> 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,
A residential no-break has no waveform to sync with as well.
Something capable of syncing to the grid and then more or less keeping pace even if the main grid goes down should cost very little today. (And when the grid goes back it shouldn't have drifted too much unless something ridiculously big happened)
When the two are aligned within a good-enough tolerance the system will switch back to it's regular state of mains + solar ( + batteries + wind + generator + etc / whatever).
These are all solved problems with commercial off the shelf components.
It looks to me like microinverters are a commercial off the shelf product?
Will a microinverter do all of the things a multi-component phase-syncing system with automatic transfer switches do? I don't see why a microinverter can't be built with these components integrated. I can't tell you if such a unit exists as I'm not well versed in the product range.
As far as a price comparison goes, I guess it only makes sense to compare a like-for-like system?
Could it be made cheaper? Probably. If you get it wrong, the grid probably doesn't care but you'll briefly pump about 500W into the device that is supposed to have 500W going out of it. The reason these are big and expensive is that it requires significant safety gear so nothing explodes even in the worst case. And that safety gear is expensive. So you sell it to people who not only can afford it but also really really need it (ie, 1MW and upwards where you enter the domain of "can fry small section of grid")
There’s no technical reason the requisite electronics can’t be built on a much smaller scale.
Home grid-tie solar inverters are clearly capable of syncing, so the electronics are already present.
Additionally producing the clean sinewave that you'd need for this is not that easy, atleast not at the quality levels you want for this (if your DAC that produces the wave is off by 1% then at a 2kW load you're going to burn up 20W somewhere that doesn't like 20W being burned up)
How is being off by 1% going to hurt anything? I'm quite sure my mains voltage is already more than 1% off.
If I get solar it had better not explode every time my air conditioner kicks on.
However, if you have your own generator it matters a lot.
If your phase is off by 1 degree then that 1 degree will burn roughly .2% of the incoming power of the grid at the inverter (which is unlikely designed to handle this). If you're off by 1% you burn 20 Watts on a device not designed for it.
If your voltage is off relative to the grid by 1% then you burn the difference, at 2kW that's about 20 Watts. And that's per volt. You'd be burning somewhere around 300 W if you happen to have the grid on the higher end of the tolerance and yours on the lower.
A grid-tie inverter gets around this by simply following along the sine wave of the grid, this can be done relatively cheaply and safely with analog components so the error can be much smaller than 1% and deep into random noise territory.
If you generate your own sine wave and compare it to an existing one it's much more difficult since you have to match amplitude and phase almost perfectly.
So with grid-tie nothing will explode. With an autotransfer nothing explodes either. Wanting to seamlessly couple back in requires a lot of care and expensive components.
Next to your offline-capable sine wave generator, put a copy of that cheap safe analog circuit.
Once you get almost in sync, crossfade over to the analog circuit. (If that's even necessary. It might be just fine to swap to it at a zero-crossing.)
Now you're completely in sync. Reconnect to the mains.
The cheapest is VFD which is basically a battery parellel to the mains which in case of a power failure interrupts mains and inserts it's own voltage. Usually labelled as "offline" or "standby" UPS since they're not active most of the time. The output frequency and voltage is the mains output and voltage until switched over, something to keep in mind if devices are sensitive to that.
These can simply switch back to mains when it's back since they usually use a simple transfer relay.
VI (Line interactive, Delta Conversion) uses the mains frequency as orientation. They don't have a transfer and can basically just compensate whatever the mains is doing to output a 230V signal. Internally they have a inverter with AC input and AC ouput which means they measure if mains is coming back from there and adapt the signal on the internal inverter for the battery.
If mains comes back on a VI they usually change frequency very abruptly which is not ideal from some devices.
VDI is completely independent of both voltage and frequency as it first converts mains AC to internal DC, simply plugs in the battery into the DC and then converts DC to AC. They don't need to synchronize at all and are the more common for datacenters since they isolate the input fairly well from output and don't have to switch anything to go from mains to backup, DC voltage is fairly good for dealing with this. They are also most expensive.
If mains comes back on a VDI they don#t do anything of notable interest other than switching the battery charger on.
The specialist devices for large installations you’re talking about are only expensive because you need more expensive parts for the far larger amounts of current you’re handling (and probably because they’re made in lower volumes than commodity inverters), not because they’re doing anything particularly difficult.
