| Scenario | Avg discharge (kW) | Heat fraction (%) | Runtime (h/day) | COP | Annual cooling kWh |
|---|---|---|---|---|---|
| Warehouse peak-shaving | 60 | 3.5 | 4 | 3.0 | 980 |
| Fast charge support | 120 | 4.0 | 2 | 2.6 | 1,108 |
| Telecom backup cycling | 25 | 2.0 | 8 | 3.5 | 343 |
- Heat load (kWth) = Average discharge power × (Heat fraction ÷ 100)
- Cooling electric (kW) = Heat load ÷ COP
- Annual active cooling hours = Runtime hours/day × Days/year × (Duty cycle ÷ 100)
- Annual cooling energy (kWh) = Cooling electric (kW) × Annual active cooling hours
- Annual energy cost = Annual cooling energy × Electricity rate
- Annual demand cost (estimate) = Peak cooling kW × Demand charge × 12
- Annual savings = Baseline total cost − Improved total cost
- NPV = −Upgrade cost + Σ (Savingsy ÷ (1 + Discount rate)y)
- Enter average discharge power and heat fraction to estimate thermal load.
- Set runtime, days per year, and duty cycle to match usage.
- Provide baseline COP and an improved COP for comparison.
- Add electricity rate and optional demand charge from your bill.
- Optionally enter upgrade cost, escalation, and discount rate.
- Press Submit to show results above the form.
- Download a CSV or PDF report using the buttons.
Cooling load drivers
Battery heat rises with electrical throughput. If average discharge is 80 kW and internal losses are 3%, thermal load is 2.4 kW(th). With 6 hours per day, 300 days per year, and 85% cooling duty, active cooling runs 1,530 hours annually.
Electrical energy translation
Cooling electricity depends on COP. At COP 2.8, 2.4 kW(th) requires 0.857 kW electric. Over 1,530 hours, that is about 1,311 kWh. Raising COP to 3.6 lowers input to 0.667 kW and energy near 1,020 kWh.
Demand charges and peak sizing
Many tariffs bill peak kW monthly. With 10 per kW-month, a 0.857 kW peak adds about 103 per year. Improving COP drops the peak to 0.667 kW and demand cost to roughly 80. Smaller peaks also reduce transformer, breaker, and feeder stress.
Financial sensitivity and escalation
Energy cost equals kWh times rate. At 0.18 per kWh, baseline energy cost is about 236 per year and improved is about 184. Add demand, and savings follow. If prices rise 3% annually, year-ten savings are ~1.30× year-one savings. Discounting at 8% converts future savings into present value.
Interpreting payback and NPV
Simple payback is upgrade cost divided by annual savings. A 2,500 upgrade saving 75 annually pays back in ~33 years, so reliability, warranty, or thermal safety may justify the choice. NPV sums discounted savings across the horizon and subtracts upgrade cost. Positive NPV indicates the upgrade beats the discount rate.
For quick screening, compare baseline and improved kWh per operating hour. In the example, cooling intensity falls from 0.857 kWh/h to 0.667 kWh/h, a 22% reduction. Multiply by fleet size: ten identical units save about 2,910 kWh yearly under the same duty pattern. and seasonal operating variability over time.
1) What does heat fraction represent?
It is the share of battery power that turns into heat. Use measured losses when available. Otherwise, 2% to 5% is a practical screening range for many operating profiles.
2) How should I choose duty cycle?
Duty cycle reflects how often cooling runs during operating hours. If cooling cycles on and off, use the average active percentage over the day, not the nameplate fan schedule.
3) Why include demand charges?
Demand charges can dominate costs when peak kW matters. This calculator estimates demand using peak cooling kW. Set demand charge to zero if your tariff is energy-only.
4) What COP value is realistic?
COP varies with ambient temperature, setpoints, and equipment. Use seasonal test data or vendor curves. For quick estimates, 2.5 to 4.0 is common for many cooling systems.
5) How is NPV calculated here?
NPV starts with negative upgrade cost, then adds discounted savings for each year. Savings can escalate by the rate escalation input, then each year is discounted using the discount rate.
6) Can I use this for multiple battery units?
Yes. Enter per-unit values and multiply annual kWh and costs by the number of units. If units differ, run separate scenarios and sum totals for portfolio planning.