GUIDE · FOR UK SOLAR INSTALLERS · 13 MIN READ

MIS 3012: The MCS Battery Storage Standard, Certification and Courses

maximum power output in MIS 3012's scope

50kW

maximum power output in MIS 3012's scope

classes of battery system (EESS)

4

classes of battery system (EESS)

per phase, all generation added up, before G99 applies

16A

per phase, all generation added up, before G99 applies

MCS certified batteries installed in 2026 to the end of September

60,000+

MCS certified batteries installed in 2026 to the end of September

Summarised from MCS's own documents and pages, read on 10 November 2026. This is a guide, not the standard: work from the current issue in the MCS Standards & Tools Library.

What MIS 3012 is, and which issue applies

MIS 3012 is the Microgeneration Installation Standard for battery storage, prepared by the MCS Battery Storage Working Group. MCS brought battery storage into its installer scheme in 2021, and says it is now its fastest growing certified technology, with more than 60,000 installed in UK homes and small businesses in 2026 to the end of September.

MCS's library lists two versions:

• MIS 3012 Issue 1.0, dated 22/11/2021, under the current installer scheme.
• MIS 3012:2025 Issue 1.0, dated 01/01/2025, under the redeveloped installer scheme. Its foreword says compliance is mandatory for MCS contractors certified to MCS:2025.

Both say the standard must be read with the IET Code of Practice for Electrical Energy Storage Systems. MIS 3012 is the battery companion to MIS 3002 for solar PV: on a solar and battery job you work to both.

What MIS 3012 covers

Battery systems for permanent buildings with a maximum power output of up to 50kW, in these use cases:

EESS classes 1 to 4

MIS 3012 classifies a system by how its parts are packaged and who answers for them. The class decides how much of the design responsibility is yours.

Limited or full scope. Under the 2021 issue you are assessed for limited scope (Classes 1, 2 and 3) or full scope (Classes 1 to 4), and a Class 4 system has to be assessed by the certification body before you can be certificated as full scope. Class 4 systems also carry extra requirements: battery installations designed to BS EN IEC 62485, automatic charge regulation, overcurrent protection and isolation as close as possible to the battery terminals, and battery health monitoring that stops charging when a battery is in question.

Key design and installation requirements

Among the requirements in MIS 3012:2025:

• Meet all legislation (it can differ between England, Wales, Scotland and Northern Ireland), assess the building with a competent professional experienced in EESS, carry out risk assessments and draw up a Construction Phase Plan under the CDM Regulations 2015 before work starts.
• Design and install to the latest IET Code of Practice for Electrical Energy Storage Systems; where requirements conflict, BS 7671 wins over MIS 3012, which wins over the Code of Practice.
• Inverters must be fully type tested to the latest ENA requirements, and the installation must follow EREC G98, G99 and, where export is limited, G100.
• Battery enclosures in dwellings at least IP2X (top surfaces IP4X), terminals at least IP3X or tool-access only.
• Locate batteries so a fire can't compromise protected escape routes, with adequate ventilation, clear of foreseeable flooding, and with fire detection where they sit in a rarely visited part of the building.
• In island mode: isolate the line and neutral conductors from the grid supply, never isolate the grid's protective earth, and don't rely on the distributor's earth; TN-S is the preferred earthing arrangement, TT where that isn't practicable.
• House current transformers so removing one can't defeat export limitation, and monitor for faulty or disconnected CTs on Class 4 systems.
• Keep the home network secure: hand the customer the device credentials, and components should meet ETSI TS 103 645 for consumer internet-connected devices.

Where the MCS contractor is responsible for notifying building control, that has to be done before handover. Self-certification instead of building control approval is only allowed through a competent person scheme that covers the work.

G98, G99 and G100 for batteries

MIS 3012 says the MCS contractor notifies the distribution network operator, following EREC G98 for installations up to and including 16A per phase, EREC G99 above that, and EREC G100 where export is limited. The 16A threshold is the total AC output of all generators at the site: the standard's own example is a 3kW solar PV system and a 3kW battery on the same single-phase supply, which together exceed 16A, so G99 applies.

MCS's Notifying DNOs page adds:

• DNOs class storage as demand when it imports from the network and as generation when it exports.
• Under G98, submit G98 Form B within 28 days of installation.
• Under G99, including installations over 3.68kW with energy storage (storage on the AC or DC side), submit Form A1-1 before installation, then the combined A3-1 and A3-2 installation document. See our G99 application guide.

