Is It Easy to Convert a Run of River Facilitiy to Operate in Storgae Mode

Two Energy Futures

MANS LÖNNROTH , ... PETER STEEN , in Solar Versus Nuclear, 1980

Short-term Regulation (day-week)

Hydro power . By expanding the capacity, joint operation with 5–7 GW wind power is throught to be possible. The existing hydro power can be interconnected with 3–5 GW wind power (31).

Fuel cells can rapidly vary their output and thus compensate for the variation in output from solar cells and wind power.

Co-generation. Through thermal stores the daily variations in electricity demand can be partly balanced.

Electric heating with hot water storage in parts of the total stock of buildings; the back–up heat output can for instance be allocated to low–load periods or periods when a surplus of electricity is produced. Control (switching on and off) can be effected through radio frequency signals over the mains.

Regulation of demand in industry. In processes where the processing heat is generated with electricity the electrical load can be affected by utilising thermal stores or by producing hydrogen by electrolysis of water. The hydrogen gas is stored when required.

Apart from these ways of regulating demand there will probably be a need for installations where the electric energy can be stored for a relatively short time, e.g. pump storage plants. In these the electric energy is transferred to potential energy of water by pumping the water up into a high–lying lake or dam. The electric energy is subsequently produced as required in the form of hydro power. Another possible alternative would be mechanical fly-wheels.

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Design of Small Hydro Generation Systems

Morteza Nazari-Heris , Behnam Mohammadi-Ivatloo , in Distributed Generation Systems, 2017

6.2 Generation Basics of Hydroelectrical Energy Systems

Hydro power generation plants are categorized as follows [ 6]:

•

Impoundment: A large hydro power system in which river water is stored in a reservoir by utilization of a dam. Electricity generation is accomplished by using water stored in the reservoir.

•

Diversion: A hydro power system that may not need the use of a dam, and utilizes a diversion facility on a portion of a river.

•

Run-of-river: This hydro power system has few requirements or no impoundment, and utilizes the water flow for electricity generation.

Most SHPs are "run-of-river" with no or limited requirement to dam or store water. The required storage reservoir of this kind of SHPs is defined as pondage. The plants containing a pondage can be utilized for water flow regulation during the time period and especially for electrical energy production in on-peak hours. A typical run-of-river SHPs scheme can be seen in Fig. 6.1. Civil works and electromechanical equipment are two general components of run-of-river SHPs. The civil works include a diversion weir and intake, desilting chamber, power channel including head race channel, forebay and spillway, penstock, powerhouse building, and tail race channel. Additionally, turbines with a governing system, and a generator with excitation system, switchgear, control, protection equipment, electrical and mechanical auxiliaries, and main transformer and switchyard equipment are enumerated as electromechanical equipment of run-of-river SHPs. Projects of run-of-river SHPs are classified in three types based on head. Low head (3–20   m), medium head (20–60   m), and high head (greater than 60   m) are the three main classifications of run-of river SHPs projects [7].

Fig. 6.1. Typical run-of-river small hydro power system scheme [3].

Components of a SHPs scheme are demonstrated in Fig. 6.2. Fundamental components of SHPs include penstock, power house, tailrace, generating plant, and allied equipment [8].

Fig. 6.2. Components of a small hydro power system scheme [3].

6.2.1 Basic Components of a Hydro Power Plant

In the following the basic components of a hydro power plant are defined:

Dam: A dam is utilized in most of the hydro power systems for holding back water, which is a large water reservoir. A dam is usually constructed across a river or a channel for utilization as water storage.

Penstock: A cavity or pipeline with a large diameter, in which conduction of water is done by opening the gates on the dams. In fact, the penstock plays the role of a conductor of water with high pressure from dams to the turbines.

Turbine: The blades of turbines are stroked by a high-pressure conduction of water, which turns the turbine. The turbine is attached to an electrical generator by a shaft. Different categories of turbines exist, which are divided into two general types: impulse turbines and reaction turbines. The different categories of turbines will be discussed in the next sections. Different types of vanes or buckets or blades are installed on a wheel, which is called the runner.

Tailrace: After working of high pressure water on the turbine, a channel carries water away from the turbine and the water re-enters to the river downstream, which is called tailrace. Moreover, the water surface in the tailrace is also referred to as tailrace.

Generator: By turning the blades of the turbine, the rotor inside the generator is turned. As a result, electric current is produced by rotating magnets inside the fixed-coil generator.

