Reviving hydro3 July 2003
Taiwan's hydro capacity is underperforming, thanks to ageing dams, siltation and a lack of cheap power to prime its pumped storage. It has plans to upgrade existing plants, as well as build new ones, as David Hayes reports
BY 2013 Taiwan's hydro power dam capacity will stand at 4608MW. In the following decade medium and large hydro power capacity will increase by just 5%, but the annual hydro power output is planned to rise by 19%.
The reason is that Taiwan, and the state-owned Taiwan Power Company (Taipower) plans to make more effective use of its considerable potential for pumped storage.
'There is still some potential hydro power to be developed but most sites with easy access or a high water head already are exploited,' said Yu Shang Hsiung, director of Taipower's power development department. 'The total potential in future for exploitation, not including resources in national parks, is 1517MW. If we include that figure the potential is 2300MW. It is unfortunate that some of this is in the national parks, as the national park authorities are reluctant to cooperate to develop these hydro reserves".
Although Taipower already operates pumped storage schemes totalling 2600MW, Hsiung pointed out that Taipower's current power system lacks sufficient low cost baseload generation to pump water cheaply to the upper reservoirs. Some 70% of Taipower's pumping power is provided by LNG-fired power plants, rather than lower cost electricity from coal or nuclear stations.
'Natural gas is expensive. It is double the cost of coal and nuclear power, so it is unreasonable to do pumped storage with LNG' Hsiung said. 'Pumped storage power automatically generates a control role in frequency and voltage regulation and has an important role to play. We are looking at new pumped storage station sites but we will not do anything before 2011 as low-cost baseload power is lacking.'
Plans to expand coal-fired generation could provide sufficient baseload power supplies to support another pumped storage schemes early in the next decade. Hsiung explained that Taipower plans to install variable speed water turbines in the next pumped storage power house to enable the station to play a more active role as an electricity voltage and frequency regulator.
'This is one reason we need to build another pumped storage scheme,' he said. 'We have conducted studies for a few years in Ilan County at a site called Danaou. The site can generate about 1000MW if we install four 250MW turbine generator sets.'
The scheme will not be an easy task as severe earth and rock floor erosion problems could affect the site. 'It's not an easy problem to solve because if we build the dam it could fill with overburden after an earthquake,' Hsiung added. 'If there were heavy rain there could be a sediment problem.'
One alternative is to use the Feitsui dam, which is currently owned by the state-run Water Bureau and is the main water source for Taipei. Feitsui dam would be used as the lower dam, requiring an upper dam to be built. 'The Water Bureau is reluctant to allow us to use this dam,' Hsiung said, 'We have not done any planning yet, but any pumped storage scheme must be at least 1000MW in size. If the scheme is less than 1000MW then it will be uneconomical for us to build and operate.'
A third option is to build a pumped storage scheme on a coastal site and use seawater instead of freshwater. The potential site is located near Hualien on the east coast where a natural bay with steep sided cliff walls could house a lower dam and penstock while the upper dam would be sited above the cliffs. An experimental coastal pumped storage scheme has been in operation in Japan for the past five years and this has encouraged Taipower. But Hsiung said: 'We wonder whether there would be a pollution problem as we would have to pump seawater to the upper dam and if the seawater escapes from the upper dam there may be a problem.'
Meanwhile, Taipower plans to build 20 to 30 grid-connected mini hydro schemes. 'We are planning the dams,' Hsiung said. 'We will submit at least two projects a year for approval for the next five to ten years.'
The first proposals were submitted for government approval early in 2003. The Chubin scheme will have one 18.2MW turbine and one 2MW turbine, while the Wusheh extension will have one 24MW turbine. The latter will involve building a new intake structure on the right bank of the reservoir about 300m upstream from the existing Wusheh dam, while a 362m tunnel will divert storage flow from Wusheh reservoir into the new plant. A new vertical 24MW Francis type unit will be installed. Construction is due to begin in July 2007 for commercial operation in mid-2011.
"First we must build the access road for construction and power plant equipment. It can take two years for this," Hsiung said. 'Most projects are underground so it takes at least five years. If we build the mini hydro scheme in a ditch it takes only two years but the site location for this is limited.'
The plants may be privately owed: 'Agricultural associations will build them," he added. 'Already the 8.8MW Wusantou scheme which started up in September 2002 has been done this way and the 12MW Hsikou mini hydro to start in October 2004 will follow this route.'
Taipower plans to offer turbine contracts for international bidding.
