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How Does A Solar Battery Work? | Energy Storage Explained. The solar cell

How Does A Solar Battery Work? | Energy Storage Explained. The solar cell

    How Does A Solar Battery Work? | Energy Storage Explained

    A solar battery can be an important addition to your solar power system. It helps you store excess electricity that you can use when your solar panels aren’t generating enough energy, and gives you more options for how to power your home.

    If you’re looking for the answer to, “How do solar batteries work?”, this article will explain what a solar battery is, solar battery science, how solar batteries work with a solar power system, and the overall benefits of using solar battery storage.

    What is a Solar Battery?

    Let’s start with a simple answer to the question, “What is a solar battery?”:

    A solar battery is a device that you can add to your solar power system to store the excess electricity generated by your solar panels.

    You can then use that stored energy to power your home at times when your solar panels don’t generate enough electricity, including nights, cloudy days, and during power outages.

    The point of a solar battery is to help you use more of the solar energy you’re creating. If you don’t have battery storage, any excess electricity from solar power goes to the grid, which means you’re generating power and providing it to other people without taking full advantage of the electricity your panels create first.

    For more information, check out our Solar Battery Guide: Benefits, Features, and Cost

    The Science of Solar Batteries

    Lithium-ion batteries are the most popular form of solar batteries currently on the market. This is the same technology used for smartphones and other high-tech batteries.

    Lithium-ion batteries work through a chemical reaction that stores chemical energy before converting it to electrical energy. The reaction occurs when lithium ions release free electrons, and those electrons flow from the negatively-charged anode to the positively-charged cathode.

    This movement is encouraged and enhanced by lithium-salt electrolyte, a liquid inside the battery that balances the reaction by providing the necessary positive ions. This flow of free electrons creates the current necessary for people to use electricity.

    When you draw electricity from the battery, the lithium ions flow back across the electrolyte to the positive electrode. At the same time, electrons move from the negative electrode to the positive electrode via the outer circuit, powering the plugged-in device.

    Home solar power storage batteries combine multiple ion battery cells with sophisticated electronics that regulate the performance and safety of the whole solar battery system. Thus, solar batteries function as rechargeable batteries that use the power of the sun as the initial input that kickstarts the whole process of creating an electrical current.

    Comparing Battery Storage Technologies

    When it comes to solar battery types, there are two common options: lithium-ion and lead-acid. Solar panel companies prefer lithium-ion batteries because they can store more energy, hold that energy longer than other batteries, and have a higher Depth of Discharge.

    Also known as DoD, Depth of Discharge is the percentage to which a battery can be used, related to its total capacity. For example, if a battery has a DoD of 95%, it can safely use up to 95% of the battery’s capacity before it needs to be recharged.

    Lithium-Ion Battery

    As mentioned earlier, battery manufacturers prefer lithium-ion battery technology for its higher DoD, reliable lifespan, ability to hold more energy for longer, and a more compact size. However, because of these numerous benefits, lithium-ion batteries are also more expensive compared to lead-acid batteries.

    Lead-Acid Battery

    Lead-acid batteries (the same technology as most car batteries) have been around for years, and have been used widely as in-home energy storage systems for off-grid power options. While they are still on the market at.friendly prices, their popularity is fading due to low DoD and shorter lifespan.

    AC Coupled Storage vs. DC Coupled Storage

    Coupling refers to how your solar panels are wired to your battery storage system, and the options are either direct current (DC) coupling or alternating current (AC) coupling. The main difference between the two lies in the path taken by the electricity that the solar panels create.

    Solar cells create DC electricity, and that DC electricity must be converted into AC electricity before it can be used by your home. However, solar batteries can only store DC electricity, so there are different ways of connecting a solar battery into your solar power system.

    DC Coupled Storage

    With DC coupling, the DC electricity created by solar panels flows through a charge controller and then directly into the solar battery. There is no current change before storage, and conversion from DC to AC only occurs when the battery sends electricity to your home, or back out into the grid.

    A DC-coupled storage battery is more efficient, because the electricity only needs to change from DC to AC once. However, DC-coupled storage typically requires a more complex installation, which can increase the initial cost and lengthen the overall installation timeline.

