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Decentralized Polygeneration Energy System Energy Storage Requirements & Challenges Cover page

Frida Nilsson Josefin Rosén

1 Bachelor of Science Thesis KTH School of Industrial Engineering and Management Energy Technology EGI-2016 SE-100 44 STOCKHOLM

Bachelor of Science Thesis EGI-2016 Decentralized Polygeneration Energy System

Frida Nilsson Josefin Rosén Approved

Examiner

Supervisor

Dr. Anders Malmquist

Sara Ghaem Sigarchian

Commissioner

Contact person

Abstract Due to the recent development of small-scale energy technologies, the energy industry is changing from a centralized to a more decentralized energy system. And because of the current problems with limited energy sources it is now important to focus on renewable energy sources and how to store the energy for later use. One solution is polygeneration system. A Polygeneration energy system is a system that combines heat, cold and power generation. Therefor it is a flexible system that can easily be modified depending on the size of the system, its application, the demands and other requirements. This project focuses on mapping different types of energy storage and the important parameters in each method. Initially the different concepts of energy storing will be described thoroughly so the reader gets an overview of the different storing methods. Thereafter the report maps the different methods and how developed they are via TRL (Technology Readiness Level). To achieve a greater knowledge of how a polygeneration systems is built and optimized, , an optimization tool can be used. One of these programs is HOMER. HOMER will be used in this project to create a wider comprehension about optimization and effects of energy storage in a polygeneration system. By using different data, the program can calculate the profit, from an economic and a geographical perspective. The demarcation has been selected by choosing a geographical area and what sorts of resources that are available in relation to it. Since the main purpose with the report consists of defining ways to store energy, the focus will be on the different battery types that exist today. A comparison between three different types of batteries will be done and further on what results they will show. The optimization in HOMER showed that it is possible to build a decentralized polygeneration system on the chosen location, Sagar Island. The system combines different renewable energy resources such as, solar and wind together with a generator, converter and batteries to create a sustainable system. The results showed a high investment cost for the energy system in all cases, despite the use of different battery types. However, the investment is profitable for the population on Sagar Island to have access to electricity and what future benefits that may provide.

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Bachelor of Science Thesis EGI-2016 Decentralized Polygeneration Energy System

Frida Nilsson Josefin Rosén Approved

Examiner

Supervisor

Dr. Anders Malmquist

Sara Ghaem Sigarchian

Commissioner

Contact person

Sammanfattning På grund av den senaste utveckling av småskaliga energisystem, där energiindustrin går från ett centrerat till ett mer decentraliserat system och bristerna som finns i samband med energikällor, är därför nu viktigt att fokusera på förnybara energikällor och hur denna energi kan lagras. En lösning till detta är polygenerationsystem. Ett polygenerationsystem bygger på ett system som kombinerar värme, kylning och effektutveckling. Därigenom är det ett flexibelt system som kan modifieras beroende på systemets storlek, efterfrågan och krav. Denna rapport fokuserar på att kartlägga olika typer av energilagring och deras viktiga parametrar. Inledningsvis beskrivs de olika energilagringskoncepten grundligt sådan att läsaren får en överblick av de olika lagringsmetoderna. Därefter kartlägger rapporten de olika metoderna samt hur utvecklade de är genom TRL (Technology Readiness Level). För att få en bättre översikt över hur ett polygenerationsystem är uppbyggt samt dess funktion kan ett optimeringsprogram användas. Ett av dessa program är HOMER. HOMER kommer att användas i denna undersökning för att skapa en bredare förståelse över hur man kan optimera ett polygenerationsystem. Med hjälp av olika indata kan programmet räkna ut systemets vinst, bland annat utifrån ett ekonomiskt samt geografiskt perspektiv. Avgränsningen har valts genom att välja ett geografiskt område samt vilka resurser som finns tillgängliga i anknytning till detta. Eftersom huvudsyftet med rapporten handlar om de olika lagringsmetoderna kommer fokus främst ligga på batterierna, där en jämförelse mellan tre olika batterityper görs och vilka resultat de medför. Optimeringen i HOMER visade att det är möjligt att konstruera ett decentraliserat polygeneration system på den valda platsen, Sagar Island. Systemet kombinerar olika förnybara energikällor så som, sol och vind tillsammans med en generator, omvandlare och batterier för att skapa ett hållbart system. Resultatet visade en hög investeringskostnad för energisystemet i alla fallen, trots användandet av olika batterityper. Emellertid är investeringen lönsam för populationen på Sagar Island att få tillgång till elektricitet och de framtida fördelar som det kan medföra.

