EngiMetric
Aerial view of rows of photovoltaic modules at a large solar farm

Stage 6 of 13 / Calculation

Size the battery storage

Size nominal and usable battery energy for autonomy and daily cycling, and estimate service life and replacement.

  • Practitioner
  • 13 stages
  • 14 min
  • Solar PV and electrical storage
Development preview Solar PV and Battery: Full Engineering Workbench
Development preview. The calculations on this journey run on existing EngiMetric engines, but the journey text and scope have not completed independent engineering review. The route is excluded from search while it remains a preview.
Professional review required.The engines are implemented and unit-tested in this repository, but the journey copy, defaults and boundary still require review by a licensed engineer before publication. The route remains a noindex preview. Current verification state: Needs engineering review.

After this stage you can

Learning objectives
  • Separate nominal, usable, reserve and cycling energy.
  • Compare the specified bank with the autonomy requirement for critical loads.
  • Explain how cycle life, calendar life and degradation set the replacement year.

The engineering

Battery sizing separates nameplate from usable energy. Depth of discharge, state of health and temperature derate the nominal figure; the reserve is held back for backup and is not available for daily arbitrage. The workbench reports each quantity instead of collapsing them into one number.

Autonomy is a resilience decision. Essential loads for a stated outage need a different bank from a system that shifts solar energy to the evening every day. The required nominal energy is compared with the specified bank, and an undersized battery produces a warning rather than being silently accepted.

Service life is the shorter of cycle life and calendar life. The replacement year and cost feed the cash flow, so a battery that fails inside the project period changes the economics. The model is a planning estimate, not a warranty prediction.

EngiMetric / solar workbench

Your project, computed stage by stage

Loading the saved project state...

Preview screen. Inputs are saved in this browser only. Resource presets and tariffs are illustrative. Failed checks stay visible; a clean summary is not a stamped design.

Inputs and outputs

What this stage owns

You own

  • Chemistry, nominal energy and coupling
  • Depth of discharge, state of health and temperature derate
  • Round-trip efficiency and charge/discharge C-rates
  • Reserve, autonomy days and backed-up AC load
  • Cycles per year, cycle life, calendar life and replacement cost

You produce

  • Usable, reserve and cycling energy (kWh)
  • Maximum charge/discharge power (kW)
  • Service life, replacement year/cost and end-of-life capacity
  • Five battery constraint checks

Your deliverable for this stage

Capstone evidence

A battery specification with usable energy, power, autonomy check, service life and replacement assumptions.

Stage assumptions, limits and sources

Provenance

Assumptions

  • Round-trip efficiency is split symmetrically between charge and discharge.
  • Capacity and efficiency are constant within a dispatch run; degradation is applied between years.
  • Replacement is a single planning event at the estimated service life.

Constraints

  • No cell-level model, thermal management load or second-life behaviour.
  • Cycle life does not vary with depth, temperature or C-rate in this screen.

Limitations

  • No warranty terms, augmentation strategy or manufacturer acceptance test.
  • No fire suppression, ventilation, clearance or transport compliance design.
  • The replacement cost is a scalar and ignores price learning and residual value.

Review status

  • Needs engineering review
  • Professional review is required before publication or use as a design basis.

Stage progress is stored in this browser only. The explanation and every limit on this page remain readable with JavaScript disabled; the calculators need it to run.

Stage kind: Calculation / Journey: solar-bess-screening / Stage: bess-sizing