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Battery Energy Storage System (BESS)

A Battery Energy Storage System (BESS) is a system designed to store electrical energy for later use. BESS units are primarily used to:

  • Store excess PV production during periods of high generation.
  • Release stored energy during periods of low or no solar production.
  • Provide grid services such as frequency regulation, peak shaving, and backup power.

Use of BESS in PVsyst

In PVsyst, BESS are used in the following systems:

  1. Stand-alone systems*: BESS ensure energy supply continuity (off-grid).

  2. Grid-connected systems, where storage can be used in several modes:

    • Self-consumption: storing excess PV energy to supply local loads later.
    • Peak shaving: storing energy produced in excess of grid limitations and injecting it when production is lower.
    • Power shifting: storing PV energy for use during periods of high electricity prices.
    • Weak grid islanding: for regions with an unstable grid, BESS are used when the grid is unavailable.

Battery Technologies in PVsyst

PVsyst simulates the battery’s state of charge (SOC), charging/discharging cycles and lifetime. It covers two main types of batteries:

  • Lead-acid batteries: first-generation storage technology, still used in some legacy systems. They are less energy-dense and require more maintenance but remain cost-effective for certain applications.
  • Lithium-ion (Li-Ion) batteries: modern storage technology with high energy density, low self-discharge, and long lifespan. They require minimal maintenance and are now the standard for most new BESS installations.