What do you know about solar electric language and panel install terminologies? I want to speak about the language and terms used in solar panel installation work.
I would like to explain some solar panel and electrical terminologies. The terms covered are in no particular order.
A solar cell is a solid-state electrical device. In solar electric language it's a (p-n junction) device that converts solar energy into electricity (DC). The p-n junction is a simple positive to negative plate connection. The process in the solar cell uses the 'photovoltaic effect'.
Electricity conversion uses a semiconductor material (silicon), which absorbs sunlight energy (photons). The PV cell consists of layers of a semiconducting material like crystalline silicon. When light shines on the cell made of (silicon) semiconductor material, photon energy transfers to an electron of the silicon atom.
During radiation if a photon hits an electron the strike raises an electron to a higher energy state. The extra energy frees this high-energy electron from an external orbit of the atom. Solar cells use a photovoltaic phenomenon to capture the energy of photons. That is an explanation more about science than solar electric language.
Energy in sunlight converts to electron energy. When these energised electrons move from their outer orbit of atoms a 'hole' in the outer orbit remains. The 'hole' left by the electron creates an electric field across the layers. This action starts a flow of direct current ("DC") electricity. This is electricity that can be used for charging batteries and powering DC electrical devices.
Solar panels are interchangeably referred to as solar modules.
By connecting many solar PV cells in series a solar panel can be made . That's done to create the desired output voltage. Panel makers arrange the PV cells in a grid-like pattern on the surface of a backing material.
In solar electric language AC is alternating current and DC is direct current. PV solar panels generate DC electricity and electrical storage batteries are also DC. This DC electricity will convert to AC electricity by using an inverter. Most household electrical appliances use AC power.
Solar Photovoltaic Systems
A solar power system generates DC electricity by the photovoltaic process in solar cells. PV also means photovoltaics. A usual PV power generating system includes solar panels in an array of panels interconnection wiring, an inverter and switching.
Solar PV systems can be grid-connected, hybrid systems or off grid where the hybrid and off grid systems charge batteries that support them being autonomous stand-alone electrical systems.
Solar Array - Solar Electric Language
A solar array is a collection of solar panels wired together in series and parallel. The wiring is arranged to create the desired energy output.
The typical residential solar array consists of many solar panels placed on a roof plane that is best oriented to the equator.
It is preferred to orient solar panels to the azimuth and altitude where they'd receive the most sunlight. In solar electric language azimuth is an angular direction from north and altitude is the elevation above the horizon.
Azimuth is the measure of orientation from north. In the Northern Hemisphere the best azimuth to face solar panels is south. In the Southern Hemisphere face panels to the north. Solar panels facing east get more intense light for the early in the day or west the intense light is in the later part of the day. Whereas, solar panels on a roof facing towards the equator have solar access for most of the day it will be most intense at midday. Take consideration of nearby shade structures, which may cast shadows onto the panel.
To compensate poor orientation use more panels to increase the solar collector area. Another strategy to get more sunlight is to use solar mounting frames to adjust the orientation of the solar collectors or use solar tracking mounts.
In solar electric language the tilt angle of a photovoltaic array is basic to panel placement. It is set relative to the horizontal. The tilt angle can fix the panel to face the sun to optimize annual energy collection. Some panels can be adjusted periodically to maximize energy output during seasonal changes.
The orientation and slope of the roof on which the panels get installed set tilt angles of the array. The tilt angle can be modified using framing between the structure and the solar array. Ground-mounted solar panels are flexible about tilt angle. They can locate, orientate and tilt for the best solar access.
The earth's equator tilt is 23.45 degrees with respect to the plane of the earth's orbit around the sun. That means as the earth orbits the sun, an observer on earth sees the sun’s location in the sky change during the year. The declination angles vary from 23.45 degrees north to 23.45 degrees south.
This means the fixed tilt solar panel facing towards the equator has a range of solar aspects between winter and summer. For tilt orientations, the angle of tilt varies between mid-winter and mid-summer.
