Distributed Energy Resources (DERs)

Distributed Energy Resources (DERs) of different types are being installed by many customers driven by their desire to contribute to the reduction of air pollution and support a greener energy production. However, one of the main problems with the renewable energy resources is the fact that they are not always available when we need them and may be available where we do not. That is why finding an adequate form of energy storage is one of the key requirements for the successful implementation of solar or wind based DERs.

One promising commercially available solution is Cellstrom's FB 10/100 - a complete energy storage system (ESS) that consists of a vanadium Redox flow battery with smart controller and configurable power electronics housed in a weatherproof container. The battery can be charged and discharged at up to 10 kW and provides 100 kWh of energy. The smart controller ensures that the battery operates at maximum efficiency at all times and allows remote observation of various battery parameters. The option of different arrangements of power electronics gives almost complete freedom in specification of electrical output (dc, single or three-phase ac).

The output of the FB 10/100 can be configured as: 48 V DC (with suitable inverters/converters);

120 V AC; 230 V AC (1-phase); 400 V AC (3-phase).

A flow battery is a type of rechargeable battery in which the energy is stored chemically in liquid electrolytes. Unlike conventional batteries, that store all of their reactive materials within the cells, a flow battery stores the electrolytes in tanks. The electrolytes are pumped through the cells when electric current flows and back into the same tanks.

There are two electrolytes, one for the positive reactions and one for the negative. The two electrolytes do not mix but are separated in the cells by an extremely thin membrane that only allows selected ions to flow through. Also in the cells are very stable porous carbon electrodes, where the critical reactions take place. As the reactions only involve the dissolved salts, the electrodes do not change physically or chemically allowing a very large number of charge and discharge cycles without significant decrease in capacity.

The cells are grouped together in blocks known as stacks with the cells being  connected electrically in series by bipolar plates, i.e. conducting plates that have positive electrolyte on one side and negative on the other. The stack voltage is the sum of the voltage of the individual cells. The energy of a battery string is limited by the poorest battery (cell). However, each cell of a flow battery is practically identical, because they share the same electrolytes. Therefore, flow batteries do not suffer the same intrinsic limitation as conventional batteries.