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1.11 Efficient Water Use In Small Hydropower Plants

Technical Description

Small hydropower plants often make inefficient use of water resources, and lack automated power generation technologies. To improve efficiency, dispatcher schedules have been worked out for many of the cascade reservoirs used for hydropower production in Latvia, including the Ciriša, Rušonu, and Aiviekstes hydropower facilities. Based upon this schedule, power generation capacity shifts from upstream reservoirs within the cascade to the downstream reservoirs so that the reservoir water levels vary from maximum supply level to minimum supply level in the upstream to downstream direction. This ensures that water is used efficiently and that each reservoir operates over its optimal range of water levels necessary for power generation purposes. For such a scheduled series of shifts in the locus of power production, it is necessary that the management authority have a good understanding of the water regime within the river basin and of the discharges needed for optimal generator operation. In Latvia, there is an established base of hydrological information which makes efficient water use possible within the national hydropower plant network. An important, related issue to the efficient use of water by hydropower generation systems within cascade reservoir series is the minimization harmful effects on environment created by erratic fluctuations in river flows and lake water levels. Use of cascade reservoirs is beneficial in that the construction costs of impoundments may also be lower.

Extent of Use

Since the early Middle Ages, watermills have been built in Latvia. In the beginning, these activities lacked a strong theoretical basis, and some watermills (and, later, small hydropower plants) lacked sufficient water to operate around the year. While an improved understanding of the hydrology, and technological advances in low head generation units, have overcome the early limitations, there has been a trend in modern times to replace small hydropower generation stations with larger schemes, as has occurred at the Great Plavinas and Riga and the reconstructed Kegums hydropower plants. The larger plants, constructed prior to the introduction of automated control systems, were often more cost effective than smaller, cascade systems give personnel costs associated with their operation. Most recently, however, there has been a shift in this policy, in an effort to achieve energy independence, that favours cascade systems of hydropower generation, in part, because of the high fuel costs associated with thermogeneration plants. To encourage the production of hydropower, the state electricity corporation, Latvenergo, is offering small hydroelectricity producers a premium of 200% in comparison to the prices paid for other sources of energy through the year 2000. Small hydropower plants have been estimated to be able to produce up to 1 000 MW/yr.

Operation and Maintenance

Determination of dispatcher schedules requires the services of both computer personnel and hydrologists. Once the schedule has been determined, regular hydrological monitoring should be undertaken to allow modifications of the regime due to intra- and inter-annual variability in river flows and lake levels. Implementation of the power production schedules requires installation of electronic control systems linking each of the generation plants and water control structures within the cascade. Maintenance is required of the electronic control systems and moving parts, such as water control gates and turbines, that form the structural elements of more effective hydropower generation.

Level of Involvement

Because of the nature of cascade reservoirs and the degree of coordination required, this technology is best implemented by local and regional watershed management administrations in cooperation with the hydropower companies.

Costs

There are no increased costs associated with the infrastructural investments required for conventional small hydropower plants. Indeed, staff and development costs may be lower as fewer operators can control a larger number of small dams.

Effectiveness of the Technology

The efficiency of water use for hydropower generation can be increased from 50% to between 90% and 98% of the annual runoff volume used to generate hydropower. This technology is also effective in regulating unscheduled or erratically-scheduled discharges and makes more efficient use of turbines.

Suitability

This technology is most suitable for use in new and existing, small hydropower plants arranged as a cascade along a water course. Similar technologies could be used for scheduling hydropower generation needs across watershed boundaries.

Advantages

This technology provides for more efficient power production, as well as enhanced water retention within the catchment area that benefits lacustrine and riverine ecosystems.

Disadvantages

The excessive or erratic regulation of water flows in rivers can threaten wetlands and fisheries.

Cultural Acceptability

This technology is well-accepted by citizens who benefit from the improved availability of electricity and water. However, greater acceptance of this technology by technical staff is needed.

Further Development of the Technology

Because of the key role that hydrological data play in this technology, better tools for environmental data collection and assessment are required.

Information Sources

Rolands Bebris, Ministry of Environmental Protection and Regional Development, 25 Peldu Str., 1494 Riga, Latvia, Tel. (371-7) 227145, fax: (371-7) 820442, e-mail: BEBRI@VARAM.GOV.LV.

Anna Egle, V/U "Meliorprojects", 11 Novembra Bulvaris 31, LV-1494 Riga, Latvia, Tel. (371-7) 228734.

Dr. hab. Ansis Ziveris, 63 - 33 Bikerniek Street, LV-1059 Riga, Latvia.

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