BESS Sizing Guide

How to Size BESS for a Weak or Unstable Grid

Quick answer: Weak-grid BESS sizing starts by defining what the site must survive: complete outages, limited grid hours, voltage/frequency instability, demand constraints or all of these. The battery must be sized in both kW and kWh, while the final architecture may also include solar PV, diesel generation and an EMS.

What data matters most in a weak-grid project?

Record grid availability by hour, outage frequency and duration, critical and non-critical loads, peak demand, voltage and frequency conditions, PV capacity, generator capacity and the required level of autonomy.

How do kW and kWh differ?

kW determines how much instantaneous load the BESS can support. kWh determines how long it can support that load. Both must satisfy the operating scenario.

Should solar and diesel be included?

Often yes, but their contribution should be modeled from actual availability and dispatch strategy rather than assumed. A hybrid microgrid can coordinate grid, solar, battery and generators to serve the site under different conditions.

Where should I start?

Use the BESS Sizing Calculator, then review Microgrid & Backup Power, Solar + BESS and Diesel + BESS.

Get a preliminary project estimate

Use Zevonexa’s free calculator, then send your actual project inputs for engineering review.

Open BESS Sizing Calculator → Request a BESS Solution →

Important sizing limitation

These examples are screening guidance, not a final electrical design or performance guarantee. Final equipment selection requires project-specific engineering, applicable standards, equipment ratings and verified site data.