Strategies for Small Hydro Upgrades
Small hydro is becoming big business as ongoing technological advances make more small sites economic to exploit. Older plants can also see substantial output and efficiency gains by upgrading from decades-old technology. Here's what you need to know to help make small plants meaningful producers.
Small hydropower is getting big. Around the world, even as traditional giant projects continue to get built-especially in developing countries-more and more attention is being directed toward the possibilities of smaller systems. The driving forces have been concern about the environmental impacts of huge dams; a shrinking number of suitable sites for major projects, particularly in Europe and North America; and substantial technological advances that have made smaller and smaller sites economic to exploit.
Hydropower in general is experiencing something of a renaissance because of growing demand for renewable energy. The rapid growth of intermittent generation from wind and solar means dispatchable renewable generation from hydro is becoming more valuable. But much of this wind and solar development is taking place in areas-like the central and southwestern U.S. and central Europe-where opportunities for large hydro projects are limited at best. That's opened up a market opportunity for small systems that can be deployed much more rapidly than larger ones. (For more on the topic, see "Small Hydro, Big Opportunity" in the May 2013 issue, "A New Day for North American Hydropower?" in the October 2014 issue, and "Small Hydropower Advances and Challenges in China" in the January 2015 issue.)
New Tricks for Old DogsWhat exactly constitutes "small" hydropower depends on who you ask, but it's generally considered projects under 30 MW or so. While lots of hydro projects of this size are being built on new sites, not all small hydro plants are new-many are quite old, with some still operating after a century or more. Many of these projects now need substantial upgrades. The good news is that opportunities for improving efficiency and output are large (Figure 1).
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| 1. New power generation. EVN's 2.7-MW Dorfmi1/4hle hydropower plant in Austria replaced a 120-year old plant on the same site in 2004, increasing overall output 10-fold. Courtesy: Voith Hydro |
According to Voith Hydro's Jim Glunt, the last decade has seen significant advances in controls, monitoring, and supervisory control and data acquisition technology. Operators are now better able to gather historical and real-time data in order to maximize efficiency or power on demand. Advances in operator control and monitoring have also allowed for more reliable and user-friendly interfaces.
Refurbishing old turbines can also reap big rewards, Glunt said.
"Typically, a customer who is rebuilding a 50-year-old or older unit can expect around 10% improvement in efficiency. The wear on the rotating components, wicket gate system, and bearing areas can be corrected to add efficiency and reliability," he said. "Sometimes in dealing with a unit rebuild of this age, there can be misalignment throughout the machine due to the tendency of the power house to move downstream. The slow movement over time is a condition that could cause increased vibration and wear through the years."
Old generators also require attention eventually.
"Generator components can be improved upon in many cases due to newer materials used in the insulating systems. One large reason to improve the generator by rewinding the stator is to eliminate the asbestos that may be present in a unit of such age," Glunt said. "Given a typical unit of this vintage, customers may want to seriously consider a rewind in order to fend off any potential failure in the winding."
One benefit to upgrading a small project versus a larger one is that the small size of the equipment means modernized systems can be modular or shop-assembled and delivered to the site in one piece, which substantially reduces construction time and complexity (Figure 2). The newest small hydro technology is also specifically designed to operate at peak efficiency with low heads, which means smaller units can be installed without reducing output or output can be increased without expanding other elements of the plant. Some decades-old small hydro plants have been able to double or triple output (or even more) by upgrading their turbine-generators, gains that are less likely with larger projects. Modern oil-free, permanent magnet turbines are also more environmentally friendly than older technology.
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| 2. Shallow dive. Voith Hydro's modular StreamDiver turbine is designed specifically for small hydro applications where heads and flows are ill suited for traditional hydropower technologies. Courtesy: Voith Hydro |
In addition to improvements that are possible from upgrading turbines and generators, one area sometimes overlooked is improvements in controls and automation. Just as operators of fossil plants have begun deploying advanced sensors and data science to improve the operations of their boilers and gas turbines, manufacturers have begun offering similar solutions for their hydro customers. Such systems allow operators to predict possible component failures and determine changes in operations that could extend component life to allow repairs at the most advantageous time. Another factor that advanced data science can help with is predicting output based on changes in local hydrology, an issue of special concern to smaller plants, which are more at the mercy of droughts than large ones (see sidebar).
| Filling the Power Gap when Hydropower Falls Short One of the challenges with small hydropower is greater sensitivity to fluctuations in rainfall, because small plants typically lack large reservoirs where excess water can be stockpiled during wet periods. Seasonal weather variations are difficult to predict, but detrimental weather affects capacity year after year in some regions (see "Drought Stresses Brazilian Electricity Market" in the November 2014 issue). Anticipating and mitigating the risk of blackouts can be challenging, so a contingency plan should be in place, such as having an on-site fleet of back-up generators or a coordinated emergency power provision to minimize downtime. Kenya, which gets more than half of its electricity from hydropower, has experienced repeated problems due to sporadic periods of low rainfall. Aggreko first started working with the national utility, KenGen, nearly 20 years ago after severe drought limited its hydroelectric generation. Speed was key to reduce the impact that the Embakasi power station's reduced output had on the population and economy, and so it was vital the project was installed and started to generate power within weeks rather than months. Myanmar faces similar challenges during its December to June dry season. With more than 70% of the country's energy supply dependent on hydropower, this intermittency exposes its population to serious power shortages. The national utility, Myanmar Electric Power Enterprise (MEPE), recently commissioned Aggreko to install interim gas-fired generation to support the national grid during the summer months (Figure 3).
Similarly, parts of Zimbabwe are suffering power shortages that have significantly restricted the country's hydropower capabilities, following one the worst droughts in 35 years. Not only does modular power help to fill the gap, in this case it also creates the opportunity for the national utility to contribute to the Southern Africa Power Pool and generate funds through international power trade. The flexibility of mobile power makes it a fitting partner throughout the lifecycle of a hydroelectric plant in addition to filling the gap during the dry season. This is particularly true during the planning and commissioning phases, where it helps to ensure that the plant is operational and can be connected to the grid on schedule, and avoid any potential investment losses or financial penalties. It can also provide support during maintenance outages, as well as black-start power when necessary, such as during a grid failure. -Marcus Saulis renewables business development manager with Aggreko. |
Such upgrades can reach across the plant. Moving from analog to digital metering and governors and from electro-mechanical to solid-state multifunction protection relays can reap dividends. But an increasing number of small hydro plants are being fully automated.
While this can reduce staffing needs, there are many things that need to be considered from an operations and maintenance standpoint, Bob Baginski of Voith Hydro's digital solutions team said.
"It's essential to monitor the mechanical equipment in the plant more closely and have a feedback loop with the remote control systems to detect wrong tendencies early and prevent forced outages. Not only the machines themselves have to be monitored, but also the plant auxiliary systems. For example the status of the dewatering pump and the HVAC system health can be crucial for reliable operation of the whole plant."
Safety is another issue with full automation, he noted.
"Is it possible to still safely shut down the unit if the main closing device is jammed? What safety devices are in place in case of a cooling water supply pipe rupture? Is automatic closure of valves implemented to prevent the plant from flooding? What is the safe shut down concept in case AC power fails? These things and more have to be taken into consideration." a-
-Thomas W. Overton, JDis a POWER associate editor.
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