Add the angle of declination to your north latitude for the best tilt in mid-winter. In the same way, reduce it by the angle of declination for mid-summer. Say your latitude is 30 degrees N; the steepest angle you want to tilt your panels in the winter is 30 + 23 = 53 degrees. And in summer, the shallowest it would be 30 - 23 = 27 degrees.
If at this location your solar panels were mounted on a 30 degree pitched roof plane that faced south then the solar panels would be fixed at the optimum for the location. That assumes there are no trees or roof projections like a chimney stack that would cast shadows on the panels during the day to reduce their effective solar access.
Solar Mounting On Ground
A solar array can be installed on open land. Large-scale ground mount solar panels are commercially used for utility-scale solar projects.
Ground mounted solar panel systems located on open land are easy to build. The framing is open lightweight material for ease to move and install. Being away from structures, they won’t leak into a roof space. No scaffoldings needed for drilling, attaching panels and bracings erecting ground mount systems. Albeit pole mount systems need secure foundations installed to design codes.
The ground-mounted solar panel system can be set at the orientation and tilt angle to optimize energy production. This usually means you can generate electricity without risk of shading. There is good access around ground-mounted solar panels for cleaning and maintenance. That access is convenient for clearing a lot of snow from panels in the winter. Also level access from ground helps to clean dust or debris from solar panels in drier sites.
Most ground mount solar systems are fixed tilt. It’s simpler to include a tracking system during installation of the mounting. Tracking increases electricity production, but extra cost upfront.
Solar Mounting Hardware
The racking and mounting equipment is used to secure solar panels to their support base. In solar electric language the solar power installations can be mounted to collect as much sunlight as possible. We put them on rooftops, trackers, or open land ground mounted to get light without shade. Racks and mounts are tailored to fit the situations. This happens whether a rooftop, pole-mount or ground-mount application is in use.
PV panels can accommodate many roof’s particular characteristics. The solar array is usually mounted parallel to the roof plane. That can either be in a portrait or landscape configuration. These mounting styles lower the array’s visual impact.
Racking can adjust to allow for specific tilt angles. Racking that tilts the solar array away from the dominant roof pitch will impact the building’s aesthetic. The jutting panels stand out visually on a building. They are more obvious than arrays that mount parallel to their roof surface.
Manufacturers often design mini-inverters, wiring and grounding options into the array’s mounting hardware. Mounting systems provide a limited airspace between the back of the modules and the roof surface. Panels mounted close to the roof surface tend to get hotter, which lowers the amount of power from the array. Ground mounted racking does not share that problem.
Solar Array - Fixed Tilt or Moving
Fixed Tilt Array
A photovoltaic array that is set on a roof at the roof's fixed angle to the horizontal is an example of a fixed tilt array. Some solar panels that are mounted on poles for energising street lighting or display advertising have a fixed tilt arrangement.
Solar panels made from silicon semiconductor materials achieve efficiencies that top at 24%. A tracker system allows the solar array to follow the path of the sun across the sky to maintain the electrical output at near maximum efficiency. This tracking mechanism is set to maximise the solar radiation incident on the photovoltaic surface. The mechanical tracking device needs to work without monitoring. To be effective and without solar electric language they need to to automatically track the sun path and reset daily.
The efficiency of solar panels improves year by year. An effective way to further improve solar panel performance is to increase the amount of light falling on the panel face. Solar trackers increase the solar panels’ output by aiming the solar panels directly into the sunlight. The tracker aligns the panel with the sun for as much of the day as possible. This energy capture strategy is cost effective. It compares well with buying and mounting extra solar panels.
Balance Of System (BOS)
The balance of system in the solar electric language is a term encompassing all components and equipment of the solar system. Albeit, BOS doesn't include the photovoltaic panels themselves.
That means anything a photovoltaic system uses making DC into AC electricity. BOS includes: mounting system, wiring, switches and safety cutoff. It includes inverters, charger/ regulator, battery bank and instruments.
A solar power system generates direct current (DC) electricity. The inverter does not produce any power itself. It modifies the DC power provided to it by the solar panel. In solar electric language a solar inverter changes DC electricity from the solar system into alternating current (AC) electricity. The best inverter device inverts the direct current flow into an alternating current in the shape of a sine wave.
