Glossary
Services
Inspection & Testing of Solar PV Systems
Solar PV Maintenance & Repairs
Solar PV & Battery Storage Installation
Other Services
Get In Touch
This glossary has been put together to assist with the terminology that you may come across when looking at Solar PV and electricity generation.
The terms used about Solar PV systems and battery storage are similar – but there are some extra terms you could come across if you’re exploring battery storage solutions.
This section is in five parts
- Electricity Terminology
- Solar PV Terminology
- Battery Storage Terminology
- Example schematic/layout of a medium-sized commercial Solar PV System using a string inverter.
- Surge Protective Devices (SPD)
Electricity Terminology
Alternating current (AC)
Alternating current is an electrical current that is used to power most of your appliances, chargers, lights and anything you plug into your power points at home. With a solar PV system, the inverter changes direct current (DC) electricity (see direct current ( ‘DC electricity’)) into alternating current (AC) electricity to use in your home.
Arc Fault Detection Devices (AFDDs)
AFDDs are protective devices installed to provide protection from arc faults. They use microprocessor technology to analyse the waveform of the electricity being used to detect any unusual signatures which would signify an arc on the circuit. This will cut off power to the affected circuit and could prevent a fire. They are far more sensitive to arcs than conventional circuit protective devices.
Baseload
Your baseload power or baseload demand is the lowest amount of electricity you use at home at any point in time, and is usually measured over a 24-hour period and can be seasonal. If you have an advanced meter you can use your interval data that shows your electricity consumption. Learning about the way you use electricity at home, including your baseload power, is a great first step when you’re working out what size solar PV system may suit your needs.
Demand
In the electricity industry, demand refers to how much electricity is needed at a particular time. For example, there is generally a high demand for electricity across the grid on cold days in winter when many people use electrical heaters, compared to warmer summer days.
Direct current (DC electricity)
Direct current (or DC electricity) is an electrical current which flows in just one direction. If you have a solar PV system at home, your solar panels will generate DC electricity and send this to the inverter to be turned into alternating current (or AC electricity) to power things in your home like your lights and appliances.
Electricity units
Electricity is the movement of electrons and often measured in watts (W), kilowatts (kW) and kilowatt-hours (kWh) . A ‘unit’ of electricity is one kilowatt-hour (kWh). The price you pay for electricity includes an electricity charge for how many units of electricity you have used from the grid.
Energy efficiency
The higher the energy efficiency rating something has, the more efficient it is. For example, a washing machine with a high energy efficiency star-rating will use less energy per wash than a lower efficiency model of the same size (with the same kind of wash settings).
Grid
When you’re exploring solar power, you’ll often find references to electricity from “the grid” or the network. This refers to the connected network of electricity infrastructure including the generators, and the transmission and distribution lines that transport electricity to homes, businesses and other grid-connected consumers. Even with a solar PV system, you’ll need to draw on electricity from the grid when your system isn’t generating enough power to meet your demand.
Irradiance
This is a measure of solar energy or light energy from the sun on the Earth at a point in time. Solar irradiance is generally highest when the sun is shining during the middle of the day, compared with early morning and late afternoon sunshine.
Kilowatt (kW)
A kilowatt is a measure of power that is 1,000 watts. You might have a 1kW appliance. Whether you use this for a minute or an hour or more, it will still need 1,000 watts (or 1kW) of power to function.
Kilowatt-Hour (kWh)
A kilowatt-hour is a measure of energy. If you run a 1kW appliance for an hour, you will be charged for 1kWh of electricity. If you used the same appliance for two hours, that would equate to 2kWh of electricity. Kilowatt-hours are measured over time.
Load
Load means the amount of electricity used by any electrical appliance or the need in a system at any given time.
Low load
As the name suggests, low load is when there’s a low amount of electricity being used or required in comparison to the amount of electricity available. For example, generally, in the middle of the day, there is a low demand for electricity in the grid as most people are at work or school, however, during this period the electricity grid is generally supplied by a high level of electricity generated by solar PV systems which can lead to a low load situation. Low load across the grid can cause challenges for the electricity system as a whole.
Lightening Protection System (LPS)
A lightning protection system (LPS) is a network of components that protects buildings and structures from lightning strikes by providing a safe path for lightning’s energy to travel to the ground.
