Calculator Inputs
Example Data Table
| Scenario | Exported (kWh) | Imported (kWh) | Export rate | Import rate | Export credit | Import cost | Net energy |
|---|---|---|---|---|---|---|---|
| Moderate export, standard rates | 320 | 540 | 0.08 | 0.18 | 25.60 | 97.20 | 71.60 |
| High export, capped credits | 900 | 700 | 0.07 | 0.20 | 63.00 | 140.00 | 77.00 |
| Low export, higher import tariff | 120 | 820 | 0.06 | 0.25 | 7.20 | 205.00 | 197.80 |
Formula Used
- Credited Export (kWh) = min(Exported kWh, Export Cap)
- Export Credit = Credited Export × Export Rate
- Import Cost = Imported kWh × Import Rate
- Energy Subtotal = Import Cost − Export Credit
- Tax = Energy Subtotal × Tax% (only if subtotal is positive)
- Total Before Rules = Energy Subtotal + Fixed + Demand + Tax
- Net Bill = apply rollover and minimum bill rules
- Generation (kWh) = System kW × Sun Hours × Days × Performance Ratio
- Self-used (kWh) = Generation × Self-consumption%
- Exported (kWh) = Generation − Self-used
- Imported (kWh) = Site Load − Self-used (min 0)
- Then the billing math matches measured mode.
How to Use This Calculator
- Choose Measured if you have meter values, otherwise use Estimated.
- Enter the billing days and pick your reporting period for records.
- Set export and import rates from your tariff or agreement.
- Add fixed, demand, tax, and optional minimum bill rules.
- Click Calculate to view the summary above the form.
- Use Download CSV or Download PDF to share results.
Field Guide: Solar Export Credits in Construction
Why export credits matter on site
Temporary power can be a major controllable operating cost on active projects. When site solar supports cabins, lighting, security, pumps, or small plant, surplus daytime production may be exported and credited against imported energy. Even a modest credit reduces the energy subtotal, and can also reduce percentage-based taxes that apply only when charges are positive. Tracking credits monthly helps validate assumptions, keeps cost codes clean, and supports smoother client reporting.
Inputs that drive the credit value
Credit value is mainly credited exported kWh multiplied by the export rate. Many programs cap the kWh eligible for credit, so this calculator includes an export cap input. Imported kWh and the import rate determine baseline cost, while fixed service fees and demand charges can dominate in low-usage months. Use the minimum bill option when the utility enforces a floor payment regardless of credits.
Planning with estimated mode
Before meters are installed, estimate generation using system size, average sun hours, billing days, and a performance ratio that reflects losses from temperature, wiring, soiling, and inverter efficiency. Example: a 10 kW array × 4.5 sun hours × 30 days × 0.80 performance ratio produces about 1,080 kWh. If self-consumption is 45%, around 594 kWh could be exported, subject to caps and tariff rules. This helps compare battery storage, load shifting, and array sizing.
Breakdown, rollover, and reporting
The breakdown separates import cost, export credit, and the resulting energy subtotal. A negative subtotal means credits exceed energy charges; with rollover enabled, that balance carries forward and payable charges can drop to zero before any minimum bill rule is applied. Use the CSV for cost-control backups and the PDF for site packs. Document meter reads, caps, and tariff references in the notes field for audit-ready records.
FAQs
1) What is a solar export credit?
A solar export credit is the bill value assigned to energy sent from your solar system to the grid. It is usually calculated as credited exported kWh multiplied by the export rate, and it offsets imported energy charges.
2) When should I use measured mode versus estimated mode?
Use measured mode when you have meter data for exported and imported kWh. Use estimated mode during planning to project generation, self-use, exports, and imports from system size, sun hours, and site load assumptions.
3) What does performance ratio represent?
Performance ratio combines real-world losses such as inverter efficiency, wiring losses, temperature effects, downtime, and soiling. A typical planning range is 0.75 to 0.90, but your equipment, maintenance, and environment can move it higher or lower.
4) How do I estimate self-consumption percentage?
Start with the share of daytime site loads that can run while solar is producing. Offices, lighting, charging, and pumps increase self-use. If you add storage or shift activities to daylight, self-consumption usually rises and exports fall.
5) What happens if credits are larger than charges?
If rollover is enabled, the calculator carries the negative subtotal forward as a credit balance and sets the current bill to zero before minimum bill rules. If rollover is disabled, the bill is clamped to zero and credits are not carried.
6) How does the export cap affect results?
Some programs only credit exports up to a monthly or annual kWh limit. When you enter an export cap, credited export kWh becomes the lesser of actual exported kWh and the cap, which reduces the export credit amount accordingly.
7) Which values should I copy from a utility invoice?
Use exported kWh, imported kWh, and the applicable export and import rates from the tariff. Add fixed service fees and any demand charge total shown for the period. If taxes apply only to energy charges, enter the matching percentage.