Homeowner Blog

Why the National Grid Capacity is First Come, First Serve.

Tok Charles · 22 May 2024

Why do we have to apply for permission to connect to the grid?

When you install a solar/battery system larger than 3.68kW per phase, you must submit an application, usually G99, for permission to connect the system from your local Distribution Network Operator (DNO). Most solar installers will do this application on your behalf, usually after you’ve settled on a final system design. 

The designers at your local DNO will look at the total capacity of the inverters included in your application and run the calculations based on the worst-case scenario to them which is when your system is exporting to the grid at full capacity.  

Example: if you plan to connect a 10kW solar inverter and a 5kW battery inverter, they will model for the worst-case scenario which would be that both inverters are exporting to the grid at maximum capacity, i.e. 15kW is being pushed out to the grid through your MPAN (electricity supply). 

The designers’ job is to work out whether the local grid network infrastructure - the transformers, substations and cabling - is strong enough to take the additional power. If it’s not strong enough to take the full capacity of the system that you are proposing, they will then revert to whoever submitted the application and let them know the largest capacity that can be installed without paying for upgrades to the local network. Often, this will include generation and export limitations. 

So, why does this mean that the capacity on your local grid is first come, first serve? 

If you live on a cul-de-sac with 10 houses, whoever installed the electricity connection to the cul-de-sac will most likely have installed a large cable from the transformer into the cul-de-sac which then branches off to the 10 houses. There will be a certain amount of capacity within that cabling to accommodate micro-generators like solar PV & battery storage, as well as to accommodate for all the houses drawing large amounts of electricity at peak time.  

If the first house then installs a solar system, some of that capacity is now taken up. When the second house comes to install solar, there will be less capacity available for them. Now, unless the local infrastructure is very old, there should be enough capacity in the cabling to accommodate for a few micro-generators, however, by the time that the 5th or 6th house is looking to get a solar PV system, they may get hit with grid restrictions such as export limitation. By the time that the 10th house gets solar, they may be stuck with the bare minimum of 3.68kW per phase and having to pay for upgrades if they want more capacity. 

It’s worth noting that the DNO must allow a minimum of 3.68kW per phase without contest, so every house should at least be able to get 8-10 panels and a hybrid battery storage system. If you’re interested in getting a larger system, it’s certainly worth cracking on with it – especially when you see your local installer’s van outside your neighbour's house. 

Here's an article by the National Grid on the different projects that will be required to prepare the grid for net-zero.

If you'd like to take advantage of the capacity before the other houses on your street, get in touch with us today and request a quote, or give us a call.

Topics: Battery storage, Off grid, Solar PV