renewable hybrid power system
TRANSCRIPT
HYBRID RENEWABLE POWER SYSTEM
Renewable Energy Sources & Energy Storage Techniques
Guided By:- Dr. V. K. Jadhav sir
Presented By:-Pravin Prakashrao Ladde, [EE]6th (G)
Puranmal Lahoti Government Polytechnic, Latur.
[email protected] [8087733733]
Abstract
The paper presents structure of Renewable Hybrid power system & latest techniques to store the energy.
All non-Renewable Energy sources like coal, diesel, radioactive elements from which we are generating
electricity are the ending and polluting sources of energy. Using Renewable energy sources like Solar energy,
Wind energy, Biomass energy, Geothermal energy, hydro power station etc. to generate electricity is the most
efficient way to generate electricity as they are non-ending and non polluting sources of electricity. But the
main problem associated with the renewable energy sources is output of these sources is not constant in
nature. So there are some difficulties of integrating these variable power sources into the existing power
grids. Energy storage systems are one of the possible solutions for reducing the effects of variable renewable
resources on networks, allowing increased renewable energy utilization, and providing flexibility and for
managing future electricity supply/demand challenges. In this paper we discuss about the energy storage
technologies that are currently engaged for power applications, including pumped hydro, compressed-air,
battery storage, hydrogen storage, super capacitor. But there is need for more research to actualize their
promising potentials.
Introduction
There is a huge potential for utilizing renewable energy sources, for example solar energy, wind
energy, hydropower, to provide a quality power supply to remote areas. The abundant energy available in
nature can be harnessed and converted to electricity in a sustainable way to supply the necessary power to
elevate the living standards of the people without access to the electricity grid.
The disadvantage of standalone power systems using renewable energy is that the availability of
renewable energy sources has daily and seasonal patterns which results in difficulties in regulating the output
power to cope with the load demand. Uncontrolled Renewable energy sources essentially have random
behaviors. eg: Solar, Wind, etc. Power production from uncontrolled sources is independent of human
intervention. Renewable Hybrid power systems may contain controlled and uncontrolled energy sources and
energy storage elements with appropriate control systems. During minimum load and maximum out-put of
these Renewable sources, we can store the energy generated by them to use during peak load conditions. [1]
The technique used to store this extra generated energy using pumped hydro Storage system is to
pump back the water in the lower reservoir which is used to generate electricity during peak load condition
To the upper reservoir using pump set so that same water can again be used to generate electricity during next
peak load conditions. [2]
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In the technique used to store energy using compressed air, extra amount of energy generated is used
to compress the atmospheric air under high pressure in the pressure tank or underground cavern or under
ground mine so than this high pressurised compressed air could use to drive the turbine during peak load
period.[3] In case of storage batteries the extra generated electricity is stored in battery banks in the form of
chemical energy to use during peak load condition using inverter.[4]
Hydrogen storage technique is also one of the best way of storing energy. During low load condition
the extra amount of electricity generated is used to decompose the water using electrolysis process. The
hydrogen generated during this process is collected and stored. This hydrogen can be used to heat water to
produce pressurised steam to drive steam turbine, also it could used to maintain the temperature of biomass
power plant during winter.[5] In case of super capacitor the extra generated energy is stored in the form charge
in capacitor specially made to store energy called super capacitor, and use that during peak load conditions.[6]
These are the objectives of the work described in this paper.
De-merits of using conventional energy sources
All the conventional energy sources like coal, oil, natural gas radioactive element are the
ending sources of energy, also using them to produce electricity increases evaporation of polluting
gases leads to global warming which is one of the critical issues in day to day life.
Fig. (1)- Percentage of pollution from power plants
Above Fig. (1) Shows the total percentage of pollution due to use of these sources as base
energy sources to power plant. We could replace these energy sources with renewable energy sources
using some techniques. At least we could increase use of more renewable sources to produce
electricity to avoid pollution and be insuring about safe future.
[7]
Fig. (2) Sources of electricity in India by installed capacity.
Fig. (2) Shows there is only 12% electricity in India is generated using renewable energy sources, so
there is great potential to increase Its use in India.
