Green Technology And Alternative Energy Storage Environmental Sciences Essay

This report was carried out to identify different type of energy and various form of storing them. Energy allow us to perform work, the parameter that determine their type, method of storing them, the form of energy to be store, capacity of energy they can store, how quickly they can store, how often they can release the energy stored are the discussion of this write up.

The forms of energy storage system available are classified under the major field of Engineering Technologies as mechanical, electrical, chemical, and thermal. They have all been explored, leading to the birth of the techniques that will be described in this write up. The types of energy storage system are Pumped‐Hydroelectric Energy Storage PHES), Compressed Air Energy Storage (CAES), Battery Energy Storage (BES), Flywheel Energy Storage (FES), Capacitors Energy Storage, Super Capacitor Energy Storage (SCES), Superconducting Magnetic Energy Storage (SMES), Hydrogen Energy Storage System (HES), Thermal Energy Storage (TES), and Electric Vehicles with references to the technologies involve and there potential capabilities

Finally a brief comparison of their various technologies is provided to the determine the best suitable one for each occasion

Introduction

Energy provide the ability to perform work, it can be potential or kinetic energy, depending on the situation, the law of conservation of energy stated that energy can neither be created nor destroyed, but energy can be converted from one form to another. Energy is stored when it is available in abundant and release out for consumption when it is not sufficient or as substitute during power failure, energy storage allows humans being to balance the supply and demand of energy, the ideas for storing energy derived from the principle of necessity is the mother of invention, as energy are stored during the time of their available to enable human perform various task during the time of scare or shortage .It is stored from primary source for convenient use at a later time when a required energy demand is to be met in a different location (answers.com/topic/energy-storage). Energy storage are employed to reduce the time or rate of mismatch between energy supply and energy demand, moreover energy storage play the role major stake holder in energy conservation

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Different type of energy storage device are available and their technologies are vary in respect to their method of storage mechanism, the capacity of energy they can store, how quickly they discharge and recharge the stored energy. In the simplest way, natural fuel like wood, coal, crude oil, petrol chemical among others are stored in piles at ware house, tanks at oil depots, pipeline at refinery because of the time dependence of the use of this energy did not correspond to the time of their availability but if demand and supply are relative the same honestly there is no need to stored energy.

Energy stored for usage are converted from one source to another, such as chemical energy stored in battery are converted to kinetic energy also wind-up clock stores potential energy in the spring tension and utilized it in days to days working operation, Storage systems such as pumped hydroelectric energy storage (PHES) have been in use since 1929 primarily to level the daily load on the network between night and day.(Connolly 2009) in all situation energy is either potential energy or kinetic energy and the sum of all the energies in a system is always constant

Energy storage system has been in operation for a very long time, firewood are store in the shed during rainy season to prevent the fire wood getting wet, it will be easy to set the fire but with the emerging technology there is great improvement through research and development as various new methods had been employed such as renewable energy which applies to wind and solar. Wind can generate energy for usage but the only limitation is that it does not blow throughout the whole day, it blows intermittently and with this unstable condition it need some form of storage mechanism to compensate for calm periods. Solar energy is also not constant, sun does not available on rainy and cloudy days including during the night time, this make it imperative to stored energy when it is available in abundant so that it can compensate for the loss of sunlight when needed for use (epoverviews.com)

Energy storage is as long as old fashion with the oldest form of energy storage was harvesting ice from lakes and rivers during winter period and stored them in well insulated warehouses. The ice were later sold during summer or used throughout the year for commercial and domestic purposes but today we use mechanical refrigeration for preserving food, cooling drinks, and air conditioning, Example of where ice storage are still using for cooling is at Hungarian Parliament Building in Budapest (energy.rochester.edu)

Energy storage technologies does not produce carbon emissions and does not rely on fossil fuels this make it an advantages, moreover energy storage system can manage power fluctuations from renewable resources. Energy storage mechanism can improve overall power quality and reliability of conventional power production, which is becoming more important for modern commercial applications.

