Free · In-browser · No sign-up

Supercapacitor Sizing Calculator | UPS, E-STATCOM & AI Data-Centre ESS

Supercapacitor energy storage is deployed in three fundamentally different operating modes, each with a distinct sizing logic. An E-STATCOM must deliver full rated power during a grid fault lasting one to three seconds, then operate continuously at low power for frequency regulation — the pack must survive both the peak event and years of continuous cycling. A UPS holds charge at the bus voltage and discharges in a single pulse: sizing is determined by voltage and current limits during the event, and lifetime by the hold conditions between events. A data-centre or AI-compute buffer runs continuous high-rate charge–discharge cycles where cell temperature and long-term degradation are the binding constraints.

Most available tools size for one scenario at beginning-of-life cell parameters. This tool covers all three profiles in a single workflow and evaluates results at three IEC 62391 aging states — beginning, mid, and end of life (ESR ×1.5/×2.0; capacitance ×0.9/×0.8) — so the pack remains feasible as it ages. Auto-sizing finds the minimum cell count meeting energy, current, thermal, and calendar-life constraints simultaneously across all three states. Lifetime uses an Arrhenius temperature model with adjustable activation energy rather than a fixed rule of thumb, and the discharge ODE is integrated with RK4 using a log-weighted effective voltage over the trajectory — consistent with cell-level LTSpice simulation models.

Independent, product-specific sizing calibrated to your shortlisted cell or module using manufacturer data, against your duty profile and lifetime target — prepared as billable engineering work by Phasor Consult.

If your browser didn't open an email draft, copy the message below and send it to mykola@phasorconsult.eu (subject: Vendor-calibrated supercapacitor sizing report).

E-STATCOM profile UPS profile Continuous cycling IEC 62391 aging states Arrhenius lifetime RK4 ODE Auto-sizing

Pre-computed sizing examples for each supported application profile. Open to see inputs and key results before running your own case.

01 — UPS / DC bus ride-through · 800 V

Industrial drive or data-centre UPS: 200 kW hold for 3 s. Cell-level, Ns = 295, Np = 4 (1180 cells). Pack operates below rated cell voltage — series-count derating is the primary lifetime lever. Temperature rise during a brief pulse is negligible; lifetime is dominated by hold voltage and coolant temperature.

Inputs

Cell rated voltage: 2.85 V
Capacitance / ESR: 3200 F · 0.25 mΩ
L_ref (rated V, 65 °C): 1500 h
DC bus voltage: 800 V
Ns / Np: 295 / 4
Coolant temperature: 25 °C
Min discharge voltage: 50 % of bus
Power · pulse time: 200 kW · 3 s
Target lifetime: 10 yr

Results

Total cells: 1180
Pack rated voltage: 840.8 V
Cell voltage at bus: 2.71 V
Energy stored (to 50 % bus): 10.4 MJ
Energy used per pulse: 0.6 MJ
V_end after 3 s: 782 V
Peak bus current: 256 A
Temp rise (pulse): < 0.1 °C
Lifetime BoL / MoL / EoL: 11.2 / 11.2 / 11.2 yr ✓

02 — Constant load / AI-compute buffer · 800 V

Data-centre power buffer for AI workload transients: 50 kW continuous, 1 s full charge–discharge cycle. Cell-level, Ns = 300, Np = 1 (300 cells). Temperature rise under continuous cycling is moderate; EoL ESR increase raises cell temperature and reduces lifetime margin, making thermal assessment across aging states essential.

Inputs

Cell rated voltage: 2.85 V
Capacitance / ESR: 3200 F · 0.25 mΩ
L_ref (rated V, 65 °C): 1500 h
DC bus voltage: 800 V
Ns / Np: 300 / 1
Coolant temperature: 25 °C
Min discharge voltage: 50 % of bus
Power · cycle time: 50 kW · 1 s
Target lifetime: 5 yr

Results

Total cells: 300
Pack rated voltage: 855.0 V
Cell voltage at bus: 2.67 V
V_end per half-cycle: 796 V
Peak bus current: 63 A
Settled ΔT — BoL / MoL / EoL: 4.9 / 7.3 / 9.8 °C
T_cell — BoL / MoL / EoL: 29.9 / 32.3 / 34.8 °C
Lifetime BoL / MoL / EoL: 9.2 / 7.9 / 6.4 yr ✓

03 — E-STATCOM · distributed storage · 1.5 kV DC bus per MMC cell (Nidec Silcovar-class)

Low-voltage building-block MMC: each submodule (“cell”) carries its own 1.5 kV DC link with a dedicated supercapacitor string, built from standard 1700 V-class IGBTs. Energy storage is distributed across all submodules rather than lumped on one bus. This example sizes one submodule for its share of duty — a ~100 MW / 10 MW system is built by replicating it across ~100 submodules per the converter's series-count and arm arrangement. Module-level supercap blocks; Ns = 17, Np = 2 per submodule (34 modules — 1224 cells each). Note: this low-voltage parallel-DC approach is not unique to Nidec — Mitsubishi's SVC-Diamond uses the same building-block philosophy.

