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You say they leave the batteries charged when the power is turning bad. Do you have a benefit of hosting the batteries at other times? For instance if the power

You say they leave the batteries charged when the power is turning bad. Do you have a benefit of hosting the batteries at other times? For instance if the power goes out when the weather isn’t bad, do you typically have enough charge to make it through the outage? I’m also curious if your neighbors benefit from your battery during outages.

mauvehaus 2y ago
De jure, I think they're pretty free to do with them what they want. De facto they leave the batteries pretty fully charged most of the time. AIUI, they'd have to have a disconnect somewhere upstream of us to let us back feed the grid during an outage, otherwise they couldn't safely work on the lines. And they'd need a way to enable and disable back feeding remotely[0] to allow them to work on anything between that hypothetical disconnect and us. At the moment, none of that exists, so only we benefit from the powerwalls. It's also 34kwh in the pair of batteries. That wouldn't add up to too many household-days if you started adding households. You'd have to do some fancy switching to not overwhelm the relatively few powerwalls in an outage. For context, based on our usage, we're at about three days of backup just for us [1]. It doesn't take much imagination to come up with a scenario where that happens where we are. We are the very last pole. [0] Which in turn requires connectivity. The cell network here is sparse, to put it mildly. We just got fiber, but that's hanging on the same poles as the power. The fail-safe mode for no grid and no connectivity is to not backfeed, but at that point, you're back where you are today. [1] It's the fridge, mostly.
- mprovost 2y ago
  You don't need internet for everything... by definition these systems are connected to the grid by wires which can transmit a limited signal. Utilities in countries such as NZ have managed load for decades by turning hot water heaters in customers' homes off and on remotely with ripple control units which transmit a signal over the power line itself. [0] [0] https://en.wikipedia.org/wiki/Zellweger_off-peak https://en.wikipedia.org/wiki/Zellweger_off-peak
  - bobbob1921 2y ago
    This is correct, an added benefit is if the power poles are actually down then the communication over the powerlines would be down, but that’s fine as power couldn’t be sent over the lines anyway in that case. What I wonder about/have concerns in regards to, is as someone else mentioned the relays required to turn on and off backfeeding in terms of electrical Utility workers having to de-energize a line to perform work. I’m not too sure that these workers can entrust their lives to the reliability of various (multiple) relays to not sporadically switch back on once the line has been confirmed as de-energized (in other words depending on the relay not to malfunction and re-energized while the workers are working upon the line ) I assume there will be some types of tools to monitor / alarm the workers for exactly this scenario (ie something they can attach to the line while it is being worked on and if it becomes re-energized an alarm will sound).
    - Shog9 2y ago
      Generally grid backfeed capability for these systems is predicated on the presence of a stable voltage and frequency already on the grid - this is both a safety measure and a practical necessity, as the inverter needs to synchronize with the grid frequency.
      - crznp 2y ago
        Just to add the terms: a "grid following" matches the grid's voltage/frequency, so it only works when connected to the grid. A "grid forming" system can set its voltage/frequency independently and can only work off-grid It sounds like mauvehaus is talking about a hybrid system that has both grid following and grid forming capabilities: switching to grid-forming as it disconnects. But that means that you can't power your neighbors.
      - screcth 2y ago
        I wonder why it is that real world systems don't use a GPS receiver to obtain a 1 Hz signal that's synchronized to the GPS clock and then generate a local 50/60 Hz clock for grid synchronization. I'm just an EE with no experience in real power systems, so this may be absurd to someone who knows how this stuff works.
- foobarian 2y ago
  Question: when an actual power outage happens, does the powerwall backup take over immediately without loss of power to the household? Or if not how long does it take to switch the grid interlock? Just wondering if this would be suitable as a UPS for my computers.
  - mauvehaus 2y ago
    It's entirely transparent. The app will notify after the power has been off for some amount of time to avoid nuisance notifications for flickers or brief outages.

mauvehaus 2y ago

De jure, I think they're pretty free to do with them what they want. De facto they leave the batteries pretty fully charged most of the time. AIUI, they'd have to have a disconnect somewhere upstream of us to let us back feed the grid during an outage, otherwise they couldn't safely work on the lines. And they'd need a way to enable and disable back feeding remotely[0] to allow them to work on anything between that hypothetical disconnect and us. At the moment, none of that exists, so only we benefit from the powerwalls. It's also 34kwh in the pair of batteries. That wouldn't add up to too many household-days if you started adding households. You'd have to do some fancy switching to not overwhelm the relatively few powerwalls in an outage. For context, based on our usage, we're at about three days of backup just for us [1]. It doesn't take much imagination to come up with a scenario where that happens where we are. We are the very last pole. [0] Which in turn requires connectivity. The cell network here is sparse, to put it mildly. We just got fiber, but that's hanging on the same poles as the power. The fail-safe mode for no grid and no connectivity is to not backfeed, but at that point, you're back where you are today. [1] It's the fridge, mostly.

mprovost 2y ago
You don't need internet for everything... by definition these systems are connected to the grid by wires which can transmit a limited signal. Utilities in countries such as NZ have managed load for decades by turning hot water heaters in customers' homes off and on remotely with ripple control units which transmit a signal over the power line itself. [0] [0] https://en.wikipedia.org/wiki/Zellweger_off-peak https://en.wikipedia.org/wiki/Zellweger_off-peak
- bobbob1921 2y ago
  This is correct, an added benefit is if the power poles are actually down then the communication over the powerlines would be down, but that’s fine as power couldn’t be sent over the lines anyway in that case. What I wonder about/have concerns in regards to, is as someone else mentioned the relays required to turn on and off backfeeding in terms of electrical Utility workers having to de-energize a line to perform work. I’m not too sure that these workers can entrust their lives to the reliability of various (multiple) relays to not sporadically switch back on once the line has been confirmed as de-energized (in other words depending on the relay not to malfunction and re-energized while the workers are working upon the line ) I assume there will be some types of tools to monitor / alarm the workers for exactly this scenario (ie something they can attach to the line while it is being worked on and if it becomes re-energized an alarm will sound).
  - Shog9 2y ago
    Generally grid backfeed capability for these systems is predicated on the presence of a stable voltage and frequency already on the grid - this is both a safety measure and a practical necessity, as the inverter needs to synchronize with the grid frequency.
    - crznp 2y ago
      Just to add the terms: a "grid following" matches the grid's voltage/frequency, so it only works when connected to the grid. A "grid forming" system can set its voltage/frequency independently and can only work off-grid It sounds like mauvehaus is talking about a hybrid system that has both grid following and grid forming capabilities: switching to grid-forming as it disconnects. But that means that you can't power your neighbors.
    - screcth 2y ago
      I wonder why it is that real world systems don't use a GPS receiver to obtain a 1 Hz signal that's synchronized to the GPS clock and then generate a local 50/60 Hz clock for grid synchronization. I'm just an EE with no experience in real power systems, so this may be absurd to someone who knows how this stuff works.
foobarian 2y ago
Question: when an actual power outage happens, does the powerwall backup take over immediately without loss of power to the household? Or if not how long does it take to switch the grid interlock? Just wondering if this would be suitable as a UPS for my computers.
- mauvehaus 2y ago
  It's entirely transparent. The app will notify after the power has been off for some amount of time to avoid nuisance notifications for flickers or brief outages.