Energy storage devices can reduce emissions by aiding the transition to newer, cleaner technologies such as renewable resources and the hydrogen economy this will definitely contribute to Kyoto obligations and penalties can be avoided

Energy Storage Plant Components

The major components parts that is required for any energy storage device is briefly explained below as every energy storage facility is comprised of three primary components:

1. Storage Medium

2. Power Conversion System (PCS)

3. Balance of Plant (BOP)

Storage Medium

Energy storage medium is the reservoir knows as accumulator for storage, this device retains the potential energy within the storage device. It ranges from mechanical (Pumped‐Hydroelectric Energy Storage), chemical (Battery Energy Storage) and electrical (Superconducting Magnetic Energy Storage) potential energy.

Power Conversion System (PCS)

Power conversion system is the medium use to convert energy from one level to another, it can convert from alternating current (AC) to direct current (DC) and vice versa as demand, for all storage devices except mechanical storage devices e.g. Pumped‐Hydroelectric and Compressed Air energy storage, a PCS is required that acts as a rectifier while the energy device is charged (AC to DC) and as an inverter when the device is discharged, also the PCS also conditions the power during conversion to ensure that no damage is done to the storage device. .(Connolly 2009)

Balance of Plant (BOP)

This comprise all the devices that are used to house the equipment, control the environment of the storage facility and provision of the connection between the power conversion system and the power source.(Connolly 2009)

Parameters of an Energy Storage Device

• Power Capacity: This is the maximum is output that an energy storage device can provide, it is usually measured in kilowatts or megawatts

• Energy Storage Capacity: This is the amount of electrical energy the device can store usually measured in kilowatt‐hours (Kwh) or megawatt‐hours (Mwh).

• Response Time: This is the length of time it takes the storage device to start releasing power.

• Round‐Trip Efficiency: This is the quantity of electricity which can be recovered as a percentage of the electricity used to charge and discharge the device.

• Efficiency: This is the quantity of energy which can be recovered as a percentage of the energy used to charge the device. .(Connolly 2009)

Method of Storing Energy

There are numbers of way of storing energy or preserving energy for future use. This method of storage varies from one source of energy to another; basically energy storage can be classified as mechanical, electrical, chemical, and thermal. Though this write up is not going to give comprehensive detail of available storage method, but for clarity we are going to list them in categories by categories in a bullet format for easy understanding:

Chemical Energy Storage

Hydrogen

Bio fuels

Batteries

Flow batteries

Electrical Energy Storage

Capacitor

Super capacitor

Superconducting magnetic energy storage (SMES)

Mechanical Energy Storage

Compressed air energy storage (CAES)

Flywheel energy storage

Hydraulic accumulator

Hydroelectric energy storage

Thermal Energy Storage

Ice Storage

Molten salt

Seasonal thermal store

Hot bricks

Parameters that determine Energy Storage Device

There are basic parameters that determine energy storage system, for easy understanding this parameter are briefly define below:

Power Capacity: This is the amount of power or maximum output that an energy storage device can provide, it is usually measured in kilowatts (kW) or megawatts (MW).

Efficiency: This is an indication of the quantity of energy that can be recovered as a percentage of the energy used to charge the device.

Response Time: This is the length of time it takes the storage device to start releasing power.

Energy Storage Capacity: This is the amount of energy the storage device can store; it is usually measured in kilowatt‐hours (KWH) or megawatt‐hours (MWH

Round‐Trip Efficiency: This is an indication of the quantity of energy which can be recovered as a percentage of the energy used to charge and discharge the device.(connelly2009)

Wind Energy Storage

Wind storage is method of storing wind energy when it is available in abundance for future use. Wind is not constant it is an intermittent energy sources which there supply by nature is unpredictable, so therefore it advisable to store it in time of their availability for later use when demand may exceed the ability to produce it. Wind energy is clean, renewable, and often rises to the top of the list when considering green energy alternatives.

Four types of wind energy storage methods are considered to be most practical or conducive to wind power. They are pumped hydro storage, compressed air storage, flywheel storage, and battery storage.

