Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.
Buy individually or both books together. Delivery is free!


powered by Surfing Waves




Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
 Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




Renewable Energy: I love tidal lagoons

Bottom of Page

1 to 27 of 27

  1.  
    • CommentAuthortony
    • CommentTimeFeb 7th 2014
     
    Let's have lots of them
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 7th 2014
     
    Yes, I know a few places they could be built.
    • CommentAuthortony
    • CommentTimeFeb 7th 2014
     
    How about the first one goes in as a trial, planning and public enquiry free?
    • CommentAuthorowlman
    • CommentTimeFeb 7th 2014
     
    You weren't thinking of Westminster were you Steamy?
    Could re name it Wetminster.:wink::bigsmile:
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 7th 2014
     
    First one is up and running now.
    Thing is they can have recreational usage as well, nice safe place to learn to sail in, maybe a bit of fishing or fish farming could take place too.
  6.  
    Does seem a good idea for gen. electric .
    What about the uncontrollable nature of nature , wont these be at the mercy of the weather and like all
    sea defences requiring constant maintenance to stop them getting washed away?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 7th 2014
     
    I would hope they were built a bit better than the sea wall down here. But having said that, it was the repaired section that failed 3 days ago, the 200 year old section is still there.
  8.  
    According to the numbers in today's Guardian article the initial Cardiff Bay scheme needs an annual subsidy of £65m to provide electricity for 120,000 homes.

    That's £550 per house per year.

    - annual output of 420GW/h and a design life of 120 years.
    - Tidal Lagoon Power has put in a development consent order under the Planning Act 2008, but must convince the government to provide subsidies of £156 per MW/h – even more than that going to offshore wind farms.
    - the Swansea Bay tidal lagoon, which as well as providing light and warmth for 120,000 local homes could also become a centre for sailing and other recreation.

    http://www.theguardian.com/business/2014/feb/06/swansea-bay-tidal-lagoon-power-planned

    I wonder what the payback would be for spending £65m a year on EWI or other eco-projects given typical savings :devil:.

    Ferdinand
  9.  
    Posted By: jamesingramwont these be at the mercy of the weather and like all
    sea defences requiring constant maintenance to stop them getting washed away?

    Hopefully they'd be used for generation and a proportion of the income would be directed to maintenance (& replacement)?
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 7th 2014 edited
     
    I think, though not 100% sure, that the £156/MWh is a guaranteed minimum, so if they can sell the power at £50/MWh (about the mean rate) then it is topped up by £105/MWh. As it is tidal, there will be times when they can guarantee to sell at a much higher rate, reducing the subsidy payment. There are also times they can guarantee not to sell, reducing the risk even more. We, as the people that buy the power are probably not allowed to see the contract though. The National Grid website may have some output figures for it though.
    •  
      CommentAuthorfostertom
    • CommentTimeFeb 7th 2014
     
    Like, the only mainline railway that makes an outright profit for its owners, so draws no govt subsidy, is GNER. The owners happen to be the govt, for several yrs since the prev private owners surrendered their contract because they couldn't begin to make it pay. Therefore the govt is preparing to re-privatise GNER, because the private sector is so much more efficient than govt agency.
    • CommentAuthorJonti
    • CommentTimeFeb 7th 2014 edited
     
    But would GNER make a profit IF it had to pay a franchise? Having said that, the railways would be better in public hands.

    Ferdinand said

    'According to the numbers in today's Guardian article the initial Cardiff Bay scheme needs an annual subsidy of £65m to provide electricity for 120,000 homes.

    That's £550 per house per year.'

    If we halved the average use that would mean 240'000 homes and if we charged these 240'000 households an average of £550 each then no need to subsidise. Simple really :wink:

    Jonti
    • CommentAuthorSeret
    • CommentTimeFeb 7th 2014
     
    Posted By: fostertomLike, the only mainline railway that makes an outright profit for its owners, so draws no govt subsidy, is GNER.


    It's no unheard of for a rail franchise to not include subsidies. I know the Gatwick Express never took any subsidy before it was absorbed into the South Central franchise.

    Folks overbidding for the rail franchises has been an issue, but hopefully in the future they won't be allowed to simply walk away when it hits the fan. This should discourage some of the silly bidding that's been going on.
    • CommentAuthorbarney
    • CommentTimeFeb 7th 2014
     
    Going back to "I love Lagoons", Taking an average 2m tidal range what is the daily average power available from 1km2 of water?

    I calculate it to be 500KW - so to displace a 1GWe thermal station we need a basin of 2000 km2 - obviously more depth would require less area - but it's still a pretty big patch of water given that the whole country is getting quite excited about significantly smaller areas of considerably less depth across Somerset.

    Water doesn't really have the energy density needed to become mainstream

    Regards

    Barney
  15.  
    Posted By: barneyGoing back to "I love Lagoons", Taking an average 2m tidal range what is the daily average power available from 1km2 of water?

