6 ms·

Word of warning: Just like solar inverters, not every home battery system is made to be grid independent. For instance, the Tesla Powerwall does, but the Sessy

Word of warning: Just like solar inverters, not every home battery system is made to be grid independent. For instance, the Tesla Powerwall does, but the Sessy home battery does not and needs an active AC sinus on the grid. Even if you do have a home battery system that can generate its own sinusoidal AC wave, you still need an (automatic) transfer switch to disconnect your home from the failed grid, otherwise your home battery might be attempting to power the entire (local) grid which of course doesn't work.

chasd00 4y ago
> otherwise your home battery might be attempting to power the entire (local) grid which of course doesn't work. and some random line worker may think there's no electricity flowing when there is.
- bityard 4y ago
  Line workers are trained to never assume a line is de-energized, those that forget don't live very long. (But yes, backfeeding the grid during an outage is dangerous and highly against code.)
- Syonyk 4y ago
  > and some random line worker may think there's no electricity flowing when there is. If you have lines in an unknown state, step 1 is to put them in a known state. For power line work, this involves grounding all the phases and neutral together at both ends of the section you intend to work on. Good luck ringing a dead short with your home inverter/generator/etc.
  - benj111 4y ago
    Off topic but I've always thought of grounding as conceptually making the entire earth a part of the circuit and so dispersing the energy over a very large area. Is that conceptualisation correct? What happens is you have say a conductive (iron rich) top layer. Is there still the potential to dangerously energise the ground? I assume so because that's basically what water and electricity does?
    - everforward 4y ago
      Not an electrician, so someone else may have better info. Grounding provides an alternate path for the flow of electricity, so if a wire comes loose and ends up touching a copper pipe or something the current gets routed into the ground rather than into pipes or flammable wood or something. Dispersal over an area isn't directly the goal, but it helps. By dispersing the current into an extremely large object, you don't really have to worry about the object building up a charge to the point where you can't flow current into it anymore. Yes, you can dangerously energize the ground. You can dangerously energize almost anything with enough voltage. E.g. a Tesla coil has enough voltage to conduct through air. Don't try to test it (obviously), but I don't think a standard 110V house grounding has enough voltage to dangerously energize ground over any significant distance.
    - gubby 4y ago
      Grounding isn't really about dispersing energy over an area, it's about creating a situation where faults can be detected and circuits automatically opened to prevent shocks or fires. It actually gets very involved to reason through the exact purpose of ground connections when you start considering all the different types and combinations of faults (indoors, outdoors, person in contact with true earth, person touching exposed metal pipe, etc etc).
Ajedi32 4y ago
What's the point of a home battery system that doesn't work when the grid is down? What else would you use the battery for?
- ok_dad 4y ago
  For homes, you store solar in it and discharge at night to reduce bills. For commercial, you do peak shaving and load shifting to reduce bills. Also, you can sell your battery capacity to some companies and they can aggregate it with other homes in your area to sell the capacity to the grid during peaks, to eek out a bit more value.
- Chris_Newton 4y ago
  What else would you use the battery for? Efficiency. You can store excess energy from local microgeneration, particularly solar, that can be used later. With our current pricing model in the UK, that is several times cheaper than selling the excess power to the grid for a token return and then paying full price to have the same amount back from your mains supply later. Some systems can even be configured to charge their battery from the mains at quiet times (when, again in a typical UK pricing model, the cost-per-unit can be much lower) if there isn’t enough local generation to fully charge it, for example in the middle of winter.
- calsy 4y ago
  A home battery system stores the excess solar energy generated during the day so you can use it at night. It's about long term savings on electricity bills.
- jandrese 4y ago
  It can be useful in cases where you have Time of Use metering. You can charge your battery in the middle of the day when energy is cheap due to solar overproduction and then draw down the battery in the evening when power is expensive. If you have it tied to solar panels you can even charge the battery with solar and then sell it back to the grid in the evening. In a few places you can even do "peak shaving" where the power company will give you a pretty nice bonus for switching your battery into grid-feed mode when the demand is so high that they are considering turning on expensive peaker plants. Most people unfortunately can't take advantage of this, but most battery packs are also suitable for off-grid use.
brnt 4y ago
> not every home battery system is made to be grid independent. In Europe you should check if grid-independence is even legal. In some places it is not.
- LtWorf 4y ago
  It's legal, they just won't pay you subsidies for solar panels.
  - brnt 4y ago
    If and how panels are incentivized varies from country to country.
- kiratp 4y ago
  I've always wondered, what if you were to wire up a panel and one light to the grid, but the then rest of the house is on a separate independent circuit? Technically the house is on-grid...
  - cryptonector 4y ago
    You could get caught if ever there's a fire, or you need an electrician and you forget to undo that before the electrician gets there, or if there's some sort of code inspection.
    - benj111 4y ago
      I don't think it's that simple. These circuits are already a thing in the form of solar powered security lights, and shed lighting kits. I suspect the dividing line is voltage? >50v systems in cars are treated differently, so maybe the same for houses, you probably don't need that much for lighting anyway.
- dijonman2 4y ago
  This is one of those laws that you should want to break. I’d rather have energy independence than follow rules.