Peak demand
Refers to the highest level of demand for electricity over a given period. Peak demand in the grid usually occurs in the mornings and evening as people awake or are returning home from work on the coldest days, typically in winter.
Power
Power is the rate at which electricity is flowing and is measured in watts or kilowatts (kW).
Renewable energy
Compared to fossil fuels and other non-renewable energy sources, renewable energy can be supplied from a source which can be replenished (or renewed). Renewable energy includes sunlight (as solar energy), wind power, tidal and wave energy and geothermal heat.
Surge Protection Device (SPD)
See section below.
Watt
This is the measure of electrical power either used by an appliance – or produced by a solar PV system, inverter or battery storage system. You might be familiar with watts as a measure of the power of a lightbulb. You’ll also find watts mentioned in the solar industry as a measure of the size of your solar PV system. For example, you might have a 3kW solar PV system, which means it can produce 3,000 watts of power.
Battery Terminology
Battery
Batteries are electrochemical devices which store energy, for example, to be used for torches and toys – and battery storage systems for homes work in a similar way.
The role of a battery for your home if you have a solar PV system is to store excess solar power that’s generated by your solar PV system, to be used at other times.
Battery capacity
This is how much energy a battery is able to store and deliver in a single discharge. Battery capacity for home battery storage solutions is usually measured in kilowatt hours (kWh).
Battery case
Just like your mobile phone case, a battery case is a tough protective case that protects the battery cell or cells inside. Unlike your mobile phone, this battery case is usually part of the battery and doesn’t need to be bought separately.
Battery cell
A battery can be a single cell battery or made up of many individual units called cells.
Battery coupling
Battery coupling is the way which an inverter works with a battery. There’s AC coupling, which converts solar power to AC before converting it back to DC for battery storage. This can result in some of the energy being lost in the two stage conversion process prior to storage.
There’s also DC coupling, where the inverter takes solar power straight to the battery as DC power without converting it to AC. This type of battery coupling is usually more efficient than AC coupling because it involves less conversions and can be suitable for bigger solar PV systems.
Battery cycle life
Battery cycle life is not the ‘life span’ of the battery but is the number of times a battery can be fully discharged before it reaches a level of degradation that it can only store 80% of its original capacity.
Battery management system (BMS)
This is a combination of software and electronics used to control the charge and discharge of a battery. Generally the BMS is built into the battery, which can help the inverter manage the battery by not charging or discharging it too much or too quickly.
Charge/discharge rate
This is a measurement of power, expressed in kilowatts (kW) to show how quickly a battery can be charged and discharged.
The higher the charge rate, the faster your battery could charge. With a lower discharge rate, your battery may last longer but you might not be able to use it to power your bigger appliances and equipment.
Cycle
A cycle is one complete sequence of the charge and discharge of a battery.
Depth of Discharge
This indicates the level or percentage of the battery that can be discharged relative to the overall capacity. Batteries don’t usually have a 100% depth of discharge because that would shorten the life span of the battery.
While older lead acid type batteries might have a depth of discharge of about 50%, Lithium ion batteries (and some other types) can have depth of discharge of around 80 to 90%. At this point, the battery would shut off and not provide any further power to help protect the life of the battery.
Discharge
Battery discharge is process of a battery sending its energy out to be used. When a battery is fully discharged there is no usable energy left.
Discharge rate
This is a measure of how quickly a battery is discharged, measured by a C rating. As an example, torch batteries would have a low C rating while an electric vehicle has a much higher C rating.
Grid Charging
This where the battery is charged from the grid, (generally at cheaper off peak/night rates), and discharged to the load, (generally at high peak tariff times). This makes a saving of the difference between the two higher and lower tariffs.
State of Charge (SOC)
This is the percentage of charge left in the battery.
Total Energy Throughput
This is the amount of energy a battery can provide over its entire life. Total energy throughput is worth considering when you’re looking at the different prices of battery storage solutions. It’s usually expressed as megawatt hours (MWh) where one MWh is equal to 10.
Solar PV Terminology
There’s a lot of technical jargon used in the solar industry. Here’s a solar glossary to help you learn more about the terms you might come across when you’re looking for a solar PV system.
AC – electricity generated by the Grid, distributed by the DNO and used to power lights and appliances.
DC – electricity generated by the PV system and sent to the inverter to be converted to AC electricity.