    AC Coupled Storage

    With AC coupling, DC electricity generated by your solar panels goes through an inverter first to be converted into AC electricity for everyday use by appliances in your home. That AC current can also be sent to a separate inverter to be converted back to DC current for storage in the solar battery. When it’s time to use the stored energy, the electricity flows out of the battery and back into an inverter to be converted back into AC electricity for your home.

    With AC-coupled storage, electricity is inverted three separate times: once when going from your solar panels into the house, another when going from the home into battery storage, and a third time when going from battery storage back into the house. Each inversion does result in some efficiency losses, so AC coupled storage is slightly less efficient than a DC coupled system.

    Unlike DC-coupled storage that only stores energy from solar panels, one of the big advantages of AC coupled storage is that it can store energy from both solar panels and the grid. This means that even if your solar panels aren’t generating enough electricity to fully charge your battery, you can still fill the battery with electricity from the grid to provide you with backup power, or to take advantage of electricity rate arbitrage.

    It’s also easier to upgrade your existing solar power system with AC-coupled battery storage, because it can just be added on top of an existing system design, instead of needing to be integrated into it. This makes AC coupled battery storage a more popular option for retrofit installations.

    How Solar Batteries Work with a Solar Power System

    This entire process starts with the solar panels on the roof generating power. Here is a step-by-step breakdown of what happens with a DC-coupled system:

    • Sunlight hits the solar panels and the energy is converted to DC electricity.
    • The electricity enters the battery and is stored as DC electricity.
    • The DC electricity then leaves the battery and enters an inverter to be converted into AC electricity the home can use.

    The process is slightly different with an AC-coupled system.

    • Sunlight hits the solar panels and the energy is converted to DC electricity.
    • The electricity enters the inverter to be converted into AC electricity the home can use.
    • Excess electricity then flows through another inverter to change back into DC electricity that can be stored for later.
    • If the house needs to use the energy stored in the battery, that electricity must flow through the inverter again to become AC electricity.

    How Solar Batteries Work with a Hybrid Inverter

    If you have a hybrid inverter, a single device can convert DC electricity into AC electricity and can also convert AC electricity into DC electricity. As a result, you don’t need two inverters in your photovoltaic (PV) system: one to convert electricity from your solar panels (solar inverter) and another to convert electricity from the solar battery (battery inverter).

    Also known as a battery-based inverter or hybrid grid-tied inverter, the hybrid inverter combines a battery inverter and solar inverter into a single piece of equipment. It eliminates the need to have two separate inverters in the same setup by functioning as an inverter for both the electricity from your solar battery and the electricity from your solar panels.

    Hybrid inverters are growing in popularity because they work with and without battery storage. You can install a hybrid inverter into your battery-less solar power system during the initial installation, giving you the option of adding solar energy storage down the line.

    Benefits of Solar Battery Storage

    Adding battery backup for solar panels is a great way of ensuring you get the most out of your solar power system. Here are some of the main benefits of a home solar battery storage system:

    Stores Excess Electricity Generation

    Your solar panel system can often produce more power than you need, especially on sunny days when no one is at home. If you don’t have solar energy battery storage, the extra energy will be sent to the grid. If you participate in a net metering program, you can earn credit for that extra generation, but it’s usually not a 1:1 ratio for the electricity you generate.

    With battery storage, the extra electricity charges up your battery for later use, instead of going to the grid. You can use the stored energy during times of lower generation, which reduces your reliance upon the grid for electricity.

    Provides Relief from Power Outages

    Since your batteries can store the excess energy created by your solar panels, your home will have electricity available during power outages and other times when the grid goes down.

    Reduces Your Carbon Footprint

    With solar panel battery storage, you can go green by making the most of the clean energy produced by your solar panel system. If that energy isn’t stored, you will rely on the grid when your solar panels don’t generate enough for your needs. However, most grid electricity is produced using fossil fuels, so you will likely be running on dirty energy when drawing from the grid.

    Provides Electricity Even After the Sun Goes Down

    When the sun goes down and solar panels aren’t generating electricity, the grid steps in to provide much-needed power if you don’t have any battery storage. With a solar battery, you’ll use more of your own solar electricity at night, giving you more energy independence and helping you keep your electric bill low.

