Distribution Network Operator (DNO)

A distribution network operator, or DNO, is the company that owns and operates the local electricity distribution network in a region of the UK. Ofgem's description is the plainest one: distribution network operators move electricity from the transmission network to homes and businesses. They own the cables, substations, transformers and service heads, and they decide what capacity is available at an address.

A DNO is not your energy supplier. The supplier sells you electricity under a contract and sends the bill; you can change supplier this afternoon. The DNO is fixed by geography and you cannot choose it. Seven DNOs operate across fourteen distribution districts: Northern Ireland Electricity, SSE, SP Energy Networks, Electricity North West, UK Power Networks, National Grid and Northern Powergrid. National Grid appears in both conversations, which is where much of the confusion comes from - it operates the transmission network and it is also one of the distribution network operators.

There are also IDNOs, independent distribution network operators, which own and maintain newer sections of network serving housing and commercial developments. An IDNO is not tied to a geographic area, is connected directly or indirectly to the main distribution network, and is regulated by Ofgem in the same way.

How to find your DNO

Two ways, both quick. The Energy Networks Association publishes a DNO search tool that takes a postcode and returns the operator and its contact details. Failing that, the Meter Point Administration Number on any electricity bill for the supply identifies it directly: the first two digits of the MPAN are the distributor ID, and each ID maps to one network operator.

DNO approval: when you notify and when you must apply first

This is where the DNO shows up in a project programme. Any installation that generates electricity or adds significant demand has to reach the DNO, and the technical rules are Engineering Recommendations G98 and G99. G98 covers fully type-tested micro-generators up to and including 16A per phase. Above 16A per phase, G99 applies, and G99 means prior permission - you cannot commission first and tell them afterwards.

• Solar PV under G98: notify the DNO within 28 days of commissioning, using G98 Form B.
• Solar PV under G99: written permission to connect is required before installation. Because MCS certification for electricity generation runs to 50kW, MCS-scope installations use Type A G99 and Form A3.1.
• Battery storage: DNOs treat storage as demand when it imports and generation when it exports. Under G98 it is Form B within 28 days; over 3.68kW with storage it is Form A1.1, submitted before installation.
• Solar PV and battery together: combined generation is usually above 16A per phase, so G99 applies. There is a fast-track route, Form A1-2, where capacity is over 3.68kW, the inverter is type-tested to G98 standards and the storage will not operate when the grid fails. It goes in before installation, but the connection time is shorter.
• Heat pumps: where new maximum demand is between 60A and 100A inclusive, apply to connect before installing and the DNO assesses supply capacity within 10 working days. Where maximum demand is 60A or less and the other criteria are met, you can connect and then notify within 28 days.

The practical point for installers is that the notification route is decided at survey, not at commissioning. A job that turns out to need prior permission after the equipment is on the van has already slipped. Renewables and electrical contractors who track the DNO step on the job record alongside the survey, the order and the commissioning date can see which jobs are waiting on someone else before the customer rings to ask.