The challenge of refurbishing hydroelectric generating stations

Although new hydroelectric generating stations are still being built all around the world, and a number of projects for future generating stations are being studied, the vast majority of stations now in operation were built over 20 years ago, and some even date back more than 50 years. There are numerous factors that make refurbishing these generating stations inevitable, the most obvious being equipment wear, fouling of pipes and greater maintenance requirements.

Not only are these refurbishments associated with repairing or replacing equipment and piping, they are also often linked to an increase in turbine-generator unit capacity. In fact, new technologies offer operators the option of increasing the power produced by turbine-generator units (additional capacity), most specifically by improving the turbine wheel blade or penstock wall profiles. For example, 50% additional capacity for a 50 MW unit translates into an increase in annual power output of 219 GWh, considering a 50% utilization factor. If we consider a production cost of 2.5 ¢/kWh and a sales price of 7 ¢/kWh, this results in a gross annual profit increase of $9.9 million. Even for a project costing only a few tens of millions of dollars, the return on investment is recovered within just a few years. In order to proceed with increasing a generating station’s capacity, the mechanical and electrical auxiliary systems connected to the turbine-generator units often require refurbishment due to the increased requirements associated with the higher turbine-generator unit capacity, such as a greater need for cooling water and for air to the air brakes and to the regulation system.

Years ago, medium and large generating stations (with capacities varying from several hundred to several thousand megawatts) were on the receiving end of many refurbishment projects, since even a slight increase in capacity resulted in significant production increases. However, with the price of electricity rising continuously, it has also become profitable to refurbish smaller generating stations, those with capacities of a few tens of megawatts. This is true for both private generating stations and those run by larger government agencies.

This white paper covers the major mechanical challenges associated with refurbishing hydroelectric power plants.