    A Quiet Solution to Backup Power Needs

    A solar power battery is a 100% noiseless backup power storage option. You get to benefit from maintenance free clean energy, and don’t have to deal with the noise that comes from a gas-powered backup generator.

    Key Takeaways

    Understanding how a solar battery works is important if you’re thinking about adding solar panel energy storage to your solar power system. Because it operates like a large rechargeable battery for your home, you can take advantage of any excess solar energy your solar panels create, giving you more control over when and how you use solar energy.

    Lithium-ion batteries are the most popular type of solar battery, and work through a chemical reaction that stores energy, and then releases it as electrical energy for use in your home. Whether you choose a DC-coupled, AC-coupled, or hybrid system, you may be able to increase the return on investment of your solar power system and reduce your reliance on the grid.

    Having the right system design is vital to making the most of your solar panels. At Palmetto, we have the expertise and experience to guide you on your clean energy journey. From solar power installation and service to system maintenance and monitoring, our solar professionals are here to help you take advantage of clean energy.

    Solar Cell

    The Solar Cell block represents a solar cell current source.

    The solar cell model includes the following components:

    Solar-Induced Current

    The block represents a single solar cell as a resistance Rs that is connected in series with a parallel combination of the following elements:

    The following illustration shows the equivalent circuit diagram:

    I = I p h − I s ( e ( V I R s ) / ( N V t ) − 1 ) − I s 2 ( e ( V I R s ) / ( N 2 V t ) − 1 ) − ( V I R s ) / R p

    • Ir is the irradiance (light intensity), in W/m 2. falling on the cell.
    • Iph0 is the measured solar-generated current for the irradiance Ir0.
    • k is the Boltzmann constant.
    • T is the Device simulation temperature parameter value.
    • q is the elementary charge on an electron.

    The quality factor varies for amorphous cells, and is typically 2 for polycrystalline cells.

    The block lets you choose between two models:

    • An 8-parameter model where the preceding equation describes the output current
    • A 5-parameter model that applies the following simplifying assumptions to the preceding equation:
    • The saturation current of the second diode is zero.
    • The impedance of the parallel resistor is infinite.

    If you choose the 5-parameter model, you can parameterize this block in terms of the preceding equivalent circuit model parameters or in terms of the short-circuit current and open-circuit voltage the block uses to derive these parameters.

    All models adjust the block resistance and current parameters as a function of temperature.

    You can model any number of solar cells connected in series using a single Solar Cell block by setting the parameter Number of series-connected cells per string to a value larger than 1. Internally the block still simulates only the equations for a single solar cell, but scales up the output voltage according to the number of cells. This results in a more efficient simulation than if equations for each cell were simulated individually.

    Temperature Dependence

    Several solar cell parameters depend on temperature. The solar cell temperature is specified by the Device simulation temperature parameter value.

    The block provides the following relationship between the solar-induced current Iph and the solar cell temperature T:

    does, solar, battery, work, energy, storage

    I p h ( T ) = I p h ( 1 T I P H 1 ( T − T m e a s ) )

    • TIPH1 is the First order temperature coefficient for Iph, TIPH1 parameter value.
    • Tmeas is the Measurement temperature parameter value.
    does, solar, battery, work, energy, storage

    The block provides the following relationship between the saturation current of the first diode Is and the solar cell temperature T:

    I s ( T ) = I s ( T T m e a s ) ( T X I S 1 N ) e ( E G ( T T m e a s − 1 ) / ( N V t ) )

    where TXIS1 is the Temperature exponent for Is, TXIS1 parameter value.

    The block provides the following relationship between the saturation current of the second diode Is2 and the solar cell temperature T:

    I s 2 ( T ) = I s 2 ( T T m e a s ) ( T X I S 2 N 2 ) e ( E G ( T T m e a s − 1 ) / ( N 2 V t ) )

    where TXIS2 is the Temperature exponent for Is2, TXIS2 parameter value.

    The block provides the following relationship between the series resistance Rs and the solar cell temperature T:

    R s ( T ) = R s ( T T m e a s ) T R S 1

    where TRS1 is the Temperature exponent for Rs, TRS1 parameter value.

