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- 1 Improved performance of hybrid photovoltaic-trigeneration systems over photovoltaic-cogen systems including effects of battery storage
- 2 Dispatch strategy and model for hybrid photovoltaic and trigeneration power systems
- 3 Optimal Scheduling of Hybrid CCHP and PV Operation for Shopping Complex Load
- 4 Institutional scale operational symbiosis of photovoltaic and cogeneration energy systems
- 5 Hybrid PV-CHP Distributed System: design aspects and realization
Improved performance of hybrid photovoltaic-trigeneration systems over photovoltaic-cogen systems including effects of battery storage
This paper presents the hybridization of CHP(Combined Heat and Power)with PV(Photovoltaic)and CCHP(Combined Cooling Heat and Power)with PV. It even explains the several advantages of using CHP+PV hybrid systems and CCHP+PV hybrid systems over conventional systems. Moreover, PV-Cogen and PV-trigen are found to be more effective at reducing emissions compared to conventional systems.
Review of PV(Photovoltaic)
-In PV technology solar energy is directly converted to electricity. The efficiency is only about 6-20%.
-The PV has irregularities due to local weather conditions. Thus, PV technology is not consistent throughout the year. So, PV technology is combined with CHP unit.
Review of CHP(Combined Heat and Power)
-The CHP unit uses fuel like natural gas, bio-gas etc to generate electricity.
-The co-generation unit also produces thermal energy which is harnessed by a heat exchanger and utilized
Review of Battery Energy
-Battery is a storage device.
-Whenever excess electricity is generated by the hybrid system, it is stored in the battery and it is utilized during the time when the CHP and PV unit fails to meet the requirement.
-Electricity generated by the PV and Cogeneration unit is used to meet electric requirements. The waste heat is harnessed by heat exchanger to provide hot water and space heating.
-Whenever, excess electricity is generated it is stored in the batteries which is used to supply electricity when PV+CHP unit fails to meet requirements.
- GHG(Green House Gas) emission reduction.
- High efficiency as most of the waste heat is utilized for heating water, space heating etc.
- Improved performance.
- Higher normalized power indices.
-In CHP there is still some amount of waste heat. So, in order to overcome this limitation PV-CCHP hybrid system are used.
-In CCHP, the remaining waste heat from the CHP is utilized by the system for air-conditioning(space cooling).
- Substantial GHG emission reduction.
- Very high efficiency(higher than PV+CHP hybrid system)
- Improved performance than CHP.
- Higher normalized power indices than CHP.
This paper purposes the dispatch strategy for hybrid system PV+CCHP that accounts for electric, space cooling and space heating. The CCHP(Combined Cooling and Heat Power) system is used to reduce the waste heat produced from CHP system. This has resulted in improving the performance by 50% over PV-CHP unit. Due to intermittency of PV technology CHP unit is combined with PV. To overcome the limitations of the CHP unit, PV+CCHP hybrid system is used. This paper explains the significant improvement in performance available in PV-CCHP systems over PV-CHP system.
-Electricity is generated by both PV and CHP unit but in order to improve the performance storage devices for electricity and thermal loads are connected with PV+CHP hybrid units.
- Inverter is used to convert DC output from PV and battery to AC outputs which are compatible with loads.
- Excess AC output produced from CHP is stored in the battery.
In this configuration, inverter(it is used to convert DC output from PV and battery to AC outputs) and CHP unit is connected in parallel.
The advantage of using parallel configuration are:
- Reduction of capacity of inverter and CHP unit.
- Better supply-demand correlation.
- Maximized CHP fuel efficiency.
- Minimized CHP maintenance costs.
In series configuration inverter and CHP are connected in series. It is easy to implement, but has several flaws,
- Lower overall system efficiencies (due to inverter and battery losses).
- Larger inverter size.
- A limited control of the CHP unit.
- This strategy is used to control the system in order to meet the electric and thermal load requirements.
- The thermal output tend to be larger than electrical output in CHP. So, this strategy tends to meet the electrical requirements first, then the thermal requirements
- When it produces excess of power, it is stored in the battery. Moreover, if batteries is at their maximum State Of Charge(SOC), then electricity is either dumped into the ground or it is penetrated into the grid. If there is excess thermal energy it is dumped as waste gas through exhaust.
This paper purposes economic optimal operation of combined cooling heating and power (CCHP) and photovoltaic solar (PV) hybrid system. The system which is simulated consists of a CCHP system, a PV system, an auxiliary boiler, an absorption chiller, a heat storage tank, and utility grids. The advantage of using CCHP, compared with conventional generation, is that it utilizes the waste heat to satisfy the thermal demand. The favorable operation of CCHP helps to minimize the operating cost and retain their investment as early as possible. There is even no fuel consumption which helps in conserving the environment.