Manufacturers of solar hardware love to charge you an extra $1000 for that extra firmware though...
When the grid comes back from a blackout, chances are that it browned out beforehand so your sync is to a low frequency and coming back it'll be high frequency because the grid wants to compensate for loads jumping back on.
Additionally the components to generate your own waveform are cheap, yes, but not that cheap, adding them to the microinverter would increase cost quite a bit.
And you'd still need a transfer switch because if you happen to be 180 degrees out of phase, which CAN HAPPEN then your panel will behave like a dead short at double grid voltage. The current flow will definitely exceed the maximum tolerances and the magic smoke goes out.
You will absolutely need a transfer switch just so you don't fry all your devices the moment the grid comes back. Even then, syncing to the grid is a rather delicate maneuver since the grid will be constantly changing phase and it'll be simpler to shut down all inverters, connect back and have it all run back up on the grid itself.
Just shut it down, flip the switch and restart. Everything else will just be prohibitively expensive because it needs to be very safe.
If you get the phase wrong then you'll either reduce the lifetime of your components or the components explode after the nearest power plant tries to pump all available power into your poor inverter.
I’m pretty sure companies like Victron Energy already make these kinds of systems - combination solar inverters and battery chargers that have transfer switches to be able to seamlessly switch to UPS mode when the grid drops out but can still export excess energy when it’s up.
And that's for what you need to allow your inverter to handle this automatically (you might need another voltage sensing channel to sense the grid-side of this breaker).
Only if you design it to. The phase locked loop would "listen" to the mains frequency and slew to match. Slew speed is simply a design parameter you can set to any value.
Your UPS handles an order of magnitude (or more) less power than a whole-home solar installation.
None of these problems are intractable of course, but you are oversimplifying the problem a little.
One can get a UPS affordably that will power 1500 watts of continuous power. Being able to supply just that much, or twice that much, from solar panels in a grid-down scenario would be tremendously useful, even if it's not enough power to fire up my welder.
Not really, but depends on the state of the infrastructure, if it was really because of a power overload, yes, but most likely "your circuit" (which could be your street or your neighborhood) got shut off, in this case there shouldn't be much difference
Yes, a phase difference of 180 can definitely happen but I guess most electronics can survive a 1/60s (I'd say even 1/10) switching time, which is probably enough to have the grid take over.
(Or of course you could have the grid and solar charging batteries then your own high power inverter for your house but that of course would mean $$$$$$)
And you'd still have to sync the inverter, having the inverter simply continue to run until it's back in sync with the grid, then just reconnect (as a previous comment wanted) is likely not an option for most consumers.
For that it would likely be cheaper to have a full DC stage as you mentioned.
It's called a line-interactive UPS. You can buy it for $200.
A line interactive UPS does not sync necessarily sync you to the grid, though the electronic will usually try to keep it in sync. It's not necessary here.
Only running at a fraction of their max available output allow enough headroom for high peak startup draw from loads, and headroom for clouds and planes passing overhead.
Frequently cutting in and out as the load regularly exceeds available supply.
Keeping the frequency sync is the easiest problem to solve, the article even covers what would happen if you tried to use a little generator to produce a sync signal.
As you said:
> Keeping the frequency sync is the easiest problem to solve
Most solar dealers have a one-size-fits-all product that they fit to nearly all homes without much modification. The homeowner thinks they are buying something that will save them a fortune and eliminate their need for grid power. In reality they discoverer that solar is persnickety and they will get nowhere near eliminating their grid reliance. And when you do the math you realise that it might take 10+ years to recoup the high cost of installation and by that point your batteries will need to be replaced and your solar panels will have lost some of their efficiency.
I know people who have gone fully off-grid in Ireland, but they don't just rely on solar. They supplement with wind turbines and in some case hydro power from streams.
Rooftop solar is popular because the payback period is short enough for homeowners - well under 10 years here for a system that is built to last at least 20. Modules built now degrade about 0.25% per year. Solar farms built now are typically financed as 25-30 year projects.
Source: I am a data analyst at a solar engineering firm.
Do you have any suggestions or recommendations on things to read or companies to look at? i.e. Tesla power?
PS: Look at taxes for Farm use vehicles fuel to get a better picture of the actual 'subsidy' vs 'tax'. The tipping point is very much a subsidy. https://www.irs.gov/businesses/small-businesses-self-employe...