What's the best Home Energy Storage option for retaining domestic stored solar power in preparation for power cuts?

It does seem that way. I’m nowhere near an expert capable of giving a proper answer, but I would assume that it might be something to do with preventing an overload or imbalance somewhere.

Off-grid batteries could be considered to be a bit like an Uninterruptable Power Supply, (or even just a giant powerbank) which can kick in and flip to battery power in the event that the mains supply goes down for any reason. Usually, this is designed to either allow you to ride the storm through a short outage, or give you enough time to safely perform graceful shutdowns on all protected equipment and take it all offline properly, so that nothing gets lost or damaged. How much load a UPS can handle and for how long very much depends on multiple factors, such as the capacity of the batteries, type of UPS and the load that’s depending on it.

But apparently, grid-connected batteries and microgeneration has to shut down if there’s a power outage on the grid.

would this mean any grid-connected battery can’t be used to supply your house in case of a power cut?

Yes, that’s correct. It’s part of the specification for G98/G99/G100 devices.

If a generation device such as a Storage Battery or PV Inverter is grid-connected for export, then it is required to de-couple its output within a few mS of a power-outage.

Moreover, when the mains supply is restored to the house, all export devices must remain disconnected for a random amount of time before automatically connecting. This ensures that there will be no surge-currents in an area when the DNO switches the Grid back on.

This may better explain why I feel that there is a lot to be gained by having at least some off-grid capability for any house with Storage Batteries.

In light of this new information @Jess_OVO you may now want to re-read the story about the low grid voltage at March End.

Sounds like off-grid storage might be the best fit for use as a back-up power supply then, @dnshorto

@Transparent, does this mean the possibility of filling batteries from the grid for use during a power-cut wouldn’t currently be allowed?

No @Jess_OVO - in fact the opposite should be the case.

Look at the diagram I posted above. Charging a Storage Battery from the mains is permitted, whether or not you export any of that electricity back to the Grid.

If that off-grid battery is to run a Heat pump or EV charge-point, then I still think that the Low Carbon Technology application should be made to the regional DNO in the usual way.

Moreover, such a configuration of Storage Battery could provide major benefits to the Distribution Grid.

a: if that area of the country currently has an excess of renewable energy generation, then it makes more sense to store it in customers’ homes than to pay compensation to the producers to remove some of the available capacity.

b: If there are losses due to phase-imbalance at the local substation, these could be reduced by adding a Smart-load, such as a Storage Battery or immersion-heater, to the phase which is drawing least current from the Grid.

c: Customers in energy-poverty could be provided with a Storage Battery by a local Housing Association, and linked to a Time Of Use tariff. That enables them to avoid taking power when it’s most expensive. There is a strong ethical dimension to this approach.

All this technology is available, but needs to be welded together using a predictive Smart-network such as the Flex Platform from Kaluza, or Kraken-Flex from Octopus.

What’s needed is a trial-site with a Storage Battery in an area with abundant generation from Grid-connected commercial Solar and Wind farms which can’t always be fed back to the National Grid. They’ll need to be put on a variable ToU tariff ahead of other customers so that the relevant algorithms can be developed.

Oh look!

I just happen to be in the ideal location with a PowerVault Battery which can’t be used for the original intended grid-support trial! 

I do hope the Smart Home Team at OVO are seriously looking into this.

Well now I am confused, @Transparent !

 

Rather than store the energy as heat, which would require a massive tank, I proposed a grid-connected battery feeding an off-grid inverter.

 

So by having a grid-connected battery but an off-grid inverter would this allow the battery to charge up from the grid but the inverter would still operate during power-cuts even though the battery isn’t able to? Does the Inverter act as another store of energy then or is it able to access the energy stored in the battery somehow? 

Hope you’re following this better than me, @dnshorto!

That 100A Off-grid Inverter draws energy solely from the battery stack @Jess_OVO

How and when the battery is re-charged is a separate issue. The householder will want to achieve that in the cheapest and greenest way possible.

An off-grid inverter continues to operate in a complete power-cut.

Great chat above, I think we’ve narrowed it down and we have an answer for you, @dnshorto:

Although I’m aware you have two inverters in play here. The Solis inverter and the Growatt AC Coupled inverter.

So where does that leave you? 

Imagine me as the future viewer of this thread who’s keen to understand their options! 

Thank you to the various contributors who responded to my question; I have been away in Scotland until today and found it frustratingly impossible to log in to my Ovo account on my cell phone in order to reply. Back on my laptop today which has given me access once more!

In particular, thank you @transparent, as before, for highly relevant answers.

When planning to install solar panels and batteries, one of my primary motivations was to make provision for future power cuts. In a 1980s house with zero provision for alternative domestic heating that will work without mains input (no flues, no fireplaces) and with household members suffering from long-term disabilities I knew I had to think ahead. All this was made abundantly clear to the solar panel company who won the contract.

Imagine my shock on learning a few days ago that the batteries as set up in the approved system CANNOT be used during a power cut. I suspect that this would have been news to the solar panel salesman too, as he had given not the slightest hint that my plan was unworkable. I had originally planned to install a diesel generator for back-up power but chose the solar-powered battery bank as a much greener (and quieter) option.

@Transparent has written of an “off-grid” battery, which could be charged from the grid when available. 

Thinking of the parallel situation on board a boat which these day may well have many of its domestic systems running on 230v ac, powered when in dock from a shore line and when at sea from batteries  via an inverter, is there a possibility here to replicate a similar system for a house?

Via a suitable changeover switch or switches, could the house be disconnected from the grid during a power cut and the battery bank take over the load? 

An “off-grid battery” suggests a whole separate item, which inevitably means extra cost.

During normal times the present battery bank is a great asset and reduces our grid consumption brilliantly, so that for much of the year I would want to keep it connected. What I need to work out is some way to utilise that stored power for those coldest, darkest days and nights when this coming winter’s power cuts are most likely to catch us out.

David

Correction: “ In a 1980s hours”, should have been  “In a 1980s HOUSE” of course.

Also, having now re-read some earlier posts on the laptop (instead of the cell phone!) I see that @Transparent is clearly discussing an off-grid INVERTER, rather than a separate battery bank. My mistake. 

Would that separate inverter be able to use the same domestic distribution system within the house, or would completely separate circuits have to be run?

The primary concern would be the gas CH boiler, which is within the same integral garage as the batteries, inverters etc, so a separate feed to that would be quite feasible.

Cooking could be by portable “camping’ type gas ring, and lighting is also easily obtained. It’s the ability to keep the house warm in  a really cold winter that concerns me.

David

To be honest, I think you’ll find that a backup diesel generator would be a terrible option for other reasons too. Not least the fact that the ones which are suitable for use as a UPS (Uninterruptable Power Supply) solution of any kind are generally pretty expensive and not easy to maintain, so they’re not really a viable option for domestic use.

This may also come as a surprise to everyone who decided to panic buy petrol and diesel recently, but there’s another flaw too! Petrol and diesel literally have use by dates! XD

Seriously, I’m not joking. If you leave that stuff just sitting in a tank for too long, it goes off and becomes unusable… And that’s assuming it hasn’t somehow evaporated before then! Because yes, that’s also a thing which can happen as well. You can literally lose an entire tank of petrol and diesel into the atmosphere. :D