    The block provides the following relationship between the parallel resistance Rp and the solar cell temperature T:

    R p ( T ) = R p ( T T m e a s ) T R P 1

    where TRP1 is the Temperature exponent for Rp, TRP1 parameter value.

    Predefined Parameterization

    There are multiple available built-in parameterizations for the Solar Cell block.

    This pre-parameterization data allows you to set up the block to represent components by specific suppliers. The parameterizations of these solar cell modules match the manufacturer data sheets. To load a predefined parameterization, double-click the Solar Cell block, click the hyperlink of the Selected part parameter and, in the Block Parameterization Manager window, select the part you want to use from the list of available components.

    The predefined parameterizations of Simscape™ components use available datsources for the parameter values. Engineering judgement and simplifying assumptions are used to fill in for missing data. As a result, expect deviations between simulated and actual physical behavior. To ensure accuracy, validate the simulated behavior against experimental data and refine component models as necessary.

    For more information about pre-parameterization and for a list of the available components, see List of Pre-Parameterized Components.

    Thermal Port

    You can expose the thermal port to model the effects of generated heat and device temperature. To expose the thermal port, set the Modeling option parameter to either:

    • No thermal port — The block does not contain a thermal port and does not simulate heat generation in the device.
    • Show thermal port — The block contains a thermal port that allows you to model the heat that conduction losses generate. For numerical efficiency, the thermal state does not affect the electrical behavior of the block.

    For more information on using thermal ports and on the Thermal Port parameters, see Simulating Thermal Effects in Semiconductors.

    The thermal port model, shown in the following illustration, represents just the thermal mass of the device. The thermal mass is directly connected to the component thermal port H. An internal Ideal Heat Flow Source block supplies a heat flow to the port and thermal mass. This heat flow represents the internally generated heat.

    The internally generated heat in the solar cell is calculated according to the equivalent circuit diagram, shown at the beginning of the reference page, in the Solar-Induced Current section. It is the sum of the i 2 R losses for each of the resistors plus the losses in each of the diodes.

    The internally generated heat due to electrical losses is a separate heating effect to that of the solar irradiation. To model thermal heating due to solar irradiation, you must account for it separately in your model and add the heat flow to the physical node connected to the solar cell thermal port.

    Examples

    Solar Cell Power Curve

    Generate the power-voltage curve for a solar array. Understanding the power-voltage curve is important for inverter design. Ideally the solar array would always be operating at peak power given the irradiance level and panel temperature.

    The solar cell

    Photovoltaic (PV) devices generate electricity directly from sunlight via an electronic process that occurs naturally in certain types of material, called semiconductors. Electrons in these materials are freed by solar energy and can be induced to travel through an electrical circuit, powering electrical devices or sending electricity to the grid.

    PV devices can be used to power anything from small electronics such as calculators and road signs up to homes and large commercial businesses.

    How does PV technology work?

    Photons strike and ionize semiconductor material on the solar panel, causing outer electrons to break free of their atomic bonds. Due to the semiconductor structure, the electrons are forced in one direction creating a flow of electrical current. Solar cells are not 100% efficient in crystalline silicon solar cells, in part because only certain light within the spectrum can be absorbed. Some of the light spectrum is reflected, some is too weak to create electricity (infrared) and some (ultraviolet) creates heat energy instead of electricity. Diagram of a typical crystalline silicon solar cell. To make this type of cell, wafers of high-purity silicon are “doped” with various impurities and fused together. The resulting structure creates a pathway for electrical current within and between the solar cells.

    Other Types of Photovoltaic Technology

    In addition to crystalline silicon (c-Si), there are two other main types of PV technology:

    • Thin-film PVis a fast-growing but small part of the commercial solar market. Many thin-film firms are start-ups developing experimental technologies. They are generally less efficient – but often cheaper – than c-Si modules.
    • In the United States, concentrating PVarrays are found primarily in the desert Southwest. They use lenses and mirrors to reflect concentrated solar energy onto high-efficiency cells. They require direct sunlight and tracking systems to be most effective.
    • Building-integrated photovoltaics serve as both the outer layer of a structure and generate electricity for on-site use or export to the grid. BIPV systems can provide savings in materials and electricity costs, reduce pollution, and add to the architectural appeal of a building.

