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Microgrid PV-CHP-Battery: literature review

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Contents

Energy management strategy for a renewable-based residential microgrid with generation and demand forecasting

Julio Pascual, Javier Barricarte, Pablo Sanchisa, Luis Marroyo.


This paper presents the management strategy for residential microgrid comprising of PV and wind turbines. By using forecasted data and correcting forecasting errors according to the SOC of the battery, the strategy manages to make a proper utilizaztion of the battery resulting in a better grid power profile.

NOTES:-

Introduction

-Microgrids include distributed generators, loads, energy storage which are controlled by one unit in order to exchange power with the grid. Addind renewable system to this can lower the cost and can provide better grid quality all around the world.

-Microgrids can be classified as either grid-connected or stand-alone. It will either have renewable generators, fossil fuel generators.

-In the field of stand-alone microgrids, when the only power sources are renewable energies, the ultimate goal is to manage the energy management system in order to keep the microgrid running and schedule different units in order to reduce the operating cost.


System description

-It consists of a grid-tied microgrid with the usual electric loads for a single-family home including a heating, ventilation and air conditioning (HVAC) system.

-PV and wind turbine are installed.

Simple moving average strategy

- Two strategies have been used: SMA(Simple moving average) and CMA(Central Moving average)

-In order to make power fluctuations smooth in power exchange with the grid low pass filter can be used.

-If the power profile changes one day to another in this case the energy balance of microgrid changes and has to be compensated by battery first. This will cause SOC of the battery to drift.

Central moving average (CMA) strategy: power forecasting

- The SMA causes lag in the grid. So, CMA is used instead of SMA. This will cause lag to disappear and there will not be any need to SOC control which will result in more better grid power profile.

Conclusion

This results in energy management strategy for a residential microgrid to obtain a smooth power profile for the energy exchange with the grid. The strategy makes use of forecasted power profiles in order to eliminate the lag in the grid power profile.


Feasibility study of renewable energy-based microgrid system in Somaliland׳s urban centers

Abdirahman Mohamed Abdilahi, Abdul Halim Mohd Yatim, Mohd Wazir Mustafa,Omar Tahseen Khalaf, Alshammari Fahad Shumran a, Faizah Mohamed Nor


This paper presents the management strategy for residential microgrid comprising of PV and wind turbines. By using forecasted data and correcting forecasting errors according to the SOC of the battery, the strategy manages to make a proper utilizaztion of the battery resulting in a better grid power profile.

NOTES:-

Introduction

-Microgrids include distributed generators, loads, energy storage which are controlled by one unit in order to exchange power with the grid. Addind renewable system to this can lower the cost and can provide better grid quality all around the world.

-Microgrids can be classified as either grid-connected or stand-alone. It will either have renewable generators, fossil fuel generators.

-In the field of stand-alone microgrids, when the only power sources are renewable energies, the ultimate goal is to manage the energy management system in order to keep the microgrid running and schedule different units in order to reduce the operating cost.


System description

-It consists of a grid-tied microgrid with the usual electric loads for a single-family home including a heating, ventilation and air conditioning (HVAC) system.

-PV and wind turbine are installed.

Simple moving average strategy

- Two strategies have been used: SMA(Simple moving average) and CMA(Central Moving average)

-In order to make power fluctuations smooth in power exchange with the grid low pass filter can be used.

-If the power profile changes one day to another in this case the energy balance of microgrid changes and has to be compensated by battery first. This will cause SOC of the battery to drift.

Central moving average (CMA) strategy: power forecasting

- The SMA causes lag in the grid. So, CMA is used instead of SMA. This will cause lag to disappear and there will not be any need to SOC control which will result in more better grid power profile.

Conclusion

This results in energy management strategy for a residential microgrid to obtain a smooth power profile for the energy exchange with the grid. The strategy makes use of forecasted power profiles in order to eliminate the lag in the grid power profile.

Hybrid PV-CHP Distributed System: design aspects and realization

M. S. Carmeli*, F. Castelli-Dezza**, G. Marchegiani***, M. Mauri**, L. Piegari*, D. Rosati*


The distributed generating system uses renewable energy, but due to the intermittency of the renewable energy they are combined with hybrid plants to combine more energy. This paper focuses on hybrid plants which uses internal combustion engine with cogeneration or tri-generation and PV technology. This paper also put light on analysing the power flow control strategies. Due to very low efficeincy of PV technology they are combined with conventional non-renewable ones to improve the performance and efficiency.