Pump Hydro Storage: This method make use of wind turbines which provide renewable energy that propel and pumps water to the upper reservoir, the wind energy is being converted to potential energy for later use, this method is similar to the utility practice of pumping water to an upper reservoir during off peak demand when electrical rates are lower and then releasing the water through a small hydro turbine to generate electricity during peak demand hours when the rates are higher (epoverviews.com)

Figure 1 Illustration of pumped hydro storage with the energy supplied by wind turbines

Source: Energy storage system, Ibrahim H. Et al 2007

Compressed air energy storage: This method uses wind energy to compress air to underground caverns or abandoned mines for the storage of wind energy. When there is increase energy demands, the compressed air is released into a gas turbine and mixed with natural gas to burn as fuel and this method generate electricity, it is advisable to consider a suitable geographic location that meet this parameter before embark on this type of storage method(epoverviews.com) example is in Texas USA.

Figure 2 Compressed Air Energy Storage (Compressor could operate from wind power)

Source: http://www.epoverviews.com/oca/Wind%20Energy%20Storage.pdf

Accessed 10/04/11

Advantages of Wind Energy

Wind energy is clean,

It is renewable,

It rises to the top of the list when considering green energy alternatives.

Limitation of Wind Energy

Wind energy is not consistent

It is not reliable to depend upon as wind is intermittent.

Chemical Storage

Chemical storage is way of storing energy through chemical process, it is achieved through accumulators. it store and release out electricity by alternating the charge and discharge phases. They transform chemical energy generated by electrochemical reactions into electrical energy and vice versa. The process is found suitable as it does not generate harmful emission

Chemical storage also involved chemical reaction such as changing the arrangement of atom in the molecules to generate energy, energy are used to break the bond between atom while new bond will also be formed to releases out energy. Chemical reaction that absorb in energy is known as Endo thermal reaction while chemical reaction that release out energy is called exothermal reaction. Fossil fuel and biomass are form of such energy storage

Hydrogen

This method involves electricity to split water into hydrogen and oxygen through a process known as electrolyse. The hydrogen produce is converted back to electricity so that when electricity is needed the hydrogen can be used to generate current through a hydrogen-powered combustion engine or fuel cell

The hydrogen produce can be store and transported to the appropriate place that is required for use.

Hydrogen storage are used for load-levelling or power quality applications, it acts as a link between the three main sectors of energy system, which are electricity, heat and transport sectors. It is the only energy storage system that allows this level of interaction between these sectors, it is a very good option for integrating large quantities of intermittent wind energy.(Connolly 2009).

Advantages of Hydrogen Storage System

Hydrogen production by electrolysis is very clean, their process and uses does not generate pollution, so is environmental friendly moreover electrolysis has become the most suitable technique for hydrogen production.(Connolly 2009)

Limitation of Hydrogen Storage System

Hydrogen energy storage is still under way and it application is not attractive for commercial purposes. Hydrogen is difficult to store for long period of time and producing hydrogen from fossil fuels is not favourable as it is four times more expensive than using the fuel itself, while reacting steam with methane produces pollution (Connolly 2009)

Electro Chemical Storage

Battery

Battery store energy chemically and converted the chemical energy to direct current at the required location that demand it. The basic electrochemical unit of the battery is the cells that store the energy, battery consists of one or more of these cells that are connected in parallel or series or mixture of both depending on the desired output voltage. The system is easy and quick to set up and batteries are now the popular demand choice for portable electronic devices and as the power supply in automotive vehicles.(Trend 2010)

Lead Acid (LA) battery

Lead acid battery is the most common energy storage device in use at present. Its success is due to its maturity relatively low cost, long lifespan, fast response, and low self discharge rate. It is made up chemical solution that contain 35% sulphuric acid and 65% water, the solution is known as electrolyte which cause the chemical reaction that produce the electron, when it is charge it stored energy and converted the energy to produce current for use. The advantages of the batteries is that it can be used for both short‐term and long‐term applications (Connolly 2009) The power and energy capacities of lead‐acid batteries are based on the size and geometry of the electrodes which implies that the capacity of the battery can be increased by increasing the surface area for each electrode and number of cell

Figure 3 Lead Acid Battery

Rechargeable batteries

Rechargeable batteries store electricity as chemical energy. It is used for load levelling in grid energy storage, as they store electricity during and off peak and used it during the peak period. The popular types include sodium‐sulphur (NaS) batteries and flow batteries. Their lives span is in the range of 10 to 15 years, this is shorter than those of PHS and CAES.

