7 ms·

Portland cement production, not concrete which consists of aggregate as well. There must be many trade offs in this design and one can imagine pure sand as ball

Portland cement production, not concrete which consists of aggregate as well. There must be many trade offs in this design and one can imagine pure sand as ballast so the concrete plays some structural role. The sea floor anchor design and high voltage underwater cables also seem like hard engineering problems.

sergeykish 6y ago
Strangely each time I see a doubt about renewable energy quick search resolves it [1]. I've thought hydro produces least, no > At a dam in Brazil, where the flooded basin is wide and the biomass volume is high the methane produced results in a pollution potential 3.5 times more than an oil-fired power plant would be. A theoretical study has indicated that globally hydroelectric reservoirs may emit 104 million metric tonnes of methane gas annually [2]. There is no green gas free energy only different cost, even nuclear. But maybe we can reduce emissions and some day catch them back. [1] https://en.wikipedia.org/wiki/Life-cycle_greenhouse_gas_emissions_of_energy_sources https://en.wikipedia.org/wiki/Life-cycle_greenhouse_gas_emis... [2] https://en.wikipedia.org/wiki/Environmental_impact_of_reservoirs#Greenhouse_gases https://en.wikipedia.org/wiki/Environmental_impact_of_reserv...
- sradman 6y ago
  Flooding land for hydro power generation can also release significant amounts of natural mercury: https://en.wikipedia.org/wiki/James_Bay_Project#Mercury_pollution https://en.wikipedia.org/wiki/James_Bay_Project#Mercury_poll...
- Retric 6y ago
  Methane’s impact is really overblown. It’s got an atmospheric half life of ~7 years and rapidly turns into CO2. Hydroelectric’s steady state is therefore already baked into the current climate and future releases are equivalent to about ~285 million metric tons of CO2. (The difference is due to CH4 being heavier than CO2.) Except the carbon in that methane comes the atmosphere so the the long term global warming impact of existing dams is approximately zero. Now increasing methane production can have an impact, but it just doesn’t stack linearly like CO2 does.
  - soperj 6y ago
    How is it overblown sorry? It's half life is actually 9.1 years, which means after nearly a decade, half of it is still left, and this is methane produced annually, so it's continually being added to. Add that to the fact that methane is 84 times better at trapping heat within the atmosphere than C02. Most methane production from Hydro isn't even counted because it's considered green.
    - Retric 6y ago
      That 84 is based on 20 years, on a 100 year timeframe it’s 21, and a 1 year timeframe it’s approaching 200. All the methane for the last N years is decaying as you move forward. Say at day 1 you released X methane that’s being directly added to the global total. Now move forward to day X0,000, in some ways your adding X methane but because a little methane is decaying from every prior day the net result is not an increase of X, but an increase of X * 1/2^(some number that keeps increasing). So, sure the hover dam is adding net methane. But after 84 years it’s less than 1/2 ^(84 /9.1) or 0.17% as much as directly measured. Further, the GWP of methane is calculated under the assumption it released from the ground where most sources like cows are releasing Carbon and Hydrogen that used to be in the atmosphere in the first place before photosynthesis etc eventually turned it into methane. Also, unlike CO2 it’s really easy to reduce considerations simply by lowering emissions. PS: I have seen several estimates around 7 years, I used 9.1 because the exact number isn’t that important.
      - sergeykish 6y ago
        Have you read article? > Warm climate reservoirs generate methane, a greenhouse gas when the reservoirs are stratified, in which the bottom layers are anoxic (i.e. they lack oxygen), leading to degradation of biomass through anaerobic processes. In warm climate it is methane generator, biomass constantly added with river flow.
        Retric 6y ago
        Yes, but I don’t think you understand what’s being described. Dam methane production is based on the amount of organic matter being added by the river which is effectively a constant over time. It’s effectively the same process as cow’s methane where decaying plants release methane in a low oxygen environment. The issue is you don’t get an accurate number for the amount of methane in the atmosphere from a dam by multiplying average annual methane release by the number of years it’s in operation. Thus the the rate of doesn’t correlate to future global warming making such statements absolutely meaningless. PS: Also, all of this is assuming the study adjusted for what happens when the dam is not there and nearly the same process occurs when the river dumps into an ocean somewhere.
brandmeyer 6y ago
True! There are alternatives that are net-absorptive, too. But until we can set a market price for CO2 emissions, current emitters will continue to treat it as a zero-cost externality.

