TECHNICAL FUNDAMENTALS
EfficiencyDegradationTCOModelling
Round-trip Efficiency and Degradation: What the Numbers Mean
Two figures decide whether storage pays back — how much energy survives a charge-discharge cycle, and how fast the pack wears out.
01Introduction
What this article covers
When people compare batteries they often quote capacity and price. The two numbers that actually drive the business case are round-trip efficiency (energy kept) and degradation (capacity lost over time).
02Technical
Round-trip efficiency
Round-trip efficiency is the ratio of energy delivered out to energy put in. Losses come from the PCS, the battery, and thermal management. It typically falls in a broad band for lithium systems; the exact value depends on rate, temperature, and state of charge.
03Technical
Why efficiency shows up in the bill
Every percentage point of loss means you must buy or generate more energy to deliver the same useful kWh. Over thousands of cycles, that compounds into real cost — so efficiency belongs in any arbitrage or self-consumption model.
04Technical
Degradation basics
Degradation is the gradual loss of capacity and rise in resistance as a pack cycles. It is driven by depth of discharge, temperature, charge rate, and total throughput. As a typical reference, LiFePO4 often delivers several thousand cycles at moderate depth of discharge.
05Technical
Planning with both numbers
A defensible model pairs efficiency with a degradation curve. Oversizing the battery slightly protects delivered energy in later years, and respecting depth-of-discharge limits slows wear. Vendor warranty and cycle figures are the basis for modelling, not guarantees.
06Related Products
Products referenced
Referenced in this article
Commercial & Industrial ESS
C&I systems specified with efficiency and aging in mind.
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Battery Storage Components
Cells and PCS where efficiency is characterised.
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10FAQ
Frequently Asked Questions
What is a good round-trip efficiency?
It varies by system and duty, but the figure matters less than using the right number in your energy model. Treat vendor data as a basis for modelling.
Does degradation mean the battery dies?
No — it means usable capacity slowly falls. Specifying depth-of-discharge limits and a small oversize keeps performance acceptable for years.
Can I slow degradation?
Yes — shallower discharges, moderate temperatures, and sensible charge rates all reduce wear. The exact rate comes from the cell datasheet and your duty.
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