For large‐scale storage batteries usually cost more than an order of magnitude more than PHS on the basis of per recharge cycle and many times higher applications and rechargeable NiMH and Li-ion dominating in high-value applications such as digital cameras, mobile phones, laptop computers and handheld devices

Advantages of Battery

It provide high efficiency,

Relatively compact size,

It easy to transport and use in various location

Limitation

The main constraint is their high cost

Battery often suffer from memory effect

Figure 4 Technology roadmap: selected Battery energy storage

Source: Technology roadmap: selected Battery energy storage materials(Trend 2010)

Figure 5 Applications of energy storage materials

Applications of energy storage materials(Trend 2010)

Electrical Energy Storage

Electrical energy storage uses forms of energy such as chemical, kinetic or potential energy to store energy, the stored energy will later be converted to electricity for usage in different location. Electrical storage system will solve the problem of variability in power flow, as electricity are store during the off peak for compensation during peak period. It can store renewable energy so that renewable generation can be scheduled to provide specific amounts of power, this will decrease the cost of integrating renewable power with the electricity grid.( pewclimate.org)

Capacitor

A capacitor is a device for storing electric charge, it is a passive electronic component made of a two conductors and separated from each other by an insulator. When potential difference passes across the conductors, a static electric field develops in the insulator known as dielectric, the capacitor charge up and stores this energy. When the power is disconnected from the circuit, the energy stored will be slowly release out. If resistor is employed in the circuit, this allow the capacitor to charge more slowly and at the same time discharge slowly

A capacitor will store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. They are mostly used in electronic devices to maintain power supply while batteries are being changed to prevent loss of information in volatile memory. (pewclimate.org)

Figure 6 Capacitor

Super capacitors

The energy storage in super capacitors is done in the form of an electric field between the two electrodes. They possessed the same characteristics with electrochemical batteries and capacitors with the exception that the dielectric is replaced by electrolyte ionic conductor in which ion movement is made along a conducting electrode.

The ultra capacitor stores energy by increasing the electric charge accumulation on the metal plates and discharges energy when the electric charges are released by the metal plates. They are capable of discharging up to 95% of the total stored energy, as opposed to batteries. They are very suitable for the continuous operation with a great number of complete charge and discharge cycles.

Ultra capacitors are used to improve quality of power as they can provide short bursts of energy under a second and store energy for a few minutes, they act as a backup power source.(Trend 2010)

Figure 7 Super capacitor

Superconducting Magnetic Energy Storage (SMES)

SMES consists of a coil with many windings of super conducting wire that stores and releases energy with increases or decreases in the current flowing through them, the stored energy is in the magnetic field produce by the direct current flowing through the superconducting coil which has been extremely cooled to a temperature below its superconducting critical temperature, despite the fact that SMES device has no moving parts but it must be refrigerated to maintain the superconducting properties of the wire materials. SMES are used to improve power quality because they provide short bursts of energy under a second and store energy for a few minutes(Techbook 2009)

Figure 8 Superconducting Magnetic Energy Storage

Superconducting Magnetic Energy Storage (SMES)

Applications: SMES is ideal for the industrial power quality market due to their ability to protects equipment from rapid momentary voltage sags and it can also stabilises fluctuations within the entire network caused by sudden changes in consumer demand levels, lightening strikes or operation switches.

Limitation: SMES has sensitivity to temperature change, the coil must be maintained at an extremely low temperature in order to store energy, moreover refrigeration can cause problem of losses within the system.

