Solar · For traders
How do you size PV strings for UK conditions - Voc at low temperature and MPPT windows?
Short answer
Calculate string Voc at the lowest expected cell temperature using the module's Voc temperature coefficient and keep it below the inverter's maximum DC input voltage; many UK designers use minus 10 °C. Check the hot-weather Vmp stays inside the MPPT window and the string current is within MPPT limits. Use each roof face on its own MPPT.
Last checked 24 September 2026 · 1 source
In more detail
- The IET PV CoP sets the design method; the minimum design temperature to use was not verified in the CoP this session (paywalled).
- Record Voc/Isc at STC and measured values per string on the PV array test report (MIS 3002 App E).
- Different orientations (e.g. east/west, north) on separate MPPTs or with MLPE.
- Plug-in devices: Voc at inverter must not exceed 120 V DC.
The facts, dated
- 01Plug-in device maximum open-circuit voltage at inverter input — 120 V DC
standard · GB · checked 24 September 2026 · GOV.UK
What we saw in the field
[QA review 2026-09-24] C2-1 AGREES; H-2 AGREES. | Earlier notes: Customer 2: south, north and garage arrays as separate strings - agrees with separate MPPT practice; homeowner's 4 NE panels only useful in summer.
Sources
Last checked: 24 September 2026