| System size (kW) | Specific yield (kWh/kW-yr) | Degradation (%) | Years | Rate (/kWh) | Emission (kgCO2/kWh) |
|---|---|---|---|---|---|
| 100 | 1550 | 0.70 | 25 | 0.12 | 0.45 |
Replace the example values with your site irradiance study, contractual rate, and grid factor.
| Year | Factor | Energy (kWh) | Lost (kWh) | Cumulative lost (kWh) | Revenue lost |
|---|---|---|---|---|---|
| 1 | 1.00000 | 155,000 | 0 | 0 | 0.00 |
| 2 | 0.99300 | 153,915 | 1,085 | 1,085 | 130.20 |
| 3 | 0.98605 | 152,838 | 2,162 | 3,247 | 259.49 |
| 4 | 0.97915 | 151,768 | 3,232 | 6,480 | 387.87 |
| 5 | 0.97229 | 150,705 | 4,295 | 10,774 | 515.36 |
| 6 | 0.96549 | 149,650 | 5,350 | 16,124 | 641.95 |
| 7 | 0.95873 | 148,603 | 6,397 | 22,521 | 767.66 |
| 8 | 0.95202 | 147,563 | 7,437 | 29,958 | 892.48 |
| 9 | 0.94535 | 146,530 | 8,470 | 38,429 | 1,016.43 |
| 10 | 0.93874 | 145,504 | 9,496 | 47,925 | 1,139.52 |
| 11 | 0.93216 | 144,485 | 10,515 | 58,439 | 1,261.74 |
| 12 | 0.92564 | 143,474 | 11,526 | 69,965 | 1,383.11 |
Baseline annual energy:
E₀ = System(kW) × SpecificYield(kWh/kW-yr)
Degradation factor (year y):
Fᵧ = (1 − d)^(y−1), where d = Degradation% ÷ 100
Annual energy with degradation:
Eᵧ = E₀ × Fᵧ
Annual lost energy:
Lᵧ = E₀ − Eᵧ
Revenue lost:
Rᵧ = Lᵧ × ElectricityRate
Carbon impact:
Cᵧ = Lᵧ × EmissionFactor
Present value revenue loss (optional):
PVᵧ = Rᵧ ÷ (1 + r)^y, where r = Discount% ÷ 100
- Enter the installed system size and site-specific yield from your design study.
- Set an annual degradation rate based on module warranty or historical data.
- Choose the analysis period to match your contract term or life-cycle plan.
- Add an electricity rate to estimate financial exposure from reduced output.
- Optional: include a discount rate to value future losses in today’s terms.
- Click Calculate Impact to view results above the form.
- Export CSV/PDF for reports, approvals, or performance documentation.
1) Why degradation matters in construction power plans
On active sites, temporary loads, cabins, lighting, and security can rely on solar. Module output typically declines each year, commonly around 0.3–1.0% annually, and that drop compounds. If you forecast energy using a flat annual value, you can understate long-term losses and overstate savings.
2) Interpreting the baseline yield input
Specific yield (kWh per kW-year) reflects solar resource, tilt, shading, and availability. A practical range for many projects is 1,200–1,800 kWh/kW-year. Pair it with your installed capacity to get baseline annual energy. Degradation is then applied year-by-year to estimate realistic delivered energy.
3) Reading the year-by-year results
The degradation factor is calculated as (1 − d)^(y−1). For example, at 0.7% degradation, year 10 output is about 94% of year 1. The table shows annual energy, annual loss, and cumulative loss so you can compare performance guarantees, decide on cleaning frequency, and quantify contingency allowances.
4) Financial exposure and present value
Revenue loss is the lost kWh multiplied by your electricity rate or avoided cost. Where budgets span multiple years, the optional discount rate converts future losses into present value, improving like-for-like comparisons between designs. Use a discount rate aligned with corporate hurdle rates or project finance assumptions.
5) Carbon impact and reporting
The emission factor converts lost energy into a carbon impact in kgCO2, useful for sustainability reporting and compliance narratives. Grid intensity can vary widely by region and time, so use a representative value from your energy team. Exporting CSV/PDF supports documentation, audits, and stakeholder approvals.
1) What degradation rate should I enter?
Use your module warranty or measured fleet data. Many modern modules fall near 0.3–1.0% per year. If you have site-specific history, use that to reflect your operating environment.
2) Does the calculator include downtime or soiling losses?
No. It isolates degradation only. To reflect downtime or soiling, reduce the specific yield input to your expected net yield before applying degradation.
3) Should I use AC or DC system size?
Enter the capacity used in your yield study for consistency. If your yield model is DC-based, use DC kW. If it is inverter-limited AC, use AC kW and matching yield.
4) What electricity rate is best for construction projects?
Use the avoided cost rate you actually displace, such as grid tariff, diesel generation cost per kWh, or a PPA rate. A blended average works when rates vary seasonally.
5) How is “Revenue lost (NPV)” calculated?
Each year’s revenue loss is discounted by (1 + r)^y, where r is the discount rate. This converts future losses into today’s value for investment comparisons.
6) Why is cumulative lost energy important?
Cumulative loss shows the total gap between a no-degradation forecast and degraded output. It helps quantify reserve energy needs, battery sizing impacts, or additional procurement exposure over time.
7) Can I use this for performance guarantee checks?
Yes, as a planning tool. Align inputs with your contract baseline, measured yield methodology, and reporting period. For formal guarantees, follow the contract’s test conditions and correction factors.