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Types of Renewable energy sources
There are many Renewable energy sources which are abundantly available for free in nature.
Solar energy.
Wind energy.
Hydro power.
Biomass energy.
Geothermal energy.
Solar energy
Solar energy freely available in nature can be used to produce electricity using solar panels and
solar energy also can be used to generate heat and store it using thermal storage. Main problem when
dealing with solar energy is that its nature is variable and depend on season and time also clouds may
cause interrupt in the output of this energy.
Wind energy.
Wind energy available in nature can also be converted in electrical energy using wind turbine.
Also the out-put of wind turbine is more in winter as compared to other seasons. In both high and low
wind pressure condition the output of wind turbine is not constant. so to get constant output to the grid
storage of electricity using battery or directly coupling wind turbines to the compressor to compress air
and use these stored energies during peak load condition is the best way.
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Hydro power.
In hydro power station potential energy stored in the water in the upper reservoir is used to rotate
turbine and generate electricity. Once the water from upper reservoir is used to generate electricity,
further electricity cannot be generated from same water as it loses its potential energy to drive turbine.
Biomass energy.
Biomass energy is the energy obtained from trees and all other bio west from forest or farms. As
an energy source, biomass can either be used directly via combustion to produce heat, or indirectly
after converting it to various forms of bio fuel.[8]
Geothermal energy.
Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the
energy that determines the temperature of matter. The geothermal energy of the Earth's crust originates
Fig.(3) – Geothermal energy extraction
From the original formation of the planet and from radioactive decay of minerals.[9] The thermal
energy is used to heat the ground water to produce high pressure steam to drive the alternator turbine.
Above Fig. (3) shows the structure of extraction of geothermal energy.
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What is hybrid Renewable power system
We have already know that all the renewable energy sources does not have constant output but
it is dependent on daily basis or seasonal basis or simply we can say it is time varying. So that we
cannot add such a variable source to the existing grid or power system because to connect these
electricity power plant to the existing grit its output should be constant in nature.
The hybrid power system is the advance technology that should be implemented to minimise
the problems of connecting these renewable sources to the existing power system using storage
technique. During the off load period the extra energy generated by the Renewable energy source is
stored may be in the form of electrical, chemical or mechanical energy to use during peak load
conditions.
The power output of solar power plant is more during summer season; also we get energy from
solar only during day time. In case of wind power station its output is more during winter or windy
season. Also the power output of biomass power plant is more during summer and less during winter
because more amount of energy is required to maintain the temperature of plant during winter. So as to
get constant output power we have to connect these power plants to each other with proper technique
to store energy during low load conditions, So as to get more stable power output. This technique is
nothing but hybrid renewable power system.
Let’s have a look towards the latest techniques to store energy.
Energy storage technique
There are so many energy storage techniques had developed to store energy so as to increase
the More use of renewable energies to conserve the conventional sources and to reduce the pollution.
Pumped hydro
Compressed air
Battery storage
Hydrogen storage
Pumped hydro
Pumped hydro is one of the best technique to store the energy. We know that in hydroelectric
power station; the electricity is generated using the potential energy stored in water of upper reservoir.
The water stored in upper reservoir with great potential energy is exerted on the prime mover which is
water turbine, that water turbine is connected to the alternator to generate electricity.
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Fig. (4) -Pumped hydro station.[2]
Above Fig.(4) shows the structure of pumped hydroelectric power station[2] .once the water
stored in upper reservoir is used to generate the electricity, it loses its potential energy and it cannot be
used to generate electricity again as it is now stored in lower reservoir. To generate electricity again
from the same water we should have to again pump the same water in the upper reservoir, that is the
thing done in this type of storing system. A huge amount of water pumps is used to pump back the
water the lower reservoir back to the upper one during low load and high output period of renewable
sources. So that to use this water again to generate electricity during peak load conditions.
