brian jonathan - fyp extended summary

DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING

EEE311 FINAL YEAR PROJECT

Power Grid Based Energy Storage System

Extended Summary

of the Requirements for the Degree

Student Name :

Student ID :

Supervisor :

Assessor :


EEE311 FINAL YEAR PROJECT


Extended Summary

In Partial Fulfillment

of the Requirements for the Degree

Bachelor of Engineering

Brian Jonathan

10119533

Moncef Tayahi

Sang Lam



EEE311 Power Grid Based Energy Storage System Brian Jonathan

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1. Introduction

The demand of energy consumption is increasing due to improving technology and growing population of

human. The most used and popular energy source is fossil fuel [1]. Fossil fuel, which is considered as a

reliable energy source, unfortunately emits pollutants and damages the environment. Another problem is,

there will be time when the usage of fossil fuels will reach its limit and their price will rise [2].

A solution to replace the usage of fossil fuels is by using a renewable energy source. During the last

decade, renewable energy became more commonly utilized for its numerous advantages. Renewable

energy is environment-friendly because it emits no pollutant and it can also fulfill the increasing energy

demand due to the fact that the sources are renewable [2].

The aim of this project is to build a wind energy storage system using a lead-acid battery. A small scale

wind turbine with a controller will be connected to a rechargeable battery, and then the output will be

interfaced to a power grid using an inverter. Although this project did not use a real wind turbine as power

source, this report will still be useful for those who want to study the usage of a small scale wind turbine

energy storage system using lead-acid battery.

A battery will store the excess energy instead of overloading the power grid. When the energy demand is

low and the wind speed is high, the battery will store energy from the wind turbine, and the stored energy

will be provided when the demand is high. This issue is important because, in the future, the energy

consumption will rapidly increase and clean energy will become a new standard for many industries and

companies.

2. Methodology

A depth observation about various energies was done before focusing on one particular form of energy.

After several readings and discussions with the final year project supervisor, it was decided that this

project will focus on wind energy. The second step is to do a research about energy storage system. After

reading several literatures and also discussion with the supervisor, it was decided that a lead-acid battery

will be used in this project to create an energy storage system, due to the reason that they have high

energy density and commonly used in energy-related industries.

Figure 1: Project Diagram from Wind Turbine to Power Grid


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The wind turbine was replaced by an AC-DC rectifier power source. This power source imitates the

power produced by the wind turbine. The design of this AC-DC rectifier power source is presented in the

picture below.

Figure 2: AC-DC rectifier power source

This circuit uses a 5A step-down transformer to change the 220 VAC to 18VAC, and then the AC output

will be converted to VDC by the bridge rectifier. Using voltage regulator, the output will be ranged from

1.2 V to 29.2V (detailed calculations are provided in the report). A potentiometer was used to simulate the

wind turbine speed. If the speed is high, the voltage output will be high. While it is good to have a high

output, the maximum voltage of the battery and maximum charging current is 14.5V. To avoid

overcharge, a controller charger was needed.

Figure 3: Controller charger circuit

The controller uses a NE555 chip and a relay to switch the charger from ‘charge’ state to ‘dump’ state.

After the circuit was built, the low and high setting point for this controller was determined, which are

11.9 V and 14.5V. These are the set points that trigger the relay from sending power to battery if the input

voltage is larger than 11.9 V but smaller than 14.5V , or dumping power to dummy load if the voltage is

bigger than 14.5V (or vice versa).

After the battery was charged, it was connected with a 150W inverter to change the DC output to AC. The

efficiency of the final output was measured using a discharge load circuit consists of 140W light bulbs,

and an energy-meter, which is a device to measure wattage. After calculating the efficiency, the output

current and battery time usage were also determined.


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3. Results

The AC-DC rectifier power supply and the controller circuit can be seen in the figure below.

Figure 4: (left) AC-DC rectifier, (right) Controller charger

Using a true RMS multimeter, the potentiometer’s output range was between 1.5V and 25V. The

optimum charging voltage was 13.5V (with charging current 1.92A). With this charging method, the

battery could be charged for 6 hours (the battery is a 12V-12Ah battery). When the controller was

connected to the AC-DC rectifier and battery, the green LED indicator would automatically turn on,

representing the ‘charge state’. If the potentiometer was changed to 14.5V, the orange LED would turn on

together with the dummy load (a small light bulb), showing the ‘dump state’.

In the report, the NP12-12T battery performance such as its capacity, charging and discharging

characteristic, initial charge current limit, and expected service life were thoroughly discussed, but due to

the limited space, they are omitted in this extended summary. The next finding is the battery and

inverter’s output characteristic. Using the discharge load circuit, the output efficiency measured was

89.33% (0.74% difference with the theoretical value), the load current was 0.605 A (0.17% difference

with the theoretical value), and the battery can provide electricity to the 140W load for 57.6 minutes.

4. Conclusion

This project has accomplished its goal which is to create a simple energy storage system. The wind

turbine output voltage is affected by the wind speed, which is simulated by the AC-DC rectifier’s

potentiometer. A controller is also used to avoid overcharge, and after the battery is charged, it provides

electricity to the load. Because the output signal is DC, it has to be converted first to AC by a 150W

inverter. The output efficiency, current, and battery usage time are also measured.

There are some limitations in this project. A real wind turbine was not used to provide a real output

signal. The total cost used in this project is 1730 RMB. Although it is still within the university budget,

buying a battery with higher capacity and a grid-tie inverter will cost a fortune, therefore this project only

uses a lead-acid battery with a smaller capacity and an off-grid inverter. Another limitation is that this

circuit is not programmable, therefore cannot be controlled by a computer.

Despite of the limitations, this project will still be useful for those who want to study about a simple wind

energy storage system using a small-scale wind turbine simulation and a lead-acid battery. This project

can be a guide for those who want to utilize a battery as energy storage because different battery has a

different capacity and performance. In the future, it is hoped that clean energy will become a new

standard for many factories, offices, or even individual residences


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References

[1] Environmental and Energy Study Institute, “Fossil Fuels,” Environmental and Energy Study

Institute, 2013. [Online]. Available: http://www.eesi.org/fossil_fuels. [Accessed November 30,

2013]

[2] M. Stiebler, Wind Energy Systems for Electric Power Generation, Berlin: Springer, 2008, p.1.

[3] A.V. Da Rosa, Fundamentals of Renewable Energy Process, 3rd

edition, Waltham: Academic

Press, 2013, pp. 9, 21, 826.

[4] A. Benzinger, “Siemens to focus its renewable energy activities on wind and hydro power,”

Siemens Press Energy Sector, 2012. [Online]. Available:

https://www.siemens.com/press/en/pressrelease/?press=/en/pressrelease/2012/energy/e201210007.h

tm [Accessed December 1, 2013]