How to determine the hydropower available at site

To determine the power available at a site, head and flow measurements must be taken. Flow is the rate at which water moves, measured in liters per minute (I/m) or gallons per minute (gpm). This can be measured by channeling the water into a pipeline, then into a container of a known volume, noting the time it takes to do so.

Head can be measured by using a transit, by siting along a level, or by using a pressure gauge at the end of the pipeline.

It is important to keep in mind that output can only be accurately determined if head and flow measurements are made correctly, so care should be taken during this process.

1.) Approximate power available at any given site can be assessed using the formula:

head (feet) x flow (gpm) / 8 — Watts
e.g., 100 feet x 30 gpm / 8 = 375 Watts

or

head (m) x flow (l/m) / 10 = Watts
e.g., 30 m x 120 I/m / 10 = 360 Watts

2.) Before considering the purchase of a Stream Engine, perform the above estimate. If it is determined that your site is viable, contact your dealer to discuss pipelines, transmission distance, and system voltage. Power from the Stream Engine is limited according to the available head.

At about 7.5 metre (25 feet), output is limited to 500 watts, 15 metre (50 feet) to 750 watts, and at a 30 metre (100 feet) head, 1000 watts can be generated, given adequate flow.

3.) The length, diameter, and type of pipeline must be determined in order to predict losses due to friction.

4.) Many factors affect system voltage including output and transmission distance. Power is usually generated at battery voltage, but where transmission distances are too great for low voltage transmission (12, 24, or 48 V), higher voltages can be generated and transformers can be effectively used to step down to battery voltage.

Planning of Hydroelectric Facilities

Hydroelectric plants are located in geographic areas where they will make economic use of hydraulic energy sources. Hydraulic energy is available wherever there is a flow of liquid and head. Head represents potential energy and is the vertical distance through which the fluid falls in the energy conversion process.

The majority of sites utilize the head developed by fresh water; however, other liquids such as salt water and treated sewage have been utilized.

The siting of a prospective hydroelectric plant requires careful evaluation of technical, economic, environmental, and social factors.

A significant portion of the project cost may be required for mitigation of environmental effects on fish and wildlife and re-location of infrastructure and population from flood plains.

Hydroelectric Plant Schemes

There are three main types of hydroelectric plant arrangements, classified according to the method of controlling the hydraulic flow at the site:

1. Run-of-the-river plants, having small amounts of water storage and thus little control of the flow through the plant.
2. Storage plants, having the ability to store water and thus control the flow through the plant on a daily or seasonal basis.
3. Pumped storage plants, in which the direction of rotation of the turbines is reversed during off-peak hours, pumping water from a lower reservoir to an upper reservoir, thus “storing energy” for later production of electricity during peak hours.

Selection of Plant Capacity, Energy, and Other Design Features

The generating capacity of a hydroelectric plant is a function of the head and flow rate of water discharged through the hydraulic turbines, as shown in equation below:

P = 9.8 η Q H

where:

P = power (kilowatts)
η= plant efficiency
Q = discharge flow rate (meter³/s)
H = head (meter)

Flow rate and head are influenced by reservoir inflow, storage characteristics, plant and equipment design features, and flow restrictions imposed by irrigation, minimum downstream releases, or flood control requirements.

Historical daily, seasonal, maximum (flood), and minimum (drought) flow con-ditions are carefully studied in the planning stages of a new development.

Plant capacity, energy, and physical features such as the dam and spillway structures are optimized through complex economic studies that consider the hydrological data, planned reservoir operation, performance characteristics of plant equipment, construction costs, the value of capacity and energy, and discount rates.

The costs of substation, transmission, telecommunications, and remote control facilities are also important considerations in the economic analysis. If the plant has storage capability, then societal benefits from flood control may be included in the economic analysis.

Another important planning consideration is the selection of the number and size of generating units installed to achieve the desired plant capacity and energy, taking into account installed unit costs, unit availability, and efficiencies at various unit power outputs.