-Energy Management System(EMS) consists of:
-CCHP system generates electricity as well as heat. Electricity is supplied to the load while heat is supplied to absorption chillers to convert it into cool air.
-It is based on the gas turbine technology. It uses natural gas as the primary source.
- PV+Utility grid:
Whenever there is shortage of supply from the CCHP system, PV+utility grid compensate for it.
- Heat Storage tank:
-If CCHP unit produce excessive heat than the demand then heat storage tank stores the excessive heat produced from the CCHP unit.
-It will discharge the heat when CCHP unit cannot fulfill the thermal demand.
- Flowchart working:
-Carbon-di-oxide gas emission is calculated(using linear calculation) by considering output power, fuel cost, thermal and electrical demand, energy price to verify the quality of CO2 gas.
-After that the time will be updated to the next interval and the system will operate continuously.
The GHG (Green House Gas) emissions have caused increased in carbon concentration in atmosphere. The GHG emission are caused due to combustion of fossil fuels like coal, oil and natural gas. Most of its energy is wasted while converting it into electricity. The GHG emission can be controlled by efficiently use of fossil fuels, use renewable energy resources, or by using CHP(Combined Heat and Power).
This paper mainly discusses on three design scenarios 1) single cogeneration + photovoltaic, 2) double cogeneration + photovoltaic, 3)single cogeneration + photovoltaic + storage. The paper also shows that how requirement of natural gas is lowered by above scenarios. The consumption of natural gas consumption can be improved by hybridizing solar with cogeneration.
Reduction of GHG:
The GHG emission can be reduced by 2 ways:-
1.Efficient use of fossil fuels:
- By utilizing waste heat produced from the fossil fuel. The waste heat is utilized for space heating or water heating. This is called cogeneration or CHP. Further the waste heat can also be utilized for air cooling. This is called tri-generation or CCHP.
- By using photovoltaic technology which directly converts sunlight into electricity. It has limitation due to weather irregularities.
So, PV+CHP can be combined to increase the efficiency of the system and reduction of the GHG emission.
- In CHP prime mover converts chemical energy into electrical energy. The maximum efficiency obtained from this is 50% and remaining is wasted in the form of heat. Using heat ex-changers this heat can be utilized for space heating and water heating. Thus, efficiency can be increased.. The electrical efficiency is 35% and thermal efficiency is 50%. Hence, there is less fuel consumption.
- The efficiency of CHP is given by:
where: Q:heat energy. E:Electrical energy. Q0:heat content of the fuel.
- The base load of the system is considered to be about 300kW. During evening the peak load is increased to 600kW. The load utilized during summer and winters are also different.
- The electrical efficiency from natural gas is between 30%-40%. In this 90% of the heat loss is utlized for hot water and air cooling.
The block diagram of the CHP system configuration scheme has been provided in the paper.
- It consists of PV panels which converts photons from sunlight directly into electrical energy.
- The output of the PV panels is DC, but the requirement for grid and appliances is AC. So, inverter is connected to convert DC to AC in order to meet the requirement.
- The solar panels are mounted on the roof of the hospital. The tilt angle of solar panel was kept at 10 degrees. 0.5m space was kept between the panels for maintenance purpose.
Design of PV+CHP hybrid system:
The main purpose is to increase the efficiency by utilizing most of the waste heat, in order to increase the efficiency,thermal energy consumption can be reduced by installing heat control mechanism which can be done by the CHP system. PV+CHP hybrid system is used.
-Scenario 1:Single PV+CHP
- This scenario explains how the CHP unit is capable of satisfying hospitals base load requirement.
- PV technology does not fulfill the hospitals load requirement, so CHP unit helps to overcome the loads shortcomings. During the night-time the CHP unit helps to meet the hospitals load requirement.
- During certain months of the year, there is excess electricity generated by PV+CHP unit. This excess electricity is fed back into the grid.
- Scenario 1 fulfills 76% of the hospitals load requirements.
-Scenario 2:Double PV+CHP
- In this scenario 2 CHP unit are coupled with each other. Double PV+CHP is more effective but is very costly due to high maintenance cost compared to scenario 1.
- It fulfills 93% of the energy requirement of the load, also whatever excess electricity is generated throughout the year is fed back into the grids.
- As there is no means to store heat energy,it does not completely fulfill the hospitals thermal requirement.
-Scenario 3:Single CHP + PV + Storage
- In scenario 3 it overcomes the shortcoming and low performance of scenario 1 and it is not as costly as in scenario 2. This is almost similar to scenario 2.
- The battery is used to smooth out the electrical load. But this scenario has shortcoming that it has low thermal supply made available to the hospital.
- It can be observed that using hybrid system helps to improve the energy performance.
- By installing PV array helps in reducing the run time of the CHP to meet load, which in turn reduces natural gas use and green house gas emission.
- Producing energy on site is far more efficient then producing energy at power plant which involves transmission losses of around 26%
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.
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.