    History of Photovoltaic Technology

    The PV effect was observed as early as 1839 by Alexandre Edmund Becquerel, and was the subject of scientific inquiry through the early twentieth century. In 1954, Bell Labs in the U.S. introduced the first solar PV device that produced a useable amount of electricity, and by 1958, solar cells were being used in a variety of small-scale scientific and commercial applications.

    The energy crisis of the 1970s saw the beginning of major interest in using solar cells to produce electricity in homes and businesses, but prohibitive (nearly 30 times higher than the current price) made large-scale applications impractical.

    Industry developments and research in the following years made PV devices more feasible and a cycle of increasing production and decreasing costs began which continues even today.

    Costs of Solar Photovoltaics

    Rapidly falling have made solar more affordable than ever. The average price of a completed PV system has dropped by 59 percent over the last decade.

    For more information on the state of the solar PV market in the US, visit our solar industry data page.

    Modern Photovoltaics

    The cost of PV has dropped dramatically as the industry has scaled up manufacturing and incrementally improved the technology with new materials. Installation costs have come down too with more experienced and trained installers. Globally, the U.S. has the third largest market for PV installations, and is continuing to rapidly grow.

    Most modern solar cells are made from either crystalline silicon or thin-film semiconductor material. Silicon cells are more efficient at converting sunlight to electricity, but generally have higher manufacturing costs. Thin-film materials typically have lower efficiencies, but can be simpler and less costly to manufacture. A specialized category of solar cells. called multi-junction or tandem cells. are used in applications requiring very low weight and very high efficiencies, such as satellites and military applications. All types of PV systems are widely used today in a variety of applications.

    There are thousands of individual photovoltaic panel models available today from hundreds of companies. Compare solar panels by their efficiency, power output, warranties, and more on EnergySage.

    Solar Cells

    Solar cells are in fact large area semiconductor diodes. Due to photovoltaic effect energy of light (energy of photons) converts into electrical current. At p-n junction, an electric field is built up which leads to the separation of the charge carriers (electrons and holes). At incidence of photon stream onto semiconductor material the electrons are released, if the energy of photons is sufficient. Contact to a solar cell is realised due to metal contacts. If the circuit is closed, meaning an electrical load is connected, then direct current flows. The energy of photons comes in packages which are called quants. The energy of each quantum depends on the wavelength of the visible light or electromagnetic waves. The electrons are released, however, the electric current flows only if the energy of each quantum is greater than WL. WV (boundaries of valence and conductive bands). The relation between frequency and incident photon energy is as follows:

    h. Planck constant (6,626·10.34 Js), μ. frequency (Hz)

    Crystalline solar cells

    Among all kinds of solar cells we describe silicon solar cells only, for they are the most widely used. Their efficiency is limited due to several factors. The energy of photons decreases at higher wavelengths. The highest wavelength when the energy of photon is still big enough to produce free electrons is 1.15 μm (valid for silicon only). Radiation with higher wavelength causes only heating up of solar cell and does not produce any electrical current. Each photon can cause only production of one electron-hole pair. So even at lower wavelengths many photons do not produce any electron-hole pairs, yet they effect on increasing solar cell temperature. The highest efficiency of silicon solar cell is around 23 %, by some other semi-conductor materials up to 30 %, which is dependent on wavelength and semiconductor material. Self loses are caused by metal contacts on the upper side of a solar cell, solar cell resistance and due to solar radiation reflectance on the upper side (glass) of a solar cell. Crystalline solar cells are usually wafers, about 0.3 mm thick, sawn from Si ingot with diameter of 10 to 15 cm. They generate approximately 35 mA of current per cm 2 area (together up to 2 A/cell) at voltage of 550 mV at full illumination. Lab solar cells have the efficiency of up to 30 %, and classically produced solar cells up to 20 %.

    Wafers and crystalline solar cells (courtesy: SolarWorld)

    Amorphous solar cells

    The efficiency of amorphous solar cells is typically between 6 and 8 %. The Lifetime of amorphous cells is shorter than the lifetime of crystalline cells. Amorphous cells have current density of up to 15 mA/cm 2. and the voltage of the cell without connected load of 0.8 V, which is more compared to crystalline cells. Their spectral response reaches maximum at the wavelengths of blue light therefore, the ideal light source for amorphous solar cells is fluorescent lamp.

