4 ms·

This is certainly a bold plan. I wonder (doubt, even) if PREPA will be able to execute it. Segmenting the grid is going to introduce a lot of trade-offs. Small

by g_sch 7y ago

This is certainly a bold plan. I wonder (doubt, even) if PREPA will be able to execute it. Segmenting the grid is going to introduce a lot of trade-offs. Smaller segments means that dips and spikes in load are going to create greater differences in frequency, and as such require faster demand response to create the same level of frequency regulation as a larger grid. Renewables such as solar and wind are already not known for being particularly friendly to grid operations as their output can vary quickly and unpredictably. On a smaller grid, these variances are going to be magnified. They also can't be used for demand response by themselves - you can't tell the sun to start shining on demand. Batteries can effectively smooth the load by providing operating reserve, but the proposed 940 MW of battery capacity (I couldn't figure out from the original report [0] how much MWh storage they are proposing -- there seem to be some numbers missing) is significantly larger than any other battery-based grid energy storage plan that I'm aware of. I hope they can pull off this plan, and they are able to make it work for the people of PR as well. [0] https://drive.google.com/open?id=1oupTRdHXRHzc6UuKUdmFp9eWKPR0CZd5 https://drive.google.com/open?id=1oupTRdHXRHzc6UuKUdmFp9eWKP...

duxup 7y ago
>I wonder (doubt, even) if PREPA will be able to execute it. Sadly this might say a lot more about PREPA than anything else.
- deleted 7y ago
  [deleted]
- g_sch 7y ago
  After looking it up, I discovered PREPA was privatized shortly after Hurricane Maria. So perhaps they have new sources of capital. Though I'm still not sure (or at least not confident) that anyone with a profit motive is going to invest heavily in Puerto Rico's grid.
  - Vivtek 7y ago
    There was talk that Duke Energy was interested in a purchase. I haven't heard anything recently.
  - jandrese 7y ago
    IIRC the PREPA privatization was more of a gift to some well connected people and less about modernizing or improving the company.
    - jtuente 7y ago
      There's corruption all around PREPA, just a nasty situation. http://ieefa.org/ieefa-report-effects-of-long-running-oil-purchase-scandal-undermine-privatization-and-contract-reform-initiatives-at-prepa/ http://ieefa.org/ieefa-report-effects-of-long-running-oil-pu...
    - andrekandre 7y ago
      also known as “disaster capitalism” [1] [1] https://en.m.wikipedia.org/wiki/The_Shock_Doctrine https://en.m.wikipedia.org/wiki/The_Shock_Doctrine
Vivtek 7y ago
The Puerto Rican grid is already partly segmented - Mayagüez was on a minigrid even before Hurricane Maria. The fact that Mayagüez was the only city on the island that retained power after the hurricane was not lost even on PREPA. (An aside: I first made it over to Mayagüez in the second week after the storm, hoping to find a cell phone I could use for Internet access - National Hardware not only had power but working telecommunications, so I could actually buy a few supplies on my Visa card. And their air conditioning was working. It was literally like walking through another world.) Adjuntas is working on getting their downtown on a separate solar minigrid. Everybody thought this was a particularly good idea this week, as the power was out downtown on Wednesday.
namibj 7y ago
Solar can be regulated pretty well. If you can get good clocks to the inverters, you could actually lock the output to the fixed grid frequency, using slower, minute phase shifts coordinated centrally to shift load across the grid by artificially creating the speed-of-light phase difference you get over long transmission lines. Without that central coordination you'd rely on the inverters being staggered to shut off at slightly different overfrequencies. This tends to make some inverters run less overall though, creating game theoretic issues you could fix by rotating that shut off slowly over the whole range, creating time averaging. Alternatively you can use inverters that