The Power of Hydro-Electric Turbines: Efficiency, Types, and Potential Energy

Hydro-electric power is based on a long history of using the force of water flowing in streams and rivers to produce Hydro energy.

Water Wheel

The waterwheel, an ancient mill used for grinding grain, has evolved over time to include more efficient water turbines such as the Pelton wheel and the Turgo Wheel. These turbines, invented in the late 19th and early 20th centuries, have high efficiencies and are ideal for generating alternating current. Water turbines efficiently convert potential energy into electrical energy, with the incompressibility of water making their design and calculations simpler. In 2020, hydro power accounted for a significant portion of the world’s electricity generation, surpassing all other renewable sources and nuclear power. In the United States, hydro-electricity contributed to a significant portion of total utility-scale electricity generation. The availability of water for hydro power production is determined by the quantity of precipitation that flows into rivers and streams in a specific area, with seasonal variations and long-term changes in precipitation patterns impacting hydro power availability.

The Water cycle in Hydro-electric Power

Understanding the water cycle is important to understanding hydro power. The water cycle has three steps:

1. Solar energy heats water on the surface of rivers, lakes, and oceans, which causes the water to evaporate and rise. This water vapor condenses into clouds and falls as precipitation—rain and snow.
2. Precipitation collects in streams and rivers, which empty into oceans and lakes, where it evaporates and begins the cycle again.
3. So, in the water cycle free thermal energy from the sun evaporates the water, this raises in atmosphere, and condenses at a cooler height.

This effectively transforms solar energy into potential energy, a process commonly seen in government-funded projects like Hoover Dam, Three Gorges Dam, and the proposed Inga II project on the Congo River in Africa. Pump storage schemes, such as Palmiet in South Africa, also serve a similar purpose. In these schemes, hydro power functions as a large battery with two dams (upper and lower). During times of low overall demand, usually in the early morning hours, water is pumped from the lower dam to the upper dam. Then, during peak demand, this water is used to generate power by flowing through the same turbines from the upper dam to the lower dam.

Impulse turbines like the Pelton and Turgo are not ideal for pump storage and general hydro turbines because they can only flow in one direction. In utility-scale projects, reaction turbines like the Kaplan and Francis turbines are preferred. Kaplan turbines are often used for pumped storage because their adjustable blade pitch allows them to function as both pumps and generators. In large government projects such as Tidal, Francis turbines are chosen for their ability to handle high volumes of water.

Hydro-electric turbines

Throughout more than 3000 years, we have discovered various methods to harness the power of water, ranging from ancient waterwheels and Archimedes Screw’s to the more contemporary Turgo Turbine.

Different Hydro-electric Turbine Types

• Francis
• Kaplan
• Crossflow
• Fixed Pitch
• Pelton
• Turgo

Different Turbines Heads and Flow regimes

• Francis: 10–600 m & 0-1000 m³/s
• Kaplan: 1–80 m & 1-1000 m³/s
• Crossflow: 4 – 100 m & 1-10 m³/s
• Fixed Pitch: 1-80 m & 1-10 m³/s
• Pelton: 50 – 1000 m & 1-60 m³/s
• Turgo: 50 – 250 m & 1-10m³/s

Two other types of water turbines that were not discussed are the Water Wheel (similar to the Crossflow turbine) and the Archimedes’ Screw, although the latter is more of a pump due to its low tolerances. If you have a stream on your property, these turbines could be options for use in river systems.

Water turbines typically achieve efficiencies of 80% or higher due to the incompressibility of water and efficient mechanical energy transfer.

Hydro-Electric Potential Energy and determination of power that can be produced.

Potential Energy Calculation

The water’s potential energy is determined by its mass, elevation, and the gravitational constant of the earth.

Potential Energy = m*g*h

• m is the mass in kg,
• g is the acceleration due to gravity (9.8 m/s2 on earth’s surface),
• h is the height in meters.

The unit of Potential Energy (PE) is kg/m²/s², which is also the unit for all energy, called Joule [J]. Power is energy/time, and 1 Watt = 1 Joule per second.

Measuring water flow:

Measuring the Head involves determining the vertical distance between the high and low points, or inlet and outlets. The equation for potential energy can be calculated from line pressure, such as tap water. Residential homes typically have a regulated municipal water pressure of 2 bar [200kPa], which is equivalent to 20.4 m Head [P/g].

Measuring the head requires finding the vertical distance between the highest and lowest points, such as inlets and outlets. The potential energy equation can be determined using line pressure, like tap water. In residential homes, the average municipal water pressure is usually around 2 bar [200kPa], which is equivalent to 20.4 m Head [P/g].

Measuring Volume in a flowing river presents a different challenge. Here is a eBook from the Food and Agriculture Organization (FAO), a specialized agency of the United Nations.

Flow through Pipes

In most micro-hydro situations, as well as utility scale projects, water flow typically occurs through pipes that lead to the unit. These units are beneficial for farms located near spill points, as they can help regenerate some of the input power or provide a cost-effective solution for accessing remote power.

Flow in both of these is limited by the pipe diameter, the smaller the pipe the lower the flow, but there are other major factors influencing them as well such as:

• Roughness: the rougher the pipe the higher the friction losses will be. Best to go with uPVC or HDPE pipe, as smoother than steel, and cheaper. Also, better for imperviousness and wont rust
• Length: Runs are by and large to be limited to less than 50m in length
• Gradient: Gradient is important and generally aim for a slope > 30 degrees to overcome friction
• Area: this is a square function of diameter – so a pipe with double the diameter will have four times the flow.
• Bends and obstructions: Utilize full bore connections when connecting pipes to prevent flow restriction similar to orifice plates. Minimize the use of bends, as a single elbow can double friction losses. If redirection is necessary, use long radius elbows to reduce resistance.

On the norm for Micro Hydro generation of up to 1KW a 3″ pipe is used, above this a 4″ [100mm] pipe is advised to deliver water to Generator and reduced just before pump to 3″ to minimize the flow losses as mentioned above.

Cost of Hydro:

For determining this and ease of calculations going to look at the following products available:

1. 12V inline
2. 500 Watt inline
3. 2000 Watt Turgo-type end of line electric generator
4. 3000 Watt Run in River

And putting this in tabular form for easier understanding. The costs are in Rand (ZAR) and for ’23:

This is the ultimate goal Utilities are striving for, starting with Hydro generation – all other efforts are overshadowed by Hydro’s exceptional Efficiency, Reliability, Availability, and Maintainability, consistently exceeding 80% even on a bad day. 🤦‍♂️

Let’s dive into Biomass, with the power of hydro making your head spin.

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