6.2.2 Hydroelectric Power Calculation

Conversion of water pressure to mechanical power is the basic operation of SHPs, which is then utilized for driving an electrical generator. Pressure head and volume flow rate are two essential components of generated power [9]. In general, the gross hydraulic power and the corresponding energy can be stated as follows [10]:

(6.1) $P_0=\mathit{\rho gQH}$

(6.2) $E_0=\mathit{\rho gQH}\mathrm{\Delta }\mathit{t}$

In which P ₀  (kW) and E ₀  (kW   h) over a time interval Δt  (h) are the gross hydraulic power and the corresponding energy, respectively. Pressure head and volume flow rate are H  (m) and Q  (m³/s), respectively. Also, ρ  (kg/m³) and g (m/s²) are water density and acceleration due to gravity, respectively.

Discussion on turbine efficiency. Efficiency is considered as the ratio of the useful work performed in a process to the total energy expended, which can be stated as follows:

(6.3) $\eta =\frac{\mathit{Powe}{r}_{\mathit{out}}}{\mathit{Powe}{r}_{\mathit{in}}}$

where η is taken into account as efficiency, and Power _in and Power _out are referred to as the expanded power and useful power, respectively. Efficiencies of a hydro power system can be classified into two general categories: hydraulic efficiency and mechanical efficiency. Hydraulic efficiency is the obtained power by the runner of a turbine per power supplied at the inlet of a turbine. The probable power loss in a turbine is between the striking jet and the vane, which results in calling this type of efficiency as hydraulic efficiency. The equation of hydraulic efficiency η _h can be stated as

(6.4) ${\eta }_h=\frac{P_R}{P_W}$

where P _R and P _W are the respective elements utilized to demonstrate the runner power and the water power.

The ratio of available power at the shaft to the runner power is defined as mechanical efficiency. For calculation of mechanical efficiency η _m considering P _S as the shaft power, the following equation can be stated:

(6.5) ${\eta }_m=\frac{P_S}{P_R}$

Considering η as the total efficiency of the turbo-generator, the hydraulic power and the corresponding energy will be

(6.6) $\eta ={\eta }_h{\eta }_m$

(6.7) $P=\eta P_0$

(6.8) $E=\eta E_0$

Modern hydro turbines have an energy conversion efficiency of 90%, which is in a range of 60%–80% in micro-hydro systems.

Example 6.1

Suppose that the flow rate of a SHPs in a certain area with a pressure head of 100   m is 1   m³/s. Calculate the hydraulic power with the consideration of total efficiency of 80% for turbo-generator and acceleration due to gravity of g  =   9.81   m/s².

Solution

As $Q=1{\mathrm{m}}^3/\mathrm{s}$ , and $H=100\mathrm{m}$ .

Then, from Eq. (6.1), $P_0=\mathit{\rho gQH}=1000\times 9.81\times 1\times 100=981000\mathrm{W}=981\mathrm{kW}$ .

Accordingly, considering Eq. (6.7), $P=\eta P_0=0.8\times 981=784.8\mathrm{kW}$ .

Example 6.2

Consider an installation of a hydro power system in a site with a net head of 100  m. Hydraulic efficiency and mechanical efficiency are assumed to be ${\eta }_d=95\%$ and ${\eta }_t=85\%$ , respectively. For a requested power of $P=600\mathrm{kW}$ , determine the required pressure head in the site.

Solution

Since ${\eta }_h=95\%$ , ${\eta }_m=85\%$ , $H=100\mathrm{m}$ , and $P=600\mathrm{kW}$ .

Moreover, $\eta ={\eta }_h\times {\eta }_m=0.95\times 0.85=0.8075$ .

Then, from Eq. (6.7), we have

$P_{\mathit{Total}}=\mathit{\eta \rho gQH}=0.8075\times 1000\times 9.81\times Q\times 100=600\mathrm{kW}$

Finally, $Q=\frac{600000}{0.8075\times 1000\times 9.81\times 100}=0.7574{\mathrm{m}}^3/\mathrm{s}$

Example 6.3

A hydro power system is considered for being installed at a site with a pressure head of 1.25  m³/s, which is available 10   h a day and has a net head of 100   m. Assume that it is expected to gain potential theoretical energy equal to 3   MWh. Is it possible to gain the expected potential energy? Additionally, calculate the hydraulic power taking into account hydraulic efficiency and mechanical efficiency of ${\eta }_d=96\%$ and ${\eta }_t=87\%$ .

