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The IET Code of Practice for Grid connected Solar Photovoltaic Systems

By: James Hoare CEng FIET FEI 

The third edition of the IET Code of Practice for Grid-connected Solar Photovoltaic Systems is expected to be released in early 2027.
 
There have been a number of significant developments in the photovoltaic (PV) sector since the publication of the second edition in 2022, which has necessitated a requirement for a revision. In four years, there have been  developments, both in terms of technology evolution, sector learning, and policy. 
 
The guidance has been updated and expanded primarily as a result of:

  • The introduction of revised technical standards, including the 4th Amendment of BS 7671 Requirements for Electrical Installations, IET Wiring Regulations, Eighteenth Edition, in 2026. 
  • A significant increase in the use of bifacial modules, not only on utility scale PV farms but also on rooftop PV projects.
  • Acceptance of almost total universal adoption of transformerless PV inverters on residential and medium scale PV systems.
  • Increased recognition of the criticality of operation and maintenance (O&M) with solar PV systems.
  • Increased awareness of PV fire concerns and availability of new guidance on fire safety.
  • Increased global risks associated with cyber security.
  • Growth in repowering of ageing PV systems.
  • Introduction of plug-in solar systems in the UK.

The preparation of third edition of the IET Code of Practice for Grid-connected Solar Photovoltaic Systems is well underway, and one of the technical authors, James Hoare, provides some insight into what we can expect of the new publication.

Regulation and technical standard updates

BS 7671:2018+A4:2026, Amendment 4 of the IET Wiring Regulations, was published by the IET and BSI on 15 April 2026. The previous version is scheduled for withdrawal on 15 October 2026; this has introduced regulation changes to the installation of PV systems and will be mandatory after this date.

IEC standard updates

In addition to BS 7671, the notable number of IEC standards referenced in the current IET Code of Practice for Grid-connected Solar Photovoltaic Systems have seen a number of updates and revisions made in the last four years.

PV module technology and increasing sizes

One of the most significant changes is the evolution of the PV module itself. In 2026, bifacial PV modules with ratings of 750 Wp+ are now available, which can output significantly larger currents than previously, together with associated compounded resistive heating losses.

When the bifacial factor is considered, the level of complexity in system design increases notably. Section 3 of the code of practice, “Solar PV array and module operating characteristics and behaviour”, has been updated to incorporate a significant update to IEC 62548-1:2023, and explains terms like BNPI, kcorr and bifaciality coefficient.

Bifacial PV modules are now appearing on rooftops as well as PV farms, and makes the understanding and need for correct design important for all sectors.

Plug-in solar systems

The built environment and ground mount PV sector has been the domain of installing organizations working to BS 7671 compliance. 2026 has seen the emergence of the concept of plug-in solar systems, which plug into a property’s installation but are an appliance, so are not covered under BS 7671.

The IET has been providing guidance and recommendations on feasibility and checks. There is a new section on plug-in solar, incorporating this IET, and additional, guidance that outlines aspects where technical knowledge and process is highly important, and that may not be available from high street stores selling the products. 

Repowering of PV systems

It is no secret that PV system performance reduces slightly each year from PV modules and inverters, and with many systems now >15 years old, the decision to replace certain equipment within the system can be justified economically whilst adding many years of additional operational life expectance. There is a new section on PV repowering.

Cyber security

The risk and consequences of cyber-attacks has been known for a long time, but the frequency, and level of sophistication, have increased significantly in the last few years and it is now a major threat to energy security. PV systems are generally connected to external communication systems, and within the latest edition, there is new section with guidance on cyber security in line with the Network and Information Systems Directive relevant for critical sectors for national infrastructure including energy, transport, health, and digital infrastructure.

PV and fire

The importance of the consideration of minimizing PV fire risk has been increasing in recent years with the significant increase in the number of PV installations. This topic was already covered in the previous two editions, but due to the high importance, it has been revised as its own dedicated section “PV systems: fire considerations”, which includes updated PV fire guidance not available in the Second Edition.

O&M

This aspect of PV systems has historically been neglected in some sectors due to incorrect sector communications that PV was “Fit & Forget”. This section has been updated further, confirming the criticality of O&M.

Health and safety

The health and safety section has been revised to provide a greater level of information and awareness of the requirements for health and safety compliance within the PV installation sector.  

Grid connection 

The section on grid connection has been updated to accommodate new standards and processes, including the Electricity Networks Association (ENA) Engineering Recommendations G99 Fast track and G100.

PV and batteries

The section on electrical energy storage systems has been significantly reduced in scope, and now directly references the  IET Code of Practice for Electrical Energy Storage Systems. This avoids duplication, and also avoids the risk of conflicting guidance between the two publications   

Array frame earthing

Inverters with electrical isolation between AC and DC were standard in the early years of grid-connected PV, but in 2026, most non-utility scale PV inverters are transformerless without AC and DC separation. With the recognized importance of O&M and post installation testing on PV systems, the code of practice is requiring the protective bonding of array frames when inverters without AC/DC isolation are installed. This will harmonize with what is required in mainland Europe.

Conclusion

The third edition of the IET Code of Practice for Grid-connected Solar Photovoltaic Systems, PV installation contains a number of timely updates, so that industry can be abreast of the fast changing landscape in this field, which is of key importance to the UK government’s approach to reducing the UK’s carbon emissions. The third edition includes updates to cover technological developments, industry practices, and legislative frameworks, since the previous edition.

About the author

James Hoare is a Chartered Engineer, and Managing Partner of consultancy LHW Partnership LLP.

He is Fellow of the IET and Energy Institute and has over 25 years PV system experience from “off grid” to utility scale and has assisted in various guidance publications and workgroups including the IET Code of Practice for Grid-connected Solar Photovoltaic Systems, 2nd Edition (2022).