NOTES:-

There are three families for Distributed Generation System (DGS):

Standalone Systems (SAS):
  • This are used to supply to remote locations which are not connected to the main grid. in such case they usually combine one or more renewable energy sources with conventional energy sources. The hybrid system assure uninterrupted power supply even when renewable energy does not operate.


Grid connected systems (GCS):
  • They operate in only grid connected mode. They are connected with one or more renewable sources.
  • By using one or more energy sources provides higher stability of power supply.
  • In GCS very small storage is equipped, in order to contribute system transient stability.


Mixed operating mode systems (MOS).:
  • They operate in grid connection mode combined with one or more renewable sources along with storage device(Battery).
  • The battery is used to supply energy during emergency period.


Hybrid System Configuration.:
  • In this PV is combined with CHP unit. It is also equipped water heat storage.
  • CHP unit has small size battery and braking resistance which are shunt connected.
  • The shunt element have three functions.

a) They allow CHP to start even in the absence of the mains.

b) they allow to store excess energy in the standalone mode.

c)They provide transient stability to the CHP system.

If shunt unit is not connected then:

a) We obtain poor dynamic response.

b)In standalone mode, if there is demand for increase in load, it wont be able to fulfill the requirement.


Hybrid system components:

- CHP unit:

  • The natural gas, fuel for Internal Combustion Engine(ICE) to generate mechanical energy by combustion of fuel. The Induction machine connected to ICE converts mechanical energy to electrical energy.
  • Thermal recovery unit recovers thermal energy using heat exchanger. The heat generated during the process produces hot water which is stored in water heat storage. The heat storage unit has temperature sensors.


- PV unit:

  • It has different PV arrays. The output is DC which is connectedd to the common DC-bus. Chopper(DC-DC converter) is used. The DC is converted to AC(inverter).


- Battery Bank:

  • It is connected to the DC-bus. This Bi-directional Chopper. So, it can supply power in both directions, form DC bus to battery during charging of battery and from battery to DC bus during discharging.
  • There are two charging steps:

1) Constant current-Bulk condition.

2) Constant Voltage- Boost condition.


-Supervisor control unit:

It has two main tasks:

  • Controls input of PV, CHP and Battery bank.
  • Controls heat storage unit and battery power flow.

There are two operation modes:

1) Normal operation mode: In this mode the whatever power PV unit is generated is fed into the load. The CHP unit priority is to satisfy thermal demand. If CHP generates more power than required by heat demand, it stores it in battery bank.

2) Standalone operation: In this mode grid is not connected. The hybrid system gives priority to fulfill the electric demand. Advantage is this operation does not require energy storage device.

The mode changing is controlled by supervisor control unit.

Optimal Operation Planning of a Photovoltaic-Cogeneration-Battery Hybrid System

S. Bando, Member, IEEE, H. Asano, Member, IEEE, T. Tokumoto, Non-member, T. Tsukada, Non-member, and T. Ogata, Non-member

This paper proposes the modelling of optimal planning of hybrid systems and economic dispatch of the hybrid system. This paper also deals with three different objective functions: minimization of cost, reduction of CO2 emission and primary energy consumption.

NOTES:

  • There is a degradation of power quality such as voltage and frequency as the renewable energy sources is fluctuating. To achieve large penetration goal of renewable source, distributed generation is considered.
  • The battery capacity can be reduced if gas engines in the hybrid system can follow the cchange in output system of renewable energy.
Micro-grids
  • In this PV+ gas engine CHP is modeled. Electrical and thermal demand were based on combined data.
  • Schematic shown in the paper consist of three gas engines, PV, steam-absorption refrigerator, gas-absorption chiller, gas boiler, and lead acid battery.
  • Electricity is supplied by the parallel operation of gas engines, PV and battery.
  • The calculation parameters are battery capacity, pv capacity and the number of gas engines.
Mathematical formulation
  • Mathematical formulation was done in order to minimize the cost to supply electricity.
  • In the PV-CHP hybrid system exhaust heat from the gas engines is utilized in order to fulfill thermal demand for the building.
  • The capacity of gas absorption chiller and boiler is determined by the maximum thermal demand.
  • The capacity of steam absorption refrigerator is determined by the maximum gas engine capacity.
  • Several parameters such as gas engines generated efficiences and heat recovery efficiency, PV efficeincy, gas price, CO2 emission coefficient etc are taken into consideration for optimized operation planning of PV-CHP hybrid system.
Conclusion

It was seen that the cO2 emission, running cost and primary energy consumption were low compared to conventional energy cost.