As $Q=1.25{\mathrm{m}}^3/\mathrm{s}$ , and $H=35\mathrm{m}$

Then, from Eqs. (6.2) and (6.8), we have

$E=\eta E_0=\mathit{\eta \rho gQH}\mathrm{\Delta }\mathit{t}$

Moreover, $\eta ={\eta }_h*{\eta }_m=0.96*0.87=0.8352$ .

So that $E=0.8352\times 1000\times 9.81\times 1.25\times 35\times 10=3584.574\mathrm{kW}\mathrm{h}$ .

So it is possible to attain the expected electrical energy. The hydraulic power is as follows:

$P=0.8352\times 1000\times 9.81\times 1.25\times 35=358.4574\mathrm{kW}$

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Environmental Impact

CHARLES SIMEONS M.A. , in Hydro-Power, 1980

Fisheries

Hydro-power can provide opportunities for improved fisheries. For instance, the North of Scotland Hydro-Electric Board have made provision for passes to allow Salmon to surmount dams and traps to enable adult Salmon to be taken so that they can be stripped of their eggs. The fertilised eggs can then be incubated and moved to new spawning grounds. A typical fish pass is shown in Fig. 198.

Fig. 198. A typical fish pass

Many dams are fitted with a fish lift shown in Fig. 199.

Fig. 199. The Borland Fish Lift

In the fish lift shown in Fig. 199 the fish are attracted into the chamber at the foot of a sloping shaft by the flow over the upper sluice. The outlet is then closed. As the water continues to pour in, the level rises and the fish rise without any effort until they reach the chamber at the top of the shaft, and, by passing over the upper sluice, swim on into the reservoir. Hatcheries may again be used.

Clearly environmental considerations and the impact of a tidal barrage are considerable and adequate safeguards must be provided. But equally benefits can be considerable too, particularly in conventional hydro-schemes where the generation of electricity is a bi-product of the harnessing of the water which enables improved irrigation to be accompanied by flood control making areas formerly unuseable become inhabitable and prosperous.

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Hydro Power

S.P. Sen , in Comprehensive Renewable Energy, 2012

Abstract

Hydro power development in India has been quite slow and did not keep pace with the development of thermal power. With large hydro potential available, especially in the Himalayas, urgency of hydropower development has been felt in recent years in view of the effect of fossil fuel in carbon emission and also climate change.

Recently, Central Electricity Authority (CEA), the central planning and controlling body in the field of power generation, has put the expeditious development of hydropower in the forefront. For this purpose, CEA has started advanced planning for the 12th 5 year Plan (2012–17) as a matter of urgency since 2008.

Eighty-seven (87) projects of 20   000   MW have been identified for this purpose. Advance planning for such projects identifying the owner of these projects, their readiness for execution, and assistance required are being monitored and provided.

To expedite the development of hydropower, the private sector is being encouraged by the Government of India to develop hydropower in the same scale as thermal power. In the 12th Plan, out of 20   000   MW about 8000   MW was proposed to be developed and owned by independent power producers (IPP). Such large involvement of private developers has opened up a new vista of hydropower development and also new challenges in a field which is still dominated by Government agencies in India and also throughout the world.

In the difficult and inhospitable terrain of the Himalayas, development of hydropower on a large scale opens up many issues of social and peripheral economic upliftment along with environmental protection and sustainable development. The hydrological and geological uncertainties and the geomorphologic behavior of the Himalayan rivers are also added factors to the difficulties. On the other hand, if large-scale development of hydropower in the Himalayas is carefully planned with priority to human development of the area it can bring a social and economical upliftment of the region.

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Introduction to hybrid AC/DC microgrids

Shivani Mishra , R.K. Viral , in Microgrids, 2022

6.6.4 Small-hydro system model

Mini hydro power plant is used in hybrid micro-grid. It is used where there is abundance of water resources or creation of water canal/linkage of river. The construction cost of hydro power plant is high but operation and maintenance cost is almost zero. This power plant is very useful due to fuel cost not involved. Its efficiency is very good ( Singh & Balchandra, 2019). This type of power plant is also useful to provide back-up at the time of shut-down. Due to the availability of water resources 24×7, it's not depended on day and night scenario.

