AC (Electrical): Alternating current. Current that changes in direction at intervals of frequency. The main grid electricity is all alternating current. In Europe, the fundamental current direction changes 100 times per second (frequency 50Hz), while in Australia and the United States, it changes 120 times per second (frequency 60Hz).
Air mass: Air mass is related to the distance that solar radiation must travel through the atmosphere. The atmospheric mass is 1, which means that the sun is in the sky and must travel through the atmosphere with a thickness of 1 to reach the surface of the earth. For a given location, this value changes throughout the day and can be calculated using trigonometric functions and the sun’s altitude angle.
Reflectivity: The amount of solar radiation reflected back by the earth’s surface at a given location.
Sun altitude angle: The angle between the position of the sun in the sky and the horizontal plane at a given time.
Ambient temperature: ambient temperature.
Ampere (A): The unit of measurement of electric current.
Amorphous (silicon): An amorphous element. Amorphous solids lack order and structure in their molecular composition. Glass is a typical amorphous solid. The same is true for amorphous silicon, which is used in some thin-film solar cells.
Azimuth: It is the angle between true north on the compass and the position of the sun. The latitude angle is measured clockwise along the horizontal plane (ground) from true north.
System balance components: refer to components other than photovoltaic modules and inverters in a photovoltaic system. The balance components include support structure, cables, circuit breakers/isolation devices, component junction boxes, photovoltaic combiner boxes, grounding devices and electric meters.
Bypass diode: A solid-state electrical component that can only pass current in one direction, allowing current to pass through a blocked or damaged battery without affecting the output of other batteries.
Circuit breaker: A device that can automatically cut off the current when an electrical fault occurs. The device usually includes arc extinguishing technology (if an arc is formed).
Concentrated solar power (CSP): This is a form of large-scale solar thermal utilization technology that uses mirrors to gather sunlight to generate electricity. In most cases, the sun’s rays are used to heat water and produce steam, which then drives steam turbines to generate electricity.
Current (I): The flow of electrons around the circuit. Traditionally, current flows from the positive electrode to the negative electrode. The SI unit of current is ampere (A).
DC (Electrical): Direct current. Not only the amplitude will not change periodically, but the current flowing in one direction is stable. The photovoltaic cell outputs direct current.
Deciduous wood: refers to trees that produce fallen leaves in winter.
Direct radiation: Solar radiation that reaches the surface of the earth directly from the sun.
Scattered radiation: Before solar radiation reaches the surface of the earth, it is dispersed or absorbed by atmospheric clouds and gases, and then released.
Dye-sensitized solar cells: an emerging technology that uses colored dyes and titanium dioxide to generate electricity.
Efficiency-Photovoltaic cell: A unit of measurement for the ratio of output power (electricity) to input power (solar radiation). Efficiency is usually used to compare photovoltaic cells.
Electromagnetic radiation (EMR): Energy that propagates through space, such as microwaves. Sunlight is a typical case of electromagnetic radiation.
Fuse: In the event of a short circuit or overcurrent, a device that protects the electrical system from damage by cutting off the power supply.
Grid-connected system: a photovoltaic system that directly outputs power to the grid. In typical cases, grid-connected photovoltaic systems have no energy storage (ie, storage batteries).
Silicon ingot: high-purity silicon block, used to cut out photovoltaic cells. The silicon bond can be polycrystalline silicon or single crystal silicon, depending on the casting method.
Exposure: The total amount of solar radiation that a person hits on the surface throughout the day, measured in peak solar hours (PSH) or kWh/m/day.
Inverter: A device that converts direct current into alternating current. The inverter is a key component of the grid-connected photovoltaic system.
Irradiance: The amount of solar radiation incident on the surface at any one time, measured in W/m² or kW/m².
Radiation: The total amount of solar energy received in a given period of time per unit area, such as one day, one month, or one year. The unit of measurement of radiation is wh/m3/time period. For a site, the annual radiation amount is usually given, using kWh/m²/annual amount. The term “exposure” refers to the amount of radiation measured in a day. Radiation is a cumulative measurement unit, not an instantaneous measurement unit; it is the sum of irradiance over a period of time.
I-V curve: a curve used to draw the output characteristics of photovoltaic cells. This curve shows the relationship between voltage and current and can be used to determine output power and efficiency.
kWh: Kilowatt-hour, a common measurement unit of energy.
Load: Refers to the amount of power and/or power-consuming equipment consumed at any given time.
Low voltage (LV): IEC defines low voltage as AC voltage 50-1000V, or ripple-free DC 120-1500V. See Volt (V).
Magnetic declination/change: The difference between geographic true north and magnetic north (such as on a compass). This value will vary significantly with location.
Maximum power point (MPP): The maximum power point that can be extracted from the photovoltaic module on the 1-V curve. Maximum Power Point Tracker (MPPT): A device that can correct the load of the photovoltaic array to make the system work at the maximum power point.
Monocrystalline silicon (Monocrytalline): refers to silicon wafers made of single crystals. The typical technique is to produce single crystal silicon from silicon seed crystals, place the silicon species in a crucible of molten silicon, and slowly pull it out while rotating.
Polycrystalline silicon (Multicrysalline): Also known as Polycrystalline, polycrystalline silicon photovoltaic cells are made of silicon wafers composed of multiple crystals. The typical technique is made by casting molten silicon blocks, which will form many small silicon crystals.
