Solar Panel ROI Calculator

Solar Panel ROI Calculator helps Compare two everyday planning options using upfront cost, recurring cost, and time horizon assumptions.

System capacity

Monthly usage

kWh

Local subsidy

KRW

Self-consumption ratio

Install cost: ₩4,500,000
Government subsidy: ₩3,090,000
Current monthly bill: ₩65,699
After-solar monthly bill: ₩23,188

Net investment

₩210,000

Annual generation

3,216 kWh

Break-even

5 months

20-year ROI

5,259.6%

IRR 258.6%

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Solar panel ROI calculator guide

This English page translates the Korean solar-panel ROI calculator and calls calculateSolarRoi. It preserves capacity, regional irradiance, panel direction, tilt, shadow loss, 2026 installation cost, government subsidy, electricity tiers, VAT 10%, fund 3.7%, SMP 105 KRW/kWh, annual degradation, inverter replacement, 20-year cash flow, break-even, IRR, and scenarios.

Installation cost and subsidies

The source uses default installation cost per kW of KRW 1,500,000 for systems up to 3 kW, KRW 1,300,000 for 3 to 10 kW, and KRW 1,100,000 above 10 kW. Total installation cost is capacity times cost per kW.

The 2026 government subsidy table applies KRW 1,030,000 per kW up to 3 kW, capped at KRW 3,100,000 for 3 kW, and KRW 800,000 per kW above 3 kW. Local and additional subsidies are subtracted separately from investment.

Generation and electricity-bill savings

Annual generation uses capacity, regional irradiance, system efficiency 0.80, direction factor, tilt factor, and shadow loss. South and optimal 30-degree tilt use 1.00 factors, while east or west and flat installation reduce generation.

Electricity-bill savings are calculated by comparing bills before and after self-consumed solar energy. The bill model includes residential tiers, base fee, energy charge, VAT 10%, and power-industry fund 3.7%. Surplus generation is valued with SMP 105 KRW/kWh.

20-year ROI model

The cash-flow model runs for 20 years. It applies annual panel degradation of 0.5%, electricity-rate increase, annual maintenance cost as a percent of installation cost, and inverter replacement in the configured year at cost per kW.

Break-even month is interpolated from yearly cumulative cash flow, and IRR is calculated by Newton-Raphson. Scenario presets change self-consumption and rate-increase assumptions to produce conservative, standard, and optimistic views.