Autonomous Mini Hybrid Hydro Power Plant

 

There is an increasing need to provide adequate electricity for use in homes, offices, industries, etc. This need arises due to several technological developments all over the world.

While many persons do not have access to electricity from the main grid, renewable energy sources including water, sun, and wind are leveraged to generate power for all. One such renewable power-generation solution is the autonomous mini hybrid hydropower plant.

Renewable energy sources including wind, hydro, solar thermal, solar photovoltaic, biomass, etc can be utilized to generate clean, sustainable, and cost-effective energy for everyone. 

The distributive nature of these energy sources makes it possible for hybrid and single sources to be designed. In addition, the strategy employed in the hybrid power systems (HPS) ensures that sustainable power is distributed at a low cost. 

On the other hand, hybrid power generation is a power generation system that combines multiple plants with different sources of energy.

The configuration of the hybrid power generation system involves three parts including a series hybrid system, a parallel hybrid system, and a hybrid switched system. Here, we will discuss a mini hybrid power plant whose renewable energy source comes from hydropower.

Mini Hybrid Hydro Power Plants

Research shows that hydropower is the oldest energy conversion in the world and it started in the 20th century.

A mini hybrid hydropower plant produces electricity by converting the kinetic energy of water to produce mechanical energy. The mechanical energy is in the form of a hydro turbine spin and it is used to turn a generator so as to produce electrical energy. Additionally, the electrical energy produced is environmentally friendly and pollution-free.

The scale power of the micro-hydro power is lower than 100 kW. Once the flow capacity and the height from the installation are higher, the electrical energy that will be produced will be higher. Electrical energy having a power range of 5-100kW that is generated from the micro-hydro power plant is used to drive irrigation pumps, agricultural and rural activities, workshops, agricultural equipment, education, etc.

The electrical energy generated from the mini hybrid hydropower plant depends on the size of the head and the hydro discharge.

The equation of the micro-hydro energy potential is given by: Ε = m . g . h; where m is the hydro mass (kg), h is head of waterfall (m), and  is the gravitational constant (m/s2). 

Low hydro flow can produce the hydro potential for electrical energy from irrigation channels. The energy produced is kinetic energy and the equation is given by; E = 1/2 〖mv〗^2; where m is the hydro mass (kg) and ν is hydro flow velocity (m/s). 

Therefore, the formula for the electrical power that is generated by the mini-hydro power plant is given by; P = 1/2 〖ρAν〗^3; where ρ is the hydro density (kg/m3), A is the cross-sectional area of hydro flow (m2), and ν is hydro flow velocity (m/s). 

Suitable Conditions for Constructing A Mini Hybrid Hydro Power Plant

The best areas to site a mini hybrid hydropower plant are locations where there are steep rivers that flow throughout the year. Examples of such areas include hilly areas of countries that have high rainfall all year round or the great mountain ranges and their foothills.

Before a site is chosen, a site survey will be carried out to know the hydrology of the site and determine actual flow and head data. Details of site hydrology can be gotten from the meteorology or irrigation department of a country. This department is usually run by the government.

With this information, you can know the annual rain patterns and changes in precipitation. Additionally, the data gathered will enable you to know the conditions of the site which will pave way for easy calculation of power and the commencement of design work. 

Water Wheel Design for Mini Hydro Power Plant

A water wheel, also known as a watermill, is a device that is used to convert the energy of moving water into mechanical or electrical energy. It is one of the earliest devices used to convert the linear motion of moving water into a rotary motion which can be used to drive any machine connected to it via a rotating shaft.

Types of Water Wheel Design

Most waterwheels are wheels that are mounted vertically which are rotating about a horizontal axle and they are grouped according to the manner in which the water is applied to the wheel, relative to the axle of the wheel.

Generally, waterwheels are large machines that rotate at low angular speeds with low efficiency as a result of loss of friction and incomplete filling of the buckets.

Whenever water pushes against the wheel buckets or paddles, torque is created on the axle. The speed of rotation and the efficiency of the waterwheel can be enhanced by directing the water at the wheel buckets from different positions on the wheel.

The commonest types of waterwheel design are the undershot waterwheel and the overshot waterwheel. Other types of waterwheels that you may need to know breastshot waterwheel and pitchback waterwheel.

Undershot Waterwheel Design

This type of water wheel is the easiest and cheapest to construct and it was commonly used and designed by the ancient Greeks and Romans.

Here, the design of the undershot waterwheel involves placing the wheel directly into a fast-flowing river with support above. The motion of the water below creates a force against the submerged wheel buckets on the lower part of the wheel causing it to rotate in one direction only relative to the direction of the water flow. 

The undershot waterwheel is used in flat geographical locations that do not have a natural slope of the land where water flow moves rapidly. Unlike other waterwheels, undershot waterwheel is very inefficient whereby about 20% of its water potential energy is used to rotate the wheel. In addition, the water potential energy of the waterwheel is used to rotate the wheel, and thereafter, it flows away.

On the other hand, the undershot waterwheel needs large quantities of water that are moving at a very high speed to rotate the wheels. This is the reason why it is located on the river banks where the potential energy of the water is very high.

 Overshot Waterwheel Design

Unlike undershot waterwheel design, the design and construction of the overshot waterwheel is more complicated such that it makes use of buckets to catch and retain water flowing in at the top of the wheel.

 

The gravitational weight of the water in the full buckets results in the rotation of the wheels around its central axis as the empty buckets on the other side of the wheel become lighter. Overshot waterwheel utilizes gravitational force to enhance its output and that of the water. This makes an overshot waterwheel to be more efficient than an undershot waterwheel because all of its water and weight are used to produce the output power.

All overshot waterwheels are constructed in a large manner so that they can have a very high head distance for the gravitational weight of the water to cause the wheel to rotate.

However, the water's potential energy is only used once to rotate the paddles, afterward, the water flows away with the rest of the water.

Breastshot Waterwheel Design

In this type of waterwheel design, water enters the buckets or paddles about half way up at axle height or just above the axle height. Afterward, the water flows out through the bottom in the direction of the rotation of the wheels.

 

A breastshot waterwheel is used in areas where the head of water is not enough to power an overshot waterwheel design from above. However, the gravitational weight of the water is used for one-quarter of the rotation. To tackle this issue, the paddles will be constructed to be wider so that they can extract the required amount of potential energy from the water.

Like pitchback waterwheel design, breastshot waterwheel utilizes the potential energy of the water twice as the breastshot is constructed to sit inside the water paving way for the wastewater to assist the wheels to rotate as it flows away downstream.