    Surface of different solar cells as seen through microscope (courtesy: Helmholtz-Zentrum Berlin)

    Solar Cell Models

    The simplest solar cell model consists of diode and current source connected parallelly. Current source current is directly proportional to the solar radiation. Diode represents PN junction of a solar cell. Equation of ideal solar cell, which represents the ideal solar cell model, is:

    IL. light-generated current [1] (A), Is. reverse saturation current [2] (A) (aproximate range 10.8 A/m 2 ) V. diode voltage (V), VT. thermal voltage (see equation below), VT = 25.7 mV at 25°C n. diode ideality factor = 1. 2 (n = 1 for ideal diode)

    Thermal voltage VT (V) can be calculated with the following equation:

    k. Boltzmann constant = 1.38·10.23 J/K, T. temperature (K) q. charge of electron = 1.6·10.19 As

    FIGURE 1: Ideal solar cell model

    FIGURE 2: Real Solar cell model with serial and parallel resistance [3] Rs and Rp, internal resistance results in voltage drop and parasitic currents

    The working point of the solar cell depends on load and solar irradiation. In the picture, I-V characteristics at short circuit and open circuit conditions can be seen. Very important point in I-U characteristics is Maximum Power Point, MPP. In practice we can seldom reach this point, because at higher solar irradition even the cell temperature increases, and consequently decreasing the output power. Series and paralell parasitic resistances have influence on I-V curve slope. As a measure for solar cell quality fill-factor, FF is used. It can be calculated with the following equation:

    IMPP. MPP current (A), VMPP. MPP voltage (V) Isc. short circuit current (A), Voc. open circuit voltage (V)

    In the case of ideal solar cell fill-factor is a function of open circuit parameters and can be calculated as follows:

    Where voc is normalised Voc voltage (V) calculated with equation below:

    k. Boltzmann constant = 1,38·10.23 J/K, T. temperature (K) q. charge of electron = 1,6·10.19 As, n. diode ideality factor (-) Voc. open circuit voltage (V)

    For detailed numerical simulations more accurate models, like two diode model, should be used. For additional explanations and further solar cell models description please see literature below.

    Solar Cell Characteristics

    Samples of solar cell I-V and power characteristics are presented on pictures below. Typical point on solar cell characteristics are open circuit (when no load is connected), short circuit and maximum power point. Presented characteristics were calculated for solar cell with following data: Voc = 0,595 mV, Isc = 4,6 A, IMPP = 4,25 A, VMPP = 0,51 V, and PMPP temperature coefficient γ =.0,005 %/K. Calculation algorithm presented in the book Photovoltaik Engineering (Wagner, see sources) was used.

    FIGURE 3: Solar cell I-V characteristics for different irradiation values

    FIGURE 4: Solar cell power characteristics for different irradiation values

    FIGURE 5: Solar cell I-V characteristics temperature dependency

    FIGURE 6: Solar cell power characteristics temperature dependency

    [1] Sometimes term photocurrent IPh is also used.
    [2] Sometimes term dark current Io is also used.
    [3] For paralell resistanse term shunt resistor Rsh is also used.

    Simulation Tools

    Open Photovoltaics Analysis Platform. Open Photovoltaics Analysis Platform (OPVAP) is a group of software used in the field of solar cells, which include analyzing experimental data, calculating optimum architecture based on your materials, and even some research assistant tools such as PicureProcess.

    Organic Photovoltaic Device Model. Organic Photovoltaic Device Model (OPVDM) is a free 1D drift diffusion model specifically designed to simulate bulk-heterojuncton organic solar cells, such as those based on the P3HT:PCBM material system. The model contains both an electrical and an optical solver, enabling both current/voltage characteristics to be simulated as well as the optical modal profile within the device. The model and it’s easy to use graphical interface is available for both Linux and Windows.

    Other Technologies. Links

    NanoFlex Power. flexible organic solar cells.

    sphelar power. spherical solar cells technology.

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