Inputs (per submodule)

Unit type: Module (36 cells)
Module capacitance / ESR: 88.9 F · 9.5 mΩ
Module R_th / C_th: 0.14 °C/W · 36 000 J/°C
L_ref (rated V, 65 °C): 1500 h
DC bus voltage (per cell): 1500 V
Ns / Np: 17 / 2
Coolant temperature: 25 °C
Fault power · pulse · cycles: 1 MW · 1.25 s · 2
Continuous power: 100 kW
Target lifetime: 20 yr

Results (per submodule)

Modules / cells: 34 / 1224
Pack rated voltage: 1744.2 V
Cell voltage at bus: 2.45 V
Fault energy (sequence): 5.0 MJ
String energy (to 50 %): 8.8 MJ
Peak cell-bus current (fault): 667 A
ΔT fault / steady-state: < 0.1 / ≈ 1.4 °C
Lifetime BoL / MoL / EoL: 43.4 / 42.6 / 41.7 yr ✓

04 — E-STATCOM · central storage · 40 kV DC bus, one ESS for all arms (Siemens / GE / Hitachi / Hyosung-class)

High-voltage central architecture: a single supercapacitor ESS on a common ~40 kV DC bus serves the whole converter — the arrangement used by Siemens SVC PLUS FS, GE, Hitachi Energy and Hyosung MMC-STATCOMs with bulk supercapacitor storage. One pack handles the entire power profile (fault boost plus continuous frequency regulation). Auto-sized at module level; Ns = 440, Np = 5 (2200 modules — 79 200 cells). The 40 kV rated voltage needs hundreds of modules in series, so a single string already provides large derating headroom; series count is then raised by the optimizer to clear the 20 yr lifetime target.

Inputs (whole system)

Unit type: Module (36 cells)
Module capacitance / ESR: 88.9 F · 9.5 mΩ
Module R_th / C_th: 0.14 °C/W · 36 000 J/°C
L_ref (rated V, 65 °C): 1500 h
DC bus voltage (central): 40 000 V
Sizing: Automatic
Coolant temperature: 25 °C
Fault power · pulse · cycles: 100 MW · 1.25 s · 2
Continuous power: 10 MW
Target lifetime: 20 yr

Results (whole system)

Modules / total cells: 2200 / 79 200
Pack rated voltage: 45 144 V
Cell voltage at bus: 2.53 V
Fault energy (sequence): 500 MJ
String energy (to 50 %): 606 MJ
Peak bus current (fault): 2500 A
ΔT fault / steady-state: < 0.1 / ≈ 3.3 °C
Lifetime BoL / MoL / EoL: 26.0 / 24.8 / 23.4 yr ✓

Phasor Consult — Supercapacitor Sizing Calculator · phasorconsult.eu/supercap

Cell / module parameters

Cell rated voltage · V

Cells in series per module

Module capacitance · F

Module ESR · mΩ

Module R_th · °C/W

Module C_th · J/°C

Application cell max temperature · °C

Lifetime model

Calendar life at rated V, 65 °C · h

Activation energy Ea · eV

Voltage halving interval · V

Lifetime estimated for this aging state

Each aging state applies derating factors to the cell's ESR and capacitance to represent degradation over service life, per IEC 62391. The tool sizes and reports lifetime for the single state you select. BoL (fresh cells) gives the primary lifetime estimate; MoL and EoL check that the configuration stays feasible at progressively degraded conditions. The three states are independent scenarios, not sequential time steps.

State	ESR factor	Capacitance factor
BoL — beginning of life	×1.0	×1.0
MoL — mid of life	×1.5	×0.9
EoL — end of life	×2.0	×0.8

System

DC bus rated voltage · V

Cells in series — Ns

Cells in parallel — Np

Coolant / air temperature · °C

Min discharge voltage · % of bus

Max ESS current · A

Max cell current · A

Max cell current time · s

Target lifetime · years

Suggests the bus voltage giving the fewest cells that meet the lifetime target, sized so the peak discharge current (at the minimum discharge voltage) stays within the Max ESS current above — set that to your converter's current rating first. It fills the voltage only; the current field is read as the limit, not overwritten.

Power profile

Pulse time · s

Assumed interval between UPS events · h

Charge/discharge cycle frequency · Hz

Power · kW

Fault pulse time · s

Grid fault power · MW

Grid fault cycles · pcs

Continuous load power · MW

Assumed interval between fault events · h

Room AC / chiller COP

If your browser didn't open an email draft, copy the message below and send it to mykola@phasorconsult.eu (subject: Review my ESS sizing case).

Results are evaluated at three IEC 62391 aging states — BoL (new), MoL (ESR ×1.5 / C ×0.9), EoL (ESR ×2.0 / C ×0.8). Auto-sizing requires all three states to pass all gates. E-STATCOM: two-phase simulation — fault sequence (ncycles × 2 × pulse time, continuous operation at fault power) followed by frequency-regulation cycling (0.1 s full cycle, 0.05 s half-cycle); lifetime is computed from the continuous phase. UPS: one discharge pulse; lifetime from the bus hold voltage and coolant temperature. Constant load: continuous charge–discharge cycling; lifetime from settled cell temperature and log-weighted mean cell voltage. Lifetime model: Arrhenius temperature factor exp(Ea/kB × (1/T_cell − 1/T_ref)), T_ref = 65 °C; Ea default 0.7 eV (typical EDLC range 0.5–0.9 eV, Kreczanik 2014). Voltage factor: life doubles per V_half below rated (default 0.1 V). Discharge ODE integrated with RK4 (50 steps), ESR-compensated — bus receives the rated power while cells supply P + I²·ESR. Cells within a module are all in series.