I’ve recently found out a DNO can impose an inverter limit on a house regardless of if it can export limit. Why? This makes no sense unless they don’t want people storing and self consuming.
What limit are you speaking of. So far I was aware dnos can, rightly, impose export (and import) restrictions to protect the network from phase imbalance, over and undervoltage etc. Are you speaking of something else and if so what (maybe post a reference?).
@transparent will almost certainly know the answer.
Apparently when you apply to connect an inverter to the grid they can impose both an export limit, which I entirely understand, and a total inverter amount for the property.
at least this seems to be what an installer is telling me.
Apparently when you apply to connect an inverter to the grid they can impose both an export limit, which I entirely understand, and a total inverter amount for the property.
at least this seems to be what an installer is telling me.
Never heard of the latter and suspect it may be bs; @transparent will know, alternatively ask your dno.
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
I’ve recently found out a DNO can impose an inverter limit on a house regardless of if it can export limit.
I disagree.
You don't even require G99 consent from your DNO if your inverters can't export to the grid!
I have a plant room where I breed off-grid inverters. Their 240v output is not synchronised to grid frequency. They have their own integral 50Hz frequency generator.
The only reason my DNO knows of these is because National Grid's Area Manager is sufficiently interested that she came and had a look... ... over a very long cup of tea 😎
The EREC rules for grid connection apply only if the inverters have the potential to export to the grid. those inverters have G98 certification.
Thus, if you have an inverter capable of outputting 240v AC in synchronisation with the 50Hz grid frequency, then you do need consent, even if you use all of that power in-house.
G99 applies if you have more than one such device installed. Typically that would be a solar inverter and a storage battery.
The EREC G99 language can be difficult to follow, so I've re-interpreted it into a series of five diagrams:
Does that start to answer the point about what the DNO licensing is about?
It can get messy if you want to install solar inverters with their own inbuilt export limitation system... and storage batteries which have a separate export limitation mechanism.
But it's still possible to achieve in 99% of cases.
Apparently when you apply to connect an inverter to the grid they can impose both an export limit, which I entirely understand, and a total inverter amount for the property.
at least this seems to be what an installer is telling me.
When applying for a G99 to connect equipment to the grid for export, the grid is imposing an export limit AND an inverter size limit, in that you apply to connect 6kWp of solar connected to a 5kW inverter, and the DNO comes back with an offer of yes but limits export to 4kW. You then have 3 months to take up the offer and notify them you have installed the equipment as agreed. You are limited to a 5kW inverter by that DNO offer. If it breaks, you can replace it with another 5kW inverter. You cannot later replace it with a 6kW inverter without making another G99 application.
I think the somewhat unique case of the Tesla PW3 has highlighted this situation more, in that it has an inverter that can be software limited at installation anywhere between 11.04kW (48A) and 3.68kW (16A) output. A G99 application may apply for 7kWp of solar and a PW3, and the DNO will approve but the inverter rating will be limited to 7kW. I'm not sure if this is the installer only applying for 7kW because this is all the solar they plan to install, or if it is the DNO specifying 7kW. Others do get the full 11.04kW inverter rating.
Then there is the case I encountered with my own application to NG, whereby we received a very limiting offer of 7kW inverter rating for the PW3 to match our installed solar but only 1kW export, significantly worse that the 3.68kW of export we already had under G98. When we discussed our objectives with NG, highlighting the export limit was too restrictive to make the project viable, they informed us of a fast track application method allowing for installation of up to two 5kW inverters with 5kW of export, so we went with that effectively trading some inverter capacity for more export (an again an example of the DNO limiting an inverter size)
Ultimately the DNO can set any restrictions they like - it's their grid and their rules, and they are responsible for maintaining it's operation and safety.
Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.
I’ve recently found out a DNO can impose an inverter limit on a house regardless of if it can export limit.
I disagree.
You don't even require G99 consent from your DNO if your inverters can't export to the grid!
I have a plant room where I breed off-grid inverters. Their 240v output is not synchronised to grid frequency. They have their own integral 50Hz frequency generator.
The only reason my DNO knows of these is because National Grid's Area Manager is sufficiently interested that she came and had a look... ... over a very long cup of tea 😎
I have to ask, are you mining cryptocurrency? What do you meant by breeding inverters?
