The right inverter for battery storage and some other Qs

[nowty]

Only G99 if hybrid inverter is over 3.68Kw, otherwise its a post install G98 notification.

Even if it's both inverter and EV charging point at the same time?

EV charging point is nothing to do with a grid tie inverter installation.
Might be a DNO notification but its a different process altogether.

[Oldgreybeard]

Even if it's both inverter and EV charging point at the same time?

Just to try and clarify what the DNOs are interested/concerned about, broadly their concerns fall into three categories:

1. Is the proposed installation going to be safe and not pose a risk to their staff working on the network, by "back powering" the network after they have isolated it for maintenance?
This is included in ALL the DNO requirements, and there is a stipulation that any connected generating device (PV panels, battery inverter system, standby generator system, electric car that has a V2G capability, wind turbine, micro hydro plant, combined heat and power unit, etc, etc) be completely isolated from their supply within 5s of a grid failure. This is primarily to allow the DNO staff a safe working environment when doing repairs.

2. Is the proposed installation going to create an overload on their network, either by drawing more power than the network can safely deliver, or by creating a local phase imbalance? This generally applies to all high power loads that require DNO consent or notification, typically things like swimming pools, hot tubs, electric car chargers, the installation of storage heaters or heat pumps, all of which must be notified to the DNO, so they can ensure the loads on their network are balanced.

3. If the installation is a microgeneration system (solar, wind, hydro, CHP, etc) then the DNO need to ensure that the phase imbalance that any generated power exported to their network doesn't cause a phase imbalance (overload is not likely for single phase installations). For generation export under 16A per phase (G98) they only require notification after the event. For generation export greater than 16A per phase then consent is required under G99 before the microgeneration system can be connected.

There are nuances to the export side, in that a large microgeneration system can be throttled down to never export more than 16A per phase, so then becomes G98, and a larger (G99) system can have it's export stopped or restricted via a G100 limiter/relay. Both these latter measures can help get around local export power limitations.

Car chargers have nothing to do with G98, G99 or G100 normally, the only exception to that are the very small number of cars that may have a V2G (voltage to grid) capability. These are vanishingly small in number, but there are signs that some popular models that have V2L (voltage to load, for running things like a kettle when camping) are being abused by complete and utter idiots that are plugging them into their homes. These people will most likely die out as Darwin's principle removes them from the gene pool . . .

[Ken]

The larger Solis Hybrid inverters, RHI 5k-48ES-5G and RHI 6K-48ES-5G - 5 & 6kW respectively both charge and discharge the battery at 5kW. (the actual power is 100A x battery voltage so when fully charged you actually get around 5.25kW. The 6kW one which I have is 6kW from the solar and can "accept" up to 8kW of PV on 2 strings. Will also provide 5kW "back up power" which switches in 20ms after grid failure. G100 (export limitation) compliant and listed on the ENA type approval register.

Datasheet here:

https://www.ginlong.com/rhi_inverter01/33228.html

Roger,
sounds good but going back before batts we used to consider that it was preferential to have a smaller inverter than kwp. Perhaps not for you with your largish PV but do you think this aspect is still relevant. IE is it a good idea to have an oversized hybrid inverter just to achieve good transfer batt rates which is then an over rated inverter for most/all of the PV generation.
Ken

[Oldgreybeard]

Roger,
sounds good but going back before batts we used to consider that it was preferential to have a smaller inverter than kwp. Perhaps not for you with your largish PV but do you think this aspect is still relevant. IE is it a good idea to have an oversized hybrid inverter just to achieve good transfer batt rates which is then an over rated inverter for most/all of the PV generation.
Ken

I agree, definitely more efficient to choose an inverter that is only just big enough, rather than one that is too large. I made this mistake a few years ago at our old house. Meant that 99% of the time the inverter was under-run and so not at all efficient. The issue I found was the standing losses when the inverter was running, but not at full power. Those losses were much higher for a big inverter than a smaller one, and were pretty much fixed by the full power rating of the inverter. This meant that all the time the system was running, even at a low power, the inverter standing losses were soaking up a fair bit of the generated power.

When we built this house I undersized the main inverter, just for that reason, and also opted to go for an AC coupled system, so the battery inverter remains shut down in standby mode (which uses next to no power) once the batteries are fully charged and the house is running from the PV output. I'm not at all convinced that hybrid inverters, especially larger ones, are that good an idea, as they most probably never shut down into standby, so will draw their standing losses all the time.

[ducabi]

Car chargers have nothing to do with G98, G99 or G100 normally, the only exception to that are the very small number of cars that may have a V2G (voltage to grid) capability. These are vanishingly small in number, but there are signs that some popular models that have V2L (voltage to load, for running things like a kettle when camping) are being abused by complete and utter idiots that are plugging them into their homes. These people will most likely die out as Darwin's principle removes them from the gene pool . . .

I've found this on my DNO's webstie. I guess I need to submit it to pre installation and if all good then there is only post-installation notification
https://www.nationalgrid.co.uk/download ... eme/527974

[Oldgreybeard]

Not normally any requirement for consent etc for a domestic charger installation That leaflet from WPD is for business customers. If the existing installation is in good order and has an isolator switch, plus is known to have a suitable power rating (will usually be either 60A or 65A maximum continuous power, the former has an 80A main fuse, the latter a 100A main fuse), then you are good to go with a charger installation, just need to notify the DNO on completion, same as with a G98 PV or battery installation.

All the problems that seem to arise come from older properties with poor or relatively low power mains supplies, one or two installers that simply don't know their arse from their elbow so start creating problems where none really exist, or properties where the existing demand is already at or close to the limit of the supply. The latter usually crops up for homes that have electric heating, hot tubs, spas, swimming pools etc, where their demand may already be close to the limit. Even then the fix is dead easy, just add load limiting to the charger. Many come with this as standard now and it removes any problem and very rarely, if ever, activates in reality, as few homes draw loads of power at night, which is when many choose to charge their cars (especially in winter).

Reading around a few electric car forums I get the very strong impression that there are lots of poor installers in this sector, mostly those working for the big charger companies. Many aren't electricians, so are doing these installations to a crib sheet of instructions and don't properly understand how to deal with any installation that is slightly different to the basic method they have been taught.

The general consensus seems to be to use a local electrician, rather than an installation company. I think that is sound advice, as the only two occasions where we've had something electrical installed by an "installer" have both been poor quality workmanship. One was a gas cooker ignition circuit wired in shockingly badly (literally), the other was a new gas boiler where the wiring was equally poor and failed the first periodic inspection we had done with about half a dozen major faults.

[ducabi]

I asked that question on DNO's chat and they asked me to submit a form but it could be just a regular response with too few details in my questions.

Anyway, your experience is not much different to mine that's why I'm trying to fully understand how exactly installation has to look like so that I can see what the professional is doing wrong.

[Oldgreybeard]

Always better to ask forgiveness rather than seek permission when dealing with official bodies, I think. Asking makes them think they have to give you an answer, and if they don't know the answer straight away they often seem to end up making hoops for you to jump through.

It was a lesson I learned early on when starting to build this house. I wrongly assumed that I had to ask permission for several things, but quickly learned that this was the wrong approach, and that "proper" builders rarely, if ever, do this, as they have learned that doing so makes a rod for their own back.

[ducabi]

So best to your knowledge and experience, when it comes to battery storage, am I correct I have to use electrician to install inverter but can connect batteries myself?

[nowty]

So best to your knowledge and experience, when it comes to battery storage, am I correct I have to use electrician to install inverter but can connect batteries myself?

Yes and that’s the oficial rules.

DC side is your side as long as you know what you are doing and are confident with it.