Sample Theoretical Framework for Pico Hydro

October 3rd, 2012  |  Published in Theoretical Framework

Theoretical Framework

A theoretical framework is a collection of interrelated concepts, like a theory but not necessarily so well worked out, guide for your research, determining what things you will measure, and what statistical relationship you will look for.  It covers the experimental and mathematical method for calculation purposes of the main electrical equipment which the project is going to used.  That main equipment is the generator, hydro power and pico hydro.  Here, also discussed the theory, parts, function, and principle from basic to complete one.

3.1 Pico hydro system

Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides and geothermal heat, which are renewable (naturally replenished).  In 2008, about 19% of global final energy consumption came from renewable, with 13%  coming from traditional biomass, which is mainly used for heating and 3.2% from hydroelectricity.  New renewable (small hydro, modern biomass, wind, solar, geothermal, and bio fuel) accounted for another 2.7% and are growing very rapidly.  The share of renewable in electricity generation is around 18%, with 15% of global electricity coming from hydroelectricity and 3% from renewable.

Hydropower is one of the most efficient renewable energy sources.  It is particularly suited to small scale application typically being far cheaper per unit (kwh) of electricity produced than wind power or solar power.  It can be used to do electrical or mechanical work.

Pico hydro is water power up to 5kw.  There are thousands of sites where people have a source of falling water but do not have electricity.  For these rural communities, pico hydro is the lowest cost technology for generating electricity  Lighting from this source is cheaper than using kerosene lamps, and safer, too.

3.2    Run of the river hydro electricity

Run of the river hydro electric system used water flowing in a river to generate power.  They don’t store any significant amount of water.  It usually involves a low level diversion weir or a stream bed intake is usually located on a fast flowing, non seasonal stream or river.

A low level diversion weir raises the level of the river water just enough so that a structure for intake can be suited on, or next to the river.  The intake has a debris screen and a submerged opening with an intake gate.  While a stream bed intake require no wire.  The water drops thru a screen inlet duct which a flush the bottom of the riverbed. It is necessary to flush out debris, as rocks and gravel will enter a stream bed intake.

With either set up, the water is carried downhill thru a pipe (called a penstock) to a power station downstream of the intake.  The power plant is located at as low a level as possible to gain maximum head on the turbine.  The water leaves the power plant and is returned to the river without altering the existing flow or water levels.  Most run of river power plant will have a dam across the full width of the river to utilized the entire river’s water for electricity generation such installation will have a very small reservoir behind the dam as there is minimal flooding, they can be considered “run of river”.  From an environmental perspective, a general recommendation is that no more than 20-50 percent of creeks flow should be diverted for a run of the river hydro system

Advantages:

  • Damming and flooding the river is not required as run of the river hydro system don’t need a reservoir.
  • People and animals living near the river don’t need to be relocated and natural habitats are preserved, reducing the environmental impact.
  • Great for small hydro set ups

Disadvantages:

  • The output of the power plant is highly dependent on natural run off.  Spring melts can create a lot of energy.
  • Conversely, dry seasoned or drought will result energy output.  This disadvantage can be reduced if a site with consistent flow is chosen.
  • Commercial sites are limited or extremely remote resulting in reduced commercial viability.

3.3    Penstock

Penstock is open or closed conduits carry water to the turbines.  They are generally made of reinforce concrete or steel.  Concrete penstock is suitable for low head as greater pressure causes rapid deterioration of concrete.  The steel penstock can be design for any head, the thickness of the penstock increases with the head or working pressure.

Penstock for hydroelectric installation is normally equipped with a gate system and a surge tank. Flow is regulated by turbine operation and is nil when turbines are not in service.  Maintenance requirements may include how water wash, manual cleaning, antifouling coating, and desiccation.

3.4    Water turbine

A water turbine (also called hydraulic turbine or hydro turbine) converts the kinetic energy of water into mechanical energy.  This mechanical energy can be converted to electrical energy and used for various commercial, industrial and commercial applications.  Micro-turbines are used to produce electricity on a small scale.  They commonly serve villages and small communities  Water turbines are used to irrigate lands and crops.