Battery rated operating temperature (NOCT): The temperature at which photovoltaic modules work under the following conditions: solar irradiance 800W/m², ambient temperature 20°C and wind speed 1m/s
Nuclear fusion: A reaction that takes place inside the sun in which atoms combine or fuse into an atom of a different element, for example, two hydrogen atoms combine to form a nitrogen atom.
Off-grid photovoltaic system: also known as stand-alone photovoltaic system. Off-grid systems are not connected to the main grid, and typically need to store electricity in batteries for subsequent use.
Ohm (Ω): The SI unit of resistance.
Open circuit voltage (Voc): The voltage at both ends of a photovoltaic cell or component under direct sunlight and when no current flows, that is, the maximum voltage that a photovoltaic cell can generate. The manufacturer’s data sheet gives Vc, and the unit of measurement is volts (V).
Passive solar energy design: refers to a building design method that efficiently utilizes solar energy. The typical situation is to increase the comfort of heat utilization and reduce the heating and cooling load.
Peak power: The maximum amount of power that a photovoltaic cell, module or array is expected to emit under standard test conditions. The typical bee power unit is bee watt (Wp), peak kilowatt (kWp) or peak megawatt (MWp)
Peak Solar Hour (PSH): A common measurement unit of exposure or daily radiation. The PSH in a day is the number of hours of output power under the rated condition of 1000/m. Therefore, it gives the equivalent electrical energy of the total electrical energy throughout the day, that is, it is the daily radiation wh/m/day divided by 1000.
Photoelectric effect: A process in which an element emits electrons after absorbing electromagnetic radiation. See electromagnetic radiation.
Photosynthesis: The process of converting sunlight, carbon dioxide and water into carbohydrates. Photosynthesis is the way for plants to survive.
Photovoltaic (PV): Refers to a device that directly generates electricity from sunlight.
Photovoltaic array: photovoltaic modules are physically and electrically connected to form an array.
Photovoltaic cell: A single semiconductor device that generates electricity when sunlight enters the surface, also known as a solar cell.
Photovoltaic modules: Photovoltaic cells are physically and electrically connected to form modules. Typically, a frame is used to clamp the photovoltaic cells together and encapsulated with a protective material (usually glass).
Polycrystalline silicon (Polycrystalline): See polycrystalline silicon (Multicrystalline).
Potential difference (electrical): The difference in potential energy between two points. If a wire is used to connect two points, current will flow. The SI unit of potential difference is volt (V).
Resistance: A measure of the ability of a material to prevent the flow of electric current. The SI unit of resistance is ohm (II). Semiconductor: A type of material used to manufacture photovoltaic cells and many electrical components. Semiconductors have the properties of both insulators and conductors, and silicon and aluminum are examples.
Short-circuit current (Isc): The current that flows through the photovoltaic cell under short-circuit conditions (that is, when there is no load or resistance). This is the maximum current that a photovoltaic cell can output, measured in amperes (A).
Silicon: A semiconductor material commonly used in the preparation of photovoltaic cells.
Solar Concentrator: A device that increases the density of light received on a solar cell, typically a lens or reflector. Concentrators can increase the output power of photovoltaic cells by increasing the amount of solar energy incident on the cells.
Solar constant: the peak solar irradiance (1367W/m²) at which solar radiation reaches the earth’s atmosphere.
Solar power generation system: A system that converts solar energy into electrical energy. Photovoltaic system is the main technology of this type of system.
Solar thermal utilization technology: a system that captures solar thermal energy, such as solar water heaters or solar concentrating power generation.
Stand-alone photovoltaic system: see off-grid photovoltaic system.
Standard Test Conditions (STC): A series of standard conditions specified for photovoltaic cell testing, so that photovoltaic cells can be compared. These conditions include solar irradiance of 1000 w/m², air quality of 1.5 and battery temperature of 25°C.
SI unit: an abbreviation for the International System of Units, a series of units used to simplify engineering calculations. This includes watts, joules, meters, and most of the units used in this book.
Thermal quality: The ability of a building to resist external temperature fluctuations. High thermal mass materials can be described as materials that slowly absorb and release thermal energy, such as concrete. Materials with low thermal mass are materials that absorb and release thermal energy quickly, such as paper.
Thin-film solar cells: solar cells prepared from materials suitable for large-area deposition. Since the semiconductor material layer is significantly thinner than conventional monocrystalline silicon and polycrystalline silicon solar cells, it is called “thin film.”
Tracking system: A support system that includes a mechanical device that can change the orientation axis and/or tilt axis of the photovoltaic array, thereby optimizing the exposure of the photovoltaic array to the sun and capturing more solar radiation.
Volt (V): A unit of measurement for voltage or potential difference. See potential difference (electrical).
Voltage drop: Voltage loss (and power loss) mainly due to cable resistance.
Watt (W): The SI measurement unit of power. A unit commonly used in photovoltaic systems, such as kilowatts (kW) equals 1000w, or megawatts (MW) equals 10000000.
Watt hour (wh): A unit of measurement of electrical energy. If a certain electrical appliance uses 1w of power for 1h, it will use 1Wh of electrical energy. The same electrical appliance works for 6 minutes and uses 0.1Wh. Kilowatt hour (kWh) is equal to 1000wh, which is also very common.
Peak Watt (Wp): The output of a photovoltaic cell under optimal conditions, usually under standard test conditions. The peak kilowatt (kWp) is often used to describe the output of a photovoltaic array. See standard test conditions (STC).