Power inverters can be entirely electronic without moving parts in the conversion process. Older inverters used a combination of mechanical rotary apparatus and electronic circuitry.
The AC output frequency of the power inverter device is 50 or 60 cycles per second (Hertz). Frequency is set matching the power line AC frequency.
The quality of the AC power produced by the inverter depends on the AC waveform. An inverter uses micro-controllers to improve the DC supply. That output is then pulsed with MOSFETs to produce the AC’s modified sine wave signal.
Power inverters have their power rating expressed in kilowatts. This is the power input that will be available to the device from the DC source.
Efficiency refers to the percentage of sunlight captured and converted into usable electricity. To calculate the efficiency of a cell divide the amount of electrical power coming from a solar cell by the amount of energy in the sunlight shining on it. Efficiency isn't a term unique to solar electric language.
When referring to a solar cell or a solar panel, efficiency in important. The amount of electricity produced from PV cells depends on a few factors:
These factors affect PV efficiency. Factors like partial shading are taken into account when considering light intensity at the shaded cell.
Cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) are two thin-film PV semiconductors materials. These materials can be placed directly on the front or back of the solar cell’s surface. Depositing one or more thin layers of CdTe or CIGS material onto a supporting substrate contributes to making a thin-film solar cell. Thin film photovoltaics are solar cell alternatives to monocrystalline silicon cells and polycrystalline silicon cells.
CdTe is the second-most common PV material. But efficiencies (in a PV cell) of CdTe aren't as high as that Si. Manufacturing CIGS cells material is challenging. Its thin cell coatings need more protection than silicon cells to give effective operation outdoors.
Solar Electric Language - Systems
Electrical (Or Utility) Grid
This term refers to the system including poles and wires that delivers electricity from suppliers to electricity consumers. Electrical grids consist of generating stations, transmission lines, and distribution lines. Generating stations produce the electrical power.
A network of high-voltage transmission lines carry power to control centres and switching yards. Distribution lines then move the electricity from the control centres to individual customers.
Grid-Connected System/Grid-Tied System
Solar photovoltaic (PV) arrays act like an electrical generating plant. They supply power into the utility network. Customers with grid-tie systems provide the grid access to their solar PV generators.
Customers of the electrical utility with their own solar panels can generate and consume their own power during the daytime. The owners of the grid-tied PV solar systems may sell their excess PV generated electrical capacity into the local utility electrical grid and be paid an agreed tariff. Local electrical grid-tied customers have access to grid power during the night when there is no solar power being generated.
Stand-Alone Electric Systems
Stand-Alone Solar System
The solar electric language for a stand-alone system is an autonomous or hybrid photovoltaic power system that is not connected to a grid. This power system need not have storage if it has a fuel generator as back-up for night operation, although most stand-alone systems could use batteries. Stand alone systems need battery storage or some other form of electrical back up to operate uninterruptedly.
Hybrid energy systems couple of two or more energy supplies technologies. For example an off-grid solar PV hybrid system may also include other sources of electricity generation, like wind or fossil fuel generators and UPS with batteries where they do not have a grid-tied back-up.
The hybrid power applications need to consider generation, energy storage and energy management if they become a decentralised autonomous power system. The hybrid electrical system may be quite diverse with a decentralised renewable power generator and battery support. Hybrid electrical systems may be regional systems using PV, wind turbine, wave energy, battery storage and use something like a propane standby generator for backup.
An interconnection agreement is a business contract between a utility company and customer. This is solar electric language for a contract between the customer and the utility allows them to connect solar power to the grid. The purpose of the interconnecting agreement is for electrical network safety.
Interconnection has two components:
- Determining technically whether a solar generator can safely and reliably interconnect with the electric grid
- Negotiating the terms and conditions of the interconnection agreement in detail
To sell solar-generated electricity to the utility a customer must connect their solar generator to the electric grid. First they must ensure their system is fully compatible with the grid. The utility agrees to buy electricity generated by the householder's solar power system. The utility agreement sets out their electricity buy and sell prices.
Net metering is a billing arrangement. It credits or charges the user according to local rates and rules.
