Solar designer

Written and checked by the Energy Merchants desk · Reviewed 3 October 2026

A solar designer is the person who plans the system. They choose and layout the panels, size the inverter and cabling, and make sure the design meets the standards. They then sign off the design as compliant.

Why accreditation applies

For a system to create STCs, the design and the installation must meet the requirements set under the Renewable Energy Target and the accreditation scheme. In the grid-connected world, the same accredited person often both designs and installs. In larger or off-grid jobs the designer is more likely to be a separate specialist, because the design carries more risk. See SPS.

In practice

The designer’s details appear on the compliance statement alongside the installer’s. A designer’s accreditation, like the installer’s, needs to be current on the date of the work. A good design record includes the single line diagram, the equipment list and the calculations for voltage drop and protection, and these are what an auditor would look at.

Design choices affect the STC claim indirectly. A system that is oversized for its inverter, for example, is a design decision, not a certificate question. See inverter oversizing.

Worked example

A commercial installer designs a 60 kW roof array, with the DC to AC ratio set within the manufacturer’s and the network’s limits. The same accredited person signs the design and, later, the installation statement. The STC count, based on panel rating, zone and deeming period, is unaffected by the inverter limit.

Common confusion

Designer and installer are separate roles on paper, even where one person fills both. A salesperson who sketches a layout for a quote is not the accredited designer. A quote drawing is not a design sign-off.

See STC trading, how STC audits work and the glossary.