The future of energy generation and storage

Latest update on Victorian power outage. No surprise that boosting local energy networks and improving energy resiliency will be the focus of the national energy ministers focus at their next meeting in March

basilio said:

On what basis do you say that SP ? That sounds a bit counter intuitive. Are you thinking of major energy intensive industrial centres mopping up all this power ? I would say such locations would be prime targets for creating and storing their own power.

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If you're connected to the grid or an interconnected local distribution system, you all work in synchronous mode, you are talking about large diverse consumer demographic on communal batteries.
As you said.
Quote:
Many thousands of households, businesses and community facilities with solar power, large batteries and plug in EVs
Multiple community battery banks storing and releasing excess power from these industrial warehouses, schools, community building hosting PV arrays.
Therefore I said.
Quote:
It will certainly be interesting, as if they are all interconnected, the major users will be depleting the storage at a much faster rate, than those in a residential environment.

So from the above:

Unless there are some form of regulating the demand side of the communal batteries, the heavy users will draw down the reserves much faster than the small user, so as I said it will be interesting how they regulate and charge the users for the installation and usage of the storage, because not everyone will have the same benefit from the storage.
Just seemed to be an obvious question from my perspective.

sptrawler said:

If you're connected to the grid or an interconnected local distribution system, you all work in synchronous mode, you are talking about large diverse consumer demographic on communal batteries.
As you said.
Quote:
Many thousands of households, businesses and community facilities with solar power, large batteries and plug in EVs
Multiple community battery banks storing and releasing excess power from these industrial warehouses, schools, community building hosting PV arrays.
Therefore I said.
Quote:
It will certainly be interesting, as if they are all interconnected, the major users will be depleting the storage at a much faster rate, than those in a residential environment.

Unless there are some form of regulating the demand side of the communal batteries, the heavy users will draw down the reserves much faster than the small user, so as I said it will be interesting how they regulate and charge the users for the installation and usage of the storage, because not everyone will have the same benefit from the storage.
Just seemed to be an obvious question from my perspective.

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Ok. Probably just unclear.

I agree that interconnected entities with PV's personal batteries, community batteries will have usage records and systems. There will be a commercial element to the project. Essentially people will store excess PV energy in interconnected batteries and this will be reused when required. There will be various charges. There will be no issue in normal operational situations.

In an outage the energy banks plus the ongoing PV input will cushion the impact of power failures.

sptrawler said:

If you're connected to the grid or an interconnected local distribution system, you all work in synchronous mode, you are talking about large diverse consumer demographic on communal batteries.
As you said.
Quote:
Many thousands of households, businesses and community facilities with solar power, large batteries and plug in EVs
Multiple community battery banks storing and releasing excess power from these industrial warehouses, schools, community building hosting PV arrays.
Therefore I said.
Quote:
It will certainly be interesting, as if they are all interconnected, the major users will be depleting the storage at a much faster rate, than those in a residential environment.

So from the above:

Unless there are some form of regulating the demand side of the communal batteries, the heavy users will draw down the reserves much faster than the small user, so as I said it will be interesting how they regulate and charge the users for the installation and usage of the storage, because not everyone will have the same benefit from the storage.
Just seemed to be an obvious question from my perspective.

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You are such a dream crusher
Remember these are the thoughts widely popular among the decision makers , most of them having no clue or knowledge of chemistry, physics or even basic domestic power facts.
We are in a nation where connecting a ceiling light is expected to be done by a dedicated professional , yet the populace decides how we will power their iphone, and worse how the smelter should be powered....
No wonder industry or what is left of it is fleeing.
Back to the pylons collapse, I try to remember anything similar in the EU while I was there... Hardly anything, pylons collapse there and in the US/Canada happens but as far as I remember mostly under the weight of sticking snow or icing, not under relatively benign winds when pylons have an expected small wind catching surface.
We need to sort this quickly, and it could be fixed faster than repairing the damages the green push is having

basilio said:

Ok. Probably just unclear.

I agree that interconnected entities with PV's personal batteries, community batteries will have usage records and systems. There will be a commercial element to the project. Essentially people will store excess PV energy in interconnected batteries and this will be reused when required. There will be various charges. There will be no issue in normal operational situations.

In an outage the energy banks plus the ongoing PV input will cushion the impact of power failures.