This net metering allows residential and commercial customers to sell any electricity they feed into the grid. A net meter records the energy sent compared to the energy received from the grid. Customers generating electricity deliver spare energy into their local power grid and get paid.
This policy originated in the U.S. in the late 1970’s. It compensated green energy proponents for investing in renewable energy. When more renewable energy gets generated than used, the utility provides a credit for it. They pay for the surplus at the full retail price.
Solar Electric Language - Batteries
Stored backup energy is available during an emergency, which involves periods of electrical grid outage. Battery power is available when the solar system cannot generate sufficient energy in real time to run appliances. Solar batteries incorporate a variety of technologies. These include (but are by no way limited to) lead acid, lithium-ion and vanadium redox flow batteries.
In a battery-based PV system, a charge controller is used. A charge controller regulates voltage and/or current to keep batteries from overcharging. It regulates the voltage and current going into the battery from the solar panels. It monitors battery voltage between the PV array and the battery bank.
Discharge Rate (C Rate)
1C rate means that the discharge current that will discharge the entire battery in 1 hour. The C rate is a measure of battery being discharged relative to its maximum capacity. The C rate is usually expressed in amperes electrical current for the time it’s taken from the battery. For a battery with a capacity of 100 AH, this equates to a discharge current or C of 100 Amps.
Depth of Discharge (DOD)
If a battery is 100% fully charged, it means the DOD of the battery is 0%. The Depth of Discharge describes how much discharge the battery has experienced. A battery that’s used 30% of its energy has 70% energy remaining. The DOD for this battery is 30%.
Solar Electricity Language Items
Shading of part of a panel caused by a tree branch, debris, or snow causes that cell or group of cells to stop working. Bypass Diodes are wired in parallel with individual solar cells in panels. The diodes provide an alternative current path around the cell or cells. In the event that a cell or section of a panel becomes faulty or open-circuited the diodes come into play.
Diodes have a cost. Some solar panels get constructed with small groups of cells wired together. Each connected group would have a built-in bypass diode protecting it.
A Diode is an electronic device that allows current to flow in one direction only. Diodes get built into the solar module and charge controller. They stop a reverse current leaking from the battery to the solar module at nighttime. This is also referred to as a blocking diode.
A junction diode is a semiconductor device with a junction between the two regions of opposite conductivity (n-type and p-type). There is a built-in potential that passes current better in one direction than the other. Solar cells are junction diodes.
Maximum Power Point Tracker (MPPT)
MPPT is an electronic DC-to-DC converter. It's a device that optimises the match between the solar array (PV panels), and the battery bank.
MPPT technology maximises the output power from the solar panel. It does that by keeping its operation on the peak of the current-voltage curve. That means holding the knee bend of P-V characteristics curve [power (watts) = volts × amps].
The MPPT charge controller converts a higher voltage DC output from solar panels to a lower voltage. That means converting higher array voltage into higher amperage. That is effective for the battery absorbing more watts from the array. Maximising the power output increases the efficiency of the solar panel.
Solar Electric Language For Electrical Measurement
Ampere is the measured unit of flow of electrons in the electric current through a conductor. An analogy for electricity is the flow of water through a pipe.
The rate of flow of electricity as the electric current is measured in Amperes. In an electrical equation the letter ‘I’ is used to represent current.
An electric current of Amp represents 1 Coulomb of unit electric charge flowing past a point in 1 second. If the term 'coulomb' is unfamiliar, it is the standard international unit of electrical charge equivalent of one ampere-second.
One amp produces an electric force of 1 volt across a resistance of 1 ohm.
One joule is equal to one "coulomb-volt". The equivalent work to moving a one coulomb electric charge through a one volt electrical potential difference. One joule per second is the watt (W), which is a standard international unit measure of power.
Most batteries get rated in AH. It is a measure of the quantity of electricity or charge. So, we can relate it to a battery with a 10 amp-hour capacity. It will continuously supply a current of 1 amp to a load for 10 hours, or 2 amps for 5 hours, or 10 amps for 1 hour before becoming completely discharged.
