ENERGY STORAGE APPLICATIONS USING DIFFERENT BATTERY TECHNOLOGIES FOR RENEWABLE ENERGY MICROGRID (SOLAR AND WIND ETC)
* B.P. Bhangale 1, P.A.Patil 2 1
Department of Physics, A.S.C College Ozar Mig Tal Niphad ,Dist.Nasik India. 2 A.O.H Consultant , Pune , India. *e-mail :
[email protected] Telephone : +91 9765580576
ABSTRACT: Energy Storage can supply more flexibility and balancing to the grid, providing a back-up to intermittent renewable energy such as solar and wind. By this way, it can improve the market introduction of renewables, accelerate the decarbonisation of the electricity grid, improve the security and efficiency of electricity transmission and distribution, stabilize market prices for electricity, while also ensuring a reliable energy supply. Different materials are tried over time to develop storage battery chemistry to yield High capacity(AmpHour) to less weight & size , cost etc. The technologies for different applications will be different such as Electrical Vehicle compare to Standard non movable storage battery. In flow battery electrodes are separated in reactor and electrolyte is stored in separate tank and flows from charged tank to discharge tank and vice versa. In supercapacitor energy is stored in the form of charge in dielectric. Energy storage can balance the fluctuations in grid supply to give reliable power. For short duration requirement battery storage can bring about frequency control and stability and for longer duration requirement , energy storage brings about energy management and backup energy. In dull period of grid , batteries get charged from primary generation and can produce energy in peak period of demand.
KEYWORDS: Battery chemistry , flow , electrolyte , micro grid , charger .
1. INTRODUCTION: The use of electricity increasing with enhancement in lifestyles , industrialization across the world and need for electrical energy demand from clean energy sources such solar and wind and another renewable energy sources compared to conventional fossil fuel like coal , natural gas or oil,diesel based generators1. The renewable resources (wind and solar ) are not stable source of energy and solar PV system varies with day time and wind generation time to time and seasonal basis 2. The peak time demand of electricity can be provided by electrical storage in to batteries or capacitors by charging them in no demand /less demand time and delivering the stored power in peak time3. To design systems for power utilities require through knowledge and
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understanding of Power Electronics ( Maximum Power Point Tracking Circuit ,Battery Charger, Inverter etc) and battery chemistry , electrode materials , electrolytes , enclosure design and Health and safety concerns to handle chemicals materials used in battery technology4. In following Fig.1 Generation profile ( dotted black line)
Fig.1 Without storage and red line with storage is shown. The renewable energy sources along with conventional generators are in system. The main demand starts from 6 a.m and ends around 9.30p.m.Pea k demand is at 5p.m to 7 p.m Without storage we need to install peak demand generator though it is used for few hours ( less than 2 hours at full capacity). If Eelectrical Storage System ( ESS) is used , the ESS is charged during low demand period ( meshed red lines from wind energy + generator) and deliver peak power to grid in blue region of peak load. The solid red line is generation profile with ESS , solar and wind. The ESS can bring reduction in OPEX and CAPEX expenditure used on Generation resources in the DISCOMS( Utility Boards in India). Harnessing with Solar PV and Wind turbine Generators , the generation can follow the peak load demand and utilization of generated energy during low demand for charging resource like ESS thus loading and stabilizing grid during low demand period.6 The power quality inside the grid system is maintained due to tracking of generated power and loads by ESS system. Reactive power also can be supplied by ESS inside the grid on demand 9. There are other energy storage technologies other than batteries such as [a] Pumped Hydro storage : Upper and Lower Dams with height difference for converting potential energy of water to electrical energy [b]Compressed air energy storage (CAES) [c] Flywheel : Mechanical energy storage for very small time [d] Superconducting magnetic storage of energy : Not commercialized yet. [e] Super capacitors : High value capacitors : mainly useful in Transport and Welding application [f] Hydrogen Fuel Cells. Compared with these technologies ESS -Batteries with different types of technologies are now commercial feasible due to High density of storage of energy , Handling in Portable and Static application , easy interface with Power
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electronics to Grid system for purpose like stabilization of Grid , momentary backup and reactive power sourcing etc.8 For Battery technology for energy storage , lots of research and innovations are taking place all over the world due to replacement of Petrol , coal , disel etc for Transport industry for realizing electrical vehicle system by companies such as Tesla , Google . Back up of electrical energy storage for longer time and compensating wind and solar PV energy for peak and low demand energy utilization curve , improvement of power quality etc. The battery chemistries or technologies are summarized below and most commercial available Li-ion storage battery technology is selected for simulation in HOMER software for Hybrid ESS system in this research work of paper.
