NaS batteries are only manufactured by one group at present, worldwide: NGK Insulators Ltd of Japan and TEPCO. The battery was originally developed as a replacement for pumped hydropower, but was later targeted at works load leveling and similar applications. Demand for NaS batteries was very weak at one time and it was feared the technology could be shelved, but surging demand has returned it to full production. According to a source at NGK Insulators, "We are running our production line at full capacity, 90MW annually, and are now considering increasing production capacity to handle expected future bookings."
17 NaS batteries
have been delivered to the Futamata wind farm, each with a storage
capacity of 2MW, for a total of 34MW. They are being used to store the
electricity generated during the night (Fig 4). In the daytime, the
battery output is scheduled to be combined with wind turbine-generated
electricity and supplied to the commercial power grid operated by
Tohoku Electric Power Co Inc of Japan.
Thanks to the introduction of large-scale storage batteries, the Futamata wind power generating plant can use a new output control method, namely constant output, or flat output. Experiments indicate that effects such as grid frequency fluctuation can be significantly reduced.
In flat control, the generating plan for the following day is prepared, based on information including annual wind data for the region, meteorological forecasts and storage capacity. The electric power utility is informed of the plan. By combining storage batteries with unpredictable wind-sourced generation, it becomes possible to prepare plans. Once the plan is known, the wind farm becomes a very handy generating system for the utility. In fact, it is possible it could lead to connections to wind power generation facilities above and beyond the limits of the connectable power levels calculated by the utilities. For example, Tohoku Electric Power might use even more wind power in the future, as Yoshinori Ichikawa, manager, Power System Engineering Dept, there explained: "If flat output control means power is generated in accordance with a plan, then it becomes possible to treat wind power as the same sort of stable power source as thermal power plants."
If generation is below planned output, however, it is possible the operator could suffer a penalty. The electric power industry is watching what happens at the Futamata plant.
Using EDLCsInvestigations have also begun into the use of storage batteries to control short-term output fluctuations in short-cycle design.
Usually the electric power utilities impose conditions on wind power operators to minimize frequency changes in the grid, such as keeping the 20-minute output fluctuation to no more than 10% of rated output. If the output fluctuation from the wind farm can be held to within this range, the utility can absorb any fluctuation by using its own generating capacity. In other words, a storage capacity sufficient for tens of minutes of electricity is sufficient to fulfill the minimum requirements imposed by the utility. And that means the system is feasible even without using large batteries like the NaS storage batteries.
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