07-02-2013, 09:37 AM
Hydropower Assessment
Hydropower Assessment.ppt (Size: 398.5 KB / Downloads: 29)
Stream flow data for hydropower studies
Daily (weekly or monthly) flow over a period of years, the longer the better. If a storage project is under consideration, the records should include one or more dry periods of years.
Minimum flow for primary power. Exclusively due to groundwater yield. If not available, it may be approximated from the minimum flow of other stream of similar characteristics.
Peak flow for design of civil works.
The above three data may be available for a long period, but if not long enough to give extreme flow, these must be estimated in some indirect manner.
FLOW DURATION CURVE
Plot of stream flow (daily, weekly or monthly) in the order of magnitude with percentage of time of their occurrence.
Calendar year method
Arrange the average monthly flow values of each year in ascending order. Then calculate the average of flow values of driest, second driest and so on for twelve months and use these 12 values to plot flow duration curve.
Total period method
Arrange entire data in ascending order and plot the flow duration curve.
Gives more accurate results.
Effect of unit of time on flow-duration curve
more accurate if time unit is low (i.e., day)
different for different time unit
smooth if time unit is more
Flow values of daily average flow is more than flow values of monthly average flow for low percentage of time. However, daily average flow is less than flow values of monthly average flow for high percentage of time.
ESTIMATE OF AVAILABLE WATER POWER
Available Head
Gross head = Reservoir level – Tail race level
Reservoir level is almost constant but water level in tail race varies with discharge in the stream. More discharge in tail race results in rise in water level and less available head.
The probable tail race level at different river stages may be determined in advance by installing a gage at this point ad rating it by current meter.
For the fixed crest of spillway, the level in the reservoir may be calculated by
Q = CLH3/2
for different discharges. By plotting curves of water surface elevation (a) above the crest of spillway and (b) at tail race site, to the same datum, the gross head would be difference of the two curves.
Available Power
With a flow duration curve available at the proposed site and the net available head ascertained, the available power may be estimated for any given wheel capacity by planimetering under the flow duration curve upto the line of wheel-discharge capacity.
Commonly wheel capacity corresponds to the flow available from 20 to 40% of the time.
Classes of Water Power
1. Primary or Firm Power
2. Secondary or Surplus power