- Gross Cost = (Microinverter unit cost × panel count) + monitoring + BOS + labor + permitting.
- Net Cost = (Gross Cost − rebate) − tax_credit% × (Gross Cost − rebate).
- Year‑1 Energy (sun-hours mode) = kW × sun_hours × 365 × performance_ratio.
- Microinverter Gain adjusts energy by (1 + gain%).
- Degradation reduces energy: kWhy = kWh1 × (1 − deg%)y−1.
- Savings = kWh × [self% × utility_rate + (1−self%) × export_rate].
- Escalation raises rates annually: ratey = rate1 × (1 + esc%)y−1.
- Net Cash Flow = savings − O&M − loan_payment − replacements.
- NPV = Σ cashflowt / (1 + discount%)t.
- IRR is the rate where NPV equals zero (bisection method).
- LCOE = PV(costs) ÷ PV(energy).
- Choose an energy method: sun-hours for early planning, or direct kWh for audited data.
- Enter microinverter unit cost and panel count to capture module-level hardware.
- Add BOS, labor, monitoring, and permitting to match your construction estimate.
- Set utility and export rates, plus self-consumption, to reflect the building load profile.
- Use realistic degradation and escalation values; keep assumptions consistent across bids.
- Optionally include replacements and financing if they affect approval decisions.
- Review payback, NPV, and the cashflow table, then export CSV or PDF.
| Scenario | Key inputs | Illustrative outputs |
|---|---|---|
| Office roof array |
6.0 kW DC, 15 panels × 400 W Microinverter: $95 each, BOS: $1,800 Labor: $4,200, Permits: $450 Sun hours: 4.5, PR: 82%, Gain: 4% Utility: $0.18/kWh, Export: $0.10/kWh, Self-use: 65% |
Net cost after incentives: varies by region Payback typically: 6–12 years (assumption dependent) NPV and IRR: improve with higher rates and self-use |
Microinverters in construction budgets
Microinverters often raise hardware line items but can reduce design risk on complex roofs. Module-level conversion supports mixed orientations, partial shading from parapets, and future rooftop equipment changes. During estimating, separate microinverter unit cost from balance-of-system and labor so procurement and install productivity remain traceable.
Energy yield drivers and site conditions
Annual production is shaped by peak sun hours, performance ratio, and shading losses. For construction projects, performance ratio should include temperature derates, conductor runs, soiling, and commissioning quality. The energy gain input models improved harvest under mismatch and shading, which is common near rooftop access paths and mechanical curbs.
Tariffs, self-consumption, and export value
Savings depend on how much solar is used on site versus exported. High daytime loads increase self-consumption and usually improve ROI. Use separate utility and export rates when net billing applies. Escalation reflects long-term utility pricing; keep it conservative when comparing bids, and document the escalation source in project notes.
Lifecycle costs, replacements, and O&M
Plan for routine maintenance such as inspections, cleaning, and monitoring subscriptions. Replacement modeling is helpful for long-life assets: set a replacement year and percent to reflect expected service events. In construction closeout, align warranties, spare units, and roof access provisions to reduce future downtime and labor mobilization costs.
Decision metrics for approvals
Payback gives a simple schedule view, while NPV and IRR capture time value of money and support capital committee review. Discount rate should match your organization’s hurdle rate or weighted cost of capital. LCOE helps compare against grid costs and alternate energy measures, especially when incentives or financing vary by site.
| Item | Value | Notes |
|---|---|---|
| System size | 6.00 kW | Sun-hours mode |
| Panels | 15 × 400 W | One microinverter per panel |
| Microinverter unit cost | $95 | Hardware only |
| Peak sun hours | 4.50 | Site average |
| Performance ratio | 82% | Losses included |
| Energy gain | 4% | Shade and mismatch uplift |
| Utility / export rates | $0.18 / $0.10 | Separate valuation |
| Self-consumption | 65% | Daytime load driven |
| Project life / discount | 25 yrs / 6% | Finance inputs |
1) What does the energy gain percentage represent?
It estimates extra production from module-level tracking under shading and mismatch. Use conservative values unless you have site studies or comparable rooftop production data.
2) Should I use sun-hours mode or direct annual energy?
Use sun-hours for early design and budgeting. Use direct kWh when you have modeled outputs, measured performance, or a finalized layout and shading analysis.
3) Why separate utility and export rates?
Many tariffs credit exported energy at a different value than imported energy. Using two rates prevents overstating savings when a portion of production is exported.
4) How is payback calculated here?
The calculator tracks cumulative net cash flow and estimates the crossing point from negative to positive. If the project never crosses within the selected life, payback is not reached.
5) What does NPV tell decision makers?
NPV converts future net savings into today’s dollars using the discount rate. A positive NPV indicates the project clears the selected hurdle rate under the modeled assumptions.
6) How should I set O&M?
For rooftop systems, include inspections, cleaning, monitoring, and minor repairs. Fixed O&M is simple; percent-of-cost scales with system size. Match your maintenance contracts when available.
7) Does financing change ROI?
Financing shifts cash flows by adding loan payments and reducing the year-zero outlay. It can improve early cash flow but increases total paid. Compare scenarios with and without financing for approvals.