Now, how does all of this relate to off grid use without batteries?
If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with, and the inverters cannot produce their own waveform. Also, they cannot operate at a reduced power output (this is more a side effect of the firmware, but it's true of the vast majority of ones out there). So they can't produce less power than the panels are creating at the moment, and they can't produce more. And they can't make a valid AC waveform out of it. You can see how this might be a problem.
If you want off grid capability from a microinverter system, you need what's called an "AC coupled system." This involves a battery bank (uh oh), and an inverter/charger that can suck power from the home's AC grid, as well as deliver it. You generally can't size this to use the whole roof, as a 10kW charger/inverter and a battery bank that can handle that sort of charge rate are really expensive. Basically, this system provides a waveform for the microinverters, sucks excess power, and eventually shuts the microinverters off (usually by pushing frequency out of spec for them). There theoretically exists a setup that can tell the microinverters to back off a bit, and with the newer UL specs, that should be easier with some of the improved ridethrough curves, but... it's complex, and nobody really does this. Generally, you only couple some of the solar panels to the AC coupled setup, because it makes a smaller charger/inverter possible. So you may AC couple 4kW of a 12kW system.
The only real way to get off grid power without batteries is to go with an inverter that has an emergency outlet. Some of the SMA inverters support this (they call it Secure Power Supply) - you feed the whole rooftop array into them, and they can, if the sun is shining, provide 1.5kW or so to a dedicated outlet - assuming there's enough solar power. So, from an 8-10kW array, on a sunny day, you can get 1.5kW by operating well below the peak power point. If the array can't keep up with current demand (a cloud goes over), the outlet shuts down. It's better than nothing, but this is just about the only way you can get battery-free off grid power. To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while. Hopefully your devices can handle intermittent power like this. If the array can source 1300W at the moment and a compressor tries to draw 1301W while starting, you collapse the array voltage and shut down the outlet. That's really hard on compressors (and everything else attached to the outlet).
If, as some nutjobs prefer, you want sustained off grid running for most of the house, you can design a system with batteries that's intended for this sort of use. I plan to build this, eventually. I'll have 8-12kW of panels on the roof, feeding into a few charge controllers. These will feed into a moderately sized battery bank under my house, and will be coupled to a large inverter that supports grid tied production as well as standalone use (probably an Outback Radian 8kW unit). I'll have most of the house downstream of the inverter, so I can run everything I care about off the inverter - I'll lose some loads like the heat pump backup coils, possibly the stove, but the rest of the house will work, and I'll have enough surge capacity to do things like run the well pump and the air conditioner. I don't expect this system to ever "pay off" in financial terms, but I value stable, reliable power, and a test lab for this sort of operation.
Or you can separate your backup power from your solar, which I'll talk about a bit later.
So... hopefully that's a bit of a technical overview of how things work. I assure you, most of the furor over this is related to how systems are installed, not "Meanie Power Company Being Evilly Evil."
If you have a typical grid tied system (microinverters or normal string inverters, so easily 95+% of installed rooftop solar), the system is technically incapable of running off grid (without additional hardware). There's no waveform to sync with, and the inverters cannot produce their own waveform. Also, they cannot operate at a reduced power output (this is more a side effect of the firmware, but it's true of the vast majority of ones out there). So they can't produce less power than the panels are creating at the moment, and they can't produce more. And they can't make a valid AC waveform out of it. You can see how this might be a problem.
If you want off grid capability from a microinverter system, you need what's called an "AC coupled system." This involves a battery bank (uh oh), and an inverter/charger that can suck power from the home's AC grid, as well as deliver it. You generally can't size this to use the whole roof, as a 10kW charger/inverter and a battery bank that can handle that sort of charge rate are really expensive. Basically, this system provides a waveform for the microinverters, sucks excess power, and eventually shuts the microinverters off (usually by pushing frequency out of spec for them). There theoretically exists a setup that can tell the microinverters to back off a bit, and with the newer UL specs, that should be easier with some of the improved ridethrough curves, but... it's complex, and nobody really does this. Generally, you only couple some of the solar panels to the AC coupled setup, because it makes a smaller charger/inverter possible. So you may AC couple 4kW of a 12kW system.