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Table of Contents Cover page ............................................................................................................................ 1 Abstract ................................................................................................................................. 2 Sammanfattning ................................................................................................................... 3 List of Tables ........................................................................................................................ 5 List of Figures ....................................................................................................................... 5 List of Equations .................................................................................................................. 5 Nomenclature ....................................................................................................................... 6 Abbreviations ........................................................................................................................ 7 1.

Introduction .................................................................................................................. 9 1.1 Energy Storage (ES) ................................................................................................................ 11 1.2 Energy Demand ...................................................................................................................... 11

2.

Objectives and Limitations ......................................................................................... 13 2.1 Objectives ............................................................................................................................... 13 2.2 Thesis Learning Objectives ................................................................................................... 13 2.3 Limitations ............................................................................................................................. 13

Polygeneration energy system – A General Overview........................................................ 14 3.

Technology ................................................................................................................. 15 3.1 Thermal Energy Storage ........................................................................................................ 15 3.1.1 Sensible Heat ............................................................................................................................................15 3.1.2 Latent Heat ...............................................................................................................................................17 3.1.3 Thermo-Chemical Heat Storage (THS) ...............................................................................................17 3.2 Electricity Storage .................................................................................................................. 18 3.2.1 Electricity Storage- Mechanical .............................................................................................................18 3.2.2 Electricity Storage- Electrochemical.....................................................................................................20 3.2.3 Electricity Storage – Electrical...............................................................................................................23 3.3 Hydrogen Storage .................................................................................................................. 25

4.

Methodology ............................................................................................................... 27 4.1 Technology Readiness Level (TRL) ...................................................................................... 27 4.2 HOMER Energy – An analyse of a polygeneration system .................................................. 28 Sagar Island ................................................................................................................................. 29 Modelling in HOMER ................................................................................................................ 29

5.

Simulation results and discussion .............................................................................. 32 Table of comparison .................................................................................................................... 35 Sensitivity Analysis ...................................................................................................................... 36

6.

Conclusions and Future Work .................................................................................... 38

References........................................................................................................................... 39 Appendix ............................................................................................................................. 42

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List of Tables Table 1: Nomenclature ................................................................................................................................. 6 Table 2: Abbreviations ................................................................................................................................. 7 Table 3: Intensium Smart........................................................................................................................... 22 Table 4: Input data for the modelling system. ........................................................................................ 31 Table 5: Input data for different batteries. .............................................................................................. 31 Table 6: The result of modelling with vanadium battery. ..................................................................... 32 Table 7: The result of modelling with lead acid battery. ....................................................................... 32 Table 8: The result of modelling with Lithium-ion battery. ................................................................ 33 Table 9: Share of produced electricity in the different cases................................................................ 34 Table 10: Comparison of energy per year in the three cases.................................................................35 Table 11: Comparison table with different fuel prices..........................................................................37 Table 12: Table of different electrical storage and their characteristics..............................................42 Table 13: Table of different thermal storage and their characteristics................................................43

List of Figures Figure 1: World energy consumption by source during the last 200 years.) ........................................ 9 Figure 2: World energy consumption per capita, by region for 2012, kWh/capita .......................... 10 Figure 3: Hourly data on the electric load during a full week, showing the possible use of a storage system............................................................................................................................................................ 11 Figure 4: Prototype of a polygeneration system that combines heat, cooling and electricity ......... 14 Figure 5: Transition between phases ........................................................................................................ 17 Figure 6: The cycle of how compressed air energy storage works ...................................................... 19 Figure 7: The cycle of how pumped stored hydropower energy storage works .............................. 20 Figure 8: Linear function of how much energy that can be stored in a capacitor. ........................... 25 Figure 9: Concept of the ideal hydrogen economy................................................................................ 25 Figure 10: Maturity level of different storage systems. ......................................................................... 27 Figure 11: Solar GHI resource, Sagar Island .......................................................................................... 29 Figure 12: Daily electric load profile of Sagar Island............................................................................. 30 Figure 13: A schematic of the chosen system ............................ Fel! Bokmärket är inte definierat. Figure 14: The cash flow graph with a lead acid battery ....................................................................... 33 Figure 15: The monthly average electric production ............................................................................. 34 Figure 16: The state of charge in the battery during the year. ............................................................. 35

