TECHNICAL INSIGHT
Load profileTariffDurationROI
How to Size a Commercial & Industrial Battery Storage System
A practical framework for turning a load profile and a tariff into a defensible battery capacity and power rating.
01Introduction
What this article covers
Sizing storage is not guesswork. It is the disciplined matching of two numbers — energy (kWh) and power (kW) — to a clearly defined objective. This article walks through the process used to scope a behind-the-meter C&I system.
02Technical
Start with the objective
Name the job first. Common C&I objectives are: peak shaving (lower demand charges), backup (ride through outages), PV self-consumption (store midday solar for evening use), and arbitrage (charge off-peak, discharge on-peak). The objective decides which constraint binds: peak shaving is power-limited, backup is energy- and autonomy-limited, PV shifting is generation-limited.
03Technical
Analyse the load profile
Pull interval meter data (typically 15-minute or hourly) for a representative period. The peak demand sets the power the PCS must deliver; the area under the curve during the targeted window sets the energy the battery must supply. Seasonal and day-type variation matters — size for the worst realistic case, not the annual average.
04Technical
Read the tariff
Demand charges are usually triggered by the highest 15-minute average in a billing period, so even a brief peak is expensive. Time-of-use rates set the value of shifting energy between windows. The savings model is only as good as the tariff data behind it; this is where most C&I business cases are won or lost.
05Technical
Capacity, power, and duration
Duration is simply energy divided by power (kWh ÷ kW = hours). A system that shaves a short, sharp peak needs high power and little energy; one that covers overnight backup needs more energy at lower power. A useful rule of thumb: define the target peak reduction in kW, then size energy for the discharge window you want to cover.
06Technical
Efficiency and degradation
Round-trip efficiency (the ratio of energy out to energy in) typically falls in a broad band for lithium systems; losses reduce the effective energy available and the economics. Over the project life, cycling fades capacity, so a modest oversizing protects performance in later years. Treat vendor efficiency and warranty figures as the basis for modelling, not as guarantees.
07Technical
Worked example (illustrative)
Consider a site with a 500 kW demand peak and a $/kW demand charge. If analysis shows a 200 kW, 2-hour shave removes the costly peak window, the target is roughly a 200 kW / 400 kWh system — then adjusted for efficiency, autonomy, and growth. This is illustrative only; every site is modelled from its own data.
08Related Products
Products referenced
Referenced in this article
Commercial & Industrial ESS
Scalable cabinet systems sized from the load and tariff study.
Explore products →Related range
Battery Storage Components
PCS and modules for larger or custom plant configurations.
Explore products →09Related Solutions
Solutions for this topic
10Related
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11FAQ
Frequently Asked Questions
What is the difference between kW and kWh for storage?
kW is power — how fast the system can charge or discharge. kWh is energy — how much it can store. Both must be sized to the objective.
How long does a 2-hour system last in a backup event?
Roughly two hours at its rated power, before efficiency and depth-of-discharge limits. Autonomy is set by the energy capacity you specify.
Can I add more later?
Often yes. Cabinet systems are frequently designed to accept added capacity as load or PV grows — confirm the PCS and enclosure headroom when scoping.
Put this into your project
Talk to StorXing about sizing, integration, and delivery for your site.