Solar Terminology

Solar panels, battery storage and electricity tariffs can involve a lot of unfamiliar terminology. This glossary explains some of the most common words and abbreviations you may see when researching a solar panel system for your home.

The exact system design, equipment and connection requirements will depend on your property, electricity usage and the size of the proposed installation.

Solar Panel and Electricity Terms

PV – Photovoltaic

PV stands for photovoltaic. It describes the process used by solar panels to convert daylight into electricity.

Solar PV panels do not need direct, bright sunshine to work. They can still generate electricity during cloudy conditions, although their output will normally be lower than on a clear, bright day.

Solar Panel or Solar Module

A solar panel, also known as a solar module, is an individual panel containing photovoltaic cells. These cells generate direct current electricity when exposed to daylight.

Modern domestic solar panels are commonly around one metre wide and approximately 1.7 to 2.3 metres long, although the exact size and power rating varies between manufacturers and models.

Solar Cell

A solar cell is one of the individual photovoltaic cells inside a solar panel. Multiple cells are connected together to form a complete solar module.

Solar Array

A solar array is a group of solar panels connected together as part of one system.

For example, a household may have an array of 10 or 12 panels installed across one or more sections of its roof.

W – Watt

A watt is a unit used to measure power. It describes the rate at which electricity is being generated or used at a particular moment.

kW – Kilowatt

A kilowatt is equal to 1,000 watts.

Solar system power, inverter output and the power used by household appliances may all be expressed in kilowatts.

For example, a 2kW electric heater uses electricity at a rate of approximately 2,000 watts while operating at full power.

Wh – Watt-hour

A watt-hour measures the amount of electricity generated, stored or used over a period of time.

kWh – Kilowatt-hour

A kilowatt-hour is equal to 1,000 watt-hours. It is the standard unit used by energy suppliers to measure the electricity you buy from the grid.

One kilowatt-hour is often described as one unit of electricity.

For example, an appliance using 1kW of power continuously for one hour would use approximately 1kWh of electricity.

Wp – Watt Peak

Watt peak is the maximum rated output of an individual solar panel under controlled Standard Test Conditions.

For example, a panel rated at 450Wp has a laboratory-tested peak rating of 450 watts.

The actual output at your property will vary according to daylight, temperature, shading, panel orientation, roof angle and other conditions.

kWp – Kilowatt Peak

Kilowatt peak describes the combined rated capacity of a solar panel array under Standard Test Conditions.

One kilowatt peak is equal to 1,000 watt peak.

For example, 10 panels rated at 450Wp each would create a solar array with a total rated capacity of 4.5kWp.

kWp describes the potential power of the system. It should not be confused with kWh, which measures how much electricity is generated or used over time.

Annual Generation

Annual generation is the estimated amount of electricity a solar panel system may produce over a year, normally measured in kWh.

This estimate will depend on factors including the property’s location, roof direction, roof pitch, system size and shading.

Estimated generation is not a guaranteed figure because weather and operating conditions vary.

Electrical Current and Inverters

DC – Direct Current

Direct current is the type of electricity produced by solar panels and commonly stored within a solar battery.

AC – Alternating Current

Alternating current is the type of electricity used by most household appliances and supplied through the electricity grid.

Solar Inverter

The inverter is one of the main components of a solar PV system.

Solar panels generate direct current electricity. The inverter converts this into alternating current electricity that can be used by household appliances or exported to the electricity grid.

Many modern inverters also provide an online portal or mobile app allowing the homeowner to monitor generation and system performance.

String Inverter

A string inverter is a central inverter connected to a group, or string, of solar panels.

It is one of the most common inverter arrangements used for domestic solar installations.

If one panel is significantly shaded, it may affect the output of other panels connected to the same string, depending on the system design.

Hybrid Inverter

A hybrid inverter combines the functions of a solar inverter and a battery inverter within one unit.

It can manage electricity from the solar panels, the battery, the home and the electricity grid.

Hybrid inverters are commonly considered when solar panels and battery storage are being installed together.

Microinverter

A microinverter is a small inverter installed on or close to an individual solar panel.

Rather than one central inverter managing the entire array, each panel can operate more independently.

