PCS sizing
Size PCS power against battery capacity and real site demand.
Use the operating target, load curve, overload behavior, voltage window and transformer boundary—not battery capacity alone.
PCS sizing decides how much power the battery system can deliver or absorb at the site. It should be checked against load profile, backup requirement, PV behavior, transformer capacity, grid phase and battery current limits.
Use this page together with PCS and battery cabinet matching before approving a cabinet or container quote.
kW and kWh answer different questions
kWh describes stored energy. kW describes power. A high-capacity battery with an undersized PCS may not support peak loads. A high-power PCS with too little battery capacity may not provide enough runtime.
PCS sizing checklist
| Check item | What to request | Why it matters |
|---|---|---|
| Load profile | Peak demand, starting load, daily curve and backup priorities. | Defines required PCS power. |
| Battery capacity | Nominal kWh, usable kWh and discharge current. | Confirms runtime and current support. |
| Overload | Short-term overload rating and load-start behavior. | Important for motors and compressors. |
| Transformer | Transformer capacity, phase and grid connection limits. | Prevents grid-side mismatch. |
| Reactive power | Power factor or reactive support requirements. | Affects PCS selection and site approval. |
Documents to request
Ask for PCS datasheet, wiring diagram, grid mode notes, BMS protocol details and commissioning support. For site inputs, use the site survey checklist.
How application changes PCS sizing
Peak shaving usually needs enough PCS power to reduce demand peaks at the correct time. Backup power needs enough power for critical loads and enough battery capacity for the outage duration. Solar self-consumption needs coordination between PV production, load behavior and battery charging. These are different sizing problems.
A common mistake is to select PCS power from a round number rather than the site load curve. Another mistake is to choose a large PCS without checking battery current and thermal limits. Both approaches can create cost or commissioning problems.
The buyer should ask for a short explanation of why a PCS size was chosen. That explanation should mention load profile, target kWh, discharge current, transformer limits, grid phase and operating mode. If those points are missing, the sizing may not be project-specific.
Evidence that supports PCS sizing
Useful evidence includes load profile, peak demand record, critical-load list, PV generation estimate, transformer capacity, grid connection information, battery current limit and PCS datasheet. These files help the buyer compare technical logic, not only model numbers.
Quotation review notes for PCS sizing
A PCS sizing quote should explain why the proposed power rating is suitable for the application. If the supplier cannot connect PCS power to load profile, backup requirement, transformer capacity or battery current, the sizing may be generic rather than project-specific.
Buyers should also ask whether the PCS rating is continuous, peak, grid-tied, backup or temperature-dependent. These details can change how the system performs during real operation.
| Quote item | Question to ask | Risk if unclear |
|---|---|---|
| Included scope | Which battery, PCS, EMS, cooling, fire and document items are included? | The buyer may compare a complete system with a partial supply. |
| Responsibility | Who supports setup, troubleshooting, spare parts and warranty claims? | Problems can move between supplier, integrator and installer. |
| Evidence timing | Which documents are available before deposit, before shipment and after commissioning? | Important evidence may arrive too late to influence the purchase decision. |
FAQ
Can I size PCS from battery capacity alone?
No. PCS sizing needs load profile and power requirements.
What causes undersized PCS?
Ignoring peak demand, motor startup, backup loads or transformer limits.
Does PV capacity affect PCS sizing?
Yes, especially in hybrid or AC-coupled solar + storage systems.
What should I send for review?
Load curve, backup list, grid phase, transformer data, battery target and operating mode.
Is a larger PCS always better?
No. It may add cost, heat, grid requirements and battery current demands.
Nameplate ratio reference
Use the documented power-to-energy ratio as a first check.
Nameplate duration is rated energy divided by rated power. It is not usable runtime; reserve SOC, efficiency, C-rate, ambient conditions and end-of-life margin must still be applied.
| Configuration | Nameplate ratio | Documented rate | Starting duty |
|---|---|---|---|
| 105 kW / 233 kWh | ≈2.22 h | 0.5C | Distributed C&I |
| 125 kW / 261.2 kWh | ≈2.09 h | 0.5C | Distributed C&I |
| 250 kW / 522.5 kWh | ≈2.09 h | 0.5C | Larger C&I cabinet |
| 1.25 MW / 3.354 MWh | ≈2.68 h | ≤0.33C | Energy-led container |
| 1.725 MW / 5.016 MWh | ≈2.91 h | ≤0.33C | Long-duration container |
| 2.5 MW / 5.016 MWh | ≈2.01 h | ≤0.5C | Higher-power container |
| 100 kW / 233 kWh hybrid | ≈2.33 h | 0.5C | PV-storage-diesel |
Related buyer guides
Continue with the next engineering decision.
Use the guide that matches the open sizing, electrical, safety or quotation question.
Peak shaving battery sizing
Translate interval load data, target demand and peak duration into kW and kWh.
Read guide2-hour vs 4-hour battery storage
Compare load shape, usable energy, SOC reserve, cycle duty and project economics.
2h vs 4h BESS400 V vs 690 V BESS
Review current, cable, switchgear, transformer and AC interface implications.
Read guideContinue the project review
Connect the next decision.
Use the related page that matches the next equipment, engineering or evidence question.
Bring the site data. Leave with a clearer BESS scope.
Share the load profile, grid voltage, target kW and kWh, installation country, ambient conditions and expected schedule.