Hydroelectricity. How immaculate is it?

Transcription

1 BUEC 663: Short Paper Natural Resource and Energy Capstone Hydroelectricity How immaculate is it? April 14, 2006 Submitted to Dr. Sid Carlson Submitted by Rahul Shrivastava

2 Hydroelectricity- how immaculate is it? Introduction Hydroelectricity is a relatively clean form of energy and does not produce any emissions, as do the conventional power generation plants. It is the largest source of renewable power in the world and contributes almost one-fifth in the total electricity generation worldwide. It is termed as the most reliable, efficient, and economical power generation among all the renewable sources. The normal efficiency of hydroelectric generation is close to 90% whereas conventional thermal plants operate with 50% efficiencies. Hydroelectric capacities are generally applied to peak-load demand, because it is very easy and quick to bring these machines on load and take out from the service. This fast response time makes them a perfect choice as a backup storage for the peak time load requirement. The water can be stored in high altitude reservoirs during off-peak hours and then utilized during the peak-demand time (pumped 1 storage hydroelectric reservoirs are sometimes used to store electricity produced by thermal plants for use during peak hours). Since long time, it is believed that hydroelectricity generation is a clean and safe process and provides numerous benefits ranging from stability to flow control (flood control) to low cost electricity to grid to reducing out pollution and 1 Though this system has net loss in terms of energy consumption but is very useful in terms of fulfilling peak-load requirement and keeping grid stable.

3 greenhouse gases. However, recent studies have shown that even this form of electricity generation has serious negative impacts. As Eric Duchemin, a consultant for the Intergovernmental Panel on Climate Change (IPCC) commented in the New Scientist story that, "Everyone thinks hydro is very clean but this is not the case". Hydroelectric generation poses critical impacts on the environment and the society. It can seriously damage the climate and adversely affect the human population displaced by the dammed river. The purpose of this paper is to put light on the environmental impacts envisaged in the recent studies, and to enlist few of the choices available for their mitigation. The reliance on hydro dams goes back to many centuries but the future development in this field should be done under new light. Hydroelectricity generation: Electricity generated by utilizing the hydropower is termed as Hydroelectricity. This hydropower can be obtained in various ways. Mostly, it is obtained from the potential energy of the dammed water released through water turbines that are connected to generators. After passing through the turbine, the water re-enters the river on the downstream side of the dam. Another source is the kinetic energy stored in the flowing water (un-dammed water) to run the water mills also called run-of-the-river system. However, the later source is less common. Tidal power is another example of the use of kinetic hydropower to generate electricity.

4 Source: As seen in the picture above, water is held in a reservoir or lake behind the dam, and this water when released through penstock spins the blades of a turbine, which in turn is connected to a generator to produce electricity. This electricity is then transferred to the grid through a network of transmission lines. The amount of electricity that can be generated at a hydroelectric plant depends on two factors. The vertical height of the water column or the head, and the flow rate, measured as volume per unit time. The electricity produced is proportional to the product of the head and the flow rate. Roughly, the amount of electricity generated can be calculated as follows: POWER (kw)= 5.9 x FLOW x HEAD Where, FLOW is measured in cubic meters per second and HEAD is in meters.

5 Thus, hydroelectric power plants can be classified into two categories: High Head power plants that utilize a dam to store large quantity of water that is later used to produce consistent and reliable electricity. These are the most common types of hydroelectric generation units. The other category is Low head power plants that utilize a low dam or no dam at all (run-of-the-river). A large volume of water is needed in such plants (see equation above). The electric output is not consistent from these plants and varies with seasonal flows of water in river. Impacts from hydroelectric generation Although hydroelectric generation is inexpensive and non-polluting, it is not the cleanest of all energy sources. Recent studies have suggested that the reservoirs for the hydroelectricity generation have serious environmental impacts besides a few negative impacts on the society. These impacts, however, must be weighed against the environmental impacts of alternative sources of electricity. Environmental impacts Greenhouse gas emissions 2 : Hydroelectric dams produce significant amounts of carbon dioxide, a potential green house gas, and methane, and in some cases produce more of these GHG than power plants running on fossil fuels. In a study to be published in Mitigation and Adaptation Strategies for Global Change, Fearnside estimates that in 1990 the greenhouse effect of emissions from 2 An article in climate change vol. 66 No. 1-2, Greenhouse Gas emissions from hydroelectric Dams: Controversies provide a Springboard for rethinking a supposedly Clean Energy Source by Philip M. Fearnside.

6 the Curuá-Una dam in Pará, Brazil, was more than three-and-a-half times what would have been produced by generating the same amount of electricity from oil 3. The reason being that large amounts of carbon tied up in trees and other plants are released when the reservoir is initially flooded and the plants rot. Then after this first pulse of decay, plant matter settling on the reservoir's bottom decomposes without oxygen, resulting in a build-up of dissolved methane. This is released into the atmosphere when water passes through the dam's turbines. According to world commission on dams 4, hydroelectric dams could generate between 1 and 28 % of all artificial GHG emissions (rotting vegetation in dams). Disrupting ecosystem: Another concern that pertains to the reservoirs is their effect on disrupting the ecosystem. Impoundment of a river causes significant level and flow change in the downstream side of the reservoir. Water released in the downstream is comparatively colder and may not contain enough oxygen for the ecosystem sustenance. This seriously affects the complete chain of bionetwork that is necessary for ecosystem sustainability and natural balance. (Aquatic as well as wildlife) Destroying fisheries: The damaging effect of the hydroelectric dams on fish can be observed in many ways. Fish get hurt or killed when trapped in the turbulences from turbines or when experience sudden pressure change at the downstream. These dams also prevent fish from swimming upstream to spawn or migrating

