Wednesday, July 1, 2009

First Wind Energy Storage for Ireland

ZBB Energy has a press release out for their flow battery system at a wind farm in Ireland. Flow batteries are a great application at wind farms. The VRB-ESS has been used at wind farms for several years in Japan and Australia, and the Irish government published a report in 2007 about integrating a VRB-ESS into a wind farm, finding that the optimum size for that installation was a 2 MW system with 6 hours of storage (12 MWHrs).

Although the ZBB is a flow battery, there are significant differences between the ZBB and the VRB-ESS. These differences must be kept in mind when planning for an installation.

The ZBB is more energy dense than the VRB - which means it takes up less space. The folks at ZBB have standardized a containerized product - a 50 kWh system that can be linked in groups of 10 to make a 500 kWh system that fits on a truck trailer. This makes the system easily transportable and potentially mobile, allowing it to be trucked to one location and then another as needed. The downside is that there is no flexibility in configuration. The 500 kWh system will deliver a maximum of 250 kW (although it has the capability of exceeding this rating by 110%) for 2 hours. If you want more hours of storage, you must by more capacity, whether you need it or not. More technical information available here...

On the other hand, the VRB is less suited for mobile applications because it is less energy dense - it needs a larger footprint - which isn't a problem at wind farms and solar PV. Since it isn't restricted by the need for a smaller footprint, it can be configured separately for capacity and storage. For example, the Irish study determined an optimum configuration was 2 MW of capacity and 6 hours of storage. At the Hokkaido wind farm, Sumitomo installed a 4 MW system with 90 minutes of storage (this installation, as well as the Irish, is able to pulse up to 150% of capacity for 10 minutes each hour).

As flow batteries, both the ZBB and the VRB can charge and discharge many times, ideal for intermittent renewable energy. However, the VRB will have a longer useful life. Both systems use a membrane that doesn't wear out from use, but will get old. As the ZBB membrane ages, the different solutions will come in contact and ruin the system. This doesn't happen with the VRB-ESS due to the single solution technology. If the membranes are replaced, usually in years 10 - 12, the system will last another 10 -12 years.

Charge Cycle:
As mentioned above, both systems can charge and discharge many times. However, the ZBB requires 4.5 hours to recharge it's 2 hour system, a 2.25:1 ratio. The VRB is closer to 1.3:1 and would take about 2.5 hours to "fill" a two hour tank.

Bottom-line, we are seeing many storage technologies becoming available for many storage applications. The growing awareness of the value of grid connected storage to integrate renewables and shave peak demand will increase the demand for flow batteries and the VRB-ESS.

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