Energy densityIn physics, energy density is the amount of energy stored in a given system or region of space per unit volume. It is sometimes confused with energy per unit mass which is properly called specific energy or . Often only the useful or extractable energy is measured, which is to say that inaccessible energy (such as rest mass energy) is ignored. In cosmological and other general relativistic contexts, however, the energy densities considered are those that correspond to the elements of the stress-energy tensor and therefore do include mass energy as well as energy densities associated with pressure.
Energy storageEnergy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic. Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms.
Home energy storageHome energy storage devices store electricity locally, for later consumption. Electrochemical energy storage products, also known as "Battery Energy Storage System" (or "BESS" for short), at their heart are rechargeable batteries, typically based on lithium-ion or lead-acid controlled by computer with intelligent software to handle charging and discharging cycles. Companies are also developing smaller flow battery technology for home use.
Metal–air electrochemical cellA metal–air electrochemical cell is an electrochemical cell that uses an anode made from pure metal and an external cathode of ambient air, typically with an aqueous or aprotic electrolyte. During discharging of a metal–air electrochemical cell, a reduction reaction occurs in the ambient air cathode while the metal anode is oxidized. The specific capacity and energy density of metal–air electrochemical cells is higher than that of lithium-ion batteries, making them a prime candidate for use in electric vehicles.
Molten-salt batteryMolten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special electric vehicles and for grid energy storage, to balance out intermittent renewable power sources such as solar panels and wind turbines.
Sodium–sulfur batteryA sodium–sulfur battery is a type of molten-salt battery that uses liquid sodium and liquid sulfur electrodes. This type of battery has a similar energy density to lithium-ion batteries, and is fabricated from inexpensive and non-toxic materials. However, due to the high operating temperature required (usually between 300 and 350 °C), as well as the highly corrosive and reactive nature of sodium and sodium polysulfides, these batteries are primarily suited for stationary energy storage applications, rather than for use in vehicles.
Renewable energyRenewable energy is energy from renewable resources that are naturally replenished on a human timescale. Renewable resources include sunlight, wind, the movement of water, and geothermal heat. Although most renewable energy sources are sustainable, some are not. For example, some biomass sources are considered unsustainable at current rates of exploitation. Renewable energy is often used for electricity generation, heating and cooling.
Lithium-ion batteryA lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. The negative electrode of a conventional lithium-ion cell is typically graphite, a form of carbon. This negative electrode is sometimes called the anode as it acts as an anode during discharge. The positive electrode is typically a metal oxide; the positive electrode is sometimes called the cathode as it acts as a cathode during discharge.
Rechargeable batteryA rechargeable battery, storage battery, or secondary cell (formally a type of energy accumulator), is a type of electrical battery which can be charged, discharged into a load, and recharged many times, as opposed to a disposable or primary battery, which is supplied fully charged and discarded after use. It is composed of one or more electrochemical cells. The term "accumulator" is used as it accumulates and stores energy through a reversible electrochemical reaction.
Nickel–metal hydride batteryA nickel metal hydride battery (NiMH or Ni–MH) is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the nickel–cadmium cell (NiCd), with both using nickel oxide hydroxide (NiOOH). However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries can have two to three times the capacity of NiCd batteries of the same size, with significantly higher energy density, although much less than lithium-ion batteries.
Grid energy storageGrid energy storage (also called large-scale energy storage) is a collection of methods used for energy storage on a large scale within an electrical power grid. Electrical energy is stored during times when electricity is plentiful and inexpensive (especially from intermittent power sources such as renewable electricity from wind power, tidal power and solar power) or when demand is low, and later returned to the grid when demand is high, and electricity prices tend to be higher.
Heavy metalsHeavy metals are generally defined as metals with relatively high densities, atomic weights, or atomic numbers. The criteria used, and whether metalloids are included, vary depending on the author and context. In metallurgy, for example, a heavy metal may be defined on the basis of density, whereas in physics the distinguishing criterion might be atomic number, while a chemist would likely be more concerned with chemical behaviour. More specific definitions have been published, none of which have been widely accepted.
Energy return on investmentIn energy economics and ecological energetics, energy return on investment (EROI), also sometimes called energy returned on energy invested (ERoEI), is the ratio of the amount of usable energy (the exergy) delivered from a particular energy resource to the amount of exergy used to obtain that energy resource. Arithmetically the EROI can be defined as: When the EROI of a source of energy is less than or equal to one, that energy source becomes a net "energy sink", and can no longer be used as a source of energy.
Lithium metal batteryLithium metal batteries are primary batteries that have metallic lithium as an anode. These types of batteries are also referred to as lithium-metal batteries after lithium-ion batteries had been invented. Most lithium metal batteries are non-rechargeable. However, rechargeable lithium metal batteries are also under development. Since 2007, Dangerous Goods Regulations differentiate between lithium metal batteries (UN 3090) and lithium-ion batteries (UN 3480). They stand apart from other batteries in their high charge density and high cost per unit.
Compressed-air energy storageCompressed-air energy storage (CAES) is a way to store energy for later use using compressed air. At a utility scale, energy generated during periods of low demand can be released during peak load periods. The first utility-scale CAES project has been built in Huntorf, Germany, and is still operational. The Huntorf plant was initially developed as a load balancer for fossil fuel-generated electricity, the global shift towards renewable energy renewed interest in CAES systems, to help highly intermittent energy sources like photovoltaics and wind satisfy fluctuating electricity demands.
Sustainable energyEnergy is sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs." Most definitions of sustainable energy include considerations of environmental aspects such as greenhouse gas emissions and social and economic aspects such as energy poverty. Renewable energy sources such as wind, hydroelectric power, solar, and geothermal energy are generally far more sustainable than fossil fuel sources.
Surface power densityIn physics and engineering, surface power density is power per unit area. The intensity of electromagnetic radiation can be expressed in W/m2. An example of such a quantity is the solar constant. Wind turbines are often compared using a specific power measuring watts per square meter of turbine disk area, which is , where r is the length of a blade. This measure is also commonly used for solar panels, at least for typical applications. Radiance is surface power density per unit of solid angle (steradians) in a specific direction.
Cost of electricity by sourceDifferent methods of electricity generation can incur a variety of different costs, which can be divided into three general categories: 1) wholesale costs, or all costs paid by utilities associated with acquiring and distributing electricity to consumers, 2) retail costs paid by consumers, and 3) external costs, or externalities, imposed on society. Wholesale costs include initial capital, operations & maintenance (O&M), transmission, and costs of decommissioning.
Lead–acid batteryThe lead–acid battery is a type of rechargeable battery first invented in 1859 by French physicist Gaston Planté. It is the first type of rechargeable battery ever created. Compared to modern rechargeable batteries, lead–acid batteries have relatively low energy density. Despite this, their ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by starter motors.
Wind powerWind power is the use of wind energy to generate useful work. Historically, wind power was used by sails, windmills and windpumps, but today it is mostly used to generate electricity. This article deals only with wind power for electricity generation. Today, wind power is generated almost completely with wind turbines, generally grouped into wind farms and connected to the electrical grid. In 2022, wind supplied over 2000 TWh of electricity, which was over 7% of world electricity and about 2% of world energy.