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Large-scale storage systems will provide the ability to use low-cost power during peak demand periods of the day, thus reducing the need for high cost plants to cycle on and off .By removing the bottlenecks within the transmission system, these facilities will also reduce power transmission losses and improve the quality and reliability of delivered power

Figure 9 Load Profile of Large Scale Enegy Storage

Source: http://www.energystoragecouncil.org/ESC%20White%20Paper%20.pdf

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Mechanical Storage

Pumped hydro storage (PHS)

Pumped hydro storage uses electricity to pump water from a lower-level reservoir to a higher elevation reservoir during of peak period and this water is released at times peak of demand to generate current. The water is release from the top elevation reservoir to operate hydroelectric generator which turned the turbines to generate electricity, it is similar to conventional hydropower plants. Pumped hydro storage is suitable for load-levelling because it can be constructed at large capacities of 100-1000s of megawatts and discharged over long periods of time(Techbook 2009)

Pump hydro storage can be design and build in many ways; the lower reservoirs can be lakes, rivers, underground caverns, or oceans while the upper reservoirs can be any higher elevated geological formation capable of storing significant amount of water

PHS is available at almost any scale with discharge times ranging from several hours to a few days. It is widely employed to generate power during peak period for commercial operations at hundreds of locations worldwide The round‐trip efficiencies of Pump hydro storage are in the range of 60% to 85%(ebookbrowse.com)

Pumped Hydroelectric Energy Storage (PHES)

Pumped hydroelectric energy storage is the most mature and largest storage technique use as of today. It consists of two large reservoirs located at different elevations, one is at the lower place such as dam the second on higher elevation to be able to provide gravitational fall to the water to drive the turbines that at lower elevation .At peak hours, the water is released to flow to a lower reservoir, and the water flow drives turbines to generate electricity. (ebookbrowse.com)

The operating system of pump hydroelectric energy system during production is similarly to a conventional hydroelectric system. and a typical PHES facility has 300 m of hydraulic head (the vertical distance between the upper and lower reservoir). The power capacity (kW) is a function of the flow rate and the hydraulic head, whilst the energy stored (kWh) is a function of the reservoir volume and hydraulic head. (Connolly 2009)

Figure 10 Pumped‐Hydroelectric Energy Storage Layout

Compressed air energy storage (CAES)

Compressed‐air energy storage uses off‐peak electricity to compress air into an underground air storage vessel such as caverns or old mines. At peak hours, the pressurized air is fed into a gas‐fired turbine to generate electricity. CAES is not widely used, currently there are only two operating CAES systems in the world. The first commercial CAES was built in Germany in 1978 and the second was built in the United States in 1991. (ebookbrowse.com)

Figure 11 Compressed Air Energy Storage facility

Fly wheel

Flywheels store energy by accelerating the rotor to a very high speed and keep the stored energy in the system as kinetic energy. It later releases the stored energy by reversing the charging process so that the motor is then used as a generator. As the flywheel discharges, the rotor slows down until eventually coming to a complete stop

The amount of stored energy is dependent on the speed, the mass and the configuration of the flywheel. It is used as short-term energy storage devices for propulsion applications such as engines or large road vehicles Flywheel can be used for power quality applications since they are free from memory effects and are capable of very frequent recharges.

Figure 12 Flywheel Energy Storage device

The amount of energy that the flywheel is capable of storing is decided by the rotor while power storage is in direct relation to the mass of the rotor and to the square of its surface speed(Connolly 2009). The most efficient way to store energy in a flywheel is to make it spin faster rather than making it heavier. The energy density within a flywheel is defined as the energy per unit mass:

Where:

E KINETIC = total kinetic energy in Joules (J)

mf = mass of the flywheel in kg

v CIRCULAR = the circular velocity of the flywheel in m/s2

σ = the specific strength of the material in Nm/kg

ρ = density of the material in kg/m3

Thermal Storage

This is a method of storing thermal energy in reservoir either as low temperature or high temperature during the period of their availability for future use. Temperature is the determine factors for this type of storage, as it can be a storage of heat to maintain materials at high temperature or storage of ice for preservation of food at low temperature, mostly they are used to compensate energy demand at specific period of time that is not available.

