“What regulations do I need to study when designing a grid connected PV system?” is a question I get asked fairly regularly. The answer isn’t completely straightforward, but the following documents are good places to start.
Solar PV Guide
The PV guide is by far the best start point for any system designer. It started life as a government-funded document – created to support early UK PV grant schemes. Two editions were originally produced, the first in 2002 and a second edition in 2006. We have just finished writing an update (within MCS) and this third edition will be released any day now.
Of all the documents listed in this blog, the PV guide is the only document that really gives detailed and specific info on the design of a PV system, particularly the DC side. Although only a guidance document, its status in the MCS scheme (and the earlier grant schemes) means that it has generally been treated as “the UK PV standard” over the years.
The new guide will be available as a free download on the MCS site – I will post a link as soon as it becomes available.
The scope of the IET wiring regulations (Requirements for Electrical Installations) covers the “design, erection and verification of electrical installations” and has a specific section (part 712) that covers PV systems.
There is obviously no avoiding BS7671 and it should already be sat on the shelf of every designer. However, designing a system using BS7671 alone would be fairly challenging — and there is much in the PV guide that doesn’t get a mention in BS7671.
There are two key documents that regulate connection to the UK grid – Engineering Recommendations G83 and G59. Published by the Electricity Networks Association, these documents set out what is expected by the distribution network operator. ER G83 covers systems up to 16A per phase; ER G59 covers larger systems (ENA website). While key documents and required reading if you need to know about the process of gaining permission to connect a system to the grid, you will need more documents in order to properly design a PV system.
Microgeneration Certification Scheme
If your PV system is 50kWp or smaller and the intention is to claim the feed in tariff, then the MCS documents are key. With regards to the design of the PV system, the following MCS document is required:
- MIS3002 Requirements for contractors undertaking the supply, design, installation, set to work, commissioning and handover of solar photovoltaic (PV) microgeneration systems
There are not actually that many technical requirements lodged in MIS3002 and it is in the process of being re-written to include even fewer. The reason for this is that most requirements are located in the other documents that it calls up – most significantly the Solar PV Guide. The new edition of the guide will absorb most of the requirements currently located in MIS3002.
Although they are not design documents it is perhaps also worth flagging the following MCS product standards:
- MCS005 Product Certification Scheme Requirements: Solar PV
- MCS012 Product Certification Scheme Requirements: Pitched Roof Installation Kits
- MCS017 Product Certification Scheme Requirements: Bespoke Building Integrated Photovoltaic Products
MCS documents can be downloaded from the MCS site.
BS EN 62446
The full title of this standard is Grid connected photovoltaic systems — minimum requirements for system documentation, commissioning tests and inspection.
As its name suggests, this isn’t a design document, but it is still relevant to a system designer. In particular, the requirements for system documentation will be of particular interest to a designer — as they may govern how items like schematics are drawn up. More information on this standard can be found on the BSi site.
I have concentrated so far on the electrical design of a PV system – but there are obviously a host of other considerations to bear in mind when mounting a PV system on a building. These include issues such as how a system gets mounted on the roof, the wind and other loads on that array and the structural implications for the building itself.
The new version of the solar PV guide provides detailed information on both electrical and mechanical design issues and is the best start point for designers. However, any designer will also need to refer to the Building regulations and other standards such as Eurocode 1
As can be seen, perhaps the most significant document in the list above - the solar PV guide - isn’t a formal standard. It is aligned however with much of the content of a draft intentional document – IEC 62548: Design Requirements for Photovoltaic (PV) Arrays.
We have been working for a while within IEC on 62548 and it was due for release fairly soon but how the information gets published is now being debated. The debate centres on how it will relate to an update to IEC60364-712 (the source of part-712 in our wiring regs). The way forward is more or less sorted and once finalised I will post an update.
A keen eyed reader will have noticed a gap for systems above 50kWp – as the solar PV guide is only really called formally for systems under MCS. Many designers and customers of larger systems still refer to the PV guide – but this is all done fairly arbitrarily. There are various ideas to address this issue – again I will post something once the details are sorted.