Energy Efficiency, Renewable Systems and Emerging Technology
Energy Efficiency, Renewable Systems and Emerging Technology
This domain tests Part 8 of BS 7671, the design choices that cut losses, and the specific requirements for PV (Section 712), EV charging (Section 722) and battery storage.
Efficiency levers
- Conductor sizing above the minimum where losses matter over long runs and long operating hours.
- High-efficacy LED and presence or daylight controls; power factor correction; harmonic assessment where non-linear loads dominate.
- Motor efficiency classes IE3 and IE4 under IEC 60034-30-1; variable speed drives where load varies.
- Load management: EV charge point de-rating, battery storage and time-of-use tariffs.
Renewables
PV: DC isolation at the array and at the inverter, string fusing where required, cable rated for DC, and string open-circuit voltage checked at the lowest expected cell temperature. EV charging: Section 722 requires 30 mA RCD protection; where a Type A device is used it must include 6 mA DC detection, otherwise a Type B device is needed.
Worked example
A string of 10 modules has Voc 41.2 V at STC and a Voc temperature coefficient of minus 0.29 %/K. At an expected minimum cell temperature of minus 10 C, the temperature difference is 35 K, so the correction factor is 1 + (0.0029 x 35) = 1.1015. String Voc = 10 x 41.2 x 1.1015 = 454 V. This, not the 412 V at STC, is compared with the inverter maximum DC input of 500 V, which leaves an acceptable margin.
Traps
Using STC open-circuit voltage for maximum voltage; ignoring the sign of the temperature coefficient; omitting either DC isolator; applying AC voltage drop assumptions to DC strings; assuming a Type A RCD alone satisfies Section 722.