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 Water in motion has kinetic energy; it is always trying to move downhill. Running water can be used to make electricity as it passes through a turbine. A turbine is a machine that creates electricity by turning a generator. (See the section on Wind) In order to harvest the kinetic energy of water, it is important to create a system where there is always enough water and enough pressure to keep the turbines going.
In the past, dams were built to create large reservoirs to ensure that turbines would run constantly. These dams were used to create potential energy in the form of stored water. Massive dams and hydroelectric plants have been built all over the world. Some of the most intense environmental conservation debates in history have surrounded the construction of dams, for example, the Glen Canyon Dam. Critics of these large projects assert that the dams make too much of an impact on the rivers and their ecosystems, making their use unsustainable.
In response to these criticisms smaller dams are now being certified to produce renewable energy if they meet certain criteria. For example the Low Impact Hydropower Institute has a set of eight criteria for certifying hydro projects as low impact. The criteria ensure that the dam have no negative impact on the plants, animals and people that rely on the river. Standards to safeguard river ecosystems include: ensuring that river flows stay high enough with appropriate seasonal variations, protecting water quality, protection of watersheds, maintaining shoreline buffer zones, and wetland protection. Certain measures must also be taken to ensure effective fish passage, and protect threatened and endangered species, preserving local cultures, and maintaining free access to recreation activities on the river. If a dam meets all of these criteria it can be certified and the electricity generated by the dam can be described as renewable.
Technology is also available that allows us to make electricity without impacting the bed of the stream at all. This is done without building a dam. Instead, a portion of the water is diverted into a pipe, is used to run a generator, and is then retuned to the stream. This method, called microhydro, is used to provide relatively small amounts of power to homes. The limitation with this method is that it is site specific. It requires a nearby stream, with enough flow, and a steep enough grade. If these conditions exist, microhydro can produce sustainable electricity inexpensively. |
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