2. MATERIALS AND METHODS: PROCEDURE : Existing commercial battery technologies are studied with their pros and corns by studying their operation , complexity in designing Electrical storage system and cost benefits and Human and Operation and safety consideration. Battery Technologies The most common commercially available the only battery technology that was economically feasible is the lead acid battery. Improved valve regulated lead-acid (VRLA) batteries are now emerging in utility systems. Advanced batteries (such as lithium ion and zinc/bromide ,Sodium sulphide) are being developed and are at different levels of size and readiness for utility operation. Following are the different types of battery available in the market. 1. Lead-Acid Battery : Lead acid batteries are relatively economical but they requires more space and operation and maintenance .The life of lead acid batteries is too short to be used in ESS and more over deteriorate if discharged below 30% or less and temperature. And replacement cost is higher. Below 5 degree centigrade the performanace is not guaranteed and hence can not be used in cold climate without heaters. They are commonly installed in uninterruptible power supply (UPS) systems as well as in renewable and distributed power systems. They have several key limitations: (i) they require relatively frequent maintenance to replace water lost in operation, (ii) They are relatively expensive compared to conventional options with limited reduction in cost expected, and (iii) Due to lead content , they are heavy, reducing their portability and increasing construction costs. In some part of world lead is banned .(iv) For maintaining Sulphuric acid density measurement is required and distilled water level maintained. This creates Human safety problem. 2. Valve Regulated Lead Acid Battery (VRLA) : VRLA is enhancement in Lead Acid basic electrochemical technology.Thease batteries are closed type with pressure regulating valve and nearly sealed type batteries and eliminate electrolyte to evaporate faster thus increasing life span and reducing operation and maintenance drastically. The released hydrogen through valve recombines with air oxygen. The major advantages of VRLAs over normal lead-acid cells are: a) the dramatic reduction in the maintenance that is necessary to keep the battery in operation, and b) the battery cells can be packaged more tightly because of the sealed construction and immobilized electrolyte ,reducing the footprint and weight of the battery. The disadvantages of VRLAs are that they are less robust than flooded lead-acid batteries, and they are more costly and shorter-lived. VRLAs are perceived as being maintenance free and safe and have become popular for standby power supplies in telecommunications applications and for uninterruptible power supplies in situations where special rooms cannot be set aside for the batteries. And more friendly in automobile Industry for application purpose in two wheeler market. 3. Lithium ion Battery (Li-Ion) : The main advantages of Li-ion batteries, compared to other advanced batteries , are: (a) High energy density (300 - 400kWh/m3, 130 kWh/ton) (b) High efficiency (near 100%) (c)Long cycle life (3,000 cycles @ 80% depth of discharge).The cathode in these batteries is a lithiated metal oxide (LiCoO2, LiMO2, etc.) and the anode is made of graphitic carbon with a layer structure. The electrolyte is made up of lithium salts (such as LiPF6) dissolved in organic carbonates. When the battery is being charged, the Lithium atoms in the cathode become ions and migrate through the electrolyte toward the carbon anode where
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the combine with external electrons and are deposited between carbon layers as lithium atoms. This process is reversed during discharge. While Li-ion batteries took over 50% of small portable market in a few years, there are some challenges for making large-scale Li-ion batteries. The main hurdle is the high cost (above $600/kWh) due to special packaging and internal overcharge protection circuits. Several companies ( Samsung , LG and many china based ) are working to reduce the manufacturing cost of Li-ion batteries to capture large energy markets. 