This may be useful on roofs with several orientations or areas of partial shading, although suitability and cost will depend on the particular installation.

Power Optimiser

A power optimiser is a device connected to an individual panel to help monitor or manage that panel’s performance.

Optimisers are normally used alongside a compatible central inverter and may help reduce the effect of differences between panels.

MPPT – Maximum Power Point Tracking

Maximum Power Point Tracking is technology used by an inverter to continually find an efficient operating point for the solar panels.

An inverter may have more than one MPPT input, allowing separate groups of panels on different roof directions to be managed independently.

Solar Battery Terminology

Battery Storage

A solar battery stores electricity for use later.

This may include surplus electricity generated by solar panels during the day or cheaper electricity imported from the grid during an off-peak tariff period.

Stored electricity may then be used during the evening, overnight or at times when household consumption is greater than solar generation.

Battery Capacity

Battery capacity describes the total amount of electricity a battery can store and is normally measured in kWh.

For example, a battery described as having a 10kWh capacity may hold approximately 10 units of electricity, although the amount available for normal use may be slightly lower.

Usable Capacity

Usable capacity is the amount of the battery’s total capacity that can normally be used.

Some batteries reserve a small percentage of their capacity to help protect the battery and maintain its long-term health.

Depth of Discharge – DoD

Depth of discharge describes the percentage of a battery’s capacity that has been used.

For example, a 90% depth of discharge means that up to 90% of the battery’s rated capacity may be available before the system retains its reserve.

Battery Cycle

A battery cycle is the equivalent of charging and discharging the battery by its full usable capacity.

Several partial charges and discharges can add together to count as one complete cycle.

Cycle Life

Cycle life is the number of charging cycles a battery is designed to complete before its usable storage capacity reduces to a stated level.

Battery warranties may be based on years, cycles, energy throughput or a combination of these conditions.

Battery Degradation

Battery degradation is the gradual reduction in the amount of electricity a battery can store as it ages and is repeatedly charged and discharged.

Some reduction in capacity over time is normal.

Charge Rate

The charge rate is the maximum power at which electricity can be added to the battery, normally measured in kW.

A battery with a large storage capacity but a low charge rate may take longer to fill.

Discharge Rate

The discharge rate is the maximum power the battery can supply to the property at one time.

For example, a battery with a 3.6kW discharge rate may not fully supply several high-powered appliances operating simultaneously, even when plenty of stored energy remains.

AC-Coupled Battery

An AC-coupled battery system has its own battery inverter and connects to the alternating current side of the property’s electrical system.

It can be a suitable option when adding battery storage to an existing solar panel installation because the original solar inverter may not need to be replaced.

Electricity from the solar panels is converted from DC to AC by the solar inverter and then converted again when it is stored in the battery.

DC-Coupled Battery

A DC-coupled battery is connected on the direct current side of the solar system, usually through a compatible hybrid inverter.

This arrangement is commonly used when solar panels and battery storage are installed at the same time.

Surplus solar electricity can normally pass directly into the battery before being converted to AC for use within the home.

State of Charge – SoC

State of charge shows how full the battery currently is, usually as a percentage.

For example, a state of charge of 70% means that approximately 70% of the battery’s usable storage remains.

Battery Management System – BMS

The Battery Management System monitors and controls the battery.

It helps manage charging, discharging, temperature, voltage and safety limits.

Backup Power

Backup power allows selected appliances or circuits to continue operating during a power cut, where a compatible battery system and backup equipment have been installed.

Not every solar battery provides backup power as standard. A normal grid-connected solar system will usually shut down during a power cut unless it has been specifically designed with suitable backup or islanding equipment.

EPS – Emergency Power Supply

An Emergency Power Supply is an output provided by some battery or inverter systems to supply selected electrical loads during a grid outage.

The available power, number of supported circuits and switchover method vary between systems.

Using and Exporting Solar Electricity

Solar Generation

Solar generation is the electricity produced by the solar panel system.

Self-Consumption

Self-consumption is the proportion of solar electricity used directly within the property rather than exported to the grid.

Using appliances during periods of solar generation or adding battery storage may increase self-consumption.

