Project inputs
Example dataset
| Scenario | kW | Yield | PR | EF | Price | Annual tCO2e | Annual value |
|---|---|---|---|---|---|---|---|
| Office roof | 250 | 1450 | 82% | 0.55 | 45 | 163.4 | 7,353 |
| Warehouse | 500 | 1550 | 80% | 0.48 | 60 | 297.6 | 17,856 |
| Site cabins | 50 | 1350 | 78% | 0.65 | 30 | 34.2 | 1,026 |
Formula used
- Annual energy (kWh): E = kW × Yield × PR
- Avoided emissions (tCO2e): T = (E × EF) / 1000
- Annual carbon value: V = T × Carbon Price
- Optional RECs value: R = (E/1000) × REC Premium
If d > 0: Factor = (1 − (1−d)n) / d
If d = 0: Factor = n
How to use this calculator
- Enter system size, expected yield, and a realistic performance ratio.
- Add the grid emission factor for the electricity your solar displaces.
- Set a carbon price used by your client, policy, or internal planning.
- Choose lifetime and degradation to estimate long-term project value.
- Optionally include certificate premiums if your market supports them.
- Press calculate to view results, then export CSV or PDF.
Baseline energy modeling for roof and ground-mount arrays
Solar sizing for construction projects starts with a kW target tied to roof area and inverter clustering. Typical annual yield ranges from 1,200–1,800 kWh per kW-year depending on latitude, shading, tilt, and soiling control. Performance ratio captures real-world losses; many commercial systems land between 75–90% after temperature, inverter, and wiring losses. Use conservative inputs for early-stage budgets, then refine later.
Converting production into avoided emissions for reporting
This calculator converts annual kWh into avoided tCO2e using a grid emission factor in kg CO2e per kWh. If your project connects to a cleaner grid, avoided emissions fall when energy stays constant. For example, 250 kW at 1,450 kWh/kW-year and 82% PR produces about 297 MWh/year; at 0.55 kg/kWh that avoids roughly 163 tCO2e annually. Align factors to the displaced source.
Carbon price assumptions used in bids and ESG cases
Carbon value is calculated from avoided tCO2e multiplied by a carbon price per tCO2e. Owners may apply an internal carbon price for design decisions, while compliance or voluntary markets may use different levels. Common ranges run from 20–150 per tCO2e depending on regional policy and sector. Testing low, mid, and high scenarios helps quantify upside and risk.
Lifetime totals and degradation over the asset period
PV output declines each year due to module aging. A degradation rate of 0.3–1.0% is common for systems, while harsher environments can be higher. The lifetime factor applies a geometric series so totals reflect declining production rather than a flat annual estimate. When comparing alternatives, keep the same lifetime and degradation assumptions to avoid skewed decisions.
Certificates and premium revenue considerations
If renewable energy certificates are monetized, the REC premium adds a value per MWh generated. Keep premium values consistent with contract terms and retirement rules. For transparent claims, document the boundary: on-site generation, the displacement factor, and whether attributes are sold or retained. Treat certificate revenue as separate from carbon value to prevent double counting in sustainability disclosures.
FAQs
Which grid emission factor should I use?
Use the operational emission factor that matches the electricity your solar displaces. Prefer your utility's published intensity or a client-approved factor. Keep it in kg CO2e per kWh, and use the same factor across scenarios for fair comparisons.
Does the result include embodied carbon of equipment?
No. The calculator estimates operational avoided emissions from displaced electricity only. Embodied carbon from modules, inverters, and mounting structures requires a lifecycle assessment approach and product-specific environmental declarations.
How can I estimate annual yield for my site?
Start with local irradiance studies, PV design software outputs, or comparable nearby systems. If you only have a rough estimate, use a conservative kWh per kW-year value and refine after shading analysis and detailed layout.
Why is performance ratio important?
Performance ratio captures real losses like temperature, inverter efficiency, wiring, and soiling. A small PR change can meaningfully shift annual MWh and avoided tCO2e. Use commissioning targets or industry benchmarks and document assumptions for reviewers.
How are lifetime totals calculated with degradation?
Annual results are summed using a geometric series factor that reduces output each year by your degradation rate. This avoids overstating lifetime production. Set lifetime and degradation consistently when comparing design options or procurement packages.
Can I add REC or certificate premiums?
Yes. Enable the REC option and enter a premium per MWh. The tool adds this revenue to the carbon value totals. Ensure contract terms allow claims, and avoid double counting if certificates are sold to another party.