Homeowner Blog

DNO Permission for Solar PV

David Woon · 20 Feb 2020

Image: Ofgem.

What is DNO permission and when do you need it?

The DNO or distribution network operator is the company responsible for distributing electricity from the National Grid to your home or business. In the UK there are 14 different district networks or DNO regions which are owned by six groups. For our installation zone, the distribution network operators which we are concerned by are Scottish & Southern Electricity (SSE), UK Power Networks (UKPN), and Western Power Distribution (WPD).

When installing solar PV or any form of electricity generation to a grid connected property, the local DNO will need to be informed. Depending on the size of the system this can either be done retrospectively, unless prior permission needs to be granted. If prior DNO permission is required for an installation this can take up to 11 weeks to be granted. The size of the PV system is based on the AC inverter rating rather than the peak DC rating of the panels.

If the system size is under 16A per phase (3.68kWp for a single phase supply or 11.04kWp for a three phase supply) then the DNO will just need to be notified within 28 days of the system’s commissioning. Prior permission is not required as the addition of such small systems is very unlikely to cause any load issues to the current infrastructure of the local grid.

However, if the solar PV system to be installed is greater than 16A per phase then prior permission will need to be granted. This is because the grid needs to conduct a network study to determine whether the local grid can handle the added load. The grid may state that additional work needs to be done prior to the installation to cope with the extra energy that the system generates. The DNO will work to a worst case scenario and will design and set requirements in line with these, even if incredibly unlikely, to ensure the security of the grid.

DNO permission is also required for any battery system that has backup functionality and that ‘islands’ the property from the grid in the event of a power cut.

electricity grid

What are the outcomes of a DNO application?

Once the DNO application has been made the DNO will conduct their assessment and will produce a connection offer. This will detail the maximum specification of the allowed connection and whether there are any associated connection charges. The typical three outcomes from the offer in order of likeliness are:

  1. The application is accepted and the system size that was requested can be installed with no additional charges or amendments.

  2. The system size is capped at a given kWp AC rating and export limitation is needed. A witness test could be required to ensure the limitation is put in place, which would incur a small fee.

  3. To install the requested system size the supply needs to be upgraded from single to three phase and the system can’t be connected until the required works have been completed. The charge for this can be very expensive and will vary from site to site.

Can you avoid DNO permission?

You cannot avoid getting DNO permission unless you are prepared to go off-grid, which is not advised. As the installed generation will be used to power grid-connected loads (with excess energy exported to the grid), the install needs to be compliant with grid regulations. DNO permission can only be avoided if the PV is to supply electricity to non-grid connected loads only, meaning these loads will only function when there is sufficient solar generation or with an off-grid battery system. Unfortunately dedicated off-grid PV and battery systems are incredibly expensive compared to a normal grid-connected system, further reducing the viability of this option.

When do you need to apply for DNO permission?

The DNO application for any project is handled in house by Spirit and we will liaise with the relevant DNO on your behalf and keep you updated with the progress. The application is usually made at point of order so we can apply for the desired system size. However, if you have a large upcoming project we are happy to apply for DNO permission at an earlier stage so that we can finalise a system size which will comply with the relevant DNO before proceeding.

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Please note that if you already have a PV system installed by Spirit then you don't need to worry - we would have taken care of the necessary DNO permission during the process!

Topics: Battery storage, Solar PV, Inverters