Battery C-Rate: Deliverable Power and Discharge Duration
How fast a battery can discharge (C-rate), and how much of that reaches the panel.
Example
You enter
- Battery nameplate (kWh) 40
- Continuous C-rate (0.5 = 0.5C) 0.5
- Depth of discharge (0-1) 0.9
- Inverter rating (kW, 0 = no limit) 15
You get
- C-rate power (cells) 20 kW
- Deliverable power 15
- Usable energy 36 kWh
- Discharge time at deliverable 2.4 h
- Inverter limited Yes
Checked against published worked examples from: SimpliPhi Power.
Details, formula, and sources
ScopeA battery's power is not its energy: the C-rate caps how fast the pack discharges (power = nameplate x C) and the inverter caps how much reaches the panel, so the deliverable power is the lesser of the two and the usable energy lasts that many hours at it. A 40 kWh pack at 0.5C pushes 20 kW, but behind a 15 kW inverter only 15 kW comes out - it runs longer at lower power. The check that keeps a designer from specifying a peak-shave or backup load the pack physically cannot deliver. Continuous, not surge, rating. A nameplate power check, not a cell-level thermal model.
Formula or tablec_rate_power_kw = nameplate_kwh x c_rate; deliverable_kw = inverter_kw > 0 ? min(c_rate_power_kw, inverter_kw) : c_rate_power_kw; usable_kwh = nameplate_kwh x dod; discharge_time_h = usable_kwh / deliverable_kw.
Source and editionThe standard battery C-rate definition (power = nameplate x C, full discharge time = 1 / C, deliverable power = the lesser of the C-rate power and the inverter rating), by name; the relations are public.
Free accessThe C-rate definition and the power/duration arithmetic are public; manufacturer discharge-rate data is published in cut sheets.
What governsEstimate. AHJ and licensed professional govern.
API field namesnameplate_kwh, c_rate, dod, inverter_kw, c_rate_power_kw, deliverable_kw, usable_kwh, discharge_time_h, inverter_limited
- C-rate power continuous power = nameplate energy x C-rate (0.5C = half the nameplate energy per hour)battery C-rate definition
- Deliverable power the lesser of the C-rate power and the inverter/PCS continuous rating (0 = no inverter limit)first principles
- Discharge time usable energy (nameplate x DoD) divided by the deliverable powerfirst principles