Compressed air
Fig.(5)- Compressed air energy storage technique[3]
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Above Fig.(5) shows the construction of Compressed air energy storage (CAES). It is a way
to store energy generated at one time for use at another time using compressed air. At utility scale,
energy generated during periods of low energy demand (off-peak) can be released to meet higher
demand periods. Small scale systems have long been used in such applications as propulsion of mine
locomotives. Large scale applications must conserve the heat energy associated with compressing air;
dissipating heat lowers the energy efficiency of the storage system [3]. Compression of air creates heat;
the air is warmer after compression. Expansion requires heat. If no extra heat is added, the air will be
much colder after expansion. If the heat generated during compression can be stored and used during
expansion, the efficiency of the storage improves considerably.[3].
Generally to use this compressed air to rotate the turbine, natural gas is mixed with the air to
increase the temperature as due to sudden compression of air, it had already lost its heat and during
using this heat to rotate turbine, temperature goes to very low value and moisture from air get converted
in to ice and liberate on the turbine to increase its weight and decries its efficiency. To get perfect
renewable based hybrid power system, we could use thermal collector to collect solar heat and use this
heat energy to increase temperature of compressed air.
A big mines, cavern are also could be used to store this large amount of compressed air under
ground level by sealing them.
Battery storage
Fig. (6) Storage of energy using battery bank
The above fig. (6) shows the storage of energy using battery bank. The more amount of energy
generated during low load conditions from solar, wind, or any other renewable energy sources is
rectified and stored in the big battery banks in the form of chemical energy.
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This same stored energy can again converted in to alternating electricity using inverter circuit
To use during peak load conditions to meet load demand. this is more efficient way to store energy but
the cost of entire system will be increases due to use of electrolytic batteries. Also the life of batteries
is low and it reduces with the more use of it[4].
Hydrogen storage
Using electrolysis process of water using fuel cell, oxygen and hydrogen is separated and the
hydrogen released during this process is stored in big tanks or using underground hydrogen storage
techniques. as volume to energy ratio of this hydrogen is very low, compressed hydrogen storage
technique is implemented mostly with thermal energy storage during compression process to increase
efficiency. The electrical energy required for the electrolysis process is derived from the renewable
energy sources during off load period.
This hydrogen can be used to heat water and convert water in to steam to drive steam turbine,
also the stored hydrogen can be used to maintain the temperature of biomass plant during winter
period, same hydrogen can be used to mix with compressed air to increase the temperature of
compressed air during its use.
Fig. (9)- Hydrogen storage techniques.
Above fig. (9) shows the typical type of generation and storage tank of hydrogen practically
used. If the amount of hydrogen to store is large, then underground cavern or salt dome may be sealed
to store these large amount of hydrogen.
These all are the techniques to store the energy so that it could be used during peak load
conditions to meet load demant. There are few more types to store energy like flywheel,capasitor,
super capasitor, thermal storage etc. which also can be implimented to store energy.
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Ideas of possible totally Renewable based hybrid power stations
Below Fig.(10) shows Ideas of possible totally renewable based hybrid power stations
Solar-wind-hydro power station.
Solar-wind-biomass power station.
Solar-wind-compressed air based power station.
Solar-wind-battery storage power plant.
Wind-compressed air geothermal energy power station.
Fig. (10)- Ideas of Possible totally Renewable based hybrid power stations
Conclusion
From the above papers we could conclude that there is huge potential to increasing the use of
totally renewable based hybrid power plant. Also the reduced use of non-renewable energy sources is
the great need of today’s lifestyle, as increased use of conventional sources increases the pollution in a
great extend. Also the non-renewable energy sources are the ending sources of energy so before they get
completely evaporated, we should be able to complete our energy needs using renewable sources
completely.
References
[1] http://en.wikipedia.org/wiki/Hybrid_renewable_energy_system
[2] http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
[3] http://en.wikipedia.org/wiki/Compressed_air_energy_storage
[4] http://en.wikipedia.org/wiki/Rechargeable_battery
[5] http://en.wikipedia.org/wiki/Hydrogen_storage
[6] http://en.wikipedia.org/wiki/Supercapacitor
[7] http://en.wikipedia.org/wiki/Electricity_sector_in_India
[8] http://en.wikipedia.org/wiki/Biomass
[9] http://en.wikipedia.org/wiki/Geothermal_energy
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