What this tool estimates
Use this calculator to estimate deliverable energy (kWh), discharge power (kW), backup runtime, and event export potential from connected electric vehicles on a jobsite.
Calculator Inputs
Formula Used
These equations are planning-level estimates. Actual dispatch depends on grid rules, hardware limits, temperature, and battery management constraints.
How to Use This Calculator
- Enter the number of EVs and each battery’s rated capacity.
- Set starting SOC and the minimum reserve SOC you must keep.
- Provide discharge power per vehicle and any site export limit.
- Add efficiency and event duration to bound exported energy.
- Optionally enter site load, price, and emissions factor.
Planning V2G Capacity for Temporary Power
Vehicle-to-grid export can reduce generator runtime and stabilize sensitive equipment during temporary works. This calculator translates vehicle counts, battery energy, and charger limits into a planning-level energy budget. Use it to quantify how many kilowatt-hours you can reliably deliver without compromising mobility needs. Document assumptions in your project notes.
Battery Energy Window and Dispatch Risk
The available energy is governed by the state-of-charge window: starting SOC minus reserve SOC, adjusted by your usable battery fraction. A tighter reserve lowers exportable energy but improves dispatch confidence when vehicles must leave unexpectedly. On busy sites, conservative reserves can prevent mid-shift power gaps.
Power, Interconnect Limits, and Event Duration
Energy delivery is also limited by power. Fleet discharge power equals per-vehicle discharge power multiplied by connected vehicles. If the site export limit is lower than fleet power, it becomes the controlling constraint. The event energy cap is export limit multiplied by event duration, which prevents overstating short dispatch windows.
Cost and Carbon Indicators for Project Decisions
When an energy price or credit is provided, the tool estimates gross value for the export event. An emissions factor converts exported kilowatt-hours into an avoided-emissions indicator for reporting and comparisons. These are screening metrics that support decisions on equipment rentals, charging schedules, and peak management.
Example Data for Three Common Scenarios
The examples below assume 90% usable fraction and 92% discharge efficiency, matching the included example table:
- Night shift backup: 4 EVs, 75 kWh each, 80% to 30% SOC, 20 kW limit, 2 h → 40.00 kWh exportable.
- Peak shaving window: 6 EVs, 60 kWh each, 90% to 40% SOC, 30 kW limit, 1.5 h → 45.00 kWh exportable.
- Small crew, short event: 2 EVs, 82 kWh each, 70% to 35% SOC, no limit, 1 h → 19.20 kWh exportable.
FAQs
1) What does “exportable energy” mean in this calculator?
It is the lesser of deliverable battery energy and the event’s power×time limit. It reflects SOC window, usable fraction, and discharge efficiency, then applies export constraints.
2) Why do I need a reserve SOC?
Reserve SOC protects vehicle availability and reduces the chance of cutting power mid-event. It also supports battery longevity by avoiding deep discharge during repeated site operations.
3) Should I use fleet discharge power or a site export limit?
Use both if applicable. Fleet discharge power defines what vehicles can supply, while the export limit reflects interconnect or program caps. The calculator uses the lower of the two.
4) How should I set discharge efficiency?
Include inverter, cabling, and control losses. If you are unsure, choose a conservative value so planning results are less likely to overstate delivered energy.
5) Can I estimate backup runtime for critical loads?
Yes. Enter the critical site load in kW. The calculator divides total deliverable kWh by that load to estimate runtime under steady conditions.
6) Why is my event export lower than total deliverable kWh?
Short events are often limited by export power and duration. Even if batteries hold more energy, the site limit and time window cap how much can actually be delivered.
7) Are the revenue and CO2 results exact?
They are screening estimates. Actual outcomes depend on tariffs, program rules, metering, and grid conditions. Use these values for planning and comparisons, not settlement.
Example Data Table
| Scenario | Vehicles | Battery (kWh) | SOC Start (%) | Reserve (%) | Discharge (kW/EV) | Export Limit (kW) | Event (h) | Exportable (kWh) |
|---|---|---|---|---|---|---|---|---|
| Night shift backup | 4 | 75 | 80 | 30 | 7 | 20 | 2 | 40.00 |
| Peak shaving window | 6 | 60 | 90 | 40 | 6 | 30 | 1.5 | 45.00 |
| Small crew, short event | 2 | 82 | 70 | 35 | 9.6 | None | 1 | 19.20 |
Example outputs assume 90% usable fraction and 92% discharge efficiency for illustration.