Another mini hydro IPP project under planning is the 19MW Ming Chien scheme in central Taiwan which the state-run Water Bureau will build as a 'build, operate, transfer' (BOT) project the first hydro power BOT scheme in Taiwan.
Waste water rights are owned by the Water Bureau, which will supply the water. Hsiung said: 'The Water Bureau wanted Taipower to build the power plant but since then plans have changed and a private company is due to co-operate with the Water Bureau to develop the project.'
Upgrading and uprating
Taipower is working on upgrading and rehabilitating several existing hydro plants.
In central Taiwan work is underway constructing a 15km diversion tunnel from Wuchieh to Sun Moon Lake to replace the existing diversion tunnel and divert the stream flow from Lishi river. Work is due for completion in April 2004.
Work is also under way to replace 70-year old turbines at the Choshui plant. The upgraded scheme will use additional water diverted from the Chichi river. A new Kaplan turbine, rated at 3.46MW, will be installed. Commercial operation is planned for July 2005.
In the south, one of the country's oldest dams, in operation for more than 90 years, is being upgraded: Chumen hydro dam, on the downstream section of Laonung river. A 2.67MW S-type turbine is due to go into operation in July 2004, replacing the existing turbine, rated at 2MW, but highly inefficient.
In the east, the Bihai scheme will have a single 61.2MW pelton turbine using a head of 417m. Begun in January 2000, commercial operation is planned for January 2006. Planning also continues for the 74.2MW Shibao scheme on Wanli river.
An 809,000m3 concrete gravity dam will be built at an elevation of 388m from the river bed. The Shibao scheme also includes diversion work at Maan Creek dam at an elevation of 472m.
The underground power house will have two vertical Francis turbines one 63MW and one 11.2MW to use the 40cm design discharge and the design head of 215m. Construction is due to begin in January 2005 with commercial operation in 2010.
In the north, work is believed to be getting underway on the 22MW Jingshan scheme on the Jingshan river, which will use the head between Liyutan reservoir and its afterbay. An underground power house will house a 22MW vertical Francis turbine for a maximum discharge of 35cm and a head of 72.8m. Commercial operation is due in January 2008.
On the Choshui river, construction is due to begin early in 2007 on the Chubin scheme, with commercial operation in mid-2011. The scheme will use tailwater from the existing Wanda dam and the proposed Wushen extension. The two vertical Francis turbines will be rated at 16MW.
Dealing with siltation
Taiwan's public water supply dams have been in the news recently due to serious siltation problems. Recent government statistics show that 277Mm3 of silt have accumulated in Taiwan's reservoirs, reducing the effective water storage capacity of 40 major reservoirs in Taiwan from 2.32Bm3 to 2.04Bm3. Storage capacity is being reduced by 11.32Mm3 per year due to the accumulation of sediment.
At a recent session of the Legislative Yuan, legislators questioned water resources officials about siltation and demanded that emergency measures be implemented to remove it.
Water resource officials were recently reported in the local press as saying that the newly-formed Water Resources Agency is currently conducting two sediment dredging projects but the projects may not be completed fully due to a lack of funds.
According to the Water Resources Agency, digging out sediment during the dry season costs less than US$6/m3, while removing silt by dredging costs around US$15/m3. If the sediment is transferred to public dumps, operated by the Construction and Planning Administration, the cost would be US$29/m3.
Water resource officials say they have negotiated with the Environmental Protection Administration (EPA) to build two coastal stations where sediment could be dumped directly into the sea, at a cost of less than US$3/m3. The EPA is still evaluating the environmental impact of dumping at sea.
One dam where siltation removal is underway is A Kung Ten reservoir in Kaohsiung county. Work started following severe flooding in the mid-1990s due to the silted reservoir's inability to hold all the water flowing into the dam.
The reservoir, which is one of the biggest in southern Taiwan, originally had a storage capacity of 20.5Mm3 in 1952. The reservoir on absorbs 500,000m3 of silt a year. And currently less than 30% of the original storage is available.
An eight-year renovation project costing US$232.9M was started at the reservoir in 1998, aiming to remove 11.6Mm3 of sediment. Water resource officials say that, after the renovation, the capacity will be increased to 19.16Mm3 from the current 5.9Mm3.
Meanwhile, the government has recently announced the launch of a five-year project, costing US$58M that will involve the eventual removal of 6.28Mm3 of silt from 13 dams. Water resource officials are due to finalise strategies shortly to remove at least 1Mm3 of silt from six major dams by the end of this year.