In the hydro power plant, Fig. 6.10 converts the pressure of head water into the speed governor through penstock turbine and then the mechanical power is converted to electricity after going through the generator, then the generated electricity is used for applications in power system (Jaszczur, Hassan, Palej, & Abdulateef, 2020). Eq. (6.3)

Figure 6.10. Small-hydro system model.

(6.3) $P=m\times g\times H_{net}\times \eta$

where P=power in watts, m=rate of mass flow in kg/s, g=gravitational force is 9.81m/s², H _net=H _gross ×0.9, η=efficiency.

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Interface with Energy Strategy

P. SILVENNOINEN , in Nuclear Fuel Cycle Optimization, 1982

Load Duration

Including hydro power, or any other renewable energy source for that matter, means that varying conditions of nature shall be taking into account. Since there exist extensive meteorological data bases, it is easy to forecast stochastically an average year within the planning interval. Optimization runs are carried out for this average year unless there are reasons for doing otherwise. One could, of course, choose an year for which the yield from renewable sources is left to be less than average.

Within the nominal year, the demand of electricity changes almost continuously. The variation can be projected on the basis of the previously accumulated consumption statistics. The time dependent load demand is usually converted into a load duration curve. Such a curve is shown in Fig. 9.1. The capacity demand varies there between the maximum and minimum values denoted in Fig. 9.1 by C_max and C_min, respectively.

Fig. 9.1. Load duration curve.

The abscissa in Fig. 9.1 gives the total length of time that the demand given as the ordinate occurs. The demand exceeds the value C_min. throughout the time interval h, whereas C_max denotes the value of the peak load. The integral over the surface bound by the load duration curve corresponds to the total demand of electricity during the time h.

For practical purposes, the load duration is often linearized. The monotonous decrease from C_max to C_min is presented by a straight line. The nominal year is divided usually into several time segments each of which is represented by an individual load duration curve.

The economic loading order is determined by the ratio of the running operating costs to the fixed annual capital costs. The lower this ratio is, the longer should the utilization time become. Among the plant types specified earlier, the nonstorable hydroelectric power corresponding to the run-off-river hydroenergy is loaded first. The hydro power is followed by nuclear power plants. The fossil back-pressure plants have to be loaded next because their operation is required by the rest of the energy sector. The fossil condensing power stations cover the layer immediately beneath the peak load. The peak load is furnished by the storable hydroenergy and, if required, by the gas turbine stations.

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Analysis, Conclusions and Prospects Consolidated Report on the Symposium1

H.D. Schilling , in Oils and Gases from Coal, 1980

2.2.1 Electricity

Apart from hydro power, electricity is produced almost exclusively in thermal power stations. The primary energy used as feedstock is first converted to thermal power by combustion; this power is subsequently transmitted by means of a suitable fluid, mostly steam, to operate a turbine which, in turn, drives a generator. This power station technology has reached a high degree of technical development also for coal firing. Power stations of such a design are clean and safe to operate today. Power station technology, however, is facing increasing difficulties which might be summarized as follows:

–

The foreseeable scarcity of mineral oil and natural gas means that these primary energies should be used for electricity production to a decreasing extent. In the Federal Republic of Germany, for instance, legislation has made the construction of oil or gas-fired power stations subject to official approval;

–

In some countries, the legal requirements with respect to pollution control have been tightened in a way that conformity with these regulations constitutes a considerable cost factor, and also results in reduced efficiency, since the required purification equipment also consumes energy;

–

The average 35 per cent efficiency of power stations is to be regarded as low. This results in relatively high emission rates and a particularly quick response of electricity production costs to price increases for primary energies. The low efficiency is conditioned by thermodynamics and by physical laws. The system implies particularly high heat discharges which, however, do not exceed a relatively low temperature level due to thermodynamic reasons.

In view of the fact that more than 25 per cent of all primary energies are used for electricity production and that, on the other hand, the heat requirements on the consumer's side are very high, this low efficiency assumed particular importance. The ECE is quite aware of the still unused potential in this field: by increased efficiency, several technical and economic advantages could be achieved simultaneously:

–

reduction of the capital-dependent costs of electricity by reducing the specific investment cost;

–

reduction of the fuel-dependent cost of electricity;

–

considerable reduction of the pollution and heat emission per kWh produced, without additional purification equipment.

Due to the significance of these features, the problems involved were given a leading place on the agenda of the Katowice Symposium.

