NPV Calculator Formula

The Solar NPV calculator is based on the formula:

Formula for the net present value (NPV) of a solar energy system.


-C_Rep over ( 1 + i ) ^ 15

+ sum from{t = 0} to{p -1} G_1 times(( P_S X S) + (P_E times (1 - S)))X (1 + i_e)^t X( 1 - d )^t / ( 1 - i )^t


NPV = Net Present Value
CIns = Installation Cost
CRep = Cost to replace the inverter at year 15
i = Future value discount rate
p = lifespan of the solar panel system
G1 = Electricity price in year 1
PS = Price of electricity for self consumption
S = Self-consumption factor
PE = Price of electricity for export
ie = Electricity price inflation
d = Solar panel degradation (annual, compounded)

See solar NPV spreadsheets to learn more about solar panel NPV calculations.

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Installers generally don't offer quotes for timeframes longer than 6 months. So here are guide prices (before grants):

  • 2kW (S): ~€5,500
  • 4kW (M) + myEddi: ~€8,500
  • 6kW (L) + battery: ~€12,500