GROWDERS – grid connected storage

  • looptijd: 2008 - 2012
  • locatie: Zutphen,
  • functie: Energieopslag
GROWDERS - grid connected storage
Within the GROWDERS project, 2 L-ion batteries an a flywheel are designed, built and combined with an energy storage inverter and a control unit.

GROWDERS – demonstration of grid connected storage.

Development and use of Renewable Energy Sources is one of the key elements in European Research. 

However connecting these sources to the electricity distribution networks causes significant effects on the management of these networks.


Leven we in 2050 in een energie-neutrale wijk? Opslag van elektriciteit in de wijk: wat, waar, hoeveel? Energiebronnen:

  • Solar panels
  • Wind generators
  • Combined heat and power (CHP)


  • stability
  • security
  • peaks in supply & demand
  • overall management


Electricity storage systems provide means to overcome technical and economic hurdles for large-scale introduction of PV and other distributed sustainable energy sources.

The costs of different storage technologies have dropped dramatically during the last years making introduction of storage systems feasible.

However, unfamiliarity with the techniques, lack of confidence and uncertainty with costs and benefits cause very large inertia by end users (utilities, investors).

Moreover, network components are designed to be technical and economic effective for a (minimum) period of 40 years, causing conservative behavior.

The latest up-to-date results of the laboratory tests of the first integrated system (Li-ion battery, inverter, overall energy management system and the connection to the local distribution grid) have been presented.

Link to the paper


PV Systems and PV Power Plants


Universiteit Utrecht, DNV GL, TU Eindhoven


Ir. Petra de Boer-Meulman




Inventory: Inventory balance equation:

  • In-efficiencies (losses) are included
  • Amount of energy stored is bounded
  • Power of decharging and charging is bounded Amount of energy stored: beginning = end

Storage placement tool

  • Implementation in Java and ILOG CPLEX 12.2
  • Validation with Plexos and Power-Factory: Loadflow series model is reasonable approximation

Network model

  • Nodes V: Users or connection points
  • Edges E: connections between nodes Directed, current flow from node i to j (upstream negative)
  • Discrete set of timeframes

Loadflow series model

Placement of storage units is fixed


  • Current on all edges in each time period
  • Voltage on all nodes in each time period charging, decharging, actual storage in nodes at each time period
  • Within constraints
  • With the objective
    Minimize the energy taken from the grid connection multiplied by their prices i.e. maximize being energy neutral

Load flow series

  • Model 3-phase alternating current physics: large computation time Apply DC approximation
  • Different from DC approximation found in other operations research papers.
  • Constant current production

Optimization of storage location

  • SLOPER model: local search through set of possible storage locations
  • To evaluate each storage location set: load flow series model
  • SLOPER = Storage Location OPtimization Efficient Routine

Concluding remarks

  • Storage systems are important to enable energy neutral neighborhoods
  • Optimization algorithms are helpful to find out which, where, how many storage systems


Energy storage inverter

the ESI (Energy Storage Inverter) is developed and supplied by Exendis. It’s a bi-directional galvanic isolated inverter/battery charger offering a window from 230 to 400 Vac 50 Hz for the mains voltage and 336 to 448 Vdc fr the battery voltage.

Its power level is 50 kW with water cooling and 30 kW with build in forced air cooling able to drain 90 kW during 10 seconds. The typical efficiency of the ESI is 94.5%.

The ESI can run in parallel with the grid, without the grid, wit a generator an with other ESI’s. The functions built into the ESI are:

  1. battery charge
  2. inverter (to island grid but also to supply active poer)
  3. peak shaving / buffering with generator


Universiteit Utrecht

  Prof. dr. Wilfried van Sark    030 253 76 11