Alternating Current (AC)
In alternating current the direction of electron flow in a conductor or semiconductor cyclically reverses direction. The electron movement rapidly fluctuates at intervals of second 60 Hertz or 60 cycles per second. (In Europe and Australia AC frequency is 50Hz.) Use a power transformer to change the voltage of an AC power source.
Direct Current (DC)
Electric current in which electrons flow consistently in one direction is direct current. This is the current that flows from batteries and solar panels. See also "alternating current".
Distributed Electrical Systems
Distributed generation refers to power generation at the point of consumption. This is different to central electricity systems that supply to network grids. A residential photovoltaic system is a distributed system.
Generating power at the point of consumption, rather than centrally, reduces the cost. The complexity and inefficiencies associated with power transmission and distribution are lower.
Solar Electric Language For Power
A circuit is the path that electrons follow from a power source through an electric circuit. The circuit through electrical devices may return through another line to the source. A circuit is closed to make electrical current flow. The electron flow may stop because the path is broken or it may find a path to ground.
1,000 watts is 1 kW. A residential sized solar PV system is around 5 kW.
A kilowatt-hour is a unit of energy, which measures the amount of power (kW) used over a given period of time (hours). Customers’ electricity usages get measured in kWh.
Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
There's stiff competition between inverter device manufacturers. You’ll find that one manufacturer is using MOSFETs and another uses IGBTs.
MOSFETs in power inverters superseded BJT switches in the late 1980's. These MOSFETs get used in low and medium power inverters up to a few kilowatts. The MOSFET is a three-terminal device available in n-channel and p-channel versions. The n-channel is more often used. Load current flows in the drain and out of the source. MOSFETs are voltage-controlled devices. They need little power to keep 'on', meaning they're less complex than BJT. But when MOSFETs are ‘on’ they offer more resistance, meaning higher power loss. That makes them less efficient as a power switch.
The Bipolar Junction Transistor (BJT)
This was the first device used for power switching. The advantage of the bipolar transistor is their low collector-emitter voltage. That means it's an efficient power switch with small power loss relative to the load power.
Insulated Gate Bipolar Transistor (IGBT)
IGBTs are hybrid devices combining features of the MOSFET (easy on and off) and the BJT (lower power losses). The advantages of the IGBT over the MOSFET and BJT raised their frequency of use.
A transformer is a static electrical device. It transfers electrical energy between two or more circuit coils through electromagnetic induction.
This device uses alternating electrical current and induction to raise or lower the voltage as the electrical energy transfers from one circuit to another.
There are types of transformers with different construction, purpose, and use as under:
Step Up Transformer and Step Down Transformer
In transmission and distribution power system network the power voltage gets adjusted. It gets 'stepped up' to lower resistance or 'stepped down' to use in appliances. Transformers are designed for robust outside use. The transformers generate heat so get cooled by air or oil.
Three Phase Transformer and Single Phase Transformer
Three Phase Transformer gets used in three phase power systems. The three-phase transformer unit is large and expensive. Use a bank of three single-phase transformers when transport size is restrictive.
Solar Electric Language - More Terms
The unit of resistance to the flow of an electric current.
Open-Circuit Voltage (Voc)
There is an "open circuit" when the terminals are not connected to anything. That means no current flows into or out of either terminal. The maximum possible voltage across a photovoltaic cell or panel occurs with nothing connected to it. This is the open circuit voltage across the cell in sunlight when no current is flowing.
We call the electrical pressure Voltage. Potential energy makes the electrical current flow in a circuit. A device such as a battery provides a potential difference in an electric circuit. Using a water analogy, the battery is like a water pump that creates pressure in the pipe causing the water to flow. In analogy with water, voltage is the 'pressure' pushing the electrons around the circuit.
A unit of voltage measured in Volts. One volt produces one ampere of current when acting against a resistance of one ohm.
Watt is the unit of electric power. When one ampere of current is flowing at a potential of one volt it produces one watt of power.
The Last Words
This blog article has been fun to write. Electrical work should always be carried out by a licensed and appropriately experienced electrician.
Sometimes electricians speak about electrical components and gauges of wiring and use electrical language in terms of standards, codes, and specification elements using words that are familiar to them but not to most people.
I hope this has helped.
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