regulate output power down with increasing frequency. A simple P (of the PID) controller to keep the frequency in check. You'd probably want a centralized I component to be applied though, for reason of preventing long-term phase drift. Just tell the inverters once a day/week what I their control loop should target, and it's solved. This low-bandwidth signal isn't hard to transmit either. Just try to force them to gradually change from the old to the new I, because otherwise you get ugly spiking/oscillations when they all apply the change. It should be slow enough that synchronous machinery on the grid sufficiently dampens any such oscillations.
- drcross 7y ago
  It's interesting to read your comment. Do you work in frequently regulation? Do you think any parallel concepts from the ethernet world could be deployed for decentralised frequency regulation where Carrier-sense multiple access with collision detection (CSMA/CD) is used?
  - namibj 7y ago
    In hope of you still reading this: No, I don't work in frequency regulation. If you want to hire me into it however, I might be interested. I don't know what sort of concepts you mean, and as I said earlier, the main issue is how you get the grid as a whole to do large-distance load-balancing/load-shifting. These decisions can't be made local for lack of insight into how loaded long-distance transmission lines are and how throttled different regions are, and therefore which regions you want the power to come from. There are certain industrial loads that can be time-shifted, and some that are only worthwhile to operate at lower prices, where reduced utilization (and thus increased capex) has to be hedged against higher energy prices (and thus increased opex). If you get fine-grained surge pricing for consumers combined with some forecasting and automatic decision making to e.g. shut devices off during surges or incentivize people to use the electric shower/kettle at a different point in time, you should get by without any fossil fuels at all. Think like adjusting clock speeds/power targets of servers depending on momentary prices, to best balance capex and opex (batch jobs only), or adjust the energy you expend on video encoding for live streams to balance perceived quality and costs. Obviously adjust EV charging. With e.g. minimal range targets for different points in time, or user-friendly ways of expressing the trade-off between higher range for the next day (and thus more freedom) and higher costs (kWh required during the EV's stay at the charger). It could even go to distribute charging stops based on forecasts for energy prices/availability, so you use the flexibility in when exactly to stop on a long trip for load-shaping the power grid.
gingabriska 7y ago
But this is today possible using cloud. Earlier we had power plants designed in the old way because we didn't have computers which could analyze and predict and neither we had the solid state thyristors. So today you can hookup lots of control systems to cloud. This is similar to flying wing aircraft which were not feasible back in time but now they are making their way into mainstream.
- pjc50 7y ago
  The problem in PR is not so much the cloud as other kinds of weather - hurricanes. Cloud-based central control is a liability in situations where infrastructure is widely damaged.
manicdee 7y ago
You can’t make the sun shine or wind blow but you can generate below capacity to have reserve available on demand, or you can add storage to provide smoothing and contingency. 1GW of battery is only a dozen projects smaller than the Hornsdale Power Reserve. It’s been done, now it is a case of replicating a successful project.
bsder 7y ago
> Segmenting the grid is going to introduce a lot of trade-offs. Smaller segments means that dips and spikes in load are going to create greater differences in frequency, and as such require faster demand response to create the same level of frequency regulation as a larger grid. Why wouldn't you make inter-grid (grid-to-grid) interconnects high voltage DC and use a DC-to-AC conversion to produce AC for intra-grid (grid-to-user) connections?

