alternative would be non-enclosed underwater turbines. Not as much energy as you're calculating, but likely much cheaper, and less damaging (although the impact on fish and other species would still have to be considered.
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non-enclosed underwater turbines
I think the ideal location for these would be in the Cook Straight, New Zealand.
Tides form a wave which circulates around New Zealand, so the tides are effectively 180° out of phase at each end of the Cook Straight.
- This leads to very strong currents within the straight (but not much tidal range).
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Logically, one would expect some pretty extreme underwater currents, and an alternative would be non-enclosed underwater turbines. Not as much energy as you're calculating, but likely much cheaper, and less damaging (although the impact on fish and other species would still have to be considered.
Tide heights vary, Liverpool has a range 10m maximum 4 minimum, Dublin is 2 to 3, evening it out 5 seems average and easy to work with.
The tides peak at both Liverpool and Dublin at the same time meaning it must outflow through the two channels, not just slosh around. The Irish sea
With such a deep body of water I would hope their would be little ecological impact, the fish could hopefully make it through the turbines, anything bigger seals dolphins whales could have access through open shipping channels at tide peaks or something like the Falkirk wheel.
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non-enclosed underwater turbines
I think the ideal location for these would be in the Cook Straight, New Zealand.
Tides form a wave which circulates around New Zealand, so the tides are effectively 180° out of phase at each end of the Cook Straight.
- This leads to very strong currents within the straight (but not much tidal range).
Surely enclosed turbines would work better?
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Windmills,of course, generally don't have dams.
In theory you would be able to harness more of the energy with a dam than simply an underwater turbine. Although there are issues with building really large dams. And, as mentioned, tides for a large body of water may not be as conducive to funneling through a dam turbine as you might hope, and you'll likely be dealing more with flow than head,
I used the term "open" to mean without a dam. You can build a tunnel (or funnel) around your turbine, and take whatever measures you wish to prevent harming fish and underwater life.
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Good point about the flow potential, but without a dam I should think the pressure will be very much reduced. There are many areas like this, gulf of california, St Lawrence Sound. If the figures add up there is much potential in dams and choke points like the one Evan__au mentioned .
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I have wondered if there is a difference between north/south bays/tidal zones and east/west ones.
So, the the Gulf of California is largely North/South, and thus it should fill up and empty synchronously.
The Mediterranean, on the other hand, is very East/West, so the two ends of the sea are moderately out of phase, potentially creating more of a circular flow within the sea.