4 ms·

> This is a bit of a nitpick, but this is a physical impossibility. On a AC electric network, if the power input is higher than the power output, the frequency

by jhgb 5y ago

> This is a bit of a nitpick, but this is a physical impossibility. On a AC electric network, if the power input is higher than the power output, the frequency of the current goes up quite quickly, until the grid collapses (because there are security to avoid frequency deviation). You cannot “not consume all the power you produce”, all you can do is not producing as much as you could. I probably should have said "all the power you could produce", since for example with photovoltaics you can produce at any moment any amount of power from zero up to the MPPT point on the I/V curve, depending on how much charge you remove from the panel. I hope this clears it up. > Btw, I'm interested by the sources of your “1.6 GWh of storage for your 1000 MW nuclear” because it sounds really low to me I used the figures in the 2018 Zerrahn et al. article: https://www.sciencedirect.com/science/article/pii/S0014292118301107 https://www.sciencedirect.com/science/article/pii/S001429211... > I did a simulation[1] a while ago based on French data, for a 100% RE scenario and my calculation arrived at around 250GWh per GW of installed capacity. Maybe you've just taken Sinn's approach instead of Zerrahn's? That number would seem to fit it.

littlestymaar 5y ago
> I used the figures in the 2018 Zerrahn et al. article: https://www.sciencedirect.com/science/article/pii/S001429211 https://www.sciencedirect.com/science/article/pii/S001429211... Thanks for the link ! > Maybe you've just taken Sinn's approach instead of Zerrahn's? That number would seem to fit it. I wasn't aware of that paper (thanks again!), but from skimming Sinn's paper, our methodology seems to be pretty similar. I'm even more excited to read Zerrahn's paper now!
- littlestymaar 5y ago
  Ok so I read Zerrahn's paper, and I have to admit I didn't expect to be that shocked by the methodology. Of course I'm a bit biased because my own work is really close to Sinn's which is criticized in this paper, but this paper really makes me think the author didn't even try to understand what Sinn studied in their paper: Zerrahn seems to believe that Sinn's scenario stores all the energy because they don't want to waste electricity, but it doesn't occur to them that Sinn's stores all that electricity because at some point the grid will needs it!. In fact, I think the culprit is just using RLDCs (residual load duration curves) instead of time series, because this way you just erase the temporal dimension of the problem, which is − unfortunately − the most important one. For instance, in my own data (France, year 2017, for the record the scenario was 100% RE) from the first of January 12am, to the 3rd at 3pm the wind capacity factor barely exceed 10%, three days in a row. For this period only you'd need 3TWh of storage[1]! No reasonable level[2] of curtailment is gonna help here. [1]: of course it doesn't have to be storage, you just need 50GW of controllable power and any fossil fuel would work (and that's what the Danish do for instance) but this is outside of the scope of this discussion, which is about how storage allows you to avoid pairing RE with fossil sources. [2]: I assume that nobody would consider something above 90% curtailment to be reasonable.
  - jhgb 5y ago
    > but it doesn't occur to them that Sinn's stores all that electricity because at some point the grid will needs it! I'm pretty sure that they understand that. What they don't understand (and what I don't understand) is why is Sinn making the amount artificially high by ignoring the economics. I immediately understood what Zerrahn was getting at, and even before I knew how different authors approached this problem in literature, I would have myself intuitively gone for an approach like Zerrahn's. MRTS is surely not a difficult concept to grasp. > For instance, in my own data (France, year 2017, for the record the scenario was 100% RE) from the first of January 12am, to the 3rd at 3pm the wind capacity factor barely exceed 10%, three days in a row. For this period only you'd need 3TWh of storage! No reasonable level[1] of curtailment is gonna help here. I can't tell you what Zerrahn's approach would tell you for the French grid. You can't really extrapolate that from German results. You'd have to pretty much re-do the whole work, including getting equivalent data for the French grid.
    - littlestymaar 5y ago
      > I'm pretty sure that they understand that. What they don't understand (and what I don't understand) is why is Sinn making the amount artificially high by ignoring the economics. I immediately understood what Zerrahn was getting at, and even before I knew how different authors approached this problem in literature, I would have myself intuitively gone for an approach like Zerrahn's. MRTS is surely not a difficult concept to grasp. It's not about being difficult to grasp, it's about whether they are the right tool for the job. Which they aren't, because the temporality of the phenomenon disappear, while it is the single most crucial factor when talking about storage: 24 hours without wind in a row have a dramatically different impact from 24 days each without wind for one hour. In the first case you need enough storage for an entire day, while in the second case all you need is one hour of storage! (And that's where the two orders of magnitude come from: «several days» being ~100 times as long as «1 hour». The storage you need is strictly superior the sum of consecutive hours with a positive residual load (minus what can be produced by you non-renewable plants), to calculate this value you must keep the time (and also factor in the availability and economics of your back-up non-renewable power supply if you want to go one step further, which neither I nor Sinn did). Sinn doesn't take economics in account, because it's not relevant to the discussion here, it's all about physics here. (And Sinn being an economist, he really deserves credit for focusing on the physics aspect). > I can't tell you what Zerrahn's approach would tell you for the French grid. You can't really extrapolate that from German results. You'd have to pretty much re-do the whole work, including getting equivalent data for the French grid. It would be easier to just grab the German data used by Zerrahn to reproduce Sinn's findings (because they claim them to be easily accessible). Maybe I'll have some time later in the week to do so.