4. Vanadium Redox Flow Battery (VRB) : VRB stores energy by employing vanadium redox couples (V2+/V3+ in the negative and V4+/V5+ in the positive half cells). These are stored in mild sulfuric acid solutions (electrolytes). During the charge/ discharge cycles, H+ ions are exchanged between the two electrolyte tanks through the hydrogen-ion permeable polymer membrane. The cell voltage is 1.4-1.6 volts. The net efficiency of this battery can be as high as 85%. Like other flow batteries, the power and energy ratings of VRB are independent of each other. VRB was pioneered in the Australian University of New South Wales (UNSW) in early 1980's. VRB storages up to 500kW, 10 hrs (5MWh) have been installed in Japan by SEI. VRBs have also been applied for power quality applications (3MW, 1.5 sec., SEI). There are new innovation in startup companies by trying different materials for electrolyte , separation diaphragm ( nano technology material ) . The advantage of this technology is charged electrolyte/discharged electrolyte is stored in tanks and size of tank defines the capacity of battery. Larger the size of tank larger will be capacity. The gases emitted during the charging / discharging caused accidents in development and hindered commercial scale development. 5. Zinc Bromine Flow Battery (ZnBr) : In each cell of a ZnBr battery, two different electrolytes flow past carbon-plastic composite electrodes in two compartments separated by a micro porous polyolefin membrane. During discharge, Zn and Br combine into zinc bromide, generating 1.8 volts across each cell. This will increase the Zn2+ and Brion density in both electrolyte tanks. During charge, metallic zinc will be deposited (plated) as a thin film on one side of the carbon-plastic composite electrode. Meanwhile, bromine evolves as a dilute solution on the other side of the membrane ,reacting with other agents (organic amines) to make thick bromine oil that sinks down to the bottom of the electrolytic tank. It is allowed to mix with the rest of the electrolyte during discharge. The net efficiency of this battery is about 75%. The ZnBr battery was developed by Exxon in the early 1970's. Over the years, many multi-kWh ZnBr batteries have been built and tested. 6. Sodium Sulfur Battery (NaS) : A NaS battery consists of liquid (molten) sulfur at the positive electrode and liquid (molten) sodium at the negative electrode as active materials separated by a solid beta alumina ceramic electrolyte. The electrolyte allows only the positive sodium ions to go through it and combine with the sulfur to form sodium polysulfides. During discharge, as positive Na+ ions flow through the electrolyte and electrons flow in the external circuit of the battery producing about 2 volts. This process is reversible as charging causes sodium polysulfides to release the positive sodium ions back through the electrolyte to recombine as elemental sodium. The battery is kept at about 300 degrees C to allow this process. NaS battery cells are efficient (about 89%) and have a pulse power capability over six times their continuous rating (for 30 seconds). This attribute enables the NaS battery to be economically used in combined power quality and peak shaving applications. NaS battery technology has been demonstrated at over 30 sites in Japan totaling more than 20 MW with stored energy suitable for 8 hours daily peak shaving. The largest NaS installation is a 6MW, 8h unit for Tokyo Electric Power company. 7. Metal-Air Battery : Metal-air batteries are the most compact and, potentially, the least expensive batteries available. They are also environmentally friendly . The main disadvantage, however, is that electrical recharging of these batteries is very difficult and inefficient. Although many manufacturers offer refuellable units where the consumed metal is mechanically replaced and processed separately, not many developers offer an electrically rechargeable battery. Rechargeable metal air batteries that are under development have a life of only a few hundred cycles and efficiency about 50%. The anodes in these batteries are commonly available metals with high energy density like aluminum or zinc that release electrons when oxidized. The cathodes or air electrodes are often made of a porous carbon structure or a metal mesh covered with proper catalysts. The electrolytes are often a good OH- ion conductor such as KOH. The electrolyte may be in liquid form or a solid polymer membrane saturated with KOH. While the high energy density and low cost of metal-air batteries may make them ideal for many primary battery applications, the electrical rechargeability feature of these batteries needs to be developed further before they can compete with other rechargeable battery technologies.
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Table : 1 : Battery Technologies and commercial Units in Electric Utilities ( Boards) Battery Type Largest Capacity Location & Comments application Lead Acid ( Flooded type)
10 MW
California USA
Efficiency 72-78%
,Frequent
maintenance
for
water loss
Lead Acid VRLA
300 KW
L.A USA
Efficiency 72-78% , Robust , safe for operation, Replacement req.
