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2,092 bytes removed, 16:43, 21 March 2013
moved "Determining the powerpotential of a site" to Hydroelectricity
When a need of power emerges, we should seek one site or several sites that could host a hydroelectric powerplant. We understand that the research begins by identifying all sources of energy such as wind, solar, biomass and so on. Our preposition considers the conclusion of this inventory as a preceeding to the decision to install a hydroelectric plant, perhaps in addition to wind turbines or solar energy collectors.
A power plant demands a drop height and a waterflow. Terrain reconnaissance on the field or on topographic map pinpoints the locations of both waterflow and a slope of the terrain. These spots are easily identified on the ground where the river flows torrentially but other locations may also be appropriate. The extent of the drop is easily to determine for a surveyor by means of a theodolite. However, the estimation of the available waterflow is much more difficult because of its variation depending on the season (see instantaneous flow and low average waterflow above). It is wise to underestimate the rate available because the powerplant should also not take off all water from the network. For example, in complete removal, the aquatic biotope will be severely disrupted by lack of water and make the spawning of fish impossible. Therefore, a reserve of waterflow should be left in the river to avoid biological depletion. It is possible that other -already authorized- waterusages impose a higher reserve waterflow.
When several sites are identified, the remoteness of the consumer is another criteria for inclusion in the feasibility analysis. Remoteness means a longer power line and makes monitoring of the plant more difficult. An electrical power line represents a important expense and is a source of powerloss.
==WaterflowAverage waterflow==
The amount of instantaneous waterflow of a river system depends on the rains, which is dependant on the season. The instantaneous waterflow varies from day to day with a minimum therof, located usually at the end of the dry season if it is marked. The concept of average flow has no interest in powerplants "along the waterstream", however, it does allow to better estimate the potential energyoutput of an infrastructure if an accumulation is envisaged. Low water flow, ie the minimum flow of the river during 24h states the minimal poweroutput potential of an installation. If the hydrological observations (measures of the flow of the river) are done for several years, it is possible to know the average minimum waterflow attained annually, or it is possible to observe it every 5 years, or -even more rare-, every 10 years. Indeed, the severity of the drought is variable depending on the year. A flow measure during 365 days can not indicate whether the observed minimum is an exceptional speed (either low or high) or rather an average minimum.
The hydrological data may be essential for the design of the proposed small hydroelectric plant. A lack of flow and thus availability of water will lead to disillusionment when the installation is working due to the large gap between the expected power output and true available power. There is of course no need to seek accurate hydrological data if the power output of the proposed installation is well below the maximum power of the site chosen for the project. Given that the turbine is to be placed near the river, it is highly desirable to know the variations of water level, to avoid seeing water invading the facilities during floods.
===Determining the powerpotential of a site===
The following mathematical formula allow to estimate the hydropower potential:
<math>P=10 x Q x H x r</math>
Knowing that:
P expresses the electrical power in kilowatt-hour of the current generator;
Q expresses the waterflow in the penstock in m³/sec;
H expresses the difference in water level between the entrance to the penstock and the leakage channel of the turbine, expressed in meters;
R is the overall efficiency of the facility, including the loss of load in the penstock, the turbine efficiency and alternator efficiency. A total efficiency of 60% is acceptable for the estimated hydroelectric potential.
As an example, with Q being 0,1 m³/sec and H being 10m we get a potential of 6kWh.
The efficiency of the turbine is a charisteristic of the machine given by the manufacturer. This efficiency depends on the waterflow. Indeed, if the inflow is, for example, only half of the expected speed (or nominal waterflow), it is easy to understand that the piece of the waterflow that will run between the rotating parts and the fixed parts without reacting on the blades of the machine does little or nothing. So the effective waterflow drops sharply and leads to an efficiency drop.
The potential of a site can be improved if the hydroelectric equipment is not a hydroelectric facility along the waterstream but equipped with an accumulation pond. In these circumstances it is possible to, for a few hours of the day, provide sufficient waterflow for periods of greater consumption of electricity. When the population of the village sleeps, they generally consume much less electricity. This decrease in electricityrequirements accompanies, through the speedregulator discussed above, a decrease in waterconsumption. The saved amount can be used at times of greater need. This accumulation pond should be considered in the context of a daily regulation. If deals around overcoming the insufficiencies of low water flows, the accumulation intake reaches a size that is outside the context of small power plants.
===Assessment of electricity needs===

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