The efficiency of thermal power stations is largely controlled by the temperature of the driving fluid upstream of the machinery, e.g. a turbine. With steam-operated power stations the combustion temperature can reach a maximum of 1800°C. The turbine inlet temperature of steam, however, must not be higher than approximately 560°C - otherwise material problems would arise - and the steam pressure must not exceed approximately 250 bar. The large temperature range between 1800°C and 560°C cannot be used for conversion due to limits set by the available materials. This means a comparatively low gross efficiency of 40 per cent maximum in base-load operation.

In peak-load operation, efficiency is considerably lower due to losses during startup and shut-down and due to the occasional operation of peak-load turbines. When subtracting the energy requirement for internal use and the not negligible transmission losses, the average efficiency of electricity generation amounts to approximately 31 per cent, i.e. only 31 per cent of the primary energy input reaches the consumer in the form of electrical energy.

For technical and economic reasons, all attempts to increase efficiency by means of higher temperatures and higher pressures of the life steam have failed up to now. A further possibility seems to be the use of additional gas turbines, which already withstand inlet temperatures of approximately 900°C; development of such systems, however, is by no means complete. Such combined gas turbine/steam turbine cycles require a clean fuel which can be produced, e.g. by steam/air gasification of coal. In this way, the high development potential of the gas turbine can be opened up to coal. According to the gas turbine inlet temperature, the efficiency may range between 40 and 47 per cent internal consumption being taken into account. For conventional steam power stations with flue gas desulphurization, the corresponding figure is 33 per cent. A successful development of this technology carried out especially by STEAG AG and Vereinigte Elektrizitätswerke Westfalen AG in the Federal Republic of Germany and by Westinghouse in the United States, the development of which has also started in Poland, could result in more effective use of coal by 17 to 35 per cent. By the same percentage, the output-related emission of pollutants is reduced without additional cleaning. The heat discharges would be reduced by 26 to 44 per cent, according to efficiency. Relative to a use of 100 million tonnes of coal the complete development of this technology would mean a savings potential of 17 to 35 million tonnes of coal.

The same applies to the use of fluidized bed combustion, even though this technology can follow gas turbine development only up to the 950°C temperature range provided additional, economically viable measures were taken. A special feature of this technology, however, is very clean operation without additional costs which can be regarded as a particular advantage. MHD-generators, the development of which is carried on above all in the USSR and the United States, also imply a highly efficient potential; successful development cannot, however, be expected before the turn of the century.

Endeavours to create a new basis for the technologies in coal-fired power stations have been intensified considerably since the last ECE Symposium on Gasification and Liquefaction of Coal held in Dusseldorf in 1976 and notable success can be observed. Obviously upstream coal gasification is of decisive importance. This development is complemented by the clean working of fluidized bed combustion which is being developed in various countries at considerable expense. Successful development of these technologies is intended to reduce specific investment costs, as well as emissions, by its increased efficiency alone. Furthermore, the respective process engineering is set up so that additional plants for flue gas desulphurization and NO_X suppression are only required to a small extent or not at all. This could be of interest, above all, for countries whose capital resources are as yet insufficient to add the purification equipment now available to their power stations. However, as long as these new technologies are not yet available on a commercial scale, additional purification equipment will need to be developed and applied within the conventional systems.

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SMALL-SCALE HYDROPOWER

L.A. KRISTOFERSON , V. BOKALDERS , in Renewable Energy Technologies, 1986

Environment

Most hydro power systems in use today are large-scale and are unfortunately hampered by many environmental problems.

Large-scale hydro power inevitably necessitates the building of dams in order to create a reservoir. There can be few technologies that so visibly and dramatically alter the face of a landscape as large dams and artificial reservoir lakes, so the decision to build such a power system carries with it a multitude of associated and frequently neglected hazards.

To begin with, flooding a valley usually necessitates mass population migration and local authorities are forced to cope with all the resettlement problems that such an exodus brings. In Egypt, the creation of Lake Nasser displaced some 80 000 people; in Ghana, 75 000 people had to be evacuated when Lake Volta was created, and the establishment of Lake Kariba in East Africa led to the resettlement of 57 000 people.

The human problems created by the establishment of large hydro power schemes are compounded by a number of environmental problems. Traditional fishing practices are disrupted by the construction of large dams, even when fish ladders are installed. Such dams can prevent fish migration to traditional fishing areas where, as a result fish stocks are decimated. In addition the reservoir and associated irrigation channels provide ideal breeding sites for snails that transmit schistosomiasis - a dehabilitating and often fatal disease that currently afflicts about 200 million people in tropical countries. Large dams also often reduce the previously-experienced, regular flooding of surrounding land which brought rich silt to the areas and also washed out salt from the soil before the dam was built.