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There is still the issue of synchronicity.
What ever power generating source you provide, it must be able to tie into the the existing frequency without a major disturbance.
there must be a reference voltage and frequency.
There has been talk of using the internet to provide the equivalent of GMT to the network to proved synchronicity, but what happens if the Internet goes down due to no power?
Mick

basilio said:

On what basis do you say that SP ? That sounds a bit counter intuitive. Are you thinking of major energy intensive industrial centres mopping up all this power ? I would say such locations would be prime targets for creating and storing their own power.

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Renewables versus non-renewables.

To make renewables work at scale in a low cost manner by its nature requires the generation and storage facilities to be geographically diverse.

Reason simply being any individual site is extremely exposed to weather variation versus a larger area where that's partially neutralised. Plus there are very few locations with a good solar resource, a good wind resource and which are suitable for pumped hydro. Very few - and any such place that does exist, is a place few are going to want to live due to that wind and steep topography.

Now if we're talking about somewhere with a mild climate, consistent sunshine and low population density then off grid becomes the cheapest way to do it simply because you don't need much equipment, because the resource is good and energy requirement is low, and the grid alternative is costly due to that low density. Plus there's generally no problem with space to put it - big single story houses on big blocks of land and typically there's sheds and so on too. Plus no issue with shading - because the neighbour's quite some distance away and if there's a tree next the house then it'll have been cut down anyway.

For metropolitan areas in southern parts of Australia though, and this includes Sydney as "southern", there's nowhere near enough energy yield from solar during the worst days of winter and that means something else is required. To make that work, you need a network both within the urban area and going to wherever you're going to get that wind, storage etc.

Same goes for industry. The alternative to a grid with generation scattered all over the place is a big power station, coal or nuclear, next to the industrial zone. Because economically getting a constant 500+ MW out of solar located all in the one location doesn't work financially, it requires just too many solar panels to cope with the depths of winter and the days where if you get 0.5 hours' worth of output for the day then you've done well. And yes that happens.

Go to an off-grid property and ultimately most are "cheating" to some extent. They'll proudly tell you they're off the grid but take a close look and odds are you're going to find gas bottles, a pile of firewood and quite likely a diesel generator too. So much for being off the grid - if the aim was energy sustainability then they'd be better off on it.

The fundamental aspect of renewables is the resource is where it is, and the only option is to move the electricity. Same with brown coal for the record. Hence in Australia we had a situation for over 30 years where Tasmania and Victoria where the only states with a proper transmission system. Tasmania started 1916 with 88kV, Victoria started in 1924 and by that time 132kV was where it was at so that's what they installed. Other states didn't get started until much later, 1950's mostly, and they started with what were at the time well proven 132kV lines meanwhile Vic and Tas both went down the track of 220kV from 1956 and 1957 respectively.

Since then there's been further progress - 275kV, 330kV, 500kV. In Australia that's where we stopped but overseas it goes further than that.

Unlike fossil fuels or nuclear where moving the resource itself is an option, albeit rather expensive in the case of coal but it can be done.

Hence the rush of new transmission projects. It's to enable the renewables since without that, the existing transmission system would be fine for a long time yet apart from maintenance. Indeed the capacity's already there, and will likely never now be used, for another big coal station in the Latrobe Valley.

That said, geographic diversity undeniably does bring some benefits depending on circumstances. Eg having generation on the load side of a network failure had obvious advantages no matter what that generation is so long as it can operate islanded.

Most notably at the moment Mortlake gas turbines (Origin), in south-western Victoria, are running base load and there's also constant running of one unit at West Kiewa hydro (AGL) as workarounds.

Smurf I wasn't necessarily seeing urban and Peri urban PV, batteries and larger community/business batteries as the total energy solution. I don't believe it would be practical for the reasons you mentioned.

In that context major power inputs from other renewable energy sources would be essential. But at the same time a large urban PV/ electric car battery/community battery system could function as a substantial energy supply and storage. Bit like a virtual power station.

Micks observation about synchronicity and ensuring various energy inputs being properly regulated is also crucial. I really hope that issue is top of the agenda when energy ministers start to get busy in March

From Evil murdoch press

I made more than $100 when Victoria’s biggest power plant suffered a crippling outage on Tuesday, leaving hundreds of thousands of people without electricity, while industrial users were ordered to shut down, sparking widespread chaos.
It’s no time to gloat – many Victorians could be left with power for “days, if not weeks” according to government officials after six transmission towers collapsed during storms, forcing AGL Energy’s Loy Yang A coal plant to go offline.

