Solar roof panels may only be connected in series up to a certain number. Exceeding the maximum system voltage may damage the components and compromise the safety of the system. To avoid this, the number of solar panels connected in series must be carefully selected so that the maximum system voltage is not exceeded, even at low temperatures. The lower the temperature, the higher the open-circuit voltage.
The following examples explain how the maximum number can be calculated.
Temperature difference to the reference temperature:
ΔT=25 °C–(-20 °C)=45 °C
Voltage increase per solar panel due to the temperature change:
ΔVsolar panel=VSTC×((ΔT × coefficient)/100)
ΔVsolar panel=8.28 V×((45 °C × 0.3%)/100)
ΔVsolar panel=8.28 V×0.135=1.1178 V
Maximum voltage per solar panel at lowest temperature:
Vmax=VSTC+ΔVsolar panel
Vmax=8.28 V+1.1178 V=9.3978V
Maximum number of solar panels permitted in series:
Nmax=Vsystem/Vmax
Nmax=(1,000 V)/(9.3978 V) ≈ 106.42
Maximum number of solar panels that can be connected in series at -20 °C: 106
Temperature difference to the reference temperature:
ΔT=25 °C−(-20 °C)=45 °C
Voltage increase per solar panel due to the temperature change:
ΔVsolar panel=VSTC×((ΔT × coefficient)/100)
ΔVsolar panel=19.33 V×((45 °C × 0.3%)/100)
ΔVsolar panel=19.33×0.135=2.60955 V
Maximum voltage per solar panel at lowest temperature:
Vmax=VSTC+ΔVsolar panel
Vmax=19.33 V+2.60955 V=21.93955 V
Maximum number of solar panels permitted in series:
Nmax=Vsystem/Vmax
Nmax=(1,000 V)/(21.93955 V) ≈ 45.59
Maximum number of solar panels that can be connected in series at -20 °C: 45
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