Distribution Network Operator (DNO)
The organisation that owns or operates a Distribution Network and is responsible for confirming requirements for the connection of generating units to the Grid.
Electricity Network
An electrical system supplied by one or more sources of voltage and comprising all the conductors and other electrical and associated equipment used to conduct electricity to convey energy to one or more Customer’s installations, street electrical fixtures, or other Networks.
Islanding
Any situation where a section of an electricity Network, containing generation, becomes physically disconnected from the DNOs distribution Network or User’s distribution Network; and one or more generators maintains a supply of electrical energy to that isolated, (islanded), Network.
Export limitation
This is the limit set by the DNO on the maximum net generation amount that a Solar PV system can export to the grid.
Feed-in-tariff
Receiving a feed-in tariff used to be a major incentive to investing in a solar PV system as the value of a feed-in tariff was once higher to encourage people to invest in residential solar. This is a payment made for electricity that you export or feed into the electricity grid generated by your solar PV system. This scheme is closed to new applications. Now, generally it is more beneficial to use more of your solar power during the day, (self-consume), rather than exporting it the grid or apply to the Smart Export Guarantee (SEG) scheme.
Grid-tied solar systems
This means the grid is used to measure the electricity produced by the solar PV system. If you use more electricity than your solar PV system generates at a particular time, the grid electricity will make up the difference so your power stays on and everything operates as usual.
Ground mount systems
Rooftop solar PV systems aren’t always the best option. Sometimes, rather than having solar panels on your roof, a ground mount solar system may be used. In this case, your solar panels would be attached to a racking (or mounting) system which is anchored into the ground.
Isc(stc)
Short-circuit current of a PV module, PV string, PV array or PV generator under standard test conditions.
Isolator/Disconnector
A mechanical switching device which, in the open position, complies with the requirements specified for isolation. An isolator is otherwise known as a disconnector. A disconnector is otherwise known as an isolator.
Inverter
Your inverter is the heart of your solar PV system. Its job is to convert direct current (DC) power into alternating current (AC) power to use in your home.
Meter
A meter is a device which records the movement of electricity into or out (export meter) of a residential or commercial property. The amount of electricity measured by the meter as being consumed by a property makes up part of the cost of your electricity bill.
Micro inverter
A micro inverter is a type of solar inverter. If your solar panels have micro inverters, these will be positioned on the back of each panel. This type of inverter can suit spaces with shading issues or panels which face in different directions.
Net generation
This is the process referring to the amount of solar power that your system exports to the grid based on your consumption of electricity compared with how much excess energy your solar PV system generates.
Panel Connector MC4
MC4 stands for “Multi-Contact 4mm” and refers to a type of connector used to connect solar panels. MC4 connectors are the industry standard for solar panel connections and are known for their reliability, durability, and ease of use.
Photovoltaic (PV)
The photovoltaic process turns light energy into electricity. In terms of solar energy, the PV solar cells turn the solar energy into a flow of electrons which is then sent as a direct current to your inverter.
PV array
A collection of solar panels that are electrically connected together to generate electricity from sunlight.
PV generator
Assembly of PV arrays and other necessary components, to form a DC. power supply unit.
PV Kilowatts peak (kWp )
Units for defining the rating of a PV module where = kW generated at stc.
PV MPPT (Maximum Power Point Tracker)
The DC input stage of an inverter designed to maximise the input from the array which varies according to irradiation and temperature.
PV self-cleaning
The cleaning effect on inclined PV systems from rain and wind Etc.
PV Standard test conditions (stc)
Test conditions specified for PV cells and modules (25 degrees Celcius, light intensity 1000W/m2, air mass 1.5).
PV string cable
Cable connecting PV modules to form a PV string, (circuit).
PV string circuit
PV modules are connected together in a series string in order for a PV array to generate the required output voltage.
PV string fuse
A fuse for an individual PV string.
Off-grid
Anything ‘off-grid’ means it’s not connected to the grid and therefore not part of the network. Properties that are off-grid need to have a large solar PV system or other generation sources and enough battery storage capacity to cover the electricity needs of the household or business without being able to access any electricity from the grid.
Self-consumption
Self-consumption is often the key to making the most of your solar PV system. It means using as much of the electricity your system produces as possible, so you need to buy less electricity from the grid. You may be able to boost your self-consumption with a few simple swaps – such as setting your dishwasher and washing machine to run during the day when solar power production is generally highest, rather than running these at night which will generally require drawing power from the grid.