But it is an opportunity to explain how a new wave of electricity retailers and tech companies, namely Tesla, are capitalising on an ageing coal-fired network and its notorious reliability problems.

A little more than a year ago, I switched to Amber Electric, a start-up backed by Commonwealth Bank, which raised $29m earlier this month to fuel its global expansion.

ASX and New Zealand-listed software company Gentrack led the raise and will help sell Amber’s SmartShift battery automation technology to the world.
SmartShift is marketed as a different style of virtual power plant.

As Amber’s co-founder and chief executive Dan Adams told me last year: “The traditional virtual power plant model is automating a consumer’s battery for the utility’s benefit. Amber’s approach is to actually automate the consumer’s battery for the consumer’s benefit.”

What this means is that customers have access to a variety of controls via Amber’s app that control how their battery dispatches power to the grid. These controls – which include charging, dispatching or preserving battery energy – are designed to override SmartShift’s automation, giving consumers more control.

The catch is, Amber has become a victim of its own success.

It has been growing too rapidly to the point a Tesla Powerwall overrides a consumer’s instructions. As part of a deal cut between the two companies, Tesla allows Amber – which offers customers wholesale pricing – to control its Powerwall batteries but there is a limit.

What transpired on Tuesday was Amber facing two choices. It could discharge all their customers batteries – even if they hadn’t elected to do so – or not discharge anyone’s battery, potentially facing the wrath of customers who couldn’t capitalise on the energy price spike.
Regardless, Amber says it did not make any extra profit from the outage, passing on the full wholesale feed in tariff – about $19 per kilowatt hour – to its customers. This compares with Victoria’s minimum FIT of 4.9c per kilowatt hour.

Meanwhile, Tesla, AGL, Origin and other virtual power plant providers were able to capture a far greater profit margin from discharging people’s batteries via their own VPPs. Tesla has been approached for comment.

As more than 500,000 Victorians were left without power, I should think myself lucky that I could still run my air conditioner as the temperature soared above 37 degrees. But when I opened the Amber app soon after the outage struck, my battery charge level was little more than 50 per cent and was exporting swiftly to the grid.

Normally, this wouldn’t be a problem but in temperatures higher than 25 degrees, solar panel efficiency begins to drop by about 0.5 per cent above every degree above that level. Combined with dark storm clouds, my system was barely producing a 1kW. My system therefore couldn’t power my home or charge my battery, which was being drained into the grid.

By 4pm, my battery level had plummeted close to the reserve level at 20 per cent. Because I was with Amber – which offers wholesale pricing – I was being handsomely compensated.

But while the FIT was high, grid electricity power prices were higher. If Tesla emptied my battery, I would be forced to pay these prices or become one of the hundreds of thousands of Victorians without power. And there was not a thing I could do about it, despite Amber’s promise of delivering customers more control.

Amber acknowledges this is “frustrating” for its customers but says if people lean into its automation system, they will be better off.

“The good news is that if you leave SmartShift to automate your battery it will make the right call in most cases, leaving you better off than you would have been without it,” the company said in an update late last month.

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During the outage on tuesday, origin enrgy/powercor limited what I could take to charge MY EV.
With the batteries at 100%, I was restricted in what I could draw out from the panels.
No matter what i set in the control panel of the 8KW 3 phase Ac EV charger, it would not run at any more than 1.7 kw.
The rest went into the grid for which they paid me the princely sum of 5 cents per kw, while selling it at the emergency wholesale rate of $19/kwhr.
Nice little earner if you can get it.
Mick

Smurf1976 said:

Mortlake gas turbines (Origin), in south-western Victoria, are running base load and there's also constant running of one unit at West Kiewa hydro (AGL) as workarounds.

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Mortlake output past 3 days below. The advantage it offers is simply that it's connected to the 500kV network in western Victoria, thus being a partial workaround to the inability to transmit to that area from the east.



West Kiewa output past 3 days. That it directly connects to the Victorian 220kV network being the significance here.



Loy Yang A output past 3 days. It wasn't the cause of the problem, just collateral damage - there'll be a proper engineering review of how it responded and whether anything ought change to prevent that happening again but ultimately it was the victim of the crash, it didn't fail of its own accord.



Unit 2 back on first, then a trip overnight, then back on again all good. Unit 3 on next and now starting up unit 4.

