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G99 application experience

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Estimable Member Member
1207 kWhs
Joined: 1 year ago
Posts: 72
Topic starter  

Having decided on the PV and battery equipment that I wish to install, and after some prompting from various areas, I decided to submit my own G99 application while still to make a decision on the supplier/installer. As a retired electronics engineer, this shouldn't pose much of a challenge. The equipment I have chosen is by no means unusual and from reading various Internet forums it is clear that there are plenty of similar installations. I submitted my application, emphasised my lack of familiarity with the process and asked the DNO to contact me with any queries. After an appropriate delay, I expected - preferably sooner rather than later - to be advised what export limit would be applied.

Once I had selected my supplier/installer they offered to chase my application. I agreed, perhaps unwisely, on the basis that they should be more familiar with the process. I then sat back to wait for some queries.
Yesterday - more than two months after I submitted my application - the DNO has provided the following information to my installer:

    Please see below voltage disturbance found on the study:
    LV disturbance on the service existing = 0.36%
    + 5.124kW Photovoltaic = 2.13% - 0.36% = 1.77%
    ++6.0kW Battery Storage = 4.57% - 0.36% = 4.21%

    G99 level of volt rise allowance = 1.7% max
    G100 level of volt rise allowance = 2.4% max

    Please note: voltage disturbance to other customers on the network can’t surpass 1.5%

Does anyone know what this means? My installer can't explain it to me and there is no narrative to show how these figures have been derived. It's not obvious to me why PV and battery are considered separately, either.

I'd be interested to hear of others' experiences of G99 applications and whether their applications have progressed more smoothly than mine. Also, what export limitations have been applied in your case - particularly in the case of separate PV and battery inverters. G100 export monitoring will surely be at the same point for both, so why not the same limit for each?

Regarding the 'disturbances' mentioned by the DNO, over the past week my grid supply has ranged from 230 - 244 V.  Not a great excursion, but larger than 1.5%.


Mars reacted
Noble Member Contributor
3640 kWhs
Joined: 2 years ago
Posts: 644

happen to know your are in MK same as me as per one of our other discussions. Western power were also concerned about voltage rise with my system as part of the application. They actually put a voltage logger on my house for a week as a precursor . I didn't see as much details as you did, it all went through my installer so I can't help you with meaning of the numbers. Their measurements proved there was no issue so they gave permission. In the last week, my voltage has varied from 222 (1am, battery and cars charging) to 245.8 (midday on a sunny day but not exporting all going into battery)

My octopus signup link
210m2 house, Samsung 16kw Gen6 ASHP Self installed: Single circulation loop , PWM modulating pump.
My public ASHP stats:
11.9kWp of PV
41kWh of Battery storage (3x Powerwall 2)
2x BEVs

Mars reacted
Estimable Member Member
1207 kWhs
Joined: 1 year ago
Posts: 72
Topic starter  

@iancalderbank In the numbers above, there is no common relationship between disturbance and power for battery and PV, for example. Some context would be useful. I quickly scanned the G99 and G100 documents but nothing jumped out at me. Although we don't know what the figures relate to, I'm mildly amused at the accuracy and resolution given my grid voltage logs. 

With your 3 Powerwalls (and, presumably, a large PV inverter) could I ask what export limits you have had applied.

Mars reacted


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