Microgeneration Model in Energy Hybrid System - Cogeneration and PV Panels

J. Galvão*, S. Leitão**, S. Malheiro**, T. Gaio***

This paper proposes the development of a hybrid energy model with solar PV panels and a small CHP (combined heating and power production) system whose primary energy source is the biomass.It also presents the several rules to achieve new energy efficiency levels.

NOTES

  • The hybrid energy model consists of following processes:

1) Cogeneration process.

2) Thermal process.

3) Electrical process.

4) PV process.

  • Cogeneration system uses biomass or ICE as primary energy sources. It provides electrical as well as thermal energy.
  • Thermal process includes heating hot water, space heating etc.
  • PV solar system is also used to produce electricity.
Energy data consumption
  • Energy and thermal demand data were considered. The three main energy sources utilized are: Electrical, fuel and gas. Their energy consumption are represented in graphical form in the paper. The most energy source consumed is electricity which contributes to around 55%
  • The energy consumption for heating and cooling varies with season. The graph shows the thermal consumption during winter days.
Energy Hybrid Concept and Solar Potential
  • This system consists of several energy sources combined together. It is used to provide electricity with low cost and low emissions.
  • The solar radiation distribution data has been provided in the paper.
  • There are two large areas in co-generation system:

1) Handling/storage of biomass.

2) Heat exchangers, filtration of gas engine/ generator.

  • If PV cant fulfill the electric demand. The additional electric demand is fulfilled by the CHP unit.
Economic Analysis
  • The PV process is combined with CHP to supply electricity during peak hours. Excess energy can be stored to electrical net.
  • The hybrid system not only fulfills the energy demand but also increases the efficiency.
Conclusion
  • Efficiency is increased by combining PV with CHP unit.
  • This system is eco-friendly i.e it does not emit GHG(Green House Gas).

Rural microgrids and its potential application in Colombia

E.E. Gaona, , C.L. Trujillo , J.A. Guacaneme


NOTES

  • A microgrid can be defined as a system characterized by a set of loads, storage systems and small-scale generation sources. Power sources can generally be of various types(renewable sources like photovoltaic or wind generators,and/or generators from fossil fuels),which fulfill local requirements for heating and power generation(Cogeneration).
  • Microgrids can exchange energy i.e.it can act as generator or load.
Microgrid concept
  • A microgrid comprises a portion of the electric distribution system in a medium and low voltage.It includes a variety of Distributed Energy Resources(DER)such as distributed generators and energy storage units,and different types of end users(electric and/or thermal loads),as well as the necessary communication equipment for energy operation and management on real time.
  • A microgrid can be either DC, AC or even a high frequency AC power grid.
  • It can be interconnected to grid or can be isolated. Depending upon the operation it has different control strategies.
  • Microgird can work autonomously when there is outage of power. This mode of operation is called isolated operation.
Types of microgrids
  • Microgrid can be classified depending upon electrical characteristics. It can be AC or DC.
  • In case of AC load it is connected to inverter which ensures adequate power quality conditions.
Storage and management as key aspects of microgrids
  • In order to store AC it is necessary to convert into DC.
  • The development of storage technologies allows greater storage capacity of electric power in DC,and power electronics.

Optimal sizing of hybrid solar micro-CHP systems for the household sector

Caterina Brandonia, Massimiliano Renzib

The paper mainly focuses on the importance of optimal sizing hybrid microgeneration systems. The parameters which should be considered for sizing phase are: energy prices,ambient conditions,energy demand,units' characteristics,electricity grid constraints. This paper also focuses on maximizing the economic and the energy savings compared to conventional generation.