by jhgb 5y ago

littlestymaar 5y ago

> I used the figures in the 2018 Zerrahn et al. article: https://www.sciencedirect.com/science/article/pii/S001429211 https://www.sciencedirect.com/science/article/pii/S001429211... Thanks for the link ! > Maybe you've just taken Sinn's approach instead of Zerrahn's? That number would seem to fit it. I wasn't aware of that paper (thanks again!), but from skimming Sinn's paper, our methodology seems to be pretty similar. I'm even more excited to read Zerrahn's paper now!

littlestymaar 5y ago
Ok so I read Zerrahn's paper, and I have to admit I didn't expect to be that shocked by the methodology. Of course I'm a bit biased because my own work is really close to Sinn's which is criticized in this paper, but this paper really makes me think the author didn't even try to understand what Sinn studied in their paper: Zerrahn seems to believe that Sinn's scenario stores all the energy because they don't want to waste electricity, but it doesn't occur to them that Sinn's stores all that electricity because at some point the grid will needs it!. In fact, I think the culprit is just using RLDCs (residual load duration curves) instead of time series, because this way you just erase the temporal dimension of the problem, which is − unfortunately − the most important one. For instance, in my own data (France, year 2017, for the record the scenario was 100% RE) from the first of January 12am, to the 3rd at 3pm the wind capacity factor barely exceed 10%, three days in a row. For this period only you'd need 3TWh of storage[1]! No reasonable level[2] of curtailment is gonna help here. [1]: of course it doesn't have to be storage, you just need 50GW of controllable power and any fossil fuel would work (and that's what the Danish do for instance) but this is outside of the scope of this discussion, which is about how storage allows you to avoid pairing RE with fossil sources. [2]: I assume that nobody would consider something above 90% curtailment to be reasonable.
- jhgb 5y ago
  > but it doesn't occur to them that Sinn's stores all that electricity because at some point the grid will needs it! I'm pretty sure that they understand that. What they don't understand (and what I don't understand) is why is Sinn making the amount artificially high by ignoring the economics. I immediately understood what Zerrahn was getting at, and even before I knew how different authors approached this problem in literature, I would have myself intuitively gone for an approach like Zerrahn's. MRTS is surely not a difficult concept to grasp. > For instance, in my own data (France, year 2017, for the record the scenario was 100% RE) from the first of January 12am, to the 3rd at 3pm the wind capacity factor barely exceed 10%, three days in a row. For this period only you'd need 3TWh of storage! No reasonable level[1] of curtailment is gonna help here. I can't tell you what Zerrahn's approach would tell you for the French grid. You can't really extrapolate that from German results. You'd have to pretty much re-do the whole work, including getting equivalent data for the French grid.
  - littlestymaar 5y ago
    > I'm pretty sure that they understand that. What they don't understand (and what I don't understand) is why is Sinn making the amount artificially high by ignoring the economics. I immediately understood what Zerrahn was getting at, and even before I knew how different authors approached this problem in literature, I would have myself intuitively gone for an approach like Zerrahn's. MRTS is surely not a difficult concept to grasp. It's not about being difficult to grasp, it's about whether they are the right tool for the job. Which they aren't, because the temporality of the phenomenon disappear, while it is the single most crucial factor when talking about storage: 24 hours without wind in a row have a dramatically different impact from 24 days each without wind for one hour. In the first case you need enough storage for an entire day, while in the second case all you need is one hour of storage! (And that's where the two orders of magnitude come from: «several days» being ~100 times as long as «1 hour». The storage you need is strictly superior the sum of consecutive hours with a positive residual load (minus what can be produced by you non-renewable plants), to calculate this value you must keep the time (and also factor in the availability and economics of your back-up non-renewable power supply if you want to go one step further, which neither I nor Sinn did). Sinn doesn't take economics in account, because it's not relevant to the discussion here, it's all about physics here. (And Sinn being an economist, he really deserves credit for focusing on the physics aspect). > I can't tell you what Zerrahn's approach would tell you for the French grid. You can't really extrapolate that from German results. You'd have to pretty much re-do the whole work, including getting equivalent data for the French grid. It would be easier to just grab the German data used by Zerrahn to reproduce Sinn's findings (because they claim them to be easily accessible). Maybe I'll have some time later in the week to do so.