updated on 22 July 2016

BESS is a power plant for renewable energy sources, equipped with all the components to provide a ready to use, compact and flexible solution.

BESS power plant

  • Lithium battery storage and BMS
  • Bidirectional converter and converter controller
  • Master controller (MC)
  • Filters and transformer

Functions

  • Limitation of overvoltage caused by RES power injection
  • Energy time shift
  • Peak shaving and load leveling
  • Frequency regulation
  • Black start
  • Compliance with grid codes
  • Scales from 15KW – up to MVA range
  • Modular units from 15 kW – 500 kW
  • On-grid and off-grid operation
  • Manages multiple renewable sources, storage system and loads
  • Distributed Energy Generation
  • Renewable integration
  • Different applications
  • Compensation of fluctuations in the generation and consumption of electricity
  • Grid stabilisation
  • Allows to level power generation, shaving peaks
  • Uninterruptible power supply
  • Fully reliable configuration and validation of any power plant

There are several technical and economical reasons to have a time shift of energy.

The battery energy storage size has to be chosen in terms both of power and energy. The BESS power plant is capable to provide a time shift of energy, so that it accumulates a certain amount of energy in the battery during a time interval, and it returns it, or part of it, in a subsequent time.

There are several technical and economical reasons to have a time shift of energy.

In an isolated power system the BESS power plant can accumulate energy when there is a surplus of generation, to return it when there is a shortage. Thus the BESS power plant can compensate for the unbalances between the generation and the load profiles.

Since generation from renewable energies depends on seasonality, the BESS power plant contributes to counteract it too. The BESS plant can absorb energy from the grid in low cost times and dispatch it during high cost times. The load energy consumption is shifted in time (load shifting) and concentrated in the low cost periods.

The energy size of BESS power plant (kWh of stored energy) is determined by the desired amount of energy to be time shifted, and it is related to the requested duration or autonomy.

The nominal power of BESS power plant (kW) is determined by the output power of the bi-directional DC/AC converter which connects the BESS to the grid (or micro grid) and by the maximum current which can be extracted by the battery during discharge. This is also related to the capacity of battery (Ah) and to its admissible rate of charge and discharge.
The designer will select the requested BESS power plant according to the rate of battery charge and discharge and to the requirements of micro grid stability.

The BESS power plant can provide grid support through grid services.

Energy Services

  • Energy time shift
  • Peak shaving/load leveling
  • Restart of power system

Power Services

  • Primary control reserve

Microgrid – Intelligent power supply

Microgrids are outstandingly suitable to cover the rapid increase in electricity consumption. It‘s not necessary to build new large power plants. Thus overloaded existing electricity transmission lines can be avoided.

The microgrid solution is able to connect and disconnect the mains very quickly. In the event of a mains failure, important facilities are provided with a safe, clean interruption-free power supply. The microgrid can absorb energy from the grid in low cost times and dispatch it during high cost times.

Architecture

Lithium Battery Storage

  • High specific power energy density, long life
  • Long cycle life
  • Safe technology
  • Flexible extension
  • Battery Management Sytem (BMS)
  • Protection due to overcharging, over discharging, overtemperature
  • Cell balancing at all times

Bidirectional converter and converter controller

The battery system is connected through a DC/AC bidirectional converter. The Bidirectional Converter is equipped with a control logic and it can operate in different modes:

Grid following – The converter acts as a current generator when it is connected to a grid

Grid forming – The converter acts as a voltage generator. This mode is used in islanded operation and the converter creates the power balance node in a multi-source micro grid.

Grid supporting – The converter acts as a voltage generator with frequency and the voltage amplitude. This operation mode is used to connect several RES source in parallel on a micro grid.

Filters and Transformer

The BESS power plant is connected to the grid through an interface stage, which includes filters and power transformer.

The transformer provides insulation between DC and AC systems, adapts the inverter output voltage to the grid voltage (LV, MV, HV grid), creates the neutral point and compensates the load unbalances during off grid operation.

The filter reduces voltage and current harmonics injected into the grid. It consists of an LCL filter to cut the harmonics due to switching frequencies and of a high frequency EMI filter.

The purpose is to maintain a low harmonic distortion, typically:
Current THD < 3% in grid connected operation
Voltage THD < 3% in islanded operation

 

Master Controller

  • defines and implements the BESS power plant control logic
  • defines the set points of the inverter controller
  • communicates with the BMS to manage the battery status

BESS can operate in two modalities:
Internal control:
The MC receives measurements from the system and the BMS and initiates the control strategy.

External control:
The MC receives the control strategy from an external controller and implements it depending on the battery status.

BESS power plants

Electrical connections

  • DC side: PV, battery system
  • AC side: Main grid or micro grid, wind/generator, user load

BESS power plants include:

  • DC/AC power converter
  • Digital control of power converter
  • LCL and EMI filters
  • Output power transformer
  • Master Controller
  • Protections and switchgear
  • Measurement points
  • Forced air cooling
  • Touch screen display
  • Battery storage system

BESS power plant applications

Go to BESS power plant applications