4 ms·

If that wikipedia article is right, then balcony solar is not legal where I live (in the US). Here, we require a hard-wired, permanently installed automatic tra

by bityard 8mo ago

If that wikipedia article is right, then balcony solar is not legal where I live (in the US). Here, we require a hard-wired, permanently installed automatic transfer switch that disconnects the solar generation from the grid when the mains power goes out. This is to protect line workers when working on downed lines.

hamdingers 8mo ago
It's probably coming soon for you, 30 states have bills announced or introduced legalizing plug-in solar and one (Utah) has already passed. They should be fairly uncontroversial. Also, there's no need for a transfer switch in any grid-tied system, whether plug-in or hard-wired. Grid-tied inverters shut off automatically if there's no grid frequency to sync to.
- jacquesm 8mo ago
  That simply is a transfer switch that is built in.
  - hamdingers 8mo ago
    What would it be transferring the load to? "Transfer switch" refers to a specific kind of switch that transfers load between two sources. There is only one source (the panels) and one load (the grid) on a grid-tied inverter, so what you're saying does not make sense. There are more complicated solar setups that do involve transfer switches, but they are not applicable to the balcony solar use case and remain uncommon even for hardwired rooftop solar.
    - jacquesm 8mo ago
      In grid tied inverters with batteries the transfer switch can be built in to the inverter or it can be an external switch that the inverter talks to. Similar to how you would use one with a generator setup. And indeed these are uncommon, mostly because they tend to be more serious devices. Victron and formerly Xantrex make nice ones, but the inverter alone probably costs more than a complete balcony solar installation. For the solar balcony and more common rooftop solar setups there is only a simple disconnect, but both a transfer switch and a disconnect are the same thing: a (usually beefy) relay, but the transfer switch variety switches your house between the inverter and the grid whereas the disconnect just physically disconnects the inverters output. The downside of that setup is that if there is no grid but you do have solar that you still have no power. Most of these wouldn't be able to power anything but the smallest installations anyway (300 W or so, typically), and don't have a battery to store any excess (as if there would be any...). As soon as you add a battery it makes good sense to use the transfer switch: you can disconnect from the grid but the inverter can keep running to power your house and if you're lucky the solar will replenish it fast enough during the day that you can hold over for a while. The big rooftop inverter that I have has a built in transfer switch but I'm not using it right now simply because I don't have a good way to route the wiring to and from the inverter. It is stuck in my garage with the main distribution panel on the other side of the house. In my old house in Canada that was all designed from scratch and there we had the house entirely off-grid with the transfer switch hooked to a genset if the power was out for longer than the battery could sustain us (48 KWh so that usually was good for a couple of days).
      - hamdingers 8mo ago
        A disconnect and a transfer switch are not a same thing, "transfer switch" refers to a specific type of switch in a specific role as I have described. Conflating the two is incorrect and benefits nobody.
        mcbishop 8mo ago
        A distinction was made: > the transfer switch variety switches your house between the inverter and the grid whereas the disconnect just physically disconnects the inverters output
        hamdingers 8mo ago
        Origionally: > That simply is a transfer switch that is built in. Then in this comment: > but both a transfer switch and a disconnect are the same thing These statements are false, and the fact that the second one was written even after being corrected once makes me think they still do not understand. This user appears to blast paragraphs upon paragraphs of irrelevant noise at anyone who responds to them so that either the comment has internal conflicts (as you noticed) or any criticism seems nitpicky.
      - mindslight 8mo ago
