Applications

The wrong duty cycle will eat a battery years before the warranty admits it.

Two systems with identical nameplate capacity can be completely different assets. Duty cycle drives degradation, degradation drives what the warranty will actually cover, and that determines the real cost of owning the thing. Sizing on kilowatt-hours alone hides all of it.

Each page here starts from the commercial objective and works backwards to the technical requirement, which is the order procurement actually needs — not the order vendor datasheets are written in.

Sound familiar?

Same nameplate. Completely different asset.

You sized the system in kilowatt-hours and never established how many times a day it would actually cycle.
The demand-charge model assumed your peak is predictable. One bad afternoon erased the month's savings.
Your tariff has a demand ratchet, so a single spike sets the billing floor for months afterwards and the battery was not controlling for it.
The DC-coupled design was cheaper right up until the interconnection study came back.
Backup runtime was quoted at full building load, because nobody separated out the circuits that genuinely have to stay up.
The system is supposed to do two jobs at once, and the control strategy has to pick one at the exact moment both of them matter.

What actually decides it

Work backwards from the money, not forwards from the datasheet.

Four things that decide whether a storage project pays, none of which are properties of the battery.

Your tariff, in detail

Whether peak shaving pays is a question about your rate schedule, not about the hardware. Demand charge structure, ratchets, time-of-use windows and any standby charge decide the answer before you have chosen a vendor.

Cycles per day, and how deep

One shallow cycle a day and three deep ones a day are different products with the same label. This single number drives degradation, warranty terms and how the asset looks in year seven.

Which loads actually have to survive

Backup sizing collapses once you separate genuinely critical circuits from everything else. Quoting runtime at full load is how a modest requirement becomes an oversized system.

Who controls the dispatch

When a system serves more than one purpose, the controller arbitrates between them. Establish which objective wins during a conflict before you sign, because that logic is the asset's actual behaviour.

Where to go next

Find the business case you are being asked to justify.

Peak shaving and demand charges

The most common behind-the-meter business case, and the one most sensitive to details of your tariff that a vendor model will gloss over.

Solar-plus-storage

Pairing generation with storage changes both the interconnection process and the incentive treatment. AC- versus DC-coupled is the first fork in the road.

Data center backup power

Where batteries supplement or displace traditional UPS and generator plant, and what the reliability requirement really demands of them.

Microgrids

Storage as one part of a system that can island from the grid. The controller and the switchgear decide as much as the battery does.

Utility-scale storage

Front-of-meter projects answer to interconnection queues, market participation rules, and a diligence standard set by lenders rather than by facilities teams.

The other three

The decision next door is probably the one biting you.

These four constraints are not independent. Change the chemistry and the code pathway moves; change the duty cycle and the economics move with it.

Technologies

Every chemistry looks the same on a spec sheet. They fail in completely different ways.

LFP, NMC, flow and sodium-ion do not just differ on price per kilowatt-hour. They differ on what happens in year eight, what your fire marshal says, and whether anyone will take the material back.

Your fire marshal is not going to negotiate with the site plan.

Separation distances, enclosure ratings and fire service access are set by a small number of standards and enforced by an official with real discretion. Finding that out late is what costs money.

Every battery you install today is a disposal invoice with a date on it.

Residual value, transport classification and who is even permitted to take the material are decided by choices you make at procurement, not at decommissioning.

What people ask before they commit.

How do I know whether peak shaving will actually pay on my site?

Pull twelve months of interval data and your full rate schedule, and model the demand charge you would have avoided. If your peaks are frequent and broad, a battery has to work hard for a small reduction. If they are sharp and infrequent, a modest system can cut a lot. The shape of the load matters more than its size.

Can one system do peak shaving and backup?

Yes, and most commercial systems are sold that way, but the two objectives compete. Energy held in reserve for an outage is energy unavailable for shaving peaks. Ask precisely how much state of charge is reserved for backup and who can change that setting, because it directly reduces the savings in the financial model.

AC-coupled or DC-coupled for solar-plus-storage?

DC-coupling can capture clipped solar production and shares an inverter, which often makes it cheaper and more efficient on a new build. AC-coupling is usually simpler to retrofit onto existing solar, easier to permit and easier to service. The interconnection process and the age of the existing array usually settle it.

What does duty cycle have to do with the warranty?

Almost everything. Most warranties cap either total energy throughput or annual cycles alongside the calendar term, and whichever cap you hit first ends the coverage. A system cycled harder than the warranty assumed can leave coverage years before the stated term expires.