NOTES:

  • Renewable or fossil fuels are used to operate combined heat and power production, providing important results in terms of energy savings and emission reduction.
  • Due to the intermittency of the Pv technology the integgration of solar with grid was a problem.This problem was mitigated by introduction of hybrid systems, consisting of coupling solar systems with micro-CHP units fueled by natural gas.
  • When dealing with hybrid systems, identifying the optimal sizing of the energy conversion systems is a tough issue due to several parameters that must be taken into account in the analysis, such as electricity and fuel price, energy loads and weather conditions.
Energy system modeling
  • The system was made up of PV, micro-CHP device (the technologies considered are ICE, Stirling, microturbine and fuel cell), a Thermal Energy Storage (TES), a cooling device (vapour compression chiller or water/LiBr absorption chiller)
  • Meteorological Year database for determining the yield of Solar system depending on solar radiation and ambient conditions.
  • The hourly values of the following quantities are used: the Direct Normal Irradiation (DNI); the global solar irradiation over a south-oriented 30degree tilted surface; the ambient temperature.
  • The efficiency of a PV panel depends on the ambient conditions, the most influential being the available solar radiation and the solar cell temperature figures.
Micro-CHP modeling
  • All the micro-CHP units were modeled on the basis of electrical efficiency and power to heat ratio.
  • The technologies considered in this work are four: ICE, Stirling engine, microturbine and fuel cell. Table is given in paper which shows comparison for all those ways of which fuel cell technique is most efficient as it has power to heat ratio =1. But it has a drawback that is its cost.
  • It shows the advantages of using different technologies depending on the application.
Optimal sizing of system
  • Electrical demand can be satisfied by the (PV),the micro-CHP unit and the electricity bought from the grid (if needed).
  • CHP unit is used to fulfill thermal demand such as space heating, hot domestic water etc.
Objective function
  • The objective is to minimize annual cost derived by implementation of such a hybrid system is given by sum of annualized capital cost of all the devices and annual operating cost of them.
  • The capital cost of each device depends on its life time and capacity recovery factor.
  • Operating cost depends on fuel cost of running CHP unit, operating and maintenance cost of the CHP unit, Cost of purchasing electric energy from grid if needed, the revenue coming from generating electric energy from solar and CHP unit.
Conclusion
  • The use of hybrid system is used to minimize the operating cost, overall system efficiency and low GHG emission compared to conventional energy source.

A study on the energy management in domestic micro-grids based on Model Predictive Control strategies

G. Bruni, S. Cordiner, V. Mulone, , V. Rocco, F. Spagnolo

The paper mainly focuses on the Model Predictive Control (MPC) logic, based on weather forecasts, has been applied to the analysis of power management in a domestic off-grid system. The system is the integration of renewable energy conversion devices (Photovoltaic, PV), a high efficiency energy conversion programmable system (a Fuel Cell, FC) and an electrochemical energy storage (batteries). The control strategy has the objective of minimizing energy costs, while maintaining the optimal environmental comfort in the house, thus optimizing the use of renewable sources.

NOTES:

  • In order to reduce energy consumption, the concept of distributed generation based on domestic microgrids, represents a valid solution in terms of efficiency.
  • The key overall microgrid objective consists of reducing the energy consumption and maximizing the use of renewable sources while continuously providing power to meet the load request and comply with quality targets (e.g. maintaining thermal comfort in buildings).
Model predictive control
  • The MPC is based on the knowledge of the system and on the prediction of its behavior
  • An operating schedule of HVAC power control is done all over the horizon control. Control actions are then decided depending on future conditions, for example by using weather forecast information.
Microgrid efficiency
  • The microgrid efficiency was evaluated according to

Efficiency= Eload/(Eres+Efes) where RES=Renewable sources, FES=Fossil fuel Sources.

The efficiency of the microgrid can be defined by the ratio between the load energy and the sum of the primary energy required from both fossil and renewable energy sources.

System costs
  • The total cost of the microgrid is made of capital, operating and maintenance costs. For batteries, HVAC and PV panels, only purchase capital costs were considered.
Simulation and results
  • The MPC strategy guarantees the required comfort conditions by also saving the use of fossil energy.
  • Fossil energy reduction is almost 6% in winter conditions (where the renewable energy available is limited) and 23% in summer conditions, when more renewable energy is available; as a consequence, the overall system efficiency parameters show an improvement, according to the saved fossil energy.
  • The MPC operation also leads to a smoother plant operation, giving a reduction of the FC and HVAC sizes and an improvement of battery operation during charge and discharge phases.