According to “Simplified Irrigation Design,”  there are two types of water turbines used for irrigation:  horizontal centrifugal pump and vertical turbine pump.  Irrigation lands use these water turbines for the control and supply of water.  Horizontal centrifugal pumps impel water from lakes, shallow wells and other water reservoirs.  Vertical turbine pumps are used for pipeline plumbing, drainage plumbing, plant and municipal water supply, petrochemical applications, high-pressure pumping and flood control.  A vertical turbine pump is commonly used whenever a liquid has to be pumped out from an underground water table, underground storage systems or open bodies of water (lakes, rivers, ponds, oceans,  and tanks).  Electric generator is a device that converts mechanical energy such as that provided by the combustion of fuel or by wind or water, into electrical energy.  It generally undergoes electromagnetic induction which works by forcibly moving a loop of wire around a stationary bar that provides an electric field, either through a permanent magnet or an electromagnet.  Motors are usually the source of mechanical energy usually for an electric generator.  But it may also come from a reciprocating or turbine steam engine, water falling through a turbine or waterwheel, an internal combustion engine, a wind turbine, a hand crank compressed air or any other source of mechanical energy.

3.5    Theory of operations

Flowing water is directed on the blades of a turbine runner, creating a force on the blades since the runner is spinning, the force acts thru a distance.  In this way, energy transferred from the water to the turbine.

Water turbine are divided into two groups; reaction turbine and impulse turbines, the precise shape of water turbine blades is a function of the supply pressure of water, and the type of impeller selected.

3.6    Reaction turbine

Reaction turbines are acted on by water, which changes pressure as it moves thru the turbine and give up its energy. They must be encased to contain the water pressure or they must be fully submerged in the water flow.

3.7    Impulse turbine

Impulse turbines change the velocity of a water jet.  The jet pushes on the turbines curved blasé which changes the direction of the flow.  The resulting change in momentum causes a force on the turbine blades since the turbines spinning the force thru a distance and the diverted water flow is left with diminished energy.

The turbine type is selected based on the speed range and power capacity of alternator to be used.  It can be noticed in the figure that pelton turbine is a quite universal turbine.  It is not always restricted to high head, but of the power transmitted is low, then the pelton will also run on low heads, although at slow rotational speed.  In this pico hydro system, Kaplan type of reaction turbine is used to generate electricity.

3.8    Generator

A generator is a machine that converts mechanical energy into electrical energy.  Generators can be subdivided into two major categories depending the electric current produced is alternating current or direct current.  The principle on which on both types of generator works is the same, the details constructed of the two may differ somewhat.

3.9    Principle of operations

In1820, Danish physicist hans Christian oersted (1777-1851) discovered that an electric current created a magnetic field around it.

French physicist andre’ marie ampere (1775-1836) then found that a coil of wire with current running thru it behaved just like a magnet.

In about 1831, English physicist Michael Faraday (1791-1867) discover the scientific principle on which generators operate: electromagnetic induction.  By reversing the work of oersted and extending the work of ampere, faraday reasoned that it a current running thru a coiled wire could produced a magnetic field, then a magnetic field could induced a current of electricity in a coil of wire.  By moving magnet back and forth in or near a coil of wire, he created an electrical current without any other soure of voltage feeding the wire.

3.10      Theory of operations

Flowing water is directed on to the blades of a turbine runner, creating a force on the blades.  Since the runner is spinning, the force acts thru a distance.  In this way, energy is transferred from the water flow to the turbine.

3.11      Alternating current generator

A magnet creates magnetic lines of force on either sides of it that move in opposite directions.  As the metal coil passes thru the magnetic field in the generator, the electrical power that is produced constantly changes.  At first, the generated electric current move in one direction (as from left to right).  Then, when the coil reaches position where it is parallel to the magnetic line of force, no current at all is produced.  As the coil continues to rotate, it cuts thru magnetic lines of force in the opposite direction, and the electrical current generated travels in the opposite direction.  The ends of the coil are attached to the metal slip rings that collect the electrical current. Each slip ring in turn is attached to a metal brush, which transfer the current to an external circuit.

Thus, a spinning coil, in a fixed magnetic field will produced an alternating current, one that travel first in one direction and then in the opposite.  The rate at which the current switches back and forth is as its frequency.  Ordinary household current alternate at a frequency of 60 times per seconds or 60 hertz.

The efficiency of an AC generator can be increased by substituting an armature for the wire coil.  An armature consists of a cylinder shaped iron core with a long piece of wire wrapped around it.  The longer piece of wire the greater the electrical current that an be generated by the armature.

3.12      Commercial generators

One of the most important uses of generator is the production of large amount electrical energy for use industry and homes, the two most common energy sources used in operating AC generators are water and steam.  Both of these energy sources have the ability to drive generator at the very high speed at which they operate most efficiently, usually no less than 1500 revolution per minutes.

In order to generate hydroelectric power, a turbine is needed.  A turbine consists of a large central shaft on which are mounted a series of fanlike vanes.  As moving water strikes the vane, it causes the magnet to rotate around a central armature, generating electricity.