There's no particular panic there, demand's low enough that other sources of supply are adequate and the reduced output from LY is not the cause of anyone being without power. Plus the issues with transmission will limit production to some extent anyway. Getting it back on is thus about avoiding unnecessary draw on the hydro storages, avoiding burning expensive gas or diesel where it could be avoided and being prepared for anything else that might fail but it's not critical in the short term, it's not the cause of anyone being in the dark right now.

basilio said:

In that context major power inputs from other renewable energy sources would be essential. But at the same time a large urban PV/ electric car battery/community battery system could function as a substantial energy supply and storage. Bit like a virtual power station.

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Agreed - we're on the same page there.

Suffice to say however I come across many who for some reason have it in their minds that the solution is to not have a grid at all - that works only until it's heavily overcast and cold at the same time then fails spectacularly.

My own solar system at home will run islanded if need be, it's set up to isolate from the network and to operate without an external frequency and voltage reference if need be. It has come in handy - not due to any major power system failure but it was certainly useful when the neighbour's tree took out the private line to my house.

At the community level, the "obvious" approach in my view is "kill two birds with the one stone". If a battery's going to be installed then put it where it serves a local purpose not just an overall purpose. Trouble is the present industry structure makes that somewhat difficult, although there's a decent example on the Yorke Peninsula (SA) with a battery having been installed that can operate islanded when supply is lost from the single circuit transmission to the area. Indeed ElectraNet, the transmission owner, owns that battery.

basilio said:

Smurf I wasn't necessarily seeing urban and Peri urban PV, batteries and larger community/business batteries as the total energy solution. I don't believe it would be practical for the reasons you mentioned.

In that context major power inputs from other renewable energy sources would be essential. But at the same time a large urban PV/ electric car battery/community battery system could function as a substantial energy supply and storage. Bit like a virtual power station.

Micks observation about synchronicity and ensuring various energy inputs being properly regulated is also crucial. I really hope that issue is top of the agenda when energy ministers start to get busy in March

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There's the problem right there, could you give me a heads up on the qualifications of the ENERGY ministers?

Smurf1976 said:

Agreed - we're on the same page there.

Suffice to say however I come across many who for some reason have it in their minds that the solution is to not have a grid at all - that works only until it's heavily overcast and cold at the same time then fails spectacularly.

My own solar system at home will run islanded if need be, it's set up to isolate from the network and to operate without an external frequency and voltage reference if need be. It has come in handy - not due to any major power system failure but it was certainly useful when the neighbour's tree took out the private line to my house.

At the community level, the "obvious" approach in my view is "kill two birds with the one stone". If a battery's going to be installed then put it where it serves a local purpose not just an overall purpose. Trouble is the present industry structure makes that somewhat difficult, although there's a decent example on the Yorke Peninsula (SA) with a battery having been installed that can operate islanded when supply is lost from the single circuit transmission to the area. Indeed ElectraNet, the transmission owner, owns that battery.

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Can you explain how to find out if my home solar is islanded please Smurf

If we were to have a blackout would our battery power fridges lights etc until flat ?

My AC would draw too much I would think, so if we don't run that, could I get a day or two from the battery and panels?

Smurf1976 said:

At the community level, the "obvious" approach in my view is "kill two birds with the one stone". If a battery's going to be installed then put it where it serves a local purpose not just an overall purpose. Trouble is the present industry structure makes that somewhat difficult, although there's a decent example on the Yorke Peninsula (SA) with a battery having been installed that can operate islanded when supply is lost from the single circuit transmission to the area. Indeed ElectraNet, the transmission owner, owns that battery.

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That's the thing that keeps bothering me, I can't really fathom how it will work unless the large storage is regulated, by either common ownership e.g Govt or by Govt regulation.

It is going to be hard enough having orderly control even on a small basis, as in say a group dwelling situation of say 50 houses or units IMO.

Imagine if only 20% of the owners have an EV, are they forced to make their EV's available to support the other residents? If there is a community battery are they allowed to charge their EV's if there is a power shortage? If they make their EV's available to support the community battery, do they get paid for the power used by the rest of their community?

There is already disputes about noise, outdoor lights, parking, I can't even imagine the problems when power becomes communal.

macca said:

Can you explain how to find out if my home solar is islanded please Smurf

If we were to have a blackout would our battery power fridges lights etc until flat ?

