FLOW DURATION CURVES OF HYDRO POWER PLANT BASIC INFORMATION AND TUTORIALS

Flow Duration Curve and Energy Calculations

As an owner/developer of a potential hydro site, you may wonder how much power your site will produce. A more exact question is how much energy it will produce – it is energy in kilowatt hours (kWh) that we buy from or sell to the electricity supplier.

Energy is a measure of the length of time we have used or produced a given amount of power. For example, if you use 1 kW (1000 W) of electricity for one hour, you have used 1 kWh of electrical energy.

A site on a stream or river that has a highly variable flow (i.e., a wide range of flows with many highs and lows) may not produce as much energy as a river that has a smaller range of flows but that is more consistent on average.

A hydrologist or professional consultant can produce a flow duration curve (FDC) for a river or stream by ordering the recorded water flows from maximum to minimum flow.

This is a way to show the probability in graph form of how many days in a year a particular flow will be exceeded. (The area below the curve is a measure of the energy potential of the river or stream.)

The FDC is used to assess the expected availability of flow over time and the power and energy at a
site and to decide on the “design flow” in order to select the turbine. Decisions can also be made on how large a generating unit should be.

If a system is to be independent of any other energy or utility backup, the design flow should be the flow that is available 95 percent of the time or more. Therefore, a stand-alone system such as a micro-hydropower system should be designed according to the flow that is available year-round; this is usually the flow during the dry season.

It is possible that some streams could dry up completely at that time. Remember that for any water source, be it a river, stream or creek, there will be a difference in flow between winter and summer, and this will affect the power output produced by a micro-hydropower system.

Flow in the stream changes continually (sometimes daily) if precipitation has occurred; however, some generalizations can be made. In southern Ontario, rivers and streams are at their highest levels in early spring and are at their lowest levels in late summer. In northern Ontario and Quebec, smaller rivers and streams are usually at their lowest levels in mid-winter and at their highest in spring.

British Columbia and Newfoundland and Labrador generally have low flows in late winter and high flows in the spring, except for the south coast of British Columbia, which has low flows in summer and high flows in winter. These variations must be considered in the estimated total energy generation expected from a site.

Ideally, minimum flow over the year should be taken to calculate the design flow to ensure that
power is available year-round. Normally, only a fraction of the available flow in the stream is used for power generation.

Therefore, FDC is less important as the size of system decreases. If the system’s generating capacity is less than 10 kW or so, FDC may not be relevant at all.

IDENTIFYING POTENTIAL SITE FOR RUN OF RIVER HYDRO POWER PLANT BASIC INFORMATION AND TUTORIALS

How to Identify a Potential Site For Hydro Power Plant?

The best geographical areas for micro-hydropower systems are those where there are steep rivers,
streams, creeks or springs flowing year-round, such as in hilly areas with high year-round rainfall.

There is micro-hydropower potential in almost all of Canada’s provinces and territories, although most potential is in British Columbia, Newfoundland and Labrador, Ontario and Quebec. To assess the suitability of a site for a microhydropower system, a pre-feasibility study should be made.

This involves surveying the site to determine the water-flow rate and the head through which the water can fall.

The best place to start is your nearest stream, or you can refer to topographical maps and hydrological records of the area you are considering. If you are new to the area, local residents are the best source of information on the nature of the stream, flow variations during the year and any abnormal flows in the past.

This will give an overall picture of annual river flow fluctuations over the seasons. If possible, flow data should be gathered over a period of at least one full year, although two to five years is ideal.

Your local utility may also have an inventory listing of potential micro-hydropower sites in your area.
A site survey is carried out for promising sites in order to gather information that is detailed enough to make power calculations and start design work.

How to Measure Potential Power and Energy

The first step is to determine the hydro potential of water flowing from the river or stream. You will
need to know the flow rate of the water and the head through which the water can fall, as defined in the following:

• The flow rate is the quantity of water flowing past a point at a given time. Typical units used for flow rate are cubic metres per second (m3/s), litres per second (lps), gallons per minute (gpm) and cubic feet per minute (cfm).

• The head is the vertical height in metres (m) or feet (ft.) from the level where the water enters the intake pipe (penstock) to the level where the water leaves the turbine housing

TYPES OF SURFACE WATERS BASIC INFORMATION AND TUTORIALS

What are the types of surface waters?

Impounding Reservoirs
Storage or impounded reservoirs are created by construction of a solid barrier (i.e., dam, weir, or barrage) across a flowing river or stream at places where minimum area of land is submerged in the water and the reservoir basin remains cup shaped with a maximum depth of water.

Impounding reservoirs are constructed across rivers, which are not able to provide the required quantity of water all year round. There are three essential parts of a reservoir: (1) a dam to hold the water back, (2) a spillway through which excess stream flow may discharge, and (3) gate chamber containing the necessary values for regulating the flow of water from the reservoir. Impounding reservoirs generally provide a fairly good quality of water.

The water is usually clear, soft, and palatable and ranks next to rainwater in purity. Contamination may occur from human and animal activities; therefore, the catchment area of an impounding reservoir should be free from human and animal intrusion.

Rivers and Streams
Rivers provide a dependable supply of water and streams to a less extent. However, rivers and streams are easily prone to gross pollution and quite unfit for drinking unless properly treated for impurities and pathogens.

The general belief that mountain streams are very pure water is often untrue. Even if there is no human habitation or cattle, there is a possibility of contamination from wild animals.

Tanks, Ponds, and Lakes
Tanks are large excavations in which surface water is stored. They are common in developing countries where they are an important source of water supply. Tanks are prone to a high level of contamination except they are specially protected by construction of elevated platforms, which limit human and animal contacts.

The tank can be subjected to sand filtration and some chlorination to improve their quality. Lakes and ponds arise when the depression of the earth’s surface with impervious beds is filled with water.

Lakes are formed when the size of the depression is very big and ponds are formed when the depression is small; while the former are generally formed in hilly areas, the latter are formed in plain areas.

Ponds are also formed when soil is excavated for constructing earthen dams, embankments, and canals. The quantity of water in the lakes depends upon its basin capacity, soil properties, porosity, annual rainfall, and catchment area.

For public supply, the quantity of water in lakes and ponds is very small and is only suitable for small towns in hilly areas. In some cases, due to the absence of other sources, large lakes become the main and permanent source of water supply.

The quality of water in large lakes is better than that of small lakes. At high altitudes, the water available will be purer due to self-purification action of bleaching, removal of bacteria, and sedimentation of suspended matter. However, stagnation of the water promotes growth of algae, weed, and vegetables with resultant bad smell and taste and impurities.

Groundwater
Groundwater results from rainwater percolating into the ground and constitutes the cheapest and most practical means of providing water to small communities. It has advantages over surface water due to the fact that the ground itself provides an effective filtration medium.

In addition, groundwater is likely to be free from pathogenic agents, therefore usually requiring no treatment. The supply is almost certain even in dry season, but the yield might be reduced.

Furthermore, it is less subject to contamination than surface water. Some disadvantages have been associated with groundwater and these include high mineral content like salts of calcium, magnesium, and iron, which renders it hard. It is also required for the water to be pumped for the purpose of access. The usual groundwater sources are wells and springs.

Wells have been classified into (1) shallow and deep wells and (2) dug and tube wells. It is important to note that once groundwater is contaminated, it is difficult to restore.