This project aimed to build a small-scale wind energy storage system using a lead-acid battery. An AC-DC rectifier circuit was used to simulate the output of a small wind turbine, charging a 12V lead-acid battery. A controller circuit regulated the charging to avoid overcharging the battery. When charged, the battery provided electricity to loads through a 150W inverter. Testing found the system could charge the battery in 6 hours and power loads for 57 minutes, with 89.3% efficiency. However, limitations included not using a real wind turbine and higher capacity components being too costly. Overall, the project demonstrated a basic wind-battery energy storage system as a model for further study.

1. 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 :
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING
EEE311 FINAL YEAR PROJECT
Power Grid Based Energy Storage System
Extended Summary
In Partial Fulfillment
of the Requirements for the Degree
Bachelor of Engineering
Brian Jonathan
10119533
Moncef Tayahi
Sang Lam
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING
Power Grid Based Energy Storage System

2. 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

3. EEE311 Power Grid Based Energy Storage System Brian Jonathan
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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]