chasd00 4y ago

> otherwise your home battery might be attempting to power the entire (local) grid which of course doesn't work. and some random line worker may think there's no electricity flowing when there is.

bityard 4y ago
Line workers are trained to never assume a line is de-energized, those that forget don't live very long. (But yes, backfeeding the grid during an outage is dangerous and highly against code.)
Syonyk 4y ago
> and some random line worker may think there's no electricity flowing when there is. If you have lines in an unknown state, step 1 is to put them in a known state. For power line work, this involves grounding all the phases and neutral together at both ends of the section you intend to work on. Good luck ringing a dead short with your home inverter/generator/etc.
- benj111 4y ago
  Off topic but I've always thought of grounding as conceptually making the entire earth a part of the circuit and so dispersing the energy over a very large area. Is that conceptualisation correct? What happens is you have say a conductive (iron rich) top layer. Is there still the potential to dangerously energise the ground? I assume so because that's basically what water and electricity does?
  - everforward 4y ago
    Not an electrician, so someone else may have better info. Grounding provides an alternate path for the flow of electricity, so if a wire comes loose and ends up touching a copper pipe or something the current gets routed into the ground rather than into pipes or flammable wood or something. Dispersal over an area isn't directly the goal, but it helps. By dispersing the current into an extremely large object, you don't really have to worry about the object building up a charge to the point where you can't flow current into it anymore. Yes, you can dangerously energize the ground. You can dangerously energize almost anything with enough voltage. E.g. a Tesla coil has enough voltage to conduct through air. Don't try to test it (obviously), but I don't think a standard 110V house grounding has enough voltage to dangerously energize ground over any significant distance.
  - gubby 4y ago
    Grounding isn't really about dispersing energy over an area, it's about creating a situation where faults can be detected and circuits automatically opened to prevent shocks or fires. It actually gets very involved to reason through the exact purpose of ground connections when you start considering all the different types and combinations of faults (indoors, outdoors, person in contact with true earth, person touching exposed metal pipe, etc etc).

Ajedi32 4y ago

What's the point of a home battery system that doesn't work when the grid is down? What else would you use the battery for?

ok_dad 4y ago
For homes, you store solar in it and discharge at night to reduce bills. For commercial, you do peak shaving and load shifting to reduce bills. Also, you can sell your battery capacity to some companies and they can aggregate it with other homes in your area to sell the capacity to the grid during peaks, to eek out a bit more value.
Chris_Newton 4y ago
What else would you use the battery for? Efficiency. You can store excess energy from local microgeneration, particularly solar, that can be used later. With our current pricing model in the UK, that is several times cheaper than selling the excess power to the grid for a token return and then paying full price to have the same amount back from your mains supply later. Some systems can even be configured to charge their battery from the mains at quiet times (when, again in a typical UK pricing model, the cost-per-unit can be much lower) if there isn’t enough local generation to fully charge it, for example in the middle of winter.
calsy 4y ago
A home battery system stores the excess solar energy generated during the day so you can use it at night. It's about long term savings on electricity bills.
jandrese 4y ago
It can be useful in cases where you have Time of Use metering. You can charge your battery in the middle of the day when energy is cheap due to solar overproduction and then draw down the battery in the evening when power is expensive. If you have it tied to solar panels you can even charge the battery with solar and then sell it back to the grid in the evening. In a few places you can even do "peak shaving" where the power company will give you a pretty nice bonus for switching your battery into grid-feed mode when the demand is so high that they are considering turning on expensive peaker plants. Most people unfortunately can't take advantage of this, but most battery packs are also suitable for off-grid use.

brnt 4y ago

> not every home battery system is made to be grid independent. In Europe you should check if grid-independence is even legal. In some places it is not.

LtWorf 4y ago
It's legal, they just won't pay you subsidies for solar panels.
- brnt 4y ago
  If and how panels are incentivized varies from country to country.
kiratp 4y ago
I've always wondered, what if you were to wire up a panel and one light to the grid, but the then rest of the house is on a separate independent circuit? Technically the house is on-grid...
- cryptonector 4y ago
  You could get caught if ever there's a fire, or you need an electrician and you forget to undo that before the electrician gets there, or if there's some sort of code inspection.
  - benj111 4y ago
    I don't think it's that simple. These circuits are already a thing in the form of solar powered security lights, and shed lighting kits. I suspect the dividing line is voltage? >50v systems in cars are treated differently, so maybe the same for houses, you probably don't need that much for lighting anyway.
dijonman2 4y ago
This is one of those laws that you should want to break. I’d rather have energy independence than follow rules.