Inverters must be fully type tested; look them up on the ENA Type Test Register. A domestic battery on an existing home can also go through ENA Connect Direct, and an export-limited system needs a G100 scheme. Not sure who the network operator is? Start with our DNO application guide.

Commissioning, labelling and handover

• Commission the system to a documented procedure that shows it is safe, installed to MIS 3012 and the manufacturer's instructions, and working to the design. Appendix A of the standard is an example commissioning checklist for domestic EESS, used alongside the BS 7671 certificates.
• Verify earth fault loop impedance and prospective fault current in every operating mode, testing the charging mode with every inverter and bi-directional converter disconnected.
• Label to Appendix C of the Code of Practice; the labels in its Figures C.2 and C.5 are always required, and C.3 on DC coupled and bespoke systems where the DC terminals aren't concealed.
• Give maintenance instructions including arc flash working procedures and the protective equipment needed, unless the whole battery enclosure goes back to the manufacturer for repair.

MCS also publishes an EESS handover document in its library, with a commissioning certificate that records the system class, whether it is island mode capable, the maximum power output and the usable capacity. On a domestic job the customer also gets financial protection for the work: MCS lists battery storage among the technologies most approved products cover (see our guide to insurance backed guarantees).

How to get MCS certified for battery storage

The route is the same as for solar PV (our MCS certification guide has the detail), with battery storage added as a technology:

1. 1

   Learn the requirements

   Read MIS 3012 for your scheme and the IET Code of Practice, plus the scheme documents in the MCS library.

2. 2

   Build a competent team

   MCS's business roles include a Main Contact, a Licensee who signs the Installer Agreement, and a Technical Supervisor who signs off every installation. In a small business one person can hold several roles.

3. 3

   Get the competency evidence

   MCS says a Nominated Technical Person shows competence with an in-date qualification or personal certification, non-regulated training approved by MCS, or an MCS approved independent assessment; MCS 025 sets the detail.

4. 4

   Pick a certification body that covers batteries

   On 10 Nov 2026 MCS listed battery storage against Amtivo Group (British Assessment Bureau), Certsure (NICEIC), NAPIT Certification, Simply Certification and the IAA.

5. 5

   Scheme checks and assessment

   MCS checks finances, how you treat customers and past complaints; the certification body assesses a site installation and your processes. Each technology needs at least one fully compliant installation for the assessment.

MCS approved battery storage courses

MCS's course finder lists the training that meets its competency requirements, filtered by technology. For battery storage it listed these on 10 November 2026:

• BPEC: Electrical Energy Storage Systems (EESS).
• EAL: Level 3 Award in the Design, Installation and Commissioning of Electrical Energy Storage Systems.
• City & Guilds: Level 3 Award in the Design, Installation and Commissioning of Small Electrical Energy Storage Systems (2923-34).
• LCL: Level 3 Award in the Design, Installation and Commissioning of Electrical Energy Storage Systems (Battery Storage).

Each course is run by training centres approved by its awarding body, so dates, places and prices come from the centres; MCS's finder links to them and can be filtered by region and by online or in-person delivery. If you are new to the trade altogether, our guide on how to become a solar installer covers the electrical qualifications that come first.

MCS 042: the battery product standard

MIS 3012 covers the installation; there is no MCS product standard for the battery itself yet. MCS opened a four-week consultation on a draft Battery Storage Product Standard, MCS 042, on 13 October 2026, written by its Battery Storage Technical Working Group of installers, manufacturers, trade associations and certification bodies. Comments were due by 11:59pm on 10 November 2026. MCS says it will review the feedback, finalise the standard and publish it, and give updates as it brings the standard into the scheme.

Batteries on commercial solar

MIS 3012 isn't only for homes: it covers any permanent building up to 50kW, and has a clause on network access in commercial and industrial premises (follow the client's IT and security policies). A bigger commercial battery is outside its scope and goes through the IET Code of Practice, BS 7671 and a G99 application, and the insurers' fire code is worth reading too (see RC62). Business customers will also ask how a battery is treated for tax: see solar panels and capital allowances.

Standards and paperwork are the part you control. Commercial jobs to put them to work on are the other part: see how to get commercial solar leads, or browse commercial solar survey appointments and pay only for appointments that are actually attended.

MIS 3012 and battery certification: FAQ