Nickel - Cadmium
27 MW
GVEA Alaska
Efficiency 75-80% , Temp range -40 to 50Deg Cent. Poisonous
,Replacement required after 2000 cycles of charge/discharge
and Heavy , 3500 cycles for replacement ,VAR compensation L-Ion
500 MW
Australia
World largest Year 2017 , Data Not avilable
Vanadium Redox
1.5 MW
Japan
Efficiency 85% , 10000 Cycles , self discharge negligible
Zink Bromide
1 MW
Kyushu Japan
Efficiency 75 % ,Bulkey , self discharge , hazardous
Metal Air
No commercial application
-
Efficiency 50% , Recharging difficult
Regenerative Fuel Cell
15MW
U.K
Efficiency 75% , negligible self discharge
ELECTRICAL STORAGE SYSTEM DESIGN : Considering all available technologies Li-Ion Battery technology is selected for design of ESS. With following System Architecture and Simulated in HOMER software ( www.homerenergy.com) and final result will be discussed . About HOMER Simulation Software : The HOMER Pro® microgrid software by HOMER Energy is the global standard for optimizing microgrid design in all sectors, from Rural village power and Island utilities to grid-connected renewable power sources. Originally developed at the National Renewable Energy Laboratory, and enhanced and distributed by HOMER Energy, HOMER (Hybrid Optimization Model for Multiple Energy Resources) nests three powerful tools in one software product, so that engineering and economics work side by side. HOMER software has technical and commercial huge database online from many system component manufacturer . The user inputs are evaluated for optimized combination of these components along with Investment economics such as IRR , Interest rates , Capital cost , operational cost , replacement cost over life time of project , generation kw/h AND Renewable energy input such as Temperature , average solar radiation , average wind speed ( Profile from Datalogger) AND Load profile , utilization of electrical energy in connected load and hourly usage etc. The output is in the form of economics such as Total net present cost , Levelized cost of energy for project life , Annualized cost , cash flows and technical statistics for each system component . Due to size limitations one project details are partially shared below… File Author : Bharati Bhangale Location : ( 180 31.2’N , 730 51.4’E) , Pune Renewable Power Source : Solar Panels 1,879 KW Storage ( Generic 100KWh , Li-Ion ) : 41 strings Dispatch Strategy : Homer Cycle charging
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System Architecture :
RPS : Renewable energy Power Source such as solar/Wind AC : Alternating Current Bus Electric Load #1 … Total A.C Electric Load Conv : Bidirectional converter (AC to DC for charging batteries And DC to AC for feeding stored power to A.C bus ) DC : Direct Current Bus 100Li : 100KW Li Ion battery pack
3. Simulation Results and Interpretation : Net Present Cost :
The net present cost (or life-cycle cost) of a Component is the present value of all the costs of installing and operating the Component over the project lifetime, minus the present value of all the revenues that it earns over the project lifetime. HOMER calculates the net present cost of each Component in the system, and of the system as whole
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The salvage value is shown as negative , the asset value at the time of salvage / disposal.
Energy Out = (Energy In + Storage Deplation ) – Losses Storage depletion happen due to internal resistance caused due to chemical process inside the battery.
From above graph the solar generation is from sun rise to sun set during the day and at peak during 12 to 2pm. For Battery Charging : Day time 7.30 am to 5.30 p.m
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The storage battery retains between 80 % to 100% charge , but during rainy season lack of charging shows during days 150 (June ) to 240(sept.) .
4. CONCLUSION : a. The Total Net Present cost of this project is $ 43,89,039.00 considering the project life of 25 Years b. Operation cost per year $ 1,21,464.00 and replacement of parts after 13.5 Years $6,04,131.00 and salvage value of project assets at the end is $50,744. c. Due to storage battery reliable un interruptible power supply for load profile considering peak demands realized. d. The levelized cost of Energy ($/KWh ) is $ 0.414 approximately Rs.26/- per unit. The major cost of component is storage media Li-Ion batteries. This cost is still high compared to Maximum demand prize of power electricity board Rs.11/- per unit. And with diesel generator price of Rs.13/- per unit. e. The Cost of replacement in case of Lead Acid battery are 8 times where as Li-Ion battery are 1 time in life time of 25 years of project.
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