Reduced silting results in the need for costly artificial fertilizers to be applied to the land, providing that it is still suitable for cultivation. Salt content build-up caused by reduced washing-out frequently leads to previously fertile land becoming infertile.

Silt, which previously reached surrounding land via flood water, now remains in the reservoirs and often causes major silting problems in the hydro power turbines. The Sanman Gorge Dam on the Yellow River in central China, for example, has lost about 75% of its 1000 MW power generating capacity due to sediment build-up.

Part of the reasoning behind the condoning of large-hydro power schemes by local and national authorities centres on the belief that local populations will benefit from the newly-established industry that such power supplies are expected to attract. In a general sense this is naturally true, given the relationship between electricity and industrial development. Unfortunately, the new industry and the supposed associated improved living standards that such industry brings, rarely affect those displaced by large-hydro schemes since energy-intensive industry only provides employment for a skilled workforce. Few local people possess the necessary skills required to qualify for jobs created by the new industries in their area. In Sumatra, for example, the US$ 2 billion Asahan aluminium production plant and hydro-electric scheme employs only 2100 of the Island's 30 million people.

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Power electronics for renewable energy systems

Muhammad Kamran , in Renewable Energy Conversion Systems, 2021

3.3.4 Half-wave controlled rectifier with resistive load

On replacing the diode in an uncontrolled rectifier with a thyristor, a controlled rectifier is formed, as shown in Fig. 3.19. During the positive half cycle, the thyristor is forward biased but because of the absence of the gate signal it remains in forward blocking mode. As soon as the thyristor is turned ON by applying the gate signal, a thyristor comes in forward conduction mode and start conducting. From the waveform of $V_{AK}$ in Fig. 3.20, we can see that the voltage is dropped across the thyristor until the gate signal is applied and after the application of the gate signal, the voltage starts appearing across the load. During the negative half cycle, the thyristor becomes reverse biased and drops all the input voltage across itself irrespective of the presence of the gate signal.

Figure 3.19. Half-wave controlled rectifier with a resistive load.

Figure 3.20. Output waveforms of a half-wave controlled rectifier with a resistive load.

The average output voltage can be determined by calculating the area under the one complete cycle using the following equation.

$V_{O(avg)}=\frac{1}{2\pi }{\int }_0^{2\pi }{V}_m\sin \left(\omega t\right)·d(\omega t)$

As $V_{Out}=0\mathrm{for}\mathrm{the}\mathrm{intervals}\left(0\le \omega t\le \alpha ,\pi \le \omega t\le 2\pi \right),$ so the above equation becomes

$V_{O(avg)}=\frac{1}{2\pi }{\int }_{\alpha }^{\pi }{V}_m\sin \left(\omega t\right)·d(\omega t)$

(3.7) $V_{O(avg)}=\frac{V_m}{\pi }\left(\frac{1+\cos \alpha }{2}\right)$

Eq. (3.7) is used to determine the average voltage at the output of the controlled half-wave rectifier with resistive load. The average value of the current is determined by the following relation.

$I_{O(avg)}=\frac{V_{O(avg)}}{R}$

The average power of the rectifier is determined by the multiplication of voltage and current. Average output power of the half-wave controlled rectifier with resistive load is determined by Eq. (3.8).

$P_{O(avg)}=V_{O(avg)}\times I_{O(avg)}$

(3.8) $P_{O(avg)}=\frac{{V_m}^2}{{\pi }^{2}R}{\left(\frac{1+\cos \alpha }{2}\right)}^2$

Example 3.2

In a micro hydro power plant, the output power is to be dumped on a DC link because of the intermittent nature of the flow. To convert the AC output to DC, a half-wave controlled rectifier is used. The input voltage from the micro hydro system is $V_{in}=170\sin \left(\omega t\right),$ If the load resistance is 100 Ω, calculate the output power for the following firing angles. Also interpret your results.

