Solar PV Voltage Drop Calculator

In accordance with industry guidance, the voltage drop for the DC solar PV string should be calculated to ensure it does not exceed the maximum permitted voltage drop at the stc between the solar array and the inverter.

2.1.4 d.c. Cables – General, 2.1.4.1 Cable Sizing
Cables should be sized in accordance with BS 7671. These calculations shall also take into account the multiplication factors in 2.1.2 of this guide.

Guidance on a method of cable sizing, including any de-rating factor requiring to be applied and typical current carrying capacities for common cable types are provided in Appendix 4 of BS 7671.

Solar DC Voltage Drop Calculations

Solar PV DC Voltage Drop Calculator

In order to carry out a volt drop calculation of the solar PV string you will need to know the resistance per meter for the specific cable type and size.

Within our Electrical Tools and Reference app (see above), we have created a new DC Volt Drop calculator with the resistance per meter for cable type Photovoltaic Solar EN 50618 H1Z2Z2-K with cable sizes ranging from 1.5mm² up to 240mm².

The DTI Guide to the installation of PV systems 2nd Edition states,

2.1.4.1 Cable sizing; Cables should be sized such that overall voltage drop at stc between the array and the inverter is <3%.

 The MCS, Guide to the Installation of Photovoltaic Systems also states,

2.1.4.1 Cable sizing; Cables should be sized such that the overall voltage drop, at array maximum operating power (stc), between the array and the inverter is <3%.

DC Voltage Drop Formula

R = Resistance per meter of the selected cable.
Ib = Load in Amps.
L = Cable length.

Volts Dropped = (L x 2) x Ib x R
Voltage Drop % = Volts Dropped / Voltage(U) x 100

For calculating voltage drop in AC circuits visit Voltage Drop Calculator.

References:
Photovoltaics in Buildings Guide to the installation of PV systems 2nd Edition – source.
Guide to the Installation of Photovoltaic Systems – source.