List of Equations Equation 1 Equation 2 Equation 3 Equation 4 Equation 5 Equation 6 Equation 7 Equation 8 Equation 9

11 15 18 21 24 28 28 28 28 5-

Nomenclature Table 1: Nomenclature

Description

Symbol

Unit

Angular velocity

ω

(rad/s)

Annual Real Discount Rate

"

(%)

#$%&'()

(kr)

Current

I

(A)

Density

ρ

(,-//0 )

Effect

W

(W)

Energy storage density

E3

(4//0 )

Entalphi

h

(,4/,-)

Heat

q

(J)

Inductance

L

(H)

Inertia constant

k

-

Inner energy

U

(J)

Kinetic energy

E7

(4)

Mass

m

(kg)

Pressure

p

(bar)

;95% 20 years

3.2.2.2 Sodium-sulphur (NaS) batteries Considering the temperature influence the Sodium-sulphur (NaS) batteries are the most advanced battery. In contrast to the lithium batteries, these batteries have their electrodes in liquid form and the electrolyte in a solid state. These batteries are mostly used today in stationary applications for grid support. To keep the electrodes in liquid form they are operating in a temperature range of 300-400 °C (Glaize). These batteries are used as an energy storage for quick charge and discharge and to contribute to new investments in distribution (International Energy Agency). Sodium is an easily accessible material, including table salt and in sulfides, which gives a relative low cost. It requires low maintenance but because sodium reacts easily with air some safety precautions is necessary. Since the sodium-based batteries uses high temperatures it is better to place them for large-scale grid storage applications and also in environments with high ambient temperatures, where other batteries not survive as long. One project example is in Japan where they use 17 sets of 2MW NaS batteries. Each battery consists of 40, 50kW modulus. As many other units they are charged during night hours when the demand for power is low and can be distributed to the grid during peak hours when the demand of power is high (International Energy Agency). 3.2.2.3 Flow batteries A flow battery is a rechargeable battery that is recharged by using two chemical components that are often separated by a membrane and dissolved in a liquid electrolyte in a system. The chemical energy is converted to electricity by allowing the external and separated stored electrolytes to be pumped through the electrochemical cells. The size of the electrochemical cell and design determines the power density of the flow battery. The energy density depends on the size of the storage tanks or the output of the batteries. The system is tapped and the energy resources are able to be recharged within the same system. Some advantages of flow batteries are low cost, modularity, easy transportability, high efficiency and being able to be deployed at a large scale. Another advantage is that flow batteries can instantly be recharged by replacing the liquid of the electrolyte (Badwal, Energy Storage Association). There are different kinds of flow batteries, for example redox flow batteries and hybrid flow batteries. The biggest difference between conventional batteries and flow batteries it the method to store energy. Flow batteries store energy in the electrolyte and conventional ones in electrode materials. Redox flow batteries are named after the chemical reduction and oxidation reactions that occurs in the batteries, which creates a current. They are often described as flexible because of their ability to separate power and energy. The power of the system is determined by the size of the stacks of electrochemical cells and the energy capacity is depending on the volume of the electrolyte, which in other words is the size of the storage tank. Due to the flexibility of the 22 -

