The reason I needed to mention SunSynk is that their inverters have two 240v mains ports, one of which operates unsynchronised during a power outage.
AFAIK they are the only G99 Approved Supplier who offers such functionality.
G98 would normally prohibit such operation under the 'anti-islanding' requirements.

The ENA also recognises their particular implementation of 'export to grid' as being capable of limitation to whatever the DNO stipulates - including 'zero export'.

Those accreditations for installation in the UK would appear to be unique.

Yes, I agree that my terminology doesn't embrace 'off-grid' in the way that it would be perceived by a crofter in Scotland, for example.

"Off-grid" means "off-grid", whether it is in the Highlands, Berlin or Tokyo. My original post is about designing a system not connected to the grid in any form. It can have advantages such as not being tied to 240v AC and thus, in some circumstances, does not need an inverter. My initial difficulty is that the Austrian Kit is not sized for UK cylinders.

It may be possible to get someone to make an adapter or alternatively purchase a Scottish-made but Euro-sized Cylinder; https://www.acv.com/gb/technology/cylinders

Cheers

Graeme

What you are suggesting doesn't seem to be off-grid, but rather balancing the grid by using home - batteries. Storing excess grid power in people's home batteries *is* better than wasting it. But this *does* need a connection to the grid.

Yes, I agree that my terminology doesn't embrace 'off-grid' in the way that it would be perceived by a crofter in Scotland, for example.

I'm suggesting that the home is supplied by a storage battery, but that the grid can be used to re-charge that battery when conditions for that are favourable.

Your grid export is constrained, regardless of external fluctuations.
Whereas I'm suggesting that recharging from the grid should be dynamic, responding to external conditions:

• price per kWh
• energy-mix
• excess generation within the same locality

For the remaining 4 months, I import during the night for usage during the day.

And that is commonly the case.
The reduced night tariffs are there to keep the Gas Turbine plants operating in Combined Cycle mode.
It's an artificially low price, which adversely affects wind-farms whose output gets curtailed.

But that day/night balance will gradually change as more EVs account for road traffic.

You don't need to have a completely separate off-grid system, incidentally.

Some inverters (SunSynk for example) can limit grid export to the grid within the figure stipulated by the DNO,
but also run the house from a battery.
During a grid-outage, the house remains supplied with electricity.

I am not sure how realistic it is for most folk to be off-grid?

Realistic in terms of price?
Or because of practical arrangements to have a storage battery installed?

What you are suggesting doesn't seem to be off-grid, but rather balancing the grid by using home - batteries. Storing excess grid power in people's home batteries *is* better than wasting it. But this *does* need a connection to the grid.

Within a year I produce 150% of my electricity need. My home battery is 11kwh which balances my daily usage and balances day to day usage in summer. But I also export continuously to the grid for 8 months of the year. For the remaining 4 months, I import during the night for usage during the day. Although I am (currently) more than self-sufficient - I need the grid to balance summer - to winter. To truly disconnect from the grid, I would need a 1000 kwh battery!!!

So in terms of my OP - I am not (normally) permitted to increase self-production on my grid-connected power circuit. There is nothing to prevent me, however, from having an *additional* off-grid power circuit. If using PV's, I still have a problem of having lots of power during the summer and not enough during winter. If used simply for powering a heating element, there is no real need for a battery within a days usage - and just silly to think of it for time-shifting across seasons. Sizing is important - because it is not connected to the main house circuit, any spare capacity is just wasted (though some must be expected). The heating element is not an issue - but powering the thermostat is. Using low voltage/wattage, can make the thermostat ineffective - resulting in blowing up your cylinder. Not pleasant. The Austrian heating element I mentioned is designed for its thermostat to be self-powering direct from panel.

But your answer made me question whether my existing system is already being "clipped" and an additional battery may be beneficial. Certainly any move away from gas space heating in winter would need additional capacity.

Thanks

Graeme

I am not sure how realistic it is for most folk to be off-grid?

Realistic in terms of price?
Or because of practical arrangements to have a storage battery installed?

The financial viability depends on what you're comparing with.

I've attended a number of regional briefings by National Grid companies, and I follow the requirements made of them by Ofgem (RIIO-ED2 Agreements etc).
They have a roadmap which charts the way forward for infrastructure upgrades.
Here's a slide from a presentation 11 months ago:

That slide refers only to the national Transmission Grid, operating at 400kv and 275kv.
How much do you think it's going to cost to increase grid capacity to these levels over the next decade?

That will have to be footed by rises in consumers' bills.

There are similar levels of increased capacity to be implemented on the regional Distribution Grid (132kV and below)
That will be paid for by increases in Daily Standing Charges as well as consumption bills.

These are levels of expenditure in excess of the HS2 rail project... which was curtailed because the UK couldn't afford it.

It would be lot cheaper to subsidise the installation of in-home batteries...
... starting with social-housing tenants, households in energy poverty and those with prepayment meters.

Since those households tend not to have access to Time-of-Use Tariffs, they have no incentive to spread their electricity demand.
Consequently they contribute greatly to the 'early evening peak':

National Grid are required to ensure that there is always enough power, so the infrastructure is designed to carry a level greater than the peak.