Off-grid electricity generation with renewable energy technologies in India: An application of HOMER

Rohit Sena, , Subhes C. Bhattacharyyab

This paper analyses hybrid off-grid systems for rural application that can provide reliable and affordable power. It also considers alternative technologies for rural India and identifies the optimal system using HOMER software. The technology combinations and the focus on residential and productive loads make this work different from others. The purpose of this paper is to propose the best hybrid technology combination for electricity generation from a mix of renewable energy resources to satisfy the electrical needs in a reliable manner of an off-grid remote village

NOTES:

  • HOMER is an optimization tool that is used to decide the system configuration for decentralized systems. It has been used both to analyse the off-grid electrification issues in the developed as well as developing countries.
  • HOMER (Hybrid Optimisation Model for Electric Renewables), developed by NREL (National Renewable Energy Laboratory, USA) appears repeatedly in the literature as a preferred tool. It can handle a large set of technologies (including PV, wind, hydro, fuel cells, and boilers), loads (AC/DC, thermal and hydrogen), and can perform hourly simulations.
Methodology
  • Following combinations have been considered.

-Small hydropower. -Wind turbines. -Solar PV. -batteries. -bio-diesel generators.

  • Integrating will help in mitigation of GHG emission.
System modelling
  • Integrating the system will help to built a complete off-grid system.
  • In a micro-power system, a component generates, delivers, converts and stores energy. In this HOMER analysis, solar PV, wind turbines, and run-off river hydropower are the intermittent resources and the bio-diesel is kept for backup. Batteries and Converter are for storing, converting electricity respectively.
System costs
  • The cost of each component in the system is the major factor for designing the system in HOMER.
  • HOMER aims to minimise the total net present cost (NPC) both in finding the optimal system configuration and in operating the system, economics play a crucial role in the simulation.
Simulation and results
  • Technically feasible and economic viable results have been obtained using HOMER software.

MODELLING AND SIMULATION OF THE COMBINED HEAT AND POWER PLANT OF A REAL INDUSTRIAL SYSTEM

Semra Öztürk, Mehlika Şengül, Nuran Yörükeren


This paper proposes a mathematical model of a Combined Heat and Power (CHP) plant. In this study, operating of CHP which produce electricity and heat in order to fulfill electrical and thermal demand. Cogeneration system are connected to auxiliary devices such as boiler, compressor, combustion chamber, gas turbine etc.

NOTES:

COGENERATION SYSTEMS AND THEIR OPERATING
  • In this CHP generates both electricity and heat simultaneously which is utilized by industries.
  • In conventional energy heat needed is obtained from the boiler which utilizes fuel. But by using CHP the waste heat produced is utilized for heating purpose, which leads to saving fuel and increasing efficiency.
  • In industries un-interrupted power supply and heating and cooling process is essential. Even outage for short period of time can cause very large lose. So using CHP along with the conventional energy can minimize the outages to a great extend.
  • By using CHP for water heating the thermal efficiency is too high. Thermal efficiency is upto 85% with fuel oil and 90% with gas applications.
  • When generating heat and electricity from the CHP only a small portion of cooling water heat can be recovered.
  • The volume of outlet power as electricity, exhaust gas temperature, steam pressure and steam quantity can be observed by this model.
Conclusion
  • Cogeneration with gas turbine provides high efficiency.
  • Low gas emission.
  • Mathematical model for control strategy was used in order to operate CHP efficiently.

An approach for the integration of renewable distributed generation in hybrid DC/AC microgrids

Abdulkerim Karabibera, Cemal Kelesb, Asim Kaygusuzb, B. Baykant Alagoz


This paper proposes an investigation of a hybrid DC/AC integration paradigm to establish microgrids (MGs) by using a conventional three-phase local power delivery system.

NOTES:

  • Renewable energy has the ability for infinite use by end users with improved control devices and techniques.
  • Integration of existing grids with renewable sources for residences responds to the need for low-cost, efficient power distribution and addresses the need to control the greenhouse effect.
  • A DC MG does not require complex voltage and frequency control mechanisms, compared to AC integration techniques, and this reduces costs spent for control and power electronics equipments.
Methodology

-Line hybrid DC/AC MGs with separated consumption and generation:

  • It has several advantages:

- It reduces power electronic equipment and maintenance costs for individuals.

- Provides manageable integration of local distributed renewable generation and conventional power delivery systems in MGs.

- The System model was simulated in MATLAB/SIMULINK.

- Six individual insulated gate bipolar transistors (IGBT) switches driven by a pulse width modulation (PWM) circuit and a low-pass filter performed the DC/AC conversion. A transformer flyback DC/DC converter was used.

Conclusion
  • Grid energy and renewable energy can continuously support each other. This integration greatly improves the endurance of power distribution interior of MGs against extreme conditions, such as outages of the grid or energy flow interruptions and it supports local energy balance in

MG.