The only real way to get off grid power without batteries is to go with an inverter that has an emergency outlet. Some of the SMA inverters support this (they call it Secure Power Supply) - you feed the whole rooftop array into them, and they can, if the sun is shining, provide 1.5kW or so to a dedicated outlet - assuming there's enough solar power. So, from an 8-10kW array, on a sunny day, you can get 1.5kW by operating well below the peak power point. If the array can't keep up with current demand (a cloud goes over), the outlet shuts down. It's better than nothing, but this is just about the only way you can get battery-free off grid power. To get any sort of stable battery-free power, you have to run the panels well, well below peak power (30-50% of peak is as high as you can really run), and even then, you have a horrifically unstable system. If the array power briefly drops below demand (perhaps an airplane has flown over), you shut down the entire output for a while. Hopefully your devices can handle intermittent power like this. If the array can source 1300W at the moment and a compressor tries to draw 1301W while starting, you collapse the array voltage and shut down the outlet. That's really hard on compressors (and everything else attached to the outlet).
If, as some nutjobs prefer, you want sustained off grid running for most of the house, you can design a system with batteries that's intended for this sort of use. I plan to build this, eventually. I'll have 8-12kW of panels on the roof, feeding into a few charge controllers. These will feed into a moderately sized battery bank under my house, and will be coupled to a large inverter that supports grid tied production as well as standalone use (probably an Outback Radian 8kW unit). I'll have most of the house downstream of the inverter, so I can run everything I care about off the inverter - I'll lose some loads like the heat pump backup coils, possibly the stove, but the rest of the house will work, and I'll have enough surge capacity to do things like run the well pump and the air conditioner. I don't expect this system to ever "pay off" in financial terms, but I value stable, reliable power, and a test lab for this sort of operation.
Or you can separate your backup power from your solar, which I'll talk about a bit later.
So... hopefully that's a bit of a technical overview of how things work. I assure you, most of the furor over this is related to how systems are installed, not "Meanie Power Company Being Evilly Evil."
"Islanding"
One term one will hear tossed about is the concept of "islanding." This refers to a chunk of the power grid (possibly a single house) that has power while the rest of the local grid is dead. It's common to hear "anti-islanding" blamed for why a home's solar can't produce power when the grid is dead. Lineworker safety is usually mentioned in the next sentence.
What this means, simply, is that a local generating system cannot (legally) feed into a dead section of power grid. For a home power system, this means that unless you have a specific mechanism for disconnecting the home from the power grid (typically called a "transfer switch"), you cannot power the local home circuits from solar or generator.
Now, that said, it's really less of an issue than it's made out to be. Backfeeding the power grid, according to some lineworkers I've talked to, is really not a big concern for two reasons. First, lineworkers assume lines are live until proven otherwise. And, second, no residential system is going to successfully backfeed a large dead section of grid. The grid without power looks an awful lot like a dead short, so the microinverters or string inverters or generator or whatever will instantly overload and shut down. It's in the regulations, but it's really not that big a concern from a technical/safety perspective.
But, if you haven't explicitly set your system up to support islanded operation with a transfer switch and battery, your solar won't power your house with the grid down.
If you want to get a rooftop solar system that powers your home with the grid down, you can do it! The hardware is out there. But such a system will be significantly more expensive than a normal grid tied system, and it will likely never "pay off" in terms of money saved. That's all.
So stop blaming the power companies for homeowners buying a grid tied system (because it's cheap) and then complaining when it won't run off grid. That's like complaining that a Mazda 3 won't tow a 20k lb trailer.
It's Not Power Companies Being Evilly Evil - It's Homeowners Being Cheap
Why have I written all this? To explain (hopefully) that the reason most solar power systems won't work off grid has literally nothing to do with power companies being evil and demanding that you buy their power. It has everything to do with the system not being designed to run off grid. Why are they designed that way? Because it's cheaper. Period. A microinverter based system is substantially cheaper than anything with batteries (which will need regular replacement), and that's what people get installed when they want a reasonably priced bit of rooftop solar to save money on their power bill.If you want to get a rooftop solar system that powers your home with the grid down, you can do it! The hardware is out there. But such a system will be significantly more expensive than a normal grid tied system, and it will likely never "pay off" in terms of money saved. That's all.
So stop blaming the power companies for homeowners buying a grid tied system (because it's cheap) and then complaining when it won't run off grid. That's like complaining that a Mazda 3 won't tow a 20k lb trailer.
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