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>because a grid connected system is supposed to shut down when the power fails, the only way out is to stop being grid connected On that note I believe there a

>because a grid connected system is supposed to shut down when the power fails, the only way out is to stop being grid connected On that note I believe there are electrical devices that automatically disconnect you from the grid. It allows you to use a battery / solar array to power the house, while not feeding back any power to the grid such that you don't harm anyone trying to fix the grid. Now whether or not this is allowed is very much dependent on which country you live in. This video is in the UK and demonstrate such a device: https://www.youtube.com/watch?v=gP51JjnWvLo https://www.youtube.com/watch?v=gP51JjnWvLo

chiefalchemist 5y ago
> Now whether or not this is allowed is very much dependent on which country you live in. So basically, to clarify, you're either 100% on the grid, or 100% off. There's no using both depending on conditions, is that it?
- ghaff 5y ago
  You can have a backup generator (with a transfer switch)--which many do in more rural areas at least in the US.
- bluGill 5y ago
  I'm not sure about Ontario, but in many places you can be grid tied which means that you use both. While it is possible to change depending on conditions, the equipment to do that isn't very common. Solar systems are just starting to come out with single outlets that can run while the sun shines without the grid, but that is rare, most assume 100% on grid, or 100% off grid.
- iso1210 5y ago
  The vehicle I'm currently sat in at the moment has a 32A electrical cable running in the back, currently pulling 2881W into a magic box provided by victron inverter/charger, that is used to charge a battery (which is currently fully charged). That battery is currently being drained at a rate of 2881W to run the equipment (via the inverter back to 230V) If I pull the 32A cable, everything carries on working (I believe it's a sub-20ms switchover). If the power goes for some other reason it carries on working. The truck can run on a 230V/13A source just as well (although when the aircon is on - not needed currently - we'll be pulling more than 13A so the battery will slowly drain). I can even plug into two different inputs. Now this is a mobile vehicle, and I'm no electrician, but my understanding is this is perfectly fine -- the victron presumably switches from the grid if the input is lost and doesn't feed anything back into the grid. Presumably the same setup could be used to power a home instead of several racks of equipment in the back of a truck.
  - jacquesm 5y ago
    That Victron box has an automatic transfer switch in it, and is certified for permanent grid connection.
- ashtonkem 5y ago
  That depends on your generation capacity and what the rules of your grid are. If you're capable of producing enough power to run your home most of the time, then being grid connected and buying peak load from the grid itself rather than browning out your own devices might be a worth while tradeoff. Most of us with grid tied solar installations (like me) transparently buy and sell electricity to and from the grid depending on day conditions. I buy from the grid overnight, and sell excess capacity during the day. Depending on how much electricity you use a battery system will smooth those out, but you need a lot of batteries to eliminate the need completely (OP mentioned 48KWh, which is about 3.5 Power Walls). In my area the grid is really reliable and fees are low, so buying batteries is not economically viable. I'm currently paying $5.24 per month for a grid tie, which is below my threshold for caring.
  - PaulDavisThe1st 5y ago
    It's also more viable to be grid tied if your winter needs are more than X times your summer needs. My 6.6kW array generates roughly 3x what we need during summer. But our home is heated in winter (at 6000' in New Mexico) using electrically powered air-source heat pumps (aka "minisplits") and that takes about 3x what we generate during the winter. Adding either on-site storage capacity or sufficient additional panels to cover our winter needs really makes no sense. The storage capacity would have to be immense, because no matter how you slice it and dice it, we do not generate enough power to heat our home for several months (and that's with adobe and some passive design). The additional panels would take up a large amount of ground space, and result in us generating 9x our needs in summer. I prefer to put my faith in the emergence of grid-scale storage solutions than try to solve this on a just-my-home level.
