Solar income calculator
Estimate revenue, monthly profit and payback from capacity, SMP, REC and construction cost. Add a loan to see the cash that actually remains.
Monthly profit after O&M
- Annual generation
- 130,000 kWh
- SMP revenue
- ₩14.9M
- REC revenue
- ₩9.3M
- Annual revenue
- ₩24.2M
- Annual O&M
- ₩3.5M
- Annual net profit
- ₩20.7M
- Total investment
- ₩180.0M
- Annual loan payment
- ₩0.0M
- Monthly cash after loan
- ₩1,727,905
Before tax, land rent and permit delays. SMP and REC change monthly and output varies with shading, soiling and inverter efficiency, so compare the conservative scenario as well. REC weights differ by site and capacity.
Three price scenarios for 100 kW (₩1.8M per kW)
| Scenario | Monthly net | Payback |
|---|---|---|
| Conservative | ₩1.4M | 10.5 yrs |
| Current | ₩1.7M | 8.7 yrs |
| Optimistic | ₩2.0M | 7.5 yrs |
Monthly SMP and REC (land)
| Month | SMP (KRW/kWh) | REC (KRW) |
|---|---|---|
| 2026.09 | 114.94 | 71,482 |
| 2026.08 | 139.07 | 70,926 |
| 2026.07 | 129.72 | 71,525 |
| 2026.06 | 112.00 | 71,975 |
| 2026.05 | 119.75 | 71,023 |
| 2026.04 | 117.78 | 71,573 |
| 2026.03 | 108.83 | 70,388 |
| 2026.02 | 106.53 | 71,294 |
| 2026.01 | 101.76 | 71,693 |
| 2025.12 | 88.84 | 72,343 |
| 2025.11 | 93.38 | 72,186 |
| 2025.10 | 98.79 | 72,331 |
SMP is the average of hourly land SMP; REC is the volume-weighted land spot average. Updated daily from Korea Power Exchange open data.
How it is calculated
Generation = capacity (kW) × yield per kW SMP revenue = generation × SMP REC revenue = generation ÷ 1,000 × weight × REC price Net profit = SMP + REC revenue − O&M Payback = total cost ÷ annual net profit
Defaults: Korea Power Exchange open data for 2026-09 (average hourly land SMP, volume-weighted land REC spot price), 1,300 kWh per kW a year, ₩35,000 O&M per kW a year, ₩1.8M construction per kW. Conservative and optimistic use the lowest and highest month of the last 12 months (±15% of last month until six months of data exist).
Questions
How much does a 100 kW solar plant earn a month?
With SMP ₩114.94/kWh, REC ₩71,482, weight 1.0 and 1,300 kWh per kW a year, revenue is about ₩24.2M a year and about ₩1.7M a month after O&M, before loan payments, tax and land rent.
How often do SMP and REC prices change?
Both move every month with fuel costs, grid conditions and REC supply. The defaults here are updated monthly; try the conservative scenario before committing.
Does this work for farmland or agrivoltaic solar?
The revenue formula is the same, but permits, grid connection and REC weights differ by site. Check land use, permits and grid capacity before trusting the numbers.
What happens when I add a loan?
Annual loan payments (equal principal and interest) are subtracted from net profit, showing the cash that actually reaches your account.