Behind the model
How the solar model works
Every number in the calculator is derived bottom-up from your inputs — no black box. Below is each formula, paired with a worked example from the default 1 MWp factory-rooftop plant at 16% CUF, saving an avoided grid tariff of ₹8/kWh. Change any input in the tool and these relationships hold.
Capacity, CUF & generation
Nameplate capacity and the capacity-utilization factor (CUF) set first-year output. The plant runs at full output from commissioning (no ramp); panel degradation erodes output each subsequent year.
Year-1 generation
MWp × CUF% × 8760 h × 1000
1 × 16% × 8760 × 1000 = 1,402 MWh
Specific yield
CUF% × 8760 (kWh per kWp)
1,402 kWh/kWp
Degradation (compounding)
gen × (1 − degradation%)^(age−1)
yr 2 = 1,395 MWh (−0.5%/yr)
Lifetime generation
Σ annual generation over the horizon
33,016 MWh over 25 yrs
CapEx — build cost
Module-and-BoS cost per Wp drives the EPC; land, evacuation/grid lines and contingency stack on top, then interest-during-construction is capitalized. Cost per Wp is an output, never an assumption when you edit components.
EPC
MWp × 1,000,000 Wp × cost/Wp
1M Wp × ₹38 = ₹3.8 Cr
Line items (evacuation, approvals…)
Σ line items (unit cost × qty)
₹3 L
Base cost
EPC + land + lines
₹3.8 Cr + ₹0 + ₹3 L = ₹3.83 Cr
Contingency
base × 3%
₹11.5 L
Interest during construction (IDC)
total × debt% × interest% × (months ÷ 12) × ½
3 mo → ₹3.62 L
Total project cost
base + contingency + IDC
₹3.98 Cr
CapEx per Wp (derived)
total project cost ÷ (MWp × 1e6)
₹39.81/Wp
OpEx — annual running cost
O&M scales with online capacity; insurance is a % of CapEx; land lease is fixed. All escalate each year.
O&M
online MWp × ₹6,00,000/MWp × (1+4%)^(yr−1)
yr 1: ₹6 L
Insurance
base CapEx × 0.25% × (1+esc)^(yr−1)
yr 1: ₹98,623
Land lease
₹0 × (1+esc)^(yr−1)
yr 1: ₹0
Total OpEx
O&M + insurance + land lease
yr 1: ₹6.99 L
Revenue — tariff or savings rate
Revenue is generation × the tariff/savings rate, escalated each year. The rate carries three Indian segments: a PPA sale price (utility auctions ₹2.5–2.6/kWh), the avoided grid tariff for captive/rooftop plants (₹7–9 commercial), or the grid tariff net of ₹1.5–2.5 open-access charges for third-party supply. Phased builds bring MWp online over time, each cohort on its own degradation clock.
Revenue / savings
generation × tariff/savings rate × (1 + esc%)^(yr−1)
yr 1: 1,402 MWh × ₹8 = ₹1.12 Cr
Escalation
rate × (1 + 3%)^(yr−1)
3%/yr (grid tariffs drift up)
Phased build (vintages)
each phase commissions on its own year, capex & debt timed to commissioning
all-at-once by default
Financing — debt, moratorium, tax & depreciation
Long-tenor project debt with an interest-only moratorium during commissioning, then the principal amortizes over the remaining tenor. Depreciation defaults to the Indian Sec 32 accelerated schedule (40% written-down value) — the tax lever behind C&I solar — with a straight-line book option. Land is excluded from the depreciable base in both methods. Tax carries losses forward.
Debt / equity split
debt = total cost × debt% ; equity = remainder
₹2.79 Cr debt · ₹1.19 Cr equity (70/30)
Principal moratorium
interest-only for the first N years from commissioning, then amortize
1 yr grace, 10 yr tenor
Equal-principal repayment
debt ÷ (tenor − moratorium) each amortizing year
₹31 L
Annuity (EMI) option
debt × r ÷ (1 − (1+r)^−(tenor−moratorium))
level-payment alternative
Interest
outstanding balance × interest rate
yr 1: ₹29.3 L
Depreciable base (land excluded)
total project cost − land
₹3.98 Cr
Depreciation — 40% WDV (Sec 32)
base × 40% × 60%^(yr−1) (declining balance)
yr 1: ₹1.59 Cr · yr 2: ₹95.5 L
Depreciation — straight-line option
base ÷ 15 yrs
₹26.5 L/yr for 15 yrs
Tax (with loss carryforward)
max(0, PBT − losses) × 25% ; losses carry forward
accelerated depreciation shelters early-year profit
Returns & coverage
The unlevered cash flows give the project view; the equity cash flows give the geared view. Project IRR uses a separate project tax that excludes the interest shield, so it is genuinely financing-independent. Construction beyond a year defers first revenue.
EBITDA
revenue − operating cost
yr 1: ₹1.05 Cr (94% margin)
Unlevered (project) FCF
EBITDA − project tax − CapEx (project tax excludes interest)
Project IRR 25.4%
Equity FCF
PAT + depreciation − principal − equity-funded CapEx
Equity IRR 50.9%
NPV
Σ unlevered FCF ÷ (1 + discount)^t
@ 10% = ₹5.42 Cr
Construction lead
ceil(months ÷ 12) − 1 extra zero-revenue years before generation
none (3 mo ≤ 12)
Payback
year cumulative unlevered cash flow first turns positive
3.8 yr
DSCR
CFADS ÷ debt service ; CFADS = EBITDA − tax (amortizing years only)
min 1.79× · avg 2.21× (yr 2 = 1.79×)
LLCR
PV(CFADS over loan life) ÷ debt
2.23×
Equity multiple (MOIC)
Σ equity cash returned ÷ equity invested
19.57×
Break-even tariff
tariff at which project NPV = 0
₹3.45/kWh
LCOE & ESG
The levelized cost of energy — discounted, so it is directly comparable to a PPA tariff or your grid rate — and what the plant displaces on the grid.
LCOE (discounted)
(capex + PV of OpEx) ÷ PV of generation, at the 10% discount rate
₹3.96/kWh (vs ₹8 tariff/savings rate)
Carbon avoided (annual)
year-1 generation × grid emission factor ÷ 1000
995 tCO₂/yr
Carbon avoided (lifetime)
Σ generation × grid emission factor ÷ 1000
23,441 tCO₂
Land footprint
MWp × 2 acres/MWp
2 acres
These are transparent planning estimates, not a quote. A real solar project needs a proper feasibility study, resource assessment and DPR — that’s where we help. Open the calculator →