    I calculate it to be 500KW - so to displace a 1GWe thermal station we need a basin of 2000 km2 - obviously more depth would require less area - but it's still a pretty big patch of water given that the whole country is getting quite excited about significantly smaller areas of considerably less depth across Somerset.

    Water doesn't really have the energy density needed to become mainstream

    Regards

    Barney


    Hmm, I think not as all the largest power stations in the world are hydroelectric. Itaipu in Brazil/Paraguay and the Three Gorges in China both produce roughly 100 TWh per year (the UK consumed 363 TWh in 2010).

    Obviously the UK doesn't have any rivers to compare with the Parana or Yangtze but most of the projections for a Severn barrage from Brean Down give about 17 TWh per year.

    Ed
    • CommentAuthorSeret
    • CommentTimeFeb 7th 2014 edited
     
    Those numbers look about right to me, assuming you're calculating mean power output. Obviously a 2m tidal range is a pretty marginal location for tidal power though. If you plonked your 1km2 lagoon in the Bristol Channel you could get 22MW to play with.
    • CommentAuthorbarney
    • CommentTimeFeb 7th 2014
     
    1J = 1 Nm

    1W = 1Mm/s

    1m3 water weighs 1000kg or approx. 10kN.

    1km2 water 2m high weighs 1000 x 1000 x 2 x 10kN = 20GN

    Average head is 1m so stored energy is 20GJ

    The tidal cycle is 11hr = 40 000s.

    The average power is 20 exp 9 /40 000 = 500 kJ/s = 500kW.

    So that 1km at say 10m head would only give you 5MW ?

    Or have I got my sums wrong

    Regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 7th 2014 edited
     
    Power = mgh

    Power = Watts
    m = mass flow rate (kg/(litre.s))
    g = gravity (9.81 m/s^2)
    h = head height (m)
    • CommentAuthorbarney
    • CommentTimeFeb 7th 2014
     
    but we are after energy, so we want the average power ?

    Regards

    Barney
    • CommentAuthorSeret
    • CommentTimeFeb 7th 2014 edited
     
    The equation for potential energy in a tidal lagoon is:

    E = 0.5Aρgh2

    Where E = energy, A = area in sq m, ρ = density (approx 1025kg m-3 for seawater), g = gravity, h = tidal range in m.

    Since the tide cycles twice per day you double that, then divide by 86400s per day to get the average power in watts. That's a bit of an artificial figure though, since the actual power output is more like a chopped sine wave. Obviously turbine efficiency comes into it too, but modern turbogenerators are pretty efficient.
    • CommentAuthorEd Davies
    • CommentTimeFeb 7th 2014
     
    https://en.wikipedia.org/wiki/Rance_Tidal_Power_Station

    “Its 24 turbines reach peak output at 240 megawatts and average 62 megawatts, … The power plant portion of the dam is 332.5 m (1,091 ft) long and the tidal basin measures 22.5 km2 (9 sq mi).”

    So 2.75 MW/km² on average.
    • CommentAuthorEd Davies
    • CommentTimeFeb 7th 2014
     
    And you could get a similar amount again by floating some PV panels on the lagoon.
    • CommentAuthorbarney
    • CommentTimeFeb 7th 2014
     
    OK - so how big a patch moving over what head do we need to displace a 1GWe thermal station ?

    If we take Rance as an example, then 330 km2

    Regards

    Barney
    •  
      CommentAuthorSteamyTea
    • CommentTimeFeb 7th 2014
     
    1GW / 62 MW = 16.13
    22.5 km^2 x 16.13 = 363 km^2

    Gravity is very weak really. RE is very diffused.
  25.  
    Don't these schemes also use pumps to increase out put. i.e. when the lagoon is at high tide and the outside is at high tide you can pump extra water into the lagoon say increase by 0.1 meter and then generate at 2.1 meter head. A gain of 20. I think this effect is used in a tidal esturary in France somewhere.

    Richard
    • CommentAuthortony
    • CommentTimeFeb 8th 2014
     
    Two linked tidal lagoons can also smooth the output of power
  27.  
    Surely there is no need to reinvent the wheel by trying to calculate the generation from the first principles of gravity and the mass of water, as the expected generation from the proposed barrage sites is already known?

    Brean Down to Lavernock, the focus of most of the proposals gives about 17 TWh/year.

    It's a little difficult to compare with a fossil fuel power station as the output will not be constant but dependent on the tide. On the other hand, many fossil fuel plants (especially gas) do not run constantly either, but are modulated to meet demand.

    But if you average out 17 TWh/year it would be 1940 MW.

    Ed

1 to 27 of 27

  1.  
Add your comments

    Username Password
  • Format comments as
 
Back to Discussions Top of Page
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press