        IIUC plug-in balcony solar is subtly different. It's basically aimed at grid-tie operation, connected by backfeeding through a standard 120V 15/20A branch circuit. On its own that's unsafe as you could have downstream loads drawing more than the 15/20A circuit ampacity, but I think the idea is still at the pinky-swear-it's-a-dedicated-receptacle-and-cross-your-fingers stage. The units likely have "protected outlets" too that likely use an internal transfer relay to disconnect from the grid side, but at 15/20A it doesn't have to be terribly beefy.
        jacquesm 8mo ago
        Yes, they're an interesting little loophole device. They are likely not going to be legal in the long run because of the overload potential, even though in practice you'd have to work at that to make it happen. After all, these are typically no more than 300 to 500 W and angled in a very unfortunate way so likely not making full power. The wiring connecting them to the distribution panel is not going to sweat handling - again, potentially - that much more power over the 16A typical limit, that's just 2A more and you are more than likely not going to have that much consumption going on on that same circuit. I have a similar situation here but at much higher power levels, a single underground cable from my garage to the house carrying 16A tri-phase and a whole raft of consumers in the garage itself. There too there is the potential for overload with both consumers and producers on the same cable. The solution there was to have a secondary distribution panel, breakers on both sides of the cables, for the consumers and for the inverter guaranteeing that none of the wiring in the panel or to the house or the consumers ever exceeds its rating. This was by far the most cost effective solution, saved adding another ground cable and relieves the main distribution panel of a lot of current going in and out of the garage.
jacquesm 8mo ago
99.9% of all inverters currently being sold has this functionality built in. That 0.1% remaining you will find in the second hand market and the bargain bin of Amazon.
rsync 8mo ago
We require transfer switches, but they do not have to be automatic transfer switches. In the United States, you are one small piece of sheet metal[1] away from any number of interesting power set ups on your side of the utility. This means a combination of two circuit breakers is now your transfer switch. This is legal with all utilities and NEC compliant, etc. If you are willing to sacrifice perfectly uninterrupted power, you can dramatically simplify your grid tie - and open up many other possibilities on your side of the physical interlock. [1] https://www.daierswitches.com/products/sd-200vl-generator-interlock-kit https://www.daierswitches.com/products/sd-200vl-generator-in...
- jacquesm 8mo ago
  Exactly. The main application of a transfer switch is that it is not going to cause your genset to backfeed into the grid. But for many solar installations that's exactly what you want anyway, so the disconnect logic for an islanding capable inverter is very much the same as for one that is exclusively grid connected, the big difference is that the islanding one will happily generate it's own phase clock if the grid is not present, but for that to work it has to keep its own system running and connected to the house distribution panel while the grid connection is down. This is much easier to do if it is all integrated into the inverter itself, but that makes for an awkward bunch of wiring, because the inverters are typically not situated right next to the entry point for the grid connection. I'd have to rewire my distribution hookup completely for that kind of functionality, or to have a remote controlled disconnect while the inverter keeps feeding the distribution panel. A transfer switch is much more applicable to emergency power or ship/shore power situations where you only use one power source at the time. For solar it is normally all on or all off or solar+battery(+wind) on all the time and backfeeding into the grid when it is available and grid power when solar+wind+battery are not available. This can get complex in a hurry, fortunately there are a number of companies that make excellent components for these applications that you can just order and hook up and call it a day, without ever having to worry if your fancy setup has the right break-before-make order and whether or not it is code compliant. And they're not expensive compared to the rest of the gear you'll need.