Having too much demand is not an option.
It would act as a drain on the 'rotary generation' sites, and the 50Hz frequency would drop.

Contrarywise, having excess supply isn't regarded as a problem.
The DNOs can make 'Offers to Connect' to thousands of potential generation companies, far in excess of what the infrastructure can support:

As a result, on days that are particularly windy or sunny, an Active Network Management mechanism kicks in, resulting in generation sites being removed from the grid, or their output curtailed. I think that's what you're referring to as "clipping or throttling power to the Grid".

An ANM plot for generation in a location where there are existing wind turbines looks like this.

Wind output is highest around the two equinoxes.

Instead of discarding that electricity, it could be usefully stored in home-batteries.
Obviously those batteries need to be close to the nodes where excess generation is going to occur.
But the data already exists to achieve such a solution.

What's lacking is the political will.

Indeed! We should be primarily considering the off-grid route.

...

Local battery storage within the home (or school, or farm) is a strategy which mitigates most the present energy problems.

Whilst I agree with the sentiment, I am not sure how realistic it is for most folk to be off-grid? In June, I exported 755kwh but last December I imported 287kwh.

@transparent - As you work with National Grid, you may help me with my understanding. As I understand it the DNO limits the size of PV installations (in this case on single phase) to prevent an overload from your PV to the Grid. Also, as a consumer, you can limit overloading from your PV to your invertor through clipping.

The DNO's interest is the integrity of the Grid, not your internal system.

Is there not some general way of clipping or even throttling power to the Grid. I don't need any higher yields in June - but I could do with a better yield in the winter months. In particular, a way that would satisfy the DNO and permit you to add more PVs to your system? [That is without going three-phase, which will cost in excess of £2K

Cheers

Graeme

we are limited by the DNO, as to how many panels we can connect up to the grid. So to be really flexible, you need to think of off-grid as well.

Indeed! We should be primarily considering the off-grid route.

The topic DIY solar upgrade - Considering adding more panels is actively exploring this route.

Two of the respondents there are been upgraded to 3-phase supplies by their DNOs, but the way in which it's subsequently been implemented within the home by the professional electrician has demonstrated that they haven't understood the fundamental basics of how 3-phase is intended to resolve the problems. Start reading at this point in that topic if you want to see how phase-imbalances can cause outages.

It's not the DNOs who are 'limiting' the deployment of grid-tied solar generation by policy, but the physics of what happens to the grid when we do so. The vast majority of UK housing stock is supplied by single-phase Feeds from the local substation. That's not the case elsewhere. Germany is rolling out 3-phase domestic supplies for good reason.

I have a partnership agreement with National Grid, which allows me access to their data and network maps.
That allows me to gather information on what's happening now...
... and what we should do in the immediate future.

Local battery storage within the home (or school, or farm) is a strategy which mitigates most the present energy problems.

And good thoughts too! Thinking flexibly is important. My main roof is East/West. Which makes the PV's only 75% efficient as South facing. However, as I have double the usable roof space - I can achieve an output of 150% as a similar South/North facing house. Additionally, the input from the panels is flatter, with higher levels first in the morning and later in the evening.

The main difficulty, as I see it, is that we are limited by the DNO, as to how many panels we can connect up to the grid. So to be really flexible, you need to think of off-grid as well.

Cheers

Graeme

Over the past few years I've been having conversations with Councillors from my Local Planning Authority.
Those have elicited some interesting insights about what is or isn't addressed by the Planning Act.
For example:

Unless you're in a designated Conservation Area or the property is Listed, you don't require planning consent to install PV panels.

Those panels do not have to be placed on your main roof.
They can be on an arbor at the bottom of the garden, or a chicken shed.
But there are height restrictions which apply to any structures within 2.4m of your boundary.

Ground-mounted panels are permissible.

There don't appear to be any restrictions on PV panels which are held in place by frames or tubs which can be moved.
You can buy plastic 'tubs' precisely for that purpose... although they seem to be as expensive as the panel itself!

Bi-facial panels do not have to face the sun because both sides generate electricity.
Some farmers in the West Country are looking into using bi-facial panels vertically, where they would double up as livestock fencing.

The aluminium frame of a solar panel isn't that much different to the aluminium used to build a greenhouse.
Some of the greenhouse sections could reasonably be 'built' by bolting PV panels together.

Just a few thoughts... 😎 

Solar thermal panels are at least 80% efficient,
whereas the max. possible efficiency from a (single sided) silicon PV panel is 23%.

I know! I have three problems - (1) I now have limited roof space - I have space on (a) south facing roof for about 3 pv panels - shaded after 12 noon and (b) another south facing roof for about 3 PV panels - shaded until 12 noon. (2) Both these locations are not good for piping to the HW tank. (3) Dont have sufficient space to increase HW tank size to accommodate lower temperatures.

Thus PV with its lower efficiency - may have some advantages with its flexibility.

BTW - As a reminder. My existing DHW is currently heated by my primary PV's for 6 summer months and Gas for 6 winter months.

Thanks for the pointer to TP Fay in Kirkby. - Appreciated.

Graeme