    - ashtonkem 5y ago
      If the grid wasn’t reliable, a hypothetical I know, it would probably be cheaper to switch over to a ground source heat pump rather than increase your panels by 3x. That would lower your winter electricity demand, albeit at the cost of significant capital expenditure.
- vkou 5y ago
  In some areas, there is both, but it requires having a correctly installed automatic disconnect, that cuts you off from the grid if the grid loses power. Many/Most home solar installations do not correctly install one, which can be dangerous to linemen.
- bentcorner 5y ago
  I'm getting a manual transfer switch installed - I live in the city (although it's rural-ish where I live) but we get occasional power outages and it's often enough (and long enough) to be worth the annoyance of getting a generator and switch installed, but not enough for me to shell out big $$$ for a natural gas generator and automatic transfer switch to ensure 100% uptime for my house.
  - jacquesm 5y ago
    This works well as long as there is a reasonably high chance of someone being in the building when the power fails. For many rural setups (for instance: weekend cottages) that isn't the case so more and more inverters come with an automatic transfer switch built in or for a small surcharge as an option.
    - ghaff 5y ago
      Or if you travel. If I ever get a generator installed (with automatic transfer switch), it would be primarily for the case of a power outage during the winter when I'm not around.
jacquesm 5y ago
This is called an 'automatic transfer switch', it basically islands your off-grid installation when the power isn't available. As you already mention whether or not it is allowed is dependent on where you live. As it was the electrical inspectors in Northern Ontario were very much in bed with the power companies and typically would find all kinds of reasons to persuade renewable energy builders to let it go and rely on grid power. Given the state of some of the homebrew systems I've seen they probably had a point. Automatic transfer switches were technically allowed but at the time I didn't know of a single installation in Northern Ontario that got a stamp of approval and was allowed to be operated un-attended in grid connected mode. There is some risk, but this is usually exaggerated, the theory goes that a lineman should be able to disconnect a segment and then it should be idle, requiring all renewable installations down-grid to disable themselves. As a rule this is fully automatic anyway because all of the grid connected inverters that I'm aware of stop working as soon as the grid fails because they use the grid to supply them with phase and frequency information required to function. But that wasn't good enough, the installation needed to be physically disconnected from the grid, requiring a very large relay and somehow it then had to reconnect if the grid came back on for a specified minimum amount of time (I forgot the details). By the time I had worked all this out I figured since I'm going to be in island mode anyway most of the time I may as well take the shortcut, cut the grid entirely (saving a considerable amount of money in the progress) and invest the difference into a nice genset (which I did, a 5.8KW Kubota diesel).
- Throwawayaerlei 5y ago
  Here in the US Midwest I recently observed some crews repairing a fault just upstream of me, and the last thing they did before reconnecting to upstream of that fault was disconnecting a set of yellow cables which were obviously grounding the downstream wires.
  - brianwawok 5y ago
    Layers of protection. Laws on what can backfeed into the grid, ground the wires, wear safety gear. No different than in computer science using both a firewall AND salting your password. The more layers, the less likely 1 mistake gets you.
ashtonkem 5y ago
Not even which country, which sub-entity within your country. Here in America it's going to vary on a state by state basis.

