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Tesla Powerwall 3 Rebate now Extended Until June 30th
Posted 14 Dec
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Quick Answer: Batteries store energy as chemical potential energy, not kinetic energy. This stored energy is released as electrical current once the battery is connected to a circuit.
This article explains exactly how batteries store and release energy, what type of energy a battery contains, and how this applies to modern solar batteries and home energy storage systems in Australia.
Batteries store energy in the form of chemical potential energy. When a battery is completely charged, chemical reactions happen inside the battery that create a difference in electrical potential between the positive and negative terminals. This energy is stored as a chemical reaction until the battery is connected to a circuit.
Once the battery is connected to a circuit, whether it be a simple AA or solar battery, a chemical reaction occurs and electrons begin moving where a current is produced.
A battery stores chemical potential energy. This is a form of potential energy — meaning it is energy that is stored and waiting to do work, rather than energy that is actively in motion (kinetic energy).
The chemical energy is held within the electrochemical reactions between the battery's anode, cathode, and electrolyte. When a circuit is completed — whether that's turning on a light, powering a phone, or a solar battery discharging into your home — that stored chemical potential energy is converted into electrical energy, which then flows as a current.
To directly answer the common question: a battery is an example of potential energy, specifically chemical potential energy. It is not kinetic energy.
A fully charged battery that is not connected to anything contains potential energy — specifically chemical potential energy. It only becomes kinetic energy once a circuit is completed and electrons begin to flow.
Solar batteries work on exactly the same principle as any other battery, just at a much larger scale. During the day, your solar panels generate DC electricity. Any excess energy not used by your home is sent to the battery, where it's stored as chemical potential energy inside the battery's cells.
In the evening, on cloudy days, or during a blackout, that stored chemical energy is converted back into electrical energy and released into your home as usable current. Solar batteries like the Tesla Powerwall, Sungrow SBR/SBH, and Fronius Reserva all rely on this same chemical-to-electrical conversion to power your home when the sun isn't shining.
Most modern batteries are Lithium Iron Phosphate (LFP or LiFePo4) which is a durable and safe battery chemistry, also used for its longevity and lower cost.
Take a rainwater tank at home connected via a hose to a garden sprinkler; the type that rotates to evenly water the lawn. If the rainwater
tank is full the sprinkler spins quite rapidly; less so as the tank empties. What is happening?
The answer is that the potential energy due to the height of the water in the tank is converted into work done, and kinetic energy
expended by the rotating water turbine. We say potential or static energy because while the tank is at rest and no water is flowing the
water has the potential to do work and expend energy
whilst it’s not actually doing any work.
When full the tank has, by virtue of the height if the water, greater potential to do work than when the level falls. The tank stores more potential energy when its full; less when empty.
Kinetic energy is the energy of motion — it's what potential energy becomes once it is released and doing work. In the water tank example, kinetic energy is the spinning sprinkler. In a battery, kinetic energy is the flow of electrons through a circuit once the battery is connected. A battery at rest stores potential energy; a battery powering a device is producing kinetic energy in the form of electrical current.
The first obvious one is a battery whereby chemical reactions, electrical energy is stored in the chemistry of the battery. Like with the water tank the energy is stored as potential energy or here as chemical potential energy; waiting in the battery to do work by forcing a flow of electrons through an outside element such as a light bulb for that potential energy to be converted electrical energy and then to light energy and heat energy in the light bulb.
Note that the light bulb doesn’t store energy, it dissipates energy and converts energy from one form to another; light and heat.
The word battery suggests an array or collection of things operating in concert. For example, we speak of a battery of cannons. In an electrical battery we are referring to more than one electrochemical cell connected, usually in series. The individual cell voltages accumulate to give us the total battery voltage. In the domestic renewables world battery nominal voltages range from 48 volts to over 500 volts.
In a lithium-ion cell the nominal or average voltage varies with the chemistry employed. 3.2 volts for lithium ferro phosphate and 3.7 volts for those cells containing nickel, manganese, cobalt. As the cell charges and discharges these voltages rise and fall. There are upper limits over which the cell’s life can be compromised and overheating may occur and lower voltages where permanent damage will occur.
In the battery manufacturing process, cells are chosen to have closely matched characteristics before being joined to form a battery. However, no matter how closely they are matched, during the charging phase individual cell voltages inevitably drift apart and this causes problems. Unchecked, some cells may rise to the dangerous overvoltage region and with some chemistries, catastrophic failure accompanied by fire.
Enter the electronic module attached to the battery called the Battery Management System (BMS). This device monitors each cell voltage, and
in some systems each cell temperature and should a cell start to deviate from the norm by more than several thousandths of a volt the BMS
switches a resistor across that cell to bleed energy from that cell until it equals the correct value. Because of the criticality of
managing cell overvoltage the reliability of the BMS is extremely important.
Self managed and managed batteries. A battery which manages itself without any outside intervention is called a self managed battery. Those
which have internal management supplemented by oversight from the connected inverter are called managed batteries. Today’s high voltage
batteries, those with nominal battery voltages above 48 volts, are exclusively managed batteries. Some, low voltage batteries are managed
batteries.
Images courtesy of Energy Renaissance and Pexels
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