The method of thermal energy storage comprise of three models, which are as follows:

Sensible Heat Storage

This occurs when heating a liquid or solid without changing phase. The amount of energy stored in this type of energy storage system depend on the change in temperature of the materials

Figure 13 Illustration of the Themis station in France

Source: Energy Storage System, Ibrahim H et al 2007

Latent Heat Storage

This method uses the liquid-solid transition of a material at constant temperature. During accumulation, the bulk material will shift from the solid state to liquid and return back to solid during retrieval process. The heat transfers between the thermal accumulator and the environment are made through a heat-transfer fluid. This occur when the heating of the materials undergoes phase transformations such as melting of ice, The amount of energy stored depend on the mass of the materials and latent heat of the materials this type of storage system operate isothermally

Bond Heat Storage

This method involve using heat to produce chemical reaction of a product and store the product which can absorb or release energy through the bond reaction, it involves an endothermic reversible reaction, which can be reversed when required to release heat.

Ice storage

Ice is one of traditional method of cooling, Ice are store during winter or harvested from river or lake in the early nineteenth century for cooling purposes during the summer and for food preservation., ice are placed in air ducts to cool and dehumidify warm air with the aid of fan example of this type of storage can be found in the Hungarian Parliament building, where harvested ice are still using to dehumidify air or cooling during the summer after more than a century of service.(energy.rochester.edu)

Applications of Energy Storage System and Appropriate Technology use

Energy storage are used for supplement during the period of shortage or failure of desired energy, it have a wide varieties of purposes, there application depend on the area of demand, capacity that can be release out at a time and duration of time to last. The below table make the analysis of their application and technology that are involved

Figure 14 Applications of Energy Storage System and Appropriate Technology use

Sources: http://prod.sandia.gov/techlib/access-control.cgi/2001/010765.pdf

Source: http://prod.sandia.gov/techlib/access-control.cgi/2001/010765.pdf

Figure 15 Benefit of Energy Storage

Conclusion

Energy storage is a very useful method that cannot be under estimated, without energy storage, life will be difficult as there will be many problems to rise up in many systems, this can led to total collapsed. They are use to balance demand and supply of energy especially during the emergency period that is very critical and compulsory. It is an important enabling technology for energy management and utilisation

It improves performance of energy systems by smoothing supply and increasing their reliability. It improve the performance of a power generating plant by load levelling Some of the renewable energy sources can only provide energy intermittently, thus storing them will always make them available for use. It enhances security of the grid by incorporating storage capacity into a smart grid will surely improve the quality and reliability of the grid

It may be cheaper to build energy storage facilities than to upgrade the power lines. Treating storage technologies as comparable to the expansion of traditional transmission facilities would increase the market penetration of storage technologies

Energy storage technologies does not produce carbon emissions and it does not rely on imported fossil fuels, this aid the transition to newer, cleaner technologies such as renewable resources. Therefore, Kyoto obligations can be met and penalties be avoided

In addition, Flywheels are a good match for a range of short term applications up to a size of several MW and Batteries have the broadest overall range of applications. Hydrogen fuelled combustion engines are a currently available technology for short-term

Compressed air energy storage and pumped hydro are best for load management when geology is available and response time in the order of minutes is acceptable

Refrences

http://www.energy.rochester.edu/storage/

http://www.energystoragecouncil.org/ESC%20White%20Paper%20.pdf

http://ebookbrowse.com/energy-storage-pdf-d38488725

http://www.answers.com/topic/energy-storage

http://www.epoverviews.com/oca/Wind%20Energy%20Storage.pdf

http://www.pewclimate.org/docUploads/Energy-Storage-Fact-Sheet.pdf

Connolly, D. (2009). “A Review of Energy Storage Technologies

For the integration of fluctuating renewable energy.”

Techbook, C. (2009). “Electric energy storage.”

Trend, G. (2010). “ENERGY STORAGE MATERIALS (BACKGROUND.”