system is easy to adapt and are suitable for storage applications within power ratings from 10 kW to 10 MW. The storage duration for the electrical energy is between 2 and 10 hours. One example of a redox flow battery is the iron-chromium flow battery, which has a lower storage duration (3 hours) and is being developed to reduce cost and become more reliable. Vanadium Redox flow batteries and Zinc-Bromine flow batteries are two other flow batteries with similar conditions and characteristics as the flow batteries that where mentioned previously. Vanadium redox (VRB) batteries is considered to be one of the most advanced batteries today. VRB has stable ions in the circuit that can be used multiple times without receiving unwanted side reactions. On the down side, VRB are expensive and has a low energy density that creates a need for big external tanks to provide enough energy. The problem with the low energy density has been overcome by creating a hybrid solution, which combines a solid lithium storage material inside the external tanks with the same architecture model as in the flow batteries. The result show that a normal flow battery could store 10 times more energy by volume compared to a VRB but was still slower to charge. It offers an interesting solution that could be developed in the future to a technology that could be applied in a polygeneration system (Energy Storage Association). 3.2.2.4 Lead acid batteries Lead-acid batteries are used in large groups to support wind and solar generation systems because of their qualities, such as good cycle life and rapid kinetics (Huggins). The strategy behind electrochemical power source is that it combines two electrodes of different materials immersed in an electrolyte. The two different electrodes have different charge and generate together with a conductor an electrical current. The type of secondary battery is determined by the different materials the electrodes and the electrolyte consist of (Pavlov). Lead-acid batteries are remarkable in that way that both the positive and the negative electrode reactions involve the same element. At the positive electrode the lead dioxide reacts with sulfuric acid to form lead sulfate and water. At the negative electrode the lead reacts with sulfate ion to form lead sulfate. The standard potential for one cell at 25 degrees is 2,048 V. Nowadays the lead-acid batteries are very commercialized and exist in many seizes and designs. They are categorized by the construction of the electrodes and the configurations of the electrolytes (Bullock). Flooded lead-acid batteries are the most common lead-acid batteries, where the cell stack is flooded with 30 to 40% of sulfuric acid. The secondly most common is the valve-regulated leadacid (VRLA) batteries, where a one-way pressure relief vent controls the pressure. Today it is still under research and development (Parker). Lead-acid batteries have been designed with a 70 years long float life, more than a thousand deep-discharge cycles, a specific energy of 40-50Wh/kg and a power of 150 to 200 W/kg. They are manufactured on each continent and more than three quarters of these products are used for automotive applications (Bullock). One project example is in Notrees Wind Storage Demonstration in United States, which uses lead-acid batteries to store and provide 36 MW output peak power with the Notrees wind farm. The purpose with this project is to demonstrate how to store the access wind energy into leadacid batteries (International Energy Agency). 3.2.3 Electricity Storage – Electrical Electricity storage use magnetic or electric fields to store electricity for later use. The most common technologies are superconducting magnetic energy storage and supercapacitors.

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3.2.3.1 Superconducting magnetic energy storage (SMES) The superconductor is a good alternative to help generate, transport cleaner energy, save energy losses and reduce carbon emissions (Weijia). The superconductor has no resistance below a certain temperature and therefore it is possible to store energy. With the use of a DC power supply, energy can be transferred into this kind of system. Later when the current is established in the superconductors the power supply can be disconnected and the energy is then stored in the magnetic material inside the coil. The material used in superconductors need to be used below a specific temperature, also called the critical temperature. Another aspect to consider is that the capacitors lose their conductive properties if the magnetic field is above a critical point (Huggins). There are two types of conductors based on this knowledge, type 1 and type 2. The difference between them is that in type 1 the conductivity is destroyed when the applied field rises above a critical value. However, in type 2, they will successively lose their conductivity. Type 2 superconductors are more useful for large-scale application because they can conduct higher currents without breakdown (Weijia). Nowadays one of the leading and most promising superconductors is the superconducting magnetic energy storage (SMES). They have a fast response time, high efficiency, high chargeand discharge time and moreover a good balance between the high density in power and energy. With these qualities the SMES system can protect the electrical grids from failures. Renewable energy sources are unstable, because they are depending on metrological factors but connecting them with a super conducting system will help their output and it will become a safer and more reliable power for consumers (Weijia). A safety procedure is necessary due to the risks that exists with this sort of storage. One safety procedure is to place them in caverns deep underground (Huggins). Moreover, superconductors are divided into two categories, low-temperature superconductors (LTS) and high-temperature superconductors (HTS). HTS works with a temperature of 77K meanwhile LTS work at 4.2K (Weijia). The disadvantaged with LTS is the need of liquid helium that is both more expensive and difficult to obtain. SMES stores energy in the magnetic field created by the current in a coil, see equation 5, which has been cooled down to a temperature below its critical temperature. The stored energy can be connected back to the power system by discharging the coil so it can be released again. Nowadays the SMES system is using HTS. T

D = gh C

Equation 5

C

The magnetic energy stored in a coil is given by equation 5, where D is the stored energy, g is the inductance and h the current (Weijia). The concept is to charge the superconducting magnet during off-peak hours and to discharge it to the power system during peak hours. HTS conductors can vary from small scale to large-scale systems and are mostly used in the electric power application. Further on SMES can be used in distributed power systems (DPS) as a backup power supply (Huggins). 3.2.3.2 Supercapacitors Electrical energy can be stored with the help of a capacitor. The easiest model contains of two parallel plates where the distance between them is filled with a dielectric material. Adding a voltage over the plates will create an electric field and between the conducting plates energy will be stored (Huggins). 24 -

The maximal energy that can be stored is the integral of the voltage-charge product. In case of a true capacitor, the amount of stored energy is going to have a linear function. As the figure 8 shows the voltage is going to fall linearly with the amount of charge.