by bityard 8mo ago

hamdingers 8mo ago

It's probably coming soon for you, 30 states have bills announced or introduced legalizing plug-in solar and one (Utah) has already passed. They should be fairly uncontroversial. Also, there's no need for a transfer switch in any grid-tied system, whether plug-in or hard-wired. Grid-tied inverters shut off automatically if there's no grid frequency to sync to.

jacquesm 8mo ago
That simply is a transfer switch that is built in.
- hamdingers 8mo ago
  What would it be transferring the load to? "Transfer switch" refers to a specific kind of switch that transfers load between two sources. There is only one source (the panels) and one load (the grid) on a grid-tied inverter, so what you're saying does not make sense. There are more complicated solar setups that do involve transfer switches, but they are not applicable to the balcony solar use case and remain uncommon even for hardwired rooftop solar.
  - jacquesm 8mo ago
    In grid tied inverters with batteries the transfer switch can be built in to the inverter or it can be an external switch that the inverter talks to. Similar to how you would use one with a generator setup. And indeed these are uncommon, mostly because they tend to be more serious devices. Victron and formerly Xantrex make nice ones, but the inverter alone probably costs more than a complete balcony solar installation. For the solar balcony and more common rooftop solar setups there is only a simple disconnect, but both a transfer switch and a disconnect are the same thing: a (usually beefy) relay, but the transfer switch variety switches your house between the inverter and the grid whereas the disconnect just physically disconnects the inverters output. The downside of that setup is that if there is no grid but you do have solar that you still have no power. Most of these wouldn't be able to power anything but the smallest installations anyway (300 W or so, typically), and don't have a battery to store any excess (as if there would be any...). As soon as you add a battery it makes good sense to use the transfer switch: you can disconnect from the grid but the inverter can keep running to power your house and if you're lucky the solar will replenish it fast enough during the day that you can hold over for a while. The big rooftop inverter that I have has a built in transfer switch but I'm not using it right now simply because I don't have a good way to route the wiring to and from the inverter. It is stuck in my garage with the main distribution panel on the other side of the house. In my old house in Canada that was all designed from scratch and there we had the house entirely off-grid with the transfer switch hooked to a genset if the power was out for longer than the battery could sustain us (48 KWh so that usually was good for a couple of days).
    - hamdingers 8mo ago
      A disconnect and a transfer switch are not a same thing, "transfer switch" refers to a specific type of switch in a specific role as I have described. Conflating the two is incorrect and benefits nobody.
      - mcbishop 8mo ago
        A distinction was made: > the transfer switch variety switches your house between the inverter and the grid whereas the disconnect just physically disconnects the inverters output
        hamdingers 8mo ago
        Origionally: > That simply is a transfer switch that is built in. Then in this comment: > but both a transfer switch and a disconnect are the same thing These statements are false, and the fact that the second one was written even after being corrected once makes me think they still do not understand. This user appears to blast paragraphs upon paragraphs of irrelevant noise at anyone who responds to them so that either the comment has internal conflicts (as you noticed) or any criticism seems nitpicky.
    - mindslight 8mo ago
      IIUC plug-in balcony solar is subtly different. It's basically aimed at grid-tie operation, connected by backfeeding through a standard 120V 15/20A branch circuit. On its own that's unsafe as you could have downstream loads drawing more than the 15/20A circuit ampacity, but I think the idea is still at the pinky-swear-it's-a-dedicated-receptacle-and-cross-your-fingers stage. The units likely have "protected outlets" too that likely use an internal transfer relay to disconnect from the grid side, but at 15/20A it doesn't have to be terribly beefy.
      - jacquesm 8mo ago
        Yes, they're an interesting little loophole device. They are likely not going to be legal in the long run because of the overload potential, even though in practice you'd have to work at that to make it happen. After all, these are typically no more than 300 to 500 W and angled in a very unfortunate way so likely not making full power. The wiring connecting them to the distribution panel is not going to sweat handling - again, potentially - that much more power over the 16A typical limit, that's just 2A more and you are more than likely not going to have that much consumption going on on that same circuit. I have a similar situation here but at much higher power levels, a single underground cable from my garage to the house carrying 16A tri-phase and a whole raft of consumers in the garage itself. There too there is the potential for overload with both consumers and producers on the same cable. The solution there was to have a secondary distribution panel, breakers on both sides of the cables, for the consumers and for the inverter guaranteeing that none of the wiring in the panel or to the house or the consumers ever exceeds its rating. This was by far the most cost effective solution, saved adding another ground cable and relieves the main distribution panel of a lot of current going in and out of the garage.

jacquesm 8mo ago

99.9% of all inverters currently being sold has this functionality built in. That 0.1% remaining you will find in the second hand market and the bargain bin of Amazon.

rsync 8mo ago

We require transfer switches, but they do not have to be automatic transfer switches. In the United States, you are one small piece of sheet metal[1] away from any number of interesting power set ups on your side of the utility. This means a combination of two circuit breakers is now your transfer switch. This is legal with all utilities and NEC compliant, etc. If you are willing to sacrifice perfectly uninterrupted power, you can dramatically simplify your grid tie - and open up many other possibilities on your side of the physical interlock. [1] https://www.daierswitches.com/products/sd-200vl-generator-interlock-kit https://www.daierswitches.com/products/sd-200vl-generator-in...

jacquesm 8mo ago
Exactly. The main application of a transfer switch is that it is not going to cause your genset to backfeed into the grid. But for many solar installations that's exactly what you want anyway, so the disconnect logic for an islanding capable inverter is very much the same as for one that is exclusively grid connected, the big difference is that the islanding one will happily generate it's own phase clock if the grid is not present, but for that to work it has to keep its own system running and connected to the house distribution panel while the grid connection is down. This is much easier to do if it is all integrated into the inverter itself, but that makes for an awkward bunch of wiring, because the inverters are typically not situated right next to the entry point for the grid connection. I'd have to rewire my distribution hookup completely for that kind of functionality, or to have a remote controlled disconnect while the inverter keeps feeding the distribution panel. A transfer switch is much more applicable to emergency power or ship/shore power situations where you only use one power source at the time. For solar it is normally all on or all off or solar+battery(+wind) on all the time and backfeeding into the grid when it is available and grid power when solar+wind+battery are not available. This can get complex in a hurry, fortunately there are a number of companies that make excellent components for these applications that you can just order and hook up and call it a day, without ever having to worry if your fancy setup has the right break-before-make order and whether or not it is code compliant. And they're not expensive compared to the rest of the gear you'll need.