Smart Export Guarantee (SEG) scheme.
If you generate renewable electricity in your home or business, you automatically feed back into the grid any electricity that you don’t use (subject to any export limitations). Under the Smart Export Guarantee ( SEG ) you will be paid for every unit of electricity that you feed back. You won’t be paid for any that you use yourself. Applicants will be asked to demonstrate that their installation and installer are suitably certified. Any tariffs offered to installations are offered under commercial contracts and not under the SEG legislation.
Smart meter
A “smart meter” is a device fitted at the mains which measures the energy coming and going from the grid. With a smart meter for your solar PV system, the inverter can measure your solar generation, self-consumption and export. This device can help keep the grid balanced by limiting how much a solar PV system can export.
Solar array
The solar array is the layout of solar panels, designed to absorb the sun’s energy to generate electricity. At home, your solar array will generally be installed on your roof and the panels positioned to catch the most sunshine.
Solar cells
Solar cells are used to make solar panels and usually made from silicone. Monocrystalline solar panels have solar cells shaped like a diamond and polycrystalline solar panels have rectangular-shaped solar cells.
Solar energy (irradiation)
Solar energy is created from sunlight. When the sun is shining, the solar energy captured by your solar panels is converted to solar power and sent as a direct current to your inverter then converted to alternating current so you can use that solar energy to power your home.
Solar Photovoltaic (PV) System
Your solar PV system includes your solar panels, inverter and safety switches and other balance of system (BoS) elements. This is the infrastructure which turns the sun’s energy into electrical energy. With a solar PV system at home, you could offset some of your household’s power needs, depending on factors such as the size of the system and your household electricity usage habits.
Solar monitoring
A solar monitoring solution might help you to use real-time solar data to make the most of your solar power. You can see the amount of solar generation, how much you’re using and get automatic fault and diagnosis alerts if there are any issues. Using a solar monitoring solution could help you identify any issues quickly and help you make the most of your solar PV system’s performance and potential benefits.
Solar power
While solar energy is directly from the sun, solar power is the electricity that is generated by a solar PV system.
String inverter
This is the most common type of solar inverter, with one or more strings of solar panels attached. Working as a set in a similar way to a string of Christmas lights, this kind of inverter converts direct current from the solar panels into alternating current to be used in our homes and businesses or exported to the grid.
Tilt angle
This is the angle of a solar panel.
Total Generation Meter
A meter that monitors the cumulative electricity generation in kWh from the PV system which is used (consumed) by the property for the demand at that time, with any excess being exported to the Grid.
Voc(stc)
Open-circuit voltage under standard test conditions across an unloaded (open) PV module, PV string, PV array, PV generator, or on the DC side of the PV inverter.
Example layout of a medium sized commercial Solar PV System using a string inverter.
Open-circuit voltage under standard test conditions across an unloaded (open) PV module, PV string, PV array, PV generator, or on the DC side of the PV inverter.
Surge Protective Devices (SPD)
SPD are used to protect the electrical installation, which consists of the consumer unit, wiring and accessories, from electrical power surges known as transient overvoltage's.
They are also used to protect sensitive, high value or critical electronic equipment connected to the installation, such as computers, safety circuits, such as fire detection systems, emergency lighting. Equipment with sensitive electronic circuitry can be vulnerable to damage by transient overvoltage’s (spikes).
The effects of a surge can result in either instant failure or damage to the equipment only evident over a longer period of time. SPDs are usually installed within the consumer unit to protect the electrical installation but different types of SPD are available to protect the installation from other incoming services, such as telephone lines and cable TV. It is important to remember that protecting the electrical installation alone and not the other services could leave another route for transient voltages to enter the installation.
There are three different types of Surge Protective Devices:
- Type 1 SPD installed at the origin, e.g. main distribution board.
- Type 2 SPD installed at sub-distribution boards (Combined Type 1 & 2 SPDs are available and are usually installed in consumer units).
- Type 3 SPD installed close to the protected load. They must only be installed as a supplement to Type 2
Where multiple devices are required to protect the installation, they must be coordinated to ensure correct operation. Items supplied by different manufacturers should be confirmed for compatibility, the installer and manufacturers of the devices are best placed to provide guidance on this.