Solar PV & Battery Systems (BS 7671 Chapter 82)

The transition toward renewable energy has fundamentally changed electrical installation design. The introduction of Chapter 82: Prosumer’s Low Voltage Electrical Installations (PEI) in BS 7671 dictates strict new guidelines for premises that both consume and produce electrical energy.

DC Array Sizing & Inverter Clipping

Modern solar panels generally produce around 200 Watts per square metre. However, in the UK climate, solar arrays rarely hit their absolute peak capability. It is standard engineering practice to "oversize" the DC solar array relative to the AC inverter (a clipping ratio of around 80%). For example, installing a 5.0 kWp array on a 4.0 kW inverter ensures the inverter works harder and more efficiently during cloudy winter months, while only marginally "clipping" peak power on the brightest summer days.

DNO Applications: G98 vs G99

Connecting generation equipment to the National Grid requires permission from the District Network Operator (DNO). The type of application depends entirely on your AC Inverter rating:

• G98 Notification: Applies to micro-generators. If your total AC generation capacity is 16 Amps or less per phase (3.68 kW on a single-phase supply), you can install the system and notify the DNO within 28 days of commissioning.
• G99 Application: If your AC generation exceeds 3.68 kW on a single-phase supply, you must submit a G99 application and receive explicit prior approval from the DNO before any installation works commence.

Battery Storage Sizing Methodology

A battery that is too small wastes excess solar energy back to the grid, while a battery that is too large will never fully charge, wasting capital investment. A highly optimized residential battery system is sized to cover the property's overnight baseload (typically 40% to 50% of the daily usage), ensuring the battery cycles completely every 24 hours.