Recent technological developments in thin-film photovoltaics (PVs), such as amorphous silicon and hybrid dye-sensitized/PV cells, are leading to new generations of portable solar arrays. These new arrays are lightweight, durable, flexible, and have been reported to achieve power efficiencies of up to 10%. Since the emergence of these flexible and foldable solar arrays, there has become a need to develop solar battery chargers for more portable batteries, such as nickel-metal hydride (NiMH) and Lithium-ion (Li-ion) batteries for military and consumer applications. This paper describes the development of a solar battery charger for Li-ion batteries. Two electrical engineering technology undergraduate students formed a senior design project team to design and implement a solar battery charger. A senior design project is an integral part of the undergraduate engineering technology degree program requirements at Northern Illinois University. All students are required to complete a two-semester-long (4 credit hours) senior design project. Charging a battery requires a regulated dc voltage. However, the voltage supplied by a solar panel can vary significantly depending upon the day, time, weather condition, and irradiation from the sun. To charge the battery with a regulated voltage, a dc-dc converter is connected between the solar panel and the battery. The main components in the solar battery charger are standard Photovoltaic solar panels (PV), a deep cycle rechargeable battery, a Single-Ended Primary Inductance Converter (SEPIC) converter, and a controller. Different types of rechargeable batteries were considered including lead-acid, Nickel Cadmium (NiCd), Nickel-metal hydride (NiMH), and Lithium-ion (Li-ion) batteries. Among these batteries, Li-ion batteries have the highest energy density and relatively low self-discharge rates, and no memory effect. A BB2588 Li-ion battery from Bren-Tronics, Inc is used for this project. The SEPIC converter is a type of dc-dc converter that can convert an unregulated input voltage into either a higher or lower output voltage. This allows the solar panel to charge the battery with a wider range of output voltage, thus flexibility is increased. Experimental results of the solar battery charger are evaluated.
Index
1. Introduction
2. Component & working of solar charger system.
3. Conclusion
Introduction
Solar energy conversion is one of the most addressed topics in the field of renewable energy. Solar radiation is usually converted into two forms of energy: thermal and electrical energy. Solar electricity has applications in many systems such as rural electricity, water pumping, and satellite communications. In the past, solar power was usually used for large-scale grid-connected systems and small remote photovoltaic plants or stand-alone systems. Recent technological development in thin-film photovoltaics (PVs) is leading to new generations of consumer portable solar panels. These new solar panels are lightweight, durable, flexible, and have been reported to achieve power efficiencies of up to 10%. The portable solar panels make solar power readily available for mobile power needs such as outdoor enthusiasts, expeditions, and campers. It also provides portable solar power for the military to extend the run time of military devices including satellite communications, two-way radios, laptop computers, thermal imaging cameras, GPS, etc. Therefore, solar power is expanding beyond its traditional applications. Solar power is harvested and stored by charging rechargeable batteries. Older solar battery chargers were mainly developed for stationary situations such as solar houses and RVs. Lead-acid batteries are usually used because lightweight is not a major factor to consider. However, since the appearance of the foldable and lightweight solar panels, the need to develop solar battery chargers for more portable batteries such as Nickel-metal hydride (NiMH) and Lithium-ion (Li-ion) batteries becomes essential. Previous work has been done to compare battery charging algorithms for stand-alone photovoltaic systems. Peak power from the solar panels was tracked for photovoltaic systems using various methods. To increase conversion efficiency, maximum power point tracking techniques, as well as optimal control, were studied and implemented. Presented in this paper is the development of a solar battery charger for Li-ion batteries. A senior design project team works on the solar battery charger under the close guidance of faculty members. To charge the battery with a regulated voltage, a dc-dc converter is designed and implemented. The dc-dc converter is connected between the solar panel and the battery. The main components in the solar battery charger are standard Photovoltaic solar panels (PV), a deep cycle rechargeable battery, a Single-Ended Primary Inductance Converter (SEPIC), and a controller.
Component of the solar charger system
1. Solar Panel
Solar panels are made of many photovoltaic (PV) cells connected in series or parallel. The PV cell is a large area p-n diode with the junction positioned close to the top surface. When the cell is illuminated, electron-hole pairs are generated by the interaction of the incident photons with the atoms of the cell. The electric field created by the cell junction causes the photon-generated electron-hole pairs to separate. The electrons drift into the n-region of the cell and the holes drift into the p-region. The conversion efficiency of PV cells is defined as the ratio between the electrical power output and the solar power impinging the cell. The efficiency of the PV cells generally is less than 30%. This means that when a cell is illuminated, it will generally convert less than 30% of the irradiance into electricity. The continuing effort to produce more efficient and low-cost PV cells result in different types of PV technologies. Major types of PV cells are singlecrystalline silicon, polycrystalline, semi-crystalline, thin films, and amorphous silicon.
2. Rechargeable Battery
Older solar battery chargers were mainly developed to charge lead-acid batteries. To reduce the weight of the solar power system for portable needs, there has become a need to develop more portable batteries including Li-ion and NiMH batteries. Different types of rechargeable batteries were considered including lead-acid, Nickel Cadmium (NiCd), Nickel-metal hydride (NiMH), and Lithium-ion (Li-ion) batteries. Among these batteries, Li-ion batteries have the highest energy density and relatively low self-discharge rates, and no memory effect.
3. Solar Charge Controller
A charge controller limits the rate at which electric current is added to or drawn from electric batteries. It prevents overcharging and may protect against overvoltage, which can reduce battery performance or lifespan and may pose a safety risk. It may also prevent completely draining ("deep discharging") a battery, or perform controlled discharges, depending on the battery technology, to protect battery life. The terms "charge controller" or "charge regulator" may refer to either a stand-alone device, or to control circuitry integrated within a battery pack, battery-powered device, or battery charger. It consists of DC-DC converters that convert unregulated DC input voltage into regulated DC output voltage. In a DC-DC converter, a transistor or MOSFET operates as an electronic switch: either completely on or completely off. Power absorbed by an ideal switch should be zero. In practice, losses will occur in a real switch due to switching and conduction losses. The efficiency of a DC-DC converter is quite high compared to a linear regulator. Several types of DC-DC converters are buck converter, boost converter, buck-boost converter, and single-ended primary inductance (SEPIC) converter.
Types of Solar Charger Controller:
There are three different types of solar charge controllers, they are:
1. Simple 1 or 2 stage controls
2. PWM (pulse width modulated)
3. Maximum power point tracking (MPPT)
The function of the Solar Charge Controller:
The most essential charge controller controls the device voltage and opens the circuit, halting the charging, when the battery voltage ascents to a certain level. More charge controllers utilized a mechanical relay to open or shut the circuit, halting or beginning power heading off to the electric storage devices. Generally, solar power systems utilize 12V batteries. Solar panels can convey much more voltage than is obliged to charge the battery. The charge voltage could be kept at the best level while the time needed to completely charge the electric storage devices is lessened. This permits the solar systems to work optimally constantly. By running higher voltage in the wires from the solar panels to the charge controller, power dissipation in the wires is diminished fundamentally. The solar charge controllers can also control the reverse power flow. The charge controllers can distinguish when no power is originating from the solar panels and open the circuit separating the solar panels from the battery devices and halting the reverse current flow.
Conclusion
The solar battery charger allows more portable usage for solar panels, such as outdoor enthusiasts and soldiers on the move. The solar battery charger includes the following components: solar panel, Li-ion battery, SEPIC converter, and controller. The SEPIC converter regulates the output voltage from the solar panels into a constant voltage, which is used to charge the battery.
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