chiefalchemist 5y ago

> Now whether or not this is allowed is very much dependent on which country you live in. So basically, to clarify, you're either 100% on the grid, or 100% off. There's no using both depending on conditions, is that it?

ghaff 5y ago
You can have a backup generator (with a transfer switch)--which many do in more rural areas at least in the US.
bluGill 5y ago
I'm not sure about Ontario, but in many places you can be grid tied which means that you use both. While it is possible to change depending on conditions, the equipment to do that isn't very common. Solar systems are just starting to come out with single outlets that can run while the sun shines without the grid, but that is rare, most assume 100% on grid, or 100% off grid.
iso1210 5y ago
The vehicle I'm currently sat in at the moment has a 32A electrical cable running in the back, currently pulling 2881W into a magic box provided by victron inverter/charger, that is used to charge a battery (which is currently fully charged). That battery is currently being drained at a rate of 2881W to run the equipment (via the inverter back to 230V) If I pull the 32A cable, everything carries on working (I believe it's a sub-20ms switchover). If the power goes for some other reason it carries on working. The truck can run on a 230V/13A source just as well (although when the aircon is on - not needed currently - we'll be pulling more than 13A so the battery will slowly drain). I can even plug into two different inputs. Now this is a mobile vehicle, and I'm no electrician, but my understanding is this is perfectly fine -- the victron presumably switches from the grid if the input is lost and doesn't feed anything back into the grid. Presumably the same setup could be used to power a home instead of several racks of equipment in the back of a truck.
- jacquesm 5y ago
  That Victron box has an automatic transfer switch in it, and is certified for permanent grid connection.
ashtonkem 5y ago
That depends on your generation capacity and what the rules of your grid are. If you're capable of producing enough power to run your home most of the time, then being grid connected and buying peak load from the grid itself rather than browning out your own devices might be a worth while tradeoff. Most of us with grid tied solar installations (like me) transparently buy and sell electricity to and from the grid depending on day conditions. I buy from the grid overnight, and sell excess capacity during the day. Depending on how much electricity you use a battery system will smooth those out, but you need a lot of batteries to eliminate the need completely (OP mentioned 48KWh, which is about 3.5 Power Walls). In my area the grid is really reliable and fees are low, so buying batteries is not economically viable. I'm currently paying $5.24 per month for a grid tie, which is below my threshold for caring.
- PaulDavisThe1st 5y ago
  It's also more viable to be grid tied if your winter needs are more than X times your summer needs. My 6.6kW array generates roughly 3x what we need during summer. But our home is heated in winter (at 6000' in New Mexico) using electrically powered air-source heat pumps (aka "minisplits") and that takes about 3x what we generate during the winter. Adding either on-site storage capacity or sufficient additional panels to cover our winter needs really makes no sense. The storage capacity would have to be immense, because no matter how you slice it and dice it, we do not generate enough power to heat our home for several months (and that's with adobe and some passive design). The additional panels would take up a large amount of ground space, and result in us generating 9x our needs in summer. I prefer to put my faith in the emergence of grid-scale storage solutions than try to solve this on a just-my-home level.
  - ashtonkem 5y ago
    If the grid wasn’t reliable, a hypothetical I know, it would probably be cheaper to switch over to a ground source heat pump rather than increase your panels by 3x. That would lower your winter electricity demand, albeit at the cost of significant capital expenditure.
vkou 5y ago
In some areas, there is both, but it requires having a correctly installed automatic disconnect, that cuts you off from the grid if the grid loses power. Many/Most home solar installations do not correctly install one, which can be dangerous to linemen.
bentcorner 5y ago
I'm getting a manual transfer switch installed - I live in the city (although it's rural-ish where I live) but we get occasional power outages and it's often enough (and long enough) to be worth the annoyance of getting a generator and switch installed, but not enough for me to shell out big $$$ for a natural gas generator and automatic transfer switch to ensure 100% uptime for my house.
- jacquesm 5y ago
  This works well as long as there is a reasonably high chance of someone being in the building when the power fails. For many rural setups (for instance: weekend cottages) that isn't the case so more and more inverters come with an automatic transfer switch built in or for a small surcharge as an option.
  - ghaff 5y ago
    Or if you travel. If I ever get a generator installed (with automatic transfer switch), it would be primarily for the case of a power outage during the winter when I'm not around.

jacquesm 5y ago

This is called an 'automatic transfer switch', it basically islands your off-grid installation when the power isn't available. As you already mention whether or not it is allowed is dependent on where you live. As it was the electrical inspectors in Northern Ontario were very much in bed with the power companies and typically would find all kinds of reasons to persuade renewable energy builders to let it go and rely on grid power. Given the state of some of the homebrew systems I've seen they probably had a point. Automatic transfer switches were technically allowed but at the time I didn't know of a single installation in Northern Ontario that got a stamp of approval and was allowed to be operated un-attended in grid connected mode. There is some risk, but this is usually exaggerated, the theory goes that a lineman should be able to disconnect a segment and then it should be idle, requiring all renewable installations down-grid to disable themselves. As a rule this is fully automatic anyway because all of the grid connected inverters that I'm aware of stop working as soon as the grid fails because they use the grid to supply them with phase and frequency information required to function. But that wasn't good enough, the installation needed to be physically disconnected from the grid, requiring a very large relay and somehow it then had to reconnect if the grid came back on for a specified minimum amount of time (I forgot the details). By the time I had worked all this out I figured since I'm going to be in island mode anyway most of the time I may as well take the shortcut, cut the grid entirely (saving a considerable amount of money in the progress) and invest the difference into a nice genset (which I did, a 5.8KW Kubota diesel).

Throwawayaerlei 5y ago
Here in the US Midwest I recently observed some crews repairing a fault just upstream of me, and the last thing they did before reconnecting to upstream of that fault was disconnecting a set of yellow cables which were obviously grounding the downstream wires.
- brianwawok 5y ago
  Layers of protection. Laws on what can backfeed into the grid, ground the wires, wear safety gear. No different than in computer science using both a firewall AND salting your password. The more layers, the less likely 1 mistake gets you.

ashtonkem 5y ago

Not even which country, which sub-entity within your country. Here in America it's going to vary on a state by state basis.