Figure 8: Linear function of how much energy that can be stored in a capacitor (Huggins).

Another factor that has to be considered is in which rate the energy can be stored. How fast the energy can be stored depends for instance on how much resistance there is (Huggins). Both supercapacitors and SMES have a high cycle of lives and high power densities but small energy densities. These qualities make the supercapacitor and SMES best suitable to cover small energy bursts to the energy systems (International energy agency).

3.3 Hydrogen Storage Hydrogen is a chemical element with many useful properties when it comes to energy storage. Hydrogen can be used as a fuel and are being considered as an alternative to fossil fuels, crude oil and natural gas. Some of the advantages of using hydrogen as an energy source are, that it is considered to be a clean, reliable and affordable energy source. Hydrogen can for example often be used directly or after some minor modifications in internal reciprocating combustion engines and in production of electricity. However, the biggest advantage is the result of the chemical process. The waste product is water and not CO or CO2 as in many other reactions (Huggins).

Figure 9: Concept of the ideal hydrogen economy

The chemical reaction is shown in figure 9, as the figure shows it is a closed cycle where nothing is destroyed or created. The result is a net flow of energy that can be used in other processes (Huggins). Hydrogen can be stored as a gas or as a liquid, nevertheless the storage of hydrogen demands special equipment. Storage of hydrogen as a gas requires a high pressure in the tanks (approximately 350-700bar) and storage of liquid requires low temperatures, since the boiling point for hydrogen is -252,8°C. The tank or containers that store hydrogen has to be well isolated 25 -

to avoid the substance to boil off. These additional costs as isolation increases the costs for this type of storage. Hydrogen can also be stored as material based on adsorption (stored on the surfaces of solids) and absorption (stored within solids). Despite of the complex storage requirements, hydrogen is an element that is used in many applications and in researches for examples about fuel cells. Hydrogen has the highest energy per mass of any fuel but because of its low ambient temperature density, hydrogen has a low energy per unit volume and large tanks are required for the storage. A development of storage methods within hydrogen is required to manage these problems (Office of Energy Efficiency & Renewable Energy). Hydrogen storage has at the current moment mostly been applied in bigger systems. This is a technology in development and could perhaps in the future be modified to smaller energy storage systems.

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4. Methodology 4.1 Technology Readiness Level (TRL) Technology Readiness Level (TRL) is a way to measure the maturity level of a certain technology. TRL was founded on the 80s by National Aeronautics and Space Administration (NASA). Based on the process of the project a TRL-value is given. It exists 9 different levels. From 1 to 9, where 1-3 correspond to the principal idea until being tested in laboratories, 3-6 correspond to experimental and modelling, while 6-9 correspond to demonstration, test and final release on the market (NASA). One approach to visualize the maturity of energy storage technologies is with this following graph, see figure 10. The most commercialized storages methods are the thermal storage followed by the electricity storage, that still are under research and development.

Figure 10: Maturity level of different storage systems (International Energy Agency).

Each storage technology was estimated by the definition of TRL and figure 10. The estimated values are later shown in the appendix. Most of the technologies are commercialized and well developed and therefore have received a high level in TRL. In other cases, when the TRL is hard to estimate, the methods have been given a range instead.

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4.2 HOMER Energy – An analyse of a polygeneration system In order to analyze a polygeneration system a micro grid software program can be used. HOMER is one of the most popular software tools to design a micro grid, which can simulate, optimize and perform a sensitivity analyze of an energy system with chosen parameters, methods and conditions. This can be used as a tool to evaluate the economic cost for the system including lifecycle and installation costs. It gives an overview of benefits from different methods based on technology and economics. Two parameters that has to be considered when evaluating the economic analyse in HOMER are Net Present Cost (NPC) and levelized Cost Of Energy (COE). These two parameters play an important role in the economic analyse in HOMER. HOMER calculates NPC of each component of the system and then for the whole system by first defining the present value of all costs for a system during its lifetime. The costs include capital cost, O&M cost, fuel cost, replacement cost, cost of buying power from grid and emissions penalties. Thereafter the present value of all the revenues that the investment earns over its lifetime. Then the present value is subtracted from the present value of all the costs. Revenues include grid sales revenue and salvage value. The total NPC is calculated by summing up the total discounted cash flows in each year of the project lifetime. The NPC can be calculated by the following formula, where PYbb,`%` is the total annualized cost, P;j is the capital recovery factor, ;
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