My AC would draw too much I would think, so if we don't run that, could I get a day or two from the battery and panels?

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Just go to your switchboard and turn off the mains.
You will then be able to find out if you can last longer than a few hours.
Mick

sptrawler said:

That's the thing that keeps bothering me, I can't really fathom how it will work unless the large storage is regulated, by either common ownership e.g Govt or by Govt regulation.
It is going to be hard enough having orderly control even on a small basis, as in say a group dwelling situation of say 50 houses or units IMO.
Imagine if only 20% of the owners have an EV, are they forced to make their EV's available to support the other residents? If there is a community battery are they allowed to charge their EV's if there is a power shortage? If they make their EV's available to support the community battery, do they get paid for the power used by the rest of their community?
There is already disputes about noise, outdoor lights, parking, I can't even imagine the problems when power becomes communal.

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I agree. Micks observations about how power companies and Amber responded to the power outage adds to the complexities.
We already have community battery projects in operation and many suggestions that car batteries and home batteries be used as virtual power plants. Clearly some careful thought needs to be done to establish technical and financial overviews. Leaving it to the markets would be a xxxxing nightmare. And the energy minister is not going to be the best person.

I think one way to go is plan and legislate a "roughly good" system for an initial 3-4 period with an ongoing review process to iron out the wrinkles. It would be better to start with something reasonable instead of waiting forever to develop the perfect model.

But there would have to be a guarantee that the rules would be revisited at 3-4 years.

basilio said:

I agree. Micks observations about how power companies and Amber responded to the power outage adds to the complexities.
We already have community battery projects in operation and many suggestions that car batteries and home batteries be used as virtual power plants. Clearly some careful thought needs to be done to establish technical and financial overviews. Leaving it to the markets would be a xxxxing nightmare. And the energy minister is not going to be the best person.

I think one way to go is plan and legislate a "roughly good" system for an initial 3-4 period with an ongoing review process to iron out the wrinkles. It would be better to start with something reasonable instead of waiting forever to develop the perfect model.

But there would have to be a guarantee that the rules would be revisited at 3-4 years.

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Agree 100%, something has to be done, we are already at the point of no return IMO.

Now the real clever stuff has to happen, we have community batteries, but I would guess they are Govt owned, so that isn't a problem.

The problem arises when people themselves have to pay for them and they have to feel they are getting a fair deal, or they won't be happy I have dealt with people long enough to know that.

Take for example that small unit complex, where some people have an EV a A/C and the 85" tv + the fridge with an ice maker, they push for a communal battery, meanwhile grandma who doesn't have a car, a computer, etc is asked to stump up for the funding, where is her advantage.
Just a simple back of the napkin thought.

Storage is the problem, solve that problem and we don't have a problem IMO.

macca said:

Can you explain how to find out if my home solar is islanded please Smurf

If we were to have a blackout would our battery power fridges lights etc until flat ?

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Starting from basics, and electrical island simply means an electrical system that is no longer (or was never) connected to the main grid.

Eg Alice Springs is an electrical island. It has its own generation but it is not (and has never been) connected to anywhere else. That makes it an electrical island.

Not to be confused with a physical island. A physical island is not an electrical island if it's connected via underwater cables to a main grid. Or overhead if the island's close enough to the shore.

Now getting closer to your home situation, under normal circumstances your solar inverter is connected to the grid and operates in parallel with it. Whatever the system (grid) frequency, that's the frequency you'll have at home. Hopefully it's 50.00Hz or very close to it - if not then something's gone wrong.

For a solar inverter to operate islanded, without the grid, requires a few things:

An absolute must is that it physically isolates connection to the grid. That is, that your solar inverter is not trying to feed into a dead distribution network. Because apart from overloading the inverter, there's a very real risk that ends up killing someone who's either working on repairing the network, or who's otherwise come in contact with it.

So there are very rigid standards about inverters disconnecting from the network immediately a failure occurs. Eg tree brings the lines down in your street = inverter disconnects immediately that external connection is lost. That's the single greatest concern with private generation, that it can't energize an otherwise dead network.

So for the inverter to be able to power the house, but without powering anything external to the property, it needs to be able to:

1. Isolate itself and the house circuits from the external supply (grid) but leave them connected to the inverter's own output.

2. Produce 230V 50Hz or close enough to it of its own accord without an external reference (the grid) since that's not available. This requires that the inverter can start itself up, and that it can match its output in real time to your consumption.

