Identify the loads that must remain powered during outage, weak-grid or hybrid operation.
MFG POWER · ENERGY STORAGE DECISIONS
BATTERY STORAGE SIZING GUIDE
Size the system from the real load, required runtime and operating conditions — not from battery capacity alone.
A storage system is correctly sized only when power, usable energy, runtime, recharge and operating margin all fit the application.
01 / START WITH THE LOAD
SIZE THE SYSTEM AROUND WHAT MUST KEEP RUNNING.
The first step is not battery selection. It is separating critical, continuous and peak loads.
Define the normal sustained power demand.
Motors, compressors and other loads may create short-duration peaks above the continuous level.
02 / POWER SIZING
THE PCS / INVERTER MUST HANDLE THE REAL kW DEMAND.
A large battery does not compensate for an undersized power-conversion stage.
Continuous kWShould cover the sustained application load.
Peak kWShould cover short surge and transient demand.
Duration of peakPeak capability is only useful if it lasts long enough for the real event.
Power factorRelevant where loads and inverter output are specified on different electrical bases.
Phase configurationSingle-phase / three-phase and imbalance can affect system architecture.
03 / ENERGY SIZING
RUNTIME COMES FROM USABLE ENERGY — NOT NAMEPLATE ENERGY.
STARTING POINT
Required usable kWh ≈ Average load kW × Required runtime hours
This is only the starting point. Real sizing must then account for operating limits and losses.
LOAD PROFILEAverage load
Use the expected operating profile, not only the maximum connected load.
RUNTIMEMinutes or hours
Define how long the battery must support the required loads.
USABLE ENERGYDelivered kWh
Focus on what the system can actually deliver within its operating window.
04 / REAL-WORLD MARGINS
THEORETICAL kWh SHOULD NOT BE THE FINAL SYSTEM SIZE.
The buyer should adjust for the conditions that reduce usable energy or future performance.
DoDDepth-of-discharge limits reduce how much nameplate capacity is intended for routine use.
Conversion efficiencyBattery, inverter / PCS and system losses reduce delivered energy.
TemperatureHot and cold conditions can affect available power, energy and life.
AgingUsable capacity declines over the service life.
ReserveSome applications need a protected energy margin.
UncertaintyReal load growth and operating variation should be considered where appropriate.
05 / RECHARGE WINDOW
A BATTERY THAT CANNOT RECOVER IN TIME IS NOT CORRECTLY SIZED.
Daily cycling, generator-supported systems and weak-grid applications all depend on recharge availability.
Can the battery recharge during the expected utility window?
Is there enough solar energy and inverter capacity to restore the battery?
Generator size, minimum loading and charging power should work together.
The battery must recover before the next expected discharge event.
06 / BUYER COMPARISON
COMPARE THE COMPLETE SIZING BASIS — NOT JUST BATTERY CAPACITY.
CheckBuyer question
Continuous kWCan the system carry the sustained load?
Peak kWCan it handle the real surge and for long enough?
Rated kWhWhat is the nominal battery capacity?
Usable kWhHow much energy is actually available to the application?
DoDWhat operating window is allowed?
EfficiencyWhat losses are included in the sizing calculation?
TemperatureAt what environmental condition is the rating valid?
End-of-life capacityWill the system still meet the required runtime later in life?
Recharge powerCan the system recover before the next discharge?
07 / COMMON SIZING MISTAKES
WHERE STORAGE SYSTEMS GET OVERSIZED OR UNDERSIZED.
01Using total connected load
This can oversize the system if many loads never operate together.
02Ignoring peak power
The battery may have enough kWh but still fail on a short surge.
03Using rated kWh as usable kWh
DoD, reserve and losses reduce delivered energy.
04Ignoring end-of-life performance
A system sized only for day-one capacity may miss future runtime targets.
05Ignoring recharge time
The battery may not recover fast enough for the next cycle.
06Adding margin without logic
Arbitrary oversizing increases cost without necessarily improving the system design.
MFG BUYER VIEW
SIZE FROM THE OPERATING CYCLE — NOT FROM A SINGLE CAPACITY NUMBER.
MFG POWER starts with the load profile, peak requirement, runtime and recharge strategy. Only then should battery capacity, PCS power and reserve margin be finalized.
The right system is not the one with the biggest kWh number. It is the one that can meet the required load, runtime and repeat operating cycle with a clear margin basis.
HAVE A LOAD LIST OR RUNTIME TARGET?
TURN IT INTO A CLEAR STORAGE SIZING BASIS.
Send the load profile, required runtime, recharge source and site condition. MFG POWER can help structure the sizing basis before supplier comparison.
Review my storage sizing