sergeykish 6y ago

Strangely each time I see a doubt about renewable energy quick search resolves it [1]. I've thought hydro produces least, no > At a dam in Brazil, where the flooded basin is wide and the biomass volume is high the methane produced results in a pollution potential 3.5 times more than an oil-fired power plant would be. A theoretical study has indicated that globally hydroelectric reservoirs may emit 104 million metric tonnes of methane gas annually [2]. There is no green gas free energy only different cost, even nuclear. But maybe we can reduce emissions and some day catch them back. [1] https://en.wikipedia.org/wiki/Life-cycle_greenhouse_gas_emissions_of_energy_sources https://en.wikipedia.org/wiki/Life-cycle_greenhouse_gas_emis... [2] https://en.wikipedia.org/wiki/Environmental_impact_of_reservoirs#Greenhouse_gases https://en.wikipedia.org/wiki/Environmental_impact_of_reserv...

sradman 6y ago
Flooding land for hydro power generation can also release significant amounts of natural mercury: https://en.wikipedia.org/wiki/James_Bay_Project#Mercury_pollution https://en.wikipedia.org/wiki/James_Bay_Project#Mercury_poll...
Retric 6y ago
Methane’s impact is really overblown. It’s got an atmospheric half life of ~7 years and rapidly turns into CO2. Hydroelectric’s steady state is therefore already baked into the current climate and future releases are equivalent to about ~285 million metric tons of CO2. (The difference is due to CH4 being heavier than CO2.) Except the carbon in that methane comes the atmosphere so the the long term global warming impact of existing dams is approximately zero. Now increasing methane production can have an impact, but it just doesn’t stack linearly like CO2 does.
- soperj 6y ago
  How is it overblown sorry? It's half life is actually 9.1 years, which means after nearly a decade, half of it is still left, and this is methane produced annually, so it's continually being added to. Add that to the fact that methane is 84 times better at trapping heat within the atmosphere than C02. Most methane production from Hydro isn't even counted because it's considered green.
  - Retric 6y ago
    That 84 is based on 20 years, on a 100 year timeframe it’s 21, and a 1 year timeframe it’s approaching 200. All the methane for the last N years is decaying as you move forward. Say at day 1 you released X methane that’s being directly added to the global total. Now move forward to day X0,000, in some ways your adding X methane but because a little methane is decaying from every prior day the net result is not an increase of X, but an increase of X * 1/2^(some number that keeps increasing). So, sure the hover dam is adding net methane. But after 84 years it’s less than 1/2 ^(84 /9.1) or 0.17% as much as directly measured. Further, the GWP of methane is calculated under the assumption it released from the ground where most sources like cows are releasing Carbon and Hydrogen that used to be in the atmosphere in the first place before photosynthesis etc eventually turned it into methane. Also, unlike CO2 it’s really easy to reduce considerations simply by lowering emissions. PS: I have seen several estimates around 7 years, I used 9.1 because the exact number isn’t that important.
    - sergeykish 6y ago
      Have you read article? > Warm climate reservoirs generate methane, a greenhouse gas when the reservoirs are stratified, in which the bottom layers are anoxic (i.e. they lack oxygen), leading to degradation of biomass through anaerobic processes. In warm climate it is methane generator, biomass constantly added with river flow.
      - Retric 6y ago
        Yes, but I don’t think you understand what’s being described. Dam methane production is based on the amount of organic matter being added by the river which is effectively a constant over time. It’s effectively the same process as cow’s methane where decaying plants release methane in a low oxygen environment. The issue is you don’t get an accurate number for the amount of methane in the atmosphere from a dam by multiplying average annual methane release by the number of years it’s in operation. Thus the the rate of doesn’t correlate to future global warming making such statements absolutely meaningless. PS: Also, all of this is assuming the study adjusted for what happens when the dam is not there and nearly the same process occurs when the river dumps into an ocean somewhere.

brandmeyer 6y ago

True! There are alternatives that are net-absorptive, too. But until we can set a market price for CO2 emissions, current emitters will continue to treat it as a zero-cost externality.