How the DNO calculates maximum generation capacity
Hi, I'm in the process of installing a system and the DNO as stipulated a maximum generation capacity of 7.2kW with an export limitation of 4.1kW. The proposed design was an 8kW inverter with export limitation, 5kW battery and 17*400w (max 6.8kW) panels. However, I'm told I need to downsize the system to a 5kW inverter and 16 panels because my DNO (SSE) considers that even though there will be an export limitation device in place, the 8kW inverter means that there is a risk that I could return 8kW to the grid - if the limitation device fails, if all panels are generating, if the battery is full and discharging etc etc. So they have a belt and braces approach in case there is a failure somewhere on my system leading to more than 7.2kW of generation and their way of achieving this is to limit the inverter to 5kW. So it seems my only choice is to reduce the inverter size and drop a panel which I want to avoid, so I wondered if there are any other options that would allow me to meet all the DNO constraints but still stick with 17 panels?
Thankyou so much for this.....I updated my DNO application installation diagram to show the CT coils etc. what you have mentioned here is very usefull.... I have also sent an additional email to my DNO reitterating what you mention above.
I have some sympathy with the DNO's there are quite a few inverters on the market....you can't expect an engineer to know and understand the peculiarities of a particular inverter. I think it critically important when making an application they have as much clear and consise information on hand to understand the operation of the system. When I looked at my application diagram - submitted by my installer.....there was nothing wrong with the diagram - it just displayed the most basic of information. I had to show the CT coil explain the locked menu and the fact that the MEL and voltage parameters could be set and locked at commisioning. I also had to explain my battery was DC only (ie not like a Tesla power wall) and was fully controlled by the inverter which has locked parameters.Etc etc.....it took me quite a while to sort out. Hopefully, my DNO can make an informed decision.....time will tell. I will let you guys know. my view is if they don't have the information they are likely to slap another limiter on the end of the system - which is nonsense....