Understanding LCOS: The Number That Actually Tells You What Battery Storage Costs
When a developer compares two battery storage offers at ₹8.2 crore and ₹9.1 crore per MWh of installed capacity, they are comparing the wrong number. Upfront capital cost tells you what you pay today. It does not tell you what storage actually costs per kWh delivered over the project's life — and that number can differ by 40% between two systems with the same nameplate capacity.
The correct metric is levelised cost of storage: LCOS. Here is what it is, how it is calculated, and what it reveals when applied to the choice between a cheap system and a well-built one.
What LCOS measures
LCOS is the total lifetime cost of a storage system divided by the total energy it delivers over its life, expressed as cost per kWh discharged. The formula captures everything the capital cost ignores:
LCOS = (Total lifetime cost) ÷ (Total lifetime energy discharged)
Total lifetime cost includes: capital expenditure (capex), annual operating and maintenance cost (opex), augmentation cost (replacing degraded cells to maintain capacity), financing cost, and end-of-life decommissioning.
Total lifetime energy discharged is: rated capacity × depth of discharge × round-trip efficiency × number of cycles over project life × (1 − average degradation over the project).
The variables that drive the difference between systems are cycle life, round-trip efficiency, and degradation rate. Capital cost is just one input.
A worked example: 5 MWh system, 15-year project
Take two hypothetical 5 MWh BESS systems.
System A — lower upfront cost, NMC chemistry, 2,500-cycle cell life at 100% DoD, 88% round-trip efficiency, non-linear degradation (7% fade in years 7–8), ₹7.8 crore/MWh capex.
System B — higher upfront cost, LFP chemistry, 6,000-cycle cell life at 100% DoD, 91% round-trip efficiency, linear 20% fade over 15 years, ₹8.8 crore/MWh capex.
At one cycle per day for 15 years, System A requires a full cell augmentation at year 8 (when capacity falls to 80% and the cycle budget is exhausted) — adding roughly ₹3.2 crore/MWh to the lifetime cost. System B does not require augmentation over the project life. System A's lower round-trip efficiency costs an additional ₹0.4 crore/MWh in auxiliary power over 15 years at Indian grid tariffs.
When all costs are summed and divided by total energy delivered, System B's LCOS comes in approximately 32% lower than System A's — despite costing 13% more upfront.
The three variables that move LCOS the most
Cycle life is the most important. A cell rated for 6,000 cycles versus 2,500 cycles is not just 2.4× "better" — in a daily-cycling grid application, it determines whether you need one augmentation, two augmentations, or none over the project life. Each augmentation event adds cell cost, mobilisation cost, downtime cost, and recommissioning cost.
Degradation curve shape matters almost as much as rated degradation. LFP's capacity fade is approximately linear — if you commission a 5 MWh system, you can model 4.0 MWh available capacity at year 10 with high confidence. NMC cells often show a "knee" in the degradation curve at year 7–9, where capacity drops sharply. For capacity contracts and PPAs, this non-linearity is a financial risk that is not captured in the nameplate spec.
Round-trip efficiency compounds over millions of kWh. A 3-percentage-point difference in efficiency (88% vs 91%) translates to roughly 3% more energy drawn from the grid per unit stored. At scale and over time, this is not a rounding error.
What this means for procurement
LCOS analysis should be mandatory at the RFQ stage. Ask every supplier for:
- The rated cycle life of their cells at the proposed DoD, with supporting test data
- The degradation curve (not just the end-of-life number, but the shape)
- The round-trip efficiency at rated power, measured DC-to-DC and AC-to-AC separately
- Their augmentation assumption — do they guarantee capacity over the project life, and at what cost?
A supplier who cannot provide items 1–3 cannot give you a credible LCOS, which means you cannot make an informed procurement decision. The upfront price is knowable without any of this. The real cost is not.
At SilicIndia Energies, our SIE-BESS5000 uses 314 Ah LFP cells rated at 6,000 cycles at 100% DoD, with a linear degradation guarantee. We model LCOS for every project we quote and provide the assumptions transparently. Contact us if you want to run the numbers for your specific project.