3. If required output from the inverter is to exceed available production from the solar, even briefly, then a battery is essential. The energy has to come from somewhere.

In practice 99%+ domestic solar inverters are not designed to operate islanded. They're designed to function in parallel with the grid only, and will shut down immediately upon loss of grid connection (regardless of the reason). That's the default design.

If in doubt, just turn the Main Switch (at the switchboard) off but leave everything else on. If the inverter stops production and doesn't restart, it's a normal inverter like the other 99%+

If you do want it to be able to run islanded then for a residential situation the practical way is to install an "off the shelf" inverter that's been designed to do that, which has gone through testing and been approved, etc. Even then, the network will be wanting to know the exact make and model, and will almost certainly send someone out to inspect the installation and do a few tests to confirm that it does what it should.

In my case I simply installed a solar inverter that's designed to operate islanded if external supply is lost and which is DC coupled to a battery (plus of course the solar panels). Normal operation it's on the grid same as any other. In the event of external supply failure, there'll be a brief loss of supply before the inverter restarts and powers the connected circuits.

Normal mode it'll aim to match its production to consumption unless the battery is full, in which case the surplus goes into the grid. Or if the battery's empty then it'll be drawn from the grid. In practice it's a bit slow in responding, that's intentional and a design requirement to dampen any potential oscillations, but it's near enough.

Islanded mode it will match production exactly to consumption, to a maximum of 5kW, unless the battery is discharged in which case it's lights out, no supply until the sun shines.

Separate to that, there are some battery systems (eg Tesla Powerwall) that are designed to work with a conventional inverter, one not designed for islanded operation, and fool it into working and to do so safely. So the battery comes with all the bits to electrically isolate from the grid in the event of supply failure and to leave the house loads and inverter connected. It then mimics the grid, that's how it fools the inverter into working - the inverter thinks its exporting into the grid and has no idea that the "grid" is actually just a box on the wall intentionally fooling it whilst the lines out in the street have been brought down in the storm. etc.

That's an approved design "off the shelf" and the easiest way to add backup (islanded) functionality to an existing system. Certainly not cheap though.

Technically all the Powerwall is doing is being the load or supply source to balance the system and doing that via its own separate inverter. So it produces 230V 50Hz and the solar inverter and loads operate. The Powerwall then just draws energy (charges the battery) or provides additional generation (discharges the battery) so to maintain constant voltage and frequency. That results in the solar inverter thinking the grid's there even though it isn't.

A lot of that explanation @Smurf1976 should make some posters understand, how little they actually understand and that is only at the isolated home situation.

Absolutely nailed it as usual, many of the readers of this thread probably have a better understanding of the issues than the politicians that draft the policy IMO.
By the way smurf for my info, if the tesla battery shuts down when the sun goes down, does it fire back up when the sun comes up, even if the grid supply still hasnt been re established?

sptrawler said:

By the way smurf for my info, if the tesla battery shuts down when the sun gors down, does it fire back up when the sun comes up, even if the grid supply still hasnt been re established?

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Tesla I'd have to find out.

Mine is a different brand, SolarEdge, and has the battery connected directly to it at DC. That is, it's an inverter designed for connection of a battery as well as solar. It can do a black start yes, it can restart itself from a full discharge once the sun comes up since the single inverter is directly receiving input from the solar.

There's also a small disposable 9V lithium battery inside. I've never looked into what purpose that serves but I assume it's to retain memory in the event of a total loss of all power. Eg no mains, no solar and no battery.

Noting also that a "flat" battery isn't completely discharged. It's set in software to simply cease operating at 12% which is done in the interests of long term life and health of the battery. Ultimately though there's still energy available below that, it'd be enough to keep the electronics powered up and ready to go until the sun shines.

For a Tesla Powerwall 2 I don't own one but to my understanding, having previous read the documentation, it cannot perform a black start from solar. Once fully discharged it'll shut down and that being so, there's nothing to "fool" the separate inverter, that's any standard inverter that wasn't designed for this mode of operation, into outputting AC power and restarting the system. That being so, if you're running islanded with a Powerwall then it's crucial to not fully discharge - once you do, you're down until there's mains available to restart.

There is of course another way of providing backup and that's a generator. It's certainly doable to safely connect a generator to power the house, via the normal lighting and power circuits, isolated from the grid. Has the downsides of noise and needing fuel but it's another option, it's doable.