(a)

$\alpha =0^0$

(b)

$\alpha ={45}^0$

(c)

$\alpha ={90}^0$

(d)

$\alpha ={135}^0$

(e)

$\alpha ={180}^0$

Solution

To calculate the output power of the half-wave controlled rectifier we use Eq. (3.8)

$P_{O(avg)}=\frac{{V_m}^2}{{\pi }^{2}R}{\left(\frac{1+\cos \alpha }{2}\right)}^2$

(a)

For $\alpha =0^0$

$P_{O(avg)}=\frac{{170}^2}{{\pi }^{2}100}{\left(\frac{1+\cos 0}{2}\right)}^2$

$P_{O(avg)}=29.3W$

(b)

For $\alpha ={45}^0$

$P_{O(avg)}=\frac{{170}^2}{{\pi }^{2}100}{\left(\frac{1+\cos 45}{2}\right)}^2$

$P_{O(avg)}=21.3W$

(c)

For $\alpha ={90}^0$

$P_{O(avg)}=\frac{{170}^2}{{\pi }^{2}100}{\left(\frac{1+\cos 90}{2}\right)}^2$

$P_{O(avg)}=7.32W$

(d)

For $\alpha ={135}^0$

$P_{O(avg)}=\frac{{170}^2}{{\pi }^{2}100}{\left(\frac{1+\cos 135}{2}\right)}^2$

$P_{O\left(avg\right)}=0.62W$

(e)

For $\alpha ={180}^0$

$P_{O(avg)}=\frac{{170}^2}{{\pi }^{2}100}{\left(\frac{1+\cos 180}{2}\right)}^2$

$P_{O(avg)}=0W$

From the above calculations of power at different firing angles we can estimate that by increasing the firing angle the power at the output is reduced.

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Wind Energy

K.A. Kavadias , in Comprehensive Renewable Energy, 2012

2.19.5.4 Stand-Alone Wind–Hydro Power Systems

Complementarity of renewable energy sources can also be exploited in wind–hydro power systems, which are based on the exploitation of both wind potential and hydraulic power in order to enhance the reliability, energy quality, and stand-alone system performance. In addition, the water storage capability of the hydroelectric system can significantly limit the intermittence of wind power generation. Thus, a stand-alone wind–hydro power system does not essentially refer to the independent production of electricity by a hydro power installation or a wind turbine, both of which supply energy to a remote consumer. The wind–hydro concept mainly refers to the integration of a wind power installation with a pumped hydro storage (PHS) system that will be able to absorb the residual wind energy during low-power demand periods and return it for consumption when wind power cannot satisfy the demand. The implementation of wind power generation with PHS is targeting mainly the range of isolated communities in remote islands with no connection to any mainland grid rather than single consumers as indicated for the systems described in the previous sections.

The integration of wind power with PHS has been investigated for at least 20 years by numerous researchers [37, 46, 50, 51]. Most of the cases analyzed refer to isolated islands with the target of minimizing the conventional fuel energy consumption and eliminating the negative environmental impacts. Combined wind–hydro energy stations can contribute to the maximum RES penetration into the load demand, which, according to research results, can even exceed 90%.

A typical wind–hydro power system capable of fulfilling the energy needs of an isolated community is presented in Figure 24 . More precisely, the hybrid system consists of

Figure 24. Combined wind–hydro installation for remote communities.

•

one or more wind turbines,

•

a small hydroelectric power plant,

•

a water pump station, and

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two or more water reservoirs at elevations h ₁ and h ₂ (h ₁  > h ₂) working in a closed circuit along with the corresponding pipelines.

The hybrid wind–hydro power plant is usually supplemented by an existing autonomous power station (APS) which usually comprises conventional internal combustion engines. The main objective of the wind–hydro station is the fulfillment of the energy demand by increasing the renewable energy source absorption and reducing the operation time of the local APS.

The sizing procedure of the wind–hydro power system includes sizing of the wind turbine and the hydro turbine, as well as the determination of the exact location, volume, and geometry of the water reservoirs along with the determination of the rated power and operational range of the water pumps and the water piping system dimensions (diameter, length).

More precisely, the rated power of the water pumps may be determined by the maximum power of the wind turbines, as the water pump must have the capability to absorb the maximum power output of the wind turbines, whereas in the case of large-scale systems, the rated power of the pump depends on the frequency distribution of the wind park's energy surplus; that is,

[14] $P_{\text{pump}}=\frac{{\rho }_{w}gH\dot{V}}{{\eta }_{\text{p}}{\eta }_{\text{el}}}$

where P _pump is the power required by the water pumps; H the pump head; $\dot{V}$ the volume flow rate; η _p the pump efficiency; η _el the electrical efficiency of the system; ρ _w the density of the water; and g the acceleration due to gravity.The static head, H, of the pump must satisfy the expression

[15] $H\ge \left(h_1-h_2\right)+\delta H_{\text{f}}=\left(h_1-h_2\right)+K_{\text{p}}{\dot{V}}^2$

where δH _f is the total hydraulic losses, both lengthwise and local, when the water reservoir is used for energy storage and K _p is the friction losses factor.