Gonna throw a spanner in there, Inverters are messing up the frequency inside your home to the point is actually is unhealthy. If you believe in that sort of things, that frequency around us can affect us, our cells etc.
Inverters are messing up the frequency inside your home to the point is actually is unhealthy. If you believe in that sort of things, that frequency around us can affect us, our cells etc.
I think you'll have to be a lot more precise than that.
Our environment is filled with waves of photons at all manner of frequencies. Place an ordinary radio wherever you choose and you can detect electromagnetic radiation over a very wide range!
My own home has a lot less mains frequency (50Hz and its harmonics) than those of most other readers here.
That's because I have DC distribution systems for lighting, computer equipment and CCTV. Ie those devices are supplied from the DC of the LiFePO4 batteries you can see in my photo.
All inverters sold in the UK have to pass radio frequency emissions tests. They are inherently safe to use.
In my area of the UK, the main airborne threats are from:
arsenic dust (old mine workings)
radon from uranium ore in the underlying rocks
Inverters don't feature in my list of hazards. In fact they get along quite well with my cells.
@transparentThe only reason my DNO knows of these is because National Grid's Area Manager is sufficiently interested that she came and had a look... ... over a very long cup of tea
@old_scientist When I applied for a G99 I asked for a 12kW inverter and was "offered" a 7kW inverter with a 4kW export limit. They agreed that the export limit can be through a password protected setting controlled by the installer. I reluctantly accepted the 7kW fixed limit as there was no possibility to discuss or appeal. The upshot of the restriction was that we have abandoned our plan for an induction hob (replacing a gas hob) as this would have habitually taken us over the 7kW limit at the worst time of the day for the Octopus Cosy tariff even though all of this usage would normally be from battery storage. This was maddening to say the least. I was quite happy to accept the export restriction and understood the reason but the import restriction makes no sense as we have 25.6kWh of battery storage and so are not heavy grid users, quite the opposite. The obvious solution to overcome the DNO objection would be for the inverter to have the capacity to distribute battery storage power internally within the house above the 7kW limit but only export/import from the grid at 7kW/4kW respectively and for these limits to be by software and verified as not exceeded by the Smart meter, on pain of a heavy fine. As far as I can tell, there are no inverters that can internally distribute more than they can import. Does anyone know differently?
@old_scientist When I applied for a G99 I asked for a 12kW inverter and was "offered" a 7kW inverter with a 4kW export limit. They agreed that the export limit can be through a password protected setting controlled by the installer. I reluctantly accepted the 7kW fixed limit as there was no possibility to discuss or appeal. The upshot of the restriction was that we have abandoned our plan for an induction hob (replacing a gas hob) as this would have habitually taken us over the 7kW limit at the worst time of the day for the Octopus Cosy tariff even though all of this usage would normally be from battery storage. This was maddening to say the least. I was quite happy to accept the export restriction and understood the reason but the import restriction makes no sense as we have 25.6kWh of battery storage and so are not heavy grid users, quite the opposite. The obvious solution to overcome the DNO objection would be for the inverter to have the capacity to distribute battery storage power internally within the house above the 7kW limit but only export/import from the grid at 7kW/4kW respectively and for these limits to be by software and verified as not exceeded by the Smart meter, on pain of a heavy fine. As far as I can tell, there are no inverters that can internally distribute more than they can import. Does anyone know differently?
@howardp99 Yes, I get how the inverter rating is limiting, especially during the evening peak in winter when cooking. I figure our ASHP and background usage may be 1.5kW and the electric cooker is another 3kW. If we then want to use the microwave or boil the kettle, we need to make sure the oven light is off first, juggling usage to try to stay under the inverter rating. Luckily we have a gas hob.
On the subject of gas hobs - we massively prefer a gas hob for cooking (personal preference). We have no mains gas supply, so save the £120 per year standing charge, which more than covers the cost of a 47kg propane bottle to supply the gas hob which we consider to be very cost effective. If we had mains gas, we'd not only have to pay the £120 SC, but then also have to buy the gas we used on top so we feel the propane bottle is a good solution for us.
Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.
