Japanese Variable Speed Pumped Storage Hydroelectricity may stabilize coming Smart Grid

We know coming Smart Grid needs "grid-scale storage" to incorporate fluctuations from lots of distributed power generators of renewable energy. But wen we hear the word "grid-scale storage", we usually imagine it is a futuristic realization. However, there already exists one that is in operation world wide. That is Pumped-Storage Hydroelectricity (PSH) power station.
As to fundamental description about PHS, visitors had better to see here and here.

According to a paper "Electrical Energy Storage - Large Scale", Japan has the second largest power capacity of PSH next to US. Since Japan is a mountainous country, there may be a lot of suitable places to build PSH power station.

Recently, I read a Nikkei economic news about state of the art PHS, named "Variable Speed Pumped Storage Hydroelectricity" (or Adjustable Speed Pumped Storage System) which is being installed at several conventional PSH plants and at new ones owned by Japanese electric power companies.

Japan has three major heavy electrical manufacturers, namely, Toshiba, Hitachi and Mitsubishi Electric. Japan's large EPCOs purchase huge equipments such as turbines and generators from these three companies mostly. A Japanese source said that the first variable speed pumped storage hydroelectricity was developed by Toshiba and installed at Yagizawa power plant owned by Tokyo EPCO in 1990.  After that, Toshiba provided several
variable speed PSHs to other EPCO and independent power producer. Also, Hitachi and Mitsubishi Electric are currently developing variable speed PSH to sell to major EPCOs in Japan. That Nikkei news told Kyusu EPCO, Kansai EPCO, Hokkaido EPCO and Tokyo EPCO had plans to install variable speed PSH of 300,000 kW - 400,000 kW from 2011 to 2020, or after. 

The advanced PSH of variable speed enables power producers to have following benefits.

- When pumping up water, power consumption of conventional PSH cannot be changed. So, it doesn't have frequency adjusting capability even when in need. While variable speed PHS can change the speed of spinning when pumping up water, it can be used as frequency adjusting equipment on behalf of high-cost thermal power plant in the grid. This is efficient not only at cost but also at CO2 reduction. 
- Since renewable energy power generation such as wind and solar would have fluctuations of power production, the grid needs adjusting functionality even in daytime. If enough capacity of variable speed PSH is installed in the grid, this problem will be solved. 
- When operating at demand peak, variable speed PSH can follow minute load change by dynamic speed control. This will reduce dependency on high cost thermal plant for peak purpose.
- Highly responsive operation of variable speed PSH would be beneficial for overall stability of the grid.

Though I don't have any clue to testify that quality of Japanese power grid is extremely high in terms of stability of frequency, requirements for above mentioned variable speed PSH from Japanese EPCOs are thought to be much higher. This high quality may have a big potential when the planned smart grids are prevailing in many countries to absorb fluctuations from renewables.