It should be noted that H and η _p depend on the operational characteristics of the selected pump.

The nominal power of the hydro installation results from the precondition that it covers the peak power demand of the system each time examined, with an optional future increase (of 20%). The exit power is given as

[16] $P_{\text{h}}={\rho }_{\text{w}}gH\prime \dot{V\prime }{\eta }_{\text{H}}\eta {\prime }_{\text{el}}$

where $\dot{V^{\prime }}$ is the flow rate of the turbine; H′ the hydro turbine head, η _H the turbine efficiency, and η′ _el the electrical efficiency of the system.

In addition, the following equation is also valid:

[17] $H\prime \le \left(h_1-h_2\right)-\delta {H\prime }_{\text{f}}=\left(h_1-h_2\right)-K_{\text{H}}{\dot{V\prime }}^2$

where h is the hydrostatic head and δH _f′ is the total hydraulic losses, both lengthwise and local, when the water circuit is used for energy production.

Note that H′ and η _H depend on the operational characteristics of the hydro turbine selected.

The dimensions of the upper water reservoir are defined by the available hydrostatic head, which depends on the relative elevation between the upper and the lower water reservoirs, and by the required levels of energy autonomy for the system. For example, by selecting d ₀ days of energy autonomy, the useful volume V _o of the water reservoir is given as

[18] $V_o=\frac{E_{\text{tot}}24d_0}{\Delta t{\eta }_{{\rm H}}{\eta }_{\text{el}}{\rho }_{w}gH\prime }=V_{\max }-V_{\min }$

where E _tot is the total energy demand for the time duration of analysis, Δt, in hours (e.g., 8760   h for 1 year); and V _max and V _min are the maximum and minimum storage capacity, respectively, of the upper water reservoir.

During a long-term energy balance analysis of a wind–hydro power system operation, the following operational situations may arise:

1.

The wind power produced is in excess of the energy demand of the system.

a)

In that case, the energy surplus is stored through operation of the water pumping system in the upper reservoir.

b)

In case the upper reservoir is full, the energy surplus is forwarded to other alternative uses, such as a water desalination plant.

2.

The electrical power demand is higher than the wind park output.

a)

In that case, the hydro turbines cover the power deficit.

b)

In case the upper reservoir is almost empty, the internal combustion engines of the APS take over the power deficit, under a scheduled operational plan.

For estimating the optimum wind–hydro configuration, advanced numerical algorithms should be used, to analytically simulate the operation of different system size combinations. By applying an analytical simulation procedure, Kaldellis and Kavadias [52] presented interesting results regarding the renewable energy possibilities in the electrification of remote islands. The study, which is presented here, concerned a medium-sized Aegean Sea island (Karpathos), and the basic scope was the maximization of RES penetration. The annual energy production of the local APS of the island was estimated at 24   400   MWh and the peak-load demand at ∼6500   kW, whereas the corresponding minimum value was 1400   kW. The island has a very high wind potential, as the long-term annual mean wind speed approaches 9.6   m   s⁻¹, at 10   m. According to their results, remarkable renewable energy penetration can be achieved ( Figure 25 ) by increasing the number of wind turbines used and the size of the water reservoirs selected through the parameter d _o which represents the number of days of energy storage autonomy.

Figure 25. Renewable energy sources penetration capability using the wind–hydro solution in the autonomous electrical system of Karpathos island.

Another interesting optimization approach for the economy enhancement of large wind–hydro installations concerns a planned hydro power production under a pattern of guaranteed energy by the hydro power system on a daily basis during the peak load demand hours. In this way, high energy-purchase prices can be realized by selling power to the local autonomous grid during the peak load demand hours [46]. Of course, in case the water stored in the upper reservoir is not enough for the fulfillment of the condition of guaranteed energy delivered to the local grid, the water pump absorbs the required energy from the grid during low-demand periods when the energy purchased price from the local grid is low.

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https://www.sciencedirect.com/science/article/pii/B9780080878720002225

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Source: https://www.sciencedirect.com/topics/engineering/hydro-power

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