Pumped Storage Facility

One of the main concerns with using Renewable Energy is that it is often difficult to predict, intermittent and inherently variable in strength. These factors create instabilities in the national power network and make it difficult to dispatch power (switch in and out as demand changes).

The Spirit of Ireland project proposes a solution to harness the Wind and make it usable on a large scale. To do this the energy must be stabilized and become immediately available when required. In other words, a cost-effective means of storing its energy. By building large Hydro Storage Reservoirs, we can store Energy from the wind in a cost effective way.

Prototypes of this project have been built in the lab to determine whether this is feasible and to investigate the viablilty of a pumped storage facility for intermittent power generation.

pumped storage model image

Vanadium Redox Flow Battery Technology

The level of renewable energy integration into national power grids is increasing significantly year on year. These sources of energy are intermittent by nature and this issue can be easily managed which penetrations of 10% or less. With strategic investment in the grid, using Ireland as an example, the level of penetration can be as high as 47%.

Flow battery technology can provide large scale power storage technology ranging from hundreds of kWh to tens of MWh's. When larger amounts of energy need to be stored it is more cost effective to consider pumped storage, although the initial capital costs are significant. Flow batteries are different from conventional batteries as they are comprised of PEM (Proton Exchange Membrane) cells, pumps, control systems and their electrolytes , which are stored in external tanks. These liquids are circulated through the cell which creates a potential difference across the cell, causing current to flow. The basic structure of a flow battery can be seen below:

structure of a flow battery

This modular structure means that flow batteries are very flexible which makes them attractive to utility companies. To increase the power output of the battery, the number and size of the cells can be increased. The capacity of the battery can also be increased by making the storage tanks larger. This ease of scaling allows batteries to be installed in stages so that a company can install a small model to establish its viability, which, once verified can then very easily add more capacity to the system provided there is space at the installation site.

The most common type of flow battery is the Vanadium Redox Flow battery. This is the case due to the stability of the chemicals and the fact that cross mixing of the electrolytes is not an issue (can be fixed by simply charging the battery). The lab has acquired a small Vanadium Redox Flow Battery from GEFC in China. The battery is very small for testing purposes and is rated at a current of 10 Amps, with a voltage of 12.5Volts giving an overall rated power of approximately 125Watts.It can provide this power at constant output for 4 hours. A small image of the battery cell itself can be seen below:

Image of the Cell from a Vanadium Redox Flow Battery

The battery will be used mainly as a proof of concept device to provide storage in the periods of time when there is insufficient power being generated from the wind turbine and the solar panels. In practice, much larger storage will be needed in terms of both power output and capacity.