7 downstream to oceans affecting fish population significantly in different regions of the river and thus creating food imbalances. Wildlife depletion: In some cases, the hydroelectric dams are built in a remote location inside forests and wildlife habitats. Access roads are made to access these remote areas through forests and wetlands, this in turn reduce the wilderness character of those regions. Moreover, this provides an easy access for people for recreational activities like game hunting, which was difficult for them earlier. Soil loss and vulnerability to droughts: Usually, dams block the silt carried by a river and very little suspended sediments pass through turbines. This leads to scouring of the riverbeds and loss of riverbanks in the downstream of river. In long run, it has a potential to reduce the fertility of the downstream lands. Also, the intermittent operation of turbines causes rapid and cyclic flow variation in the river, which in turn contributes to erosion of sand bars and riverbanks. Dams have potential to alter permanently the geography of regions. They create large reservoirs over lands often composed of wetlands, which are important for wildlife habitats, and low lying flood plains, often the most fertile crop land in the area. These reservoirs need replenishment rate that can keep up with the desired usage rate. In case of insufficient intake of water, chances are that less water would be released downstream. This means that areas downstream are vulnerable to droughts, and greater probabilities exist of converting them into dry lands if the condition persists for a longer time.

8 Social impacts Displacing human population: This is a well-known impact caused by the hydroelectric dams. A river when impounded by a dam for hydroelectric generation floods a large area upstream of the river and forces people and animal living on that land to displace from there. This affects the tradition pattern of their living and the compensations provided to them most often aren t comparable to the true cost of displacement (loss of ancestral and cultural heritage). For some of the people who are being displaced, this type of circumstances can create very difficult situation as they are totally dependent on the land in the dam-affected area and learning new trade elsewhere for living is almost impossible for them and the may end up in poverty. High installation costs: The initial capital cost is very high and cost overruns 5 are common due to its long construction period. Another reason for high costs is that these hydroelectric plants operate where suitable waterways are available; many of the best of these sites have already been developed and so the remaining sites are more remote and expensive to develop. Loss of land to reservoirs: The flooding water of the confiscated river encroach all the irrigable land, forestland, fertile land, and natural animal habitat upstream of the dam. The coverage area depends upon the size of the dam. Larger dams have more serious impacts then the smaller dams. 5 According to cost over-runs of construction are 56% on average.

9 Impact mitigation Fish passage 6 : Creating upstream fish passages using fish ladders or elevators, or by trapping and hauling the fish upstream by truck, and downstream fish passages by diverting fish from turbine intakes using screens or racks or even underwater lights and sounds, and by maintaining a minimum spill flow past the turbine are some of the options available to address fish population problem. Water Quality and Flow: Hydropower plants can cause low dissolved oxygen levels in the water, a problem that is harmful to riparian habitats and to the downstream ecosystem. The problem can be addressed by using various aeration techniques. This increases the average temperature in the released water and also improves its oxygen content. Maintaining minimum flows of water downstream of a hydropower installation is also critical for the survival of riparian habitats. Hence, strict water management, aeration and cooling are necessary to ensure that rivers downstream receive an even flow of oxygenated water. Environmentally friendly turbines: Environmentally friendly turbines, also called "fish friendly" turbines, are being developed. These aim to reduce fish mortality when passing through the turbine, while also increasing water quality by maintaining dissolved oxygen concentrations. New turbine designs minimize damages to fish and can pass % of fish through them. Run-of-the-river electricity generation: These types of hydroelectric generators generally have a smaller impact on the environment. These run-of-the-river plants

10 do not require dams that upset ecosystems and damage fisheries. Recently, a similar system is installed near Vancouver; water from the Mamquam River near Vancouver will turn turbines to generate 25 megawatts of electricity. Conclusion: While hydroelectric system seems relatively clean and safe in comparison to coal-fired or nuclear energy, it has significant impact on the environment that wasn t envisaged few years ago. They are the main cause for considerable alteration in upstream and downstream water levels and subsequently on the environment in long run. Hydroelectric generation, at present, is the most efficient way to produce energy and at a much higher efficiency than that of any other source. Nevertheless, contrary to popular belief that hydroelectricity is emission free generation, recent studies have shown that large dams have potential to emit greenhouse gases and some times the amount can be significantly more than that from a conventional thermal plant. It means that hydroelectricity generation is not as clean as it is projected to the world. Also, it presents other undesirable environmental effects like degradation of fish habitats, deterioration of downstream water quality, soil erosion, wildlife disruption etc. These are a few of the serious concerns that need to be addressed in the current as well as future hydroelectric plants. A variety of mitigation techniques are now being used to address these environmental issues. Environmentally friendly turbines are under development that will minimize fish

11 mortality. The next phase of hydropower, however, should focus on smaller hydro units that are less disruptive environmentally but still useful in supplying electricity to remote areas. Planners of new hydro facilities pay careful attention to minimizing environmental impact. Habitats tend to adjust to new water levels over time, but they never fully recover. Thus the prospects for increased use of hydroelectricity are limited, and there are few remaining viable sites in North America where new hydroelectric generators would produce minimal environmental damage. As truly said, 'Prevention is better than cure', and the same also holds true for mitigation of environmental and human impacts of hydroelectric generation. It would be worthwhile to abandon projects when the environmental and social costs to be paid are high. The main criteria for choice of a project should be its sustainability in all respect. It is hard to evaluate the true cost of environmental and social damages and it might possible that the alternatives to hydroelectric projects might be worse but planners should include all the aspects of development in examining cost-benefit analysis. But hydroelectricity still holds promises for our future energy need.

12 References: 1. Idaho National Laboratory website: ml hydroelectric _power hydro.html 10.