3.13      Electronic controller

An electronic controller is connected to the generator.  This matches the electrical power that is produced to the electrical load that are connected, and stop the voltage from changing as device are switched on and off.

3.14      Distribution system

Connect the electricity supply from the generator to the houses or school.  This is often one of the most expensive parts of the system.

3.15     Electrical load

Usually, connected inside houses.  This is a general name given to any device that uses the electricity generated.  The type of load connected to a pico hydro scheme depends largely on the amount of power generated.  Proper used of power connected to the same generator.

3.16      Calculation of hydro power
The two vital factors to consider are the flow and the head of the stream or river,  The flow is the volume of water which can be captured and redirected to turn the turbine generator, and the head is the distance the water will fall on its way to the generator.  The larger the flow example the more water there is, and the higher the head to electricity.  Double the flow and double the power double the head and double the power again.

A low head site has a head of below 10 meters.  In this case you need to have a good volume of water flow if you are to generate much electricity.  A high site has a head of above 20 meters.  In this case you ca get away with not having a large flow of water; because gravity will give what you have an energy boost.

The key equation to remember is the following:

Power = Head x Flow x Gravity

Where power is measured in Watts, head in metres, flow in litres per second, and acceleration due to gravity in metres per second.

The acceleration due to gravity is approximately 9.81 metres per second – i.e. each second on object is falling, its speed increases by 9.81 metres per second (until it hits its terminal velocity)

Therefore it is very simple to calculate how much hydro power you can generate.  Let’s say for example that you have a flow of 20 litres per second with a head of 12 metres.  Put those figures in the equation and you will see that:

12 x 20 x 9.81 = 2,354 Watts

3.17      Real world hydro power calculation

In the calculation of hydro power , it is not possible to tap all of its power – nothing is 100% efficient.  However, hydro power turbine generator is very efficient when compared to wind turbine generator and solar panel.  Efficiencies of around 70% can be expected which is to say that 70% of the hydraulic energy of the flowing water can be turned into mechanical energy spinning the turbine generator.  The remaining 30% is lost.  Energy is again lost in converting the mechanical energy into electrical energy ad so at the end of the day you can expect a complete system efficiency of around 50-60%.

3.18      Variable on load power station

The function of power station is to deliver power to a large number of consumers.  However, the power demands of different consumer vary in accordance with their activities  The result of this variation in demand is that load on the power station is never constant.; rather it varies from time to time.  Most the complexities of modern power plant operation arise from the inherent variability of the load demand by the users.  Unfortunately, electrical power cannot be stored and therefore the power station must produce power as and when demanded to meet the requirement of the consumer.  A load given can be represented as a curve showing the variation of load on the power station with reference to time.

Pico hydro is hydro power with a maximum electrical output of five kilowatts.  Hydro power systems of this size benefit in terms of cost and simplicity from different approaches in the design, planning and installation than those which are applied to larger hydro power.  Recent innovations in pico hydro technology have made it an economic source of power even in some of the worlds poorest and most inaccessible places.  It is also a versatile power source. AC electricity can be produced enabling standard electrical appliances to be used and the electricity can be distributed to a whole village.  Common examples of devices which can be powered by pico hydro are light bulbs, radio’s, televisions, refrigerators and food processors.  Mechanical power can be utilized with some designs  This is useful for direct drive of machinery such as workshop tools, grains mills and other agro-processing equipment.

Om a global scale, a very substantial market exists in developing countries for pico hydro systems (up to 5kW).  There are several reasons for the existence of this market.

  • Often, small communities are without electricity even in countries with extensive grid electrification.  Despite the high demand for electrification, grid connection of small communities remains unattractive to utilities due to the relatively low power consumption
  • Only small water flows are required for pico hydro so there are numerous suitable sites.  A small stream or spring often provides enough water.
  • Pico hydro equipment is small and compact.  The component parts can be easily transported into remote and inaccessible regions.
  • Local manufacture is possible.  The design principles and fabrication processes can be easily learned.  This keeps some equipment costs in proportion with local wages.
  •  The number of houses connected to each scheme is small, typically under 100 households.  It is therefore easier to raise the required capital and to manage maintenance and revenue collection.
  • Carefully designed pico hydro schemes have a lower cost per kilowatt than solar or wind power.  Diesel generator systems, although initially cheaper, have a higher cost per kilowatt over their lifetime because of the associated fuel costs.

Excerpt from the Project Study for Rural Electrification by Jerome dela Cruz, Kenneth Aquino, Wilgem Regino Crespo, John Andrew Molino and Rosauro Fernando Jr of BPSU.

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