Project Inputs
Example Data Table
Use these values to validate your setup and compare scenarios.
| Scenario | Billing Demand (kW) | Rate (per kW) | Solar AC (kW) | Coincident (%) | Battery Power (kW) | Battery Energy (kWh) | Peak Window (hrs) |
|---|---|---|---|---|---|---|---|
| Baseline (Solar only) | 250 | 12.50 | 120 | 55 | 0 | 0 | 1.00 |
| Solar + Battery shaving | 250 | 12.50 | 120 | 55 | 60 | 120 | 1.00 |
| Short billing interval | 250 | 12.50 | 120 | 40 | 60 | 60 | 0.25 |
Formula Used
For detailed utility tariffs, consider multiple peak periods and interval data. This tool is designed for preliminary design and tender comparisons.
How to Use This Calculator
- Enter the month’s billed peak demand and the demand charge rate.
- Set the solar AC size and a realistic coincident factor for peak time.
- If using storage, add battery power, energy, efficiency, and reserve.
- Select the peak window matching your billing interval assumptions.
- Click Calculate to see net demand and savings above the form.
- Download CSV or PDF to share with procurement and stakeholders.
Demand Charges in Construction Power Budgets
Demand charges are billed on the single highest metered kW each month. On construction sites, cranes, hoists, compressors, welders, pumps, and batching starts can create short peaks that lock in a higher charge for all days. Using billed demand and the demand rate, this calculator produces a baseline monthly cost and lets you test peak-shaving strategies.
Coincident Solar Output at Site Peak
Solar reduces billed demand only when it produces during the peak interval. The coincident factor converts installed AC capacity to expected kW at peak time. Example: 120 kW AC at 55% contributes 66 kW. Use lower factors for late-afternoon peaks, seasonal shading, dust, or conservative tender allowances when interval data is limited.
Battery Constraints Across the Peak Window
Storage can shave peaks that solar misses. Battery contribution is constrained by inverter power and by delivered energy across the chosen peak window. Delivered energy is reduced by reserve state of charge and efficiency. The model limits battery kW to the smaller of rated power and delivered kWh divided by peak hours, helping you evaluate 15-minute versus one-hour billing intervals.
Interpreting Savings for Planning and Procurement
The results summarize net billing demand, demand charges before and after, and estimated savings. Review the reduction percentage to ensure it matches practical site operations. Combine generation with controls such as staggering equipment starts, limiting simultaneous lifts, or rescheduling high loads. For final design, verify assumptions with interval data and tariff details.
Example Data for Tender Comparisons
Example data: Baseline demand 250 kW, demand rate 12.50 per kW, solar 120 kW AC, coincident factor 55%, battery 60 kW and 120 kWh, peak window 1.0 hour, reserve 10%, efficiency 92%. The model indicates roughly 126 kW peak reduction and net demand near 124 kW. Capture peak timing and constraints in Notes for audit-ready exports.
FAQs
1) What is a demand charge?
It is a utility fee based on the highest measured power draw (kW) during the billing period. It is separate from energy charges, which are based on total kWh consumed.
2) How do I choose the coincident solar factor?
Match it to when your site peak occurs. Midday peaks can use higher factors; late-afternoon peaks often require lower factors due to declining solar output and shading effects.
3) Why does peak window matter?
Billed demand can be based on 15-minute or hourly intervals. A shorter window allows a battery to cover peaks with less energy, while longer windows require more delivered kWh.
4) Does battery efficiency change peak shaving?
Yes. Lower efficiency means less delivered energy for the same stored energy. This reduces sustained discharge capability across the peak window and can lower the modeled battery kW contribution.
5) Can solar alone eliminate demand charges?
Only if solar output reliably coincides with the highest demand interval and is large enough. Many sites peak in the evening or during equipment starts, where storage or controls may be needed.
6) Is this suitable for final tariff compliance?
It is intended for planning and tender evaluation. For final compliance, validate with interval meter data, seasonal tariff structures, and any additional demand components in your utility schedule.
7) What should I include in notes for auditing?
Record peak timing, key loads, shading risks, battery dispatch assumptions, and the chosen peak window. This makes exports defensible during design review and procurement negotiations.