Now I know I'm getting replies from folks in the trade - I'm losing track of the jargon! Anyway, ok, G98, G99 are look-up-able, albeit mostly from the PoV of what's changed from before.

I guess in terms of normal homes with relatively few inhabitants, it's only electric showers (and potentially EVs), that exceed the 3.xkW as single appliances. I imagine that to make best use of solar (PV and/or thermal) one should restore the hot water storage that was removed when the combi boiler was put in - before my occupancy - and replace, or supplement, the shower with one run off the hot water tank. 

Hi Gideon, why not use the combi boiler for showering? Reduce the load on the electrical system. You could even keep the electric shower and install a thermostatic mixer valve shower on another wall. So you would have the choice of either.

I wonder. Is the G98 16A/phase limit on what's generated or what's exported?

I'm just wondering about the possibility of an EESS that had a larger inverter (or combination of inverters) that could supply large internal loads (>16A/phase) but was programmed/configured in such a way that no more than 16A/phase could ever leave the prosumer's installation.

G98 (www.energynetworks.org/.../ENA_EREC_G98_Issue_1_Amendment_4_(2019).pdf) seems to generally talk about generator capacity, but in the actual definition of ‘Registered Capacity’ (which is what the 16A/phase limit is applied to) it talks about ‘maximum level of Active Power deliverable from the Micro-generating Plant’ - where ‘Plant’ is defined as the overall prosumer's installation, rather than any individual generator. I suspect it's not a consideration they had in mind when writing the words, but it seems like it could be interpreted as being a limit on ‘export’ rather than ‘generation’.

   - Andy.

You may want to work out whether any changes you are thinking of will cost you more than they ever save.

I already have a hot water tank.  It's normally heated by has, but has an immersion heater as a backup.  Paying to have a solar diverter professionally fitted to heat the tank with spare solar power would have cost me about 4 years worth of gas to heat the tank.

That figure is rather approximate, as the amount of gas needed to heat a tank of water from warm to hot is so small it barely registers on my gas meter.

There are inverters that will monitor the export using a current clamp.  They can then limit the export to 16A, even if your home is using some power and they are generating more than that.  Inverters with an integrated battery will probably have a current clamp anyway, to avoid running the battery flat exporting power to the grid.

That's the sort of thing that needs discussing with the installer, who may need to consult the DNO to ensure it's approved.

If the grid in your area is reasonably solid, you might get permission to export more than 16A anyway.

AJJewsbury: 
 

I wonder. Is the G98 16A/phase limit on what's generated or what's exported?

I'm just wondering about the possibility of an EESS that had a larger inverter (or combination of inverters) that could supply large internal loads (>16A/phase) but was programmed/configured in such a way that no more than 16A/phase could ever leave the prosumer's installation.

G98 (www.energynetworks.org/.../Resource library/ENA_EREC_G98_Issue_1_Amendment_4_(2019).pdf) seems to generally talk about generator capacity, but in the actual definition of ‘Registered Capacity’ (which is what the 16A/phase limit is applied to) it talks about ‘maximum level of Active Power deliverable from the Micro-generating Plant’ - where ‘Plant’ is defined as the overall prosumer's installation, rather than any individual generator. I suspect it's not a consideration they had in mind when writing the words, but it seems like it could be interpreted as being a limit on ‘export’ rather than ‘generation’.

   - Andy.

It's what's generated (total possible generation including parallel grid-connected inverter output) plain and simple. Regulation 22(2) of ESQCR explains what we know as the “G98 route”.

If Reg 22(2) conditions are not met, or (in the opinion of at least some DNOs) Regulation 21 applies, then it's G99.

Also, G100 would apply to export limiting systems such as the one you describe - you need to demonstrate to the DNO that the export limit works properly.

Hi, I don't think this particular combi can do showers. It's not really capable of a viable bath, and washing up requires careful juggling of tap aperture to get the water warm enough. Other combis I know can be fine. And I'm not sure that we'll ever directly replace it, if it lasts into the heat pump era. 

Whilst the energy going into you battery is “free” solar, taking it out of the battery will eventually expire.

An interesting exercise is to use the battery supplier's data to work out the theoretical number of charge/discharge cycles it is capable of (for various depth and rate of discharge) and get the kWh it is supposed to be capable of delivering and then divide the cost of a replacement battery by the above kWh and see what each kWh (unit) will cost………………………

The last time I did this it came to around 46p/kWh……

Regards

BOD

Yes, I do think there's an awful lot of dubious sales bull, which perhaps is allowed to pass because it is, as it were, written in green ink.

I'm fairly green of thinking, but I also suspect that in many cases, the cost of something, or more exactly the whole-life-system-and-use cost, is a reasonable proxy for the total environmental damage it causes.

Put it another way, “your” hypothetical fully electric Rolls-Royce causes more pollution than my (equally hypothetical) little petrol Citroën. 

Perhaps the community can comment on this proposal for a 100% solar solution charging a new heat store for 90 minutes and then using the existing 10KW shower.  The idea is to run two 240 VAC devices at 110 VAC so they run at one quarter power.  New heat store is an insulated 120 litre immersion heater tank, like the one you installed before a Combi boiler was put in - but with no connection to the gas boiler, installed by a plumber.  Existing 10KW shower is always run at quarter power (2.5KW) from the 110V output of a 3000VA, 240/110V transformer, like the ones seen at many building sites that drives power tools, installed by an electrician.  The electric heating element in the immersion has to be switchable, not sure how this could be done in practice.  Full power from grid for 20 minutes for when there is not enough sun.  A quarter power at 110V from a second building site transformer for 90 minutes for when there is sufficient sun.