by g_sch 7y ago

duxup 7y ago

>I wonder (doubt, even) if PREPA will be able to execute it. Sadly this might say a lot more about PREPA than anything else.

deleted 7y ago
[deleted]
g_sch 7y ago
After looking it up, I discovered PREPA was privatized shortly after Hurricane Maria. So perhaps they have new sources of capital. Though I'm still not sure (or at least not confident) that anyone with a profit motive is going to invest heavily in Puerto Rico's grid.
- Vivtek 7y ago
  There was talk that Duke Energy was interested in a purchase. I haven't heard anything recently.
- jandrese 7y ago
  IIRC the PREPA privatization was more of a gift to some well connected people and less about modernizing or improving the company.
  - jtuente 7y ago
    There's corruption all around PREPA, just a nasty situation. http://ieefa.org/ieefa-report-effects-of-long-running-oil-purchase-scandal-undermine-privatization-and-contract-reform-initiatives-at-prepa/ http://ieefa.org/ieefa-report-effects-of-long-running-oil-pu...
  - andrekandre 7y ago
    also known as “disaster capitalism” [1] [1] https://en.m.wikipedia.org/wiki/The_Shock_Doctrine https://en.m.wikipedia.org/wiki/The_Shock_Doctrine

Vivtek 7y ago

The Puerto Rican grid is already partly segmented - Mayagüez was on a minigrid even before Hurricane Maria. The fact that Mayagüez was the only city on the island that retained power after the hurricane was not lost even on PREPA. (An aside: I first made it over to Mayagüez in the second week after the storm, hoping to find a cell phone I could use for Internet access - National Hardware not only had power but working telecommunications, so I could actually buy a few supplies on my Visa card. And their air conditioning was working. It was literally like walking through another world.) Adjuntas is working on getting their downtown on a separate solar minigrid. Everybody thought this was a particularly good idea this week, as the power was out downtown on Wednesday.

namibj 7y ago

Solar can be regulated pretty well. If you can get good clocks to the inverters, you could actually lock the output to the fixed grid frequency, using slower, minute phase shifts coordinated centrally to shift load across the grid by artificially creating the speed-of-light phase difference you get over long transmission lines. Without that central coordination you'd rely on the inverters being staggered to shut off at slightly different overfrequencies. This tends to make some inverters run less overall though, creating game theoretic issues you could fix by rotating that shut off slowly over the whole range, creating time averaging. Alternatively you can use inverters that regulate output power down with increasing frequency. A simple P (of the PID) controller to keep the frequency in check. You'd probably want a centralized I component to be applied though, for reason of preventing long-term phase drift. Just tell the inverters once a day/week what I their control loop should target, and it's solved. This low-bandwidth signal isn't hard to transmit either. Just try to force them to gradually change from the old to the new I, because otherwise you get ugly spiking/oscillations when they all apply the change. It should be slow enough that synchronous machinery on the grid sufficiently dampens any such oscillations.

drcross 7y ago
It's interesting to read your comment. Do you work in frequently regulation? Do you think any parallel concepts from the ethernet world could be deployed for decentralised frequency regulation where Carrier-sense multiple access with collision detection (CSMA/CD) is used?
- namibj 7y ago
  In hope of you still reading this: No, I don't work in frequency regulation. If you want to hire me into it however, I might be interested. I don't know what sort of concepts you mean, and as I said earlier, the main issue is how you get the grid as a whole to do large-distance load-balancing/load-shifting. These decisions can't be made local for lack of insight into how loaded long-distance transmission lines are and how throttled different regions are, and therefore which regions you want the power to come from. There are certain industrial loads that can be time-shifted, and some that are only worthwhile to operate at lower prices, where reduced utilization (and thus increased capex) has to be hedged against higher energy prices (and thus increased opex). If you get fine-grained surge pricing for consumers combined with some forecasting and automatic decision making to e.g. shut devices off during surges or incentivize people to use the electric shower/kettle at a different point in time, you should get by without any fossil fuels at all. Think like adjusting clock speeds/power targets of servers depending on momentary prices, to best balance capex and opex (batch jobs only), or adjust the energy you expend on video encoding for live streams to balance perceived quality and costs. Obviously adjust EV charging. With e.g. minimal range targets for different points in time, or user-friendly ways of expressing the trade-off between higher range for the next day (and thus more freedom) and higher costs (kWh required during the EV's stay at the charger). It could even go to distribute charging stops based on forecasts for energy prices/availability, so you use the flexibility in when exactly to stop on a long trip for load-shaping the power grid.

gingabriska 7y ago

But this is today possible using cloud. Earlier we had power plants designed in the old way because we didn't have computers which could analyze and predict and neither we had the solid state thyristors. So today you can hookup lots of control systems to cloud. This is similar to flying wing aircraft which were not feasible back in time but now they are making their way into mainstream.

pjc50 7y ago
The problem in PR is not so much the cloud as other kinds of weather - hurricanes. Cloud-based central control is a liability in situations where infrastructure is widely damaged.

manicdee 7y ago

You can’t make the sun shine or wind blow but you can generate below capacity to have reserve available on demand, or you can add storage to provide smoothing and contingency. 1GW of battery is only a dozen projects smaller than the Hornsdale Power Reserve. It’s been done, now it is a case of replicating a successful project.

bsder 7y ago

> Segmenting the grid is going to introduce a lot of trade-offs. Smaller segments means that dips and spikes in load are going to create greater differences in frequency, and as such require faster demand response to create the same level of frequency regulation as a larger grid. Why wouldn't you make inter-grid (grid-to-grid) interconnects high voltage DC and use a DC-to-AC conversion to produce AC for intra-grid (grid-to-user) connections?