Grid Import

Grid import is electricity drawn from your electricity supplier when the home requires more power than the solar panels and battery are providing.

Export

Export is surplus electricity sent from the property to the electricity distribution network.

Export normally happens when the solar panels are generating more electricity than the home is using and any connected battery is full or unable to accept the surplus.

Export Tariff

An export tariff is a tariff through which an electricity supplier pays an eligible customer for electricity exported to the grid.

Rates, eligibility conditions and contract terms vary between suppliers.

SEG – Smart Export Guarantee

The Smart Export Guarantee is the current scheme through which eligible small-scale renewable electricity generators can receive payment from participating electricity suppliers for measured electricity exported to the grid.

Suppliers set their own payment rates and eligibility conditions, and an appropriate export meter is required.

FIT – Feed-in Tariff

The Feed-in Tariff was a government-supported scheme that paid eligible renewable electricity generators for electricity generated and, in some cases, exported.

The FIT scheme closed to new applicants on 1 April 2019. Existing eligible installations registered under the scheme may continue to receive payments under their original arrangements.

Smart Meter

A smart meter records electricity imported from the grid and can send meter readings automatically to the energy supplier.

A suitable smart meter may also record electricity exported to the grid for an export tariff.

Export Meter

An export meter records the amount of electricity sent from the property to the grid.

For many domestic installations, this function may be provided by a compatible smart meter.

Time-of-Use Tariff

A time-of-use tariff charges different electricity rates at different times of the day.

A battery may be programmed to charge using lower-priced electricity during off-peak periods and discharge when electricity is more expensive.

Tariff rates and availability can change, so they should be checked directly with the relevant electricity supplier.

Export Limitation

An export limitation restricts the maximum amount of electricity a solar and battery system can send to the local electricity network.

This may be required by the Distribution Network Operator where the local network cannot accept the system’s full potential export.

Zero Export

A zero-export system is configured to prevent electricity from being exported to the grid.

Generation may instead be used within the property, directed into a battery or reduced by the system controls.

Roof and Installation Terms

Mounting System

The mounting system is the collection of rails, roof hooks, brackets, clamps and fixings used to securely attach solar panels to a roof or another structure.

The appropriate mounting method will depend on the roof covering, roof structure, panel layout and installation design.

On-Roof Solar Panels

On-roof panels are mounted above the existing roof covering using rails and roof fixings.

This is one of the most common installation methods for existing homes.

In-Roof Solar Panels

In-roof panels are fitted into the roof covering rather than sitting on rails above it.

They can provide a more integrated appearance and are often considered during a new build or roof replacement.

Roof Orientation

Roof orientation is the compass direction the roof faces.

South-facing roofs can often produce strong annual generation, but east-facing and west-facing roofs may also be suitable and can spread generation across the morning and afternoon.

Roof Pitch

Roof pitch is the angle or steepness of the roof.

The pitch can affect the amount of sunlight received, the panel layout and the installation method.

Shading

Shading occurs when buildings, trees, chimneys, roof features or other objects reduce the daylight reaching one or more panels.

Shading can reduce generation, so it should be considered during the system survey and design.

Scaffolding

Scaffolding provides a safe working platform for roof installation and is commonly required when fitting solar panels to a house.

The scaffolding requirements can vary depending on roof height, property access and site conditions.

Bird Protection

Bird protection normally refers to mesh fitted around the edge of an on-roof solar array to discourage birds from nesting beneath the panels.

It should be installed without drilling into or damaging the panels.

Grid Connection and Certification

DNO – Distribution Network Operator

The Distribution Network Operator is the company responsible for the local electricity cables, substations and network that deliver electricity to properties in a particular region.

The DNO is separate from the energy supplier that sends your electricity bill.

G98

G98 is the connection process commonly used for fully type-tested small generation systems with an aggregate capacity of no more than 16 amps per phase, which is approximately 3.68kW per phase.

Qualifying installations may generally be installed under a fit-and-notify process, with the DNO notified in accordance with the applicable requirements.

G99

G99 is generally relevant to generation systems that exceed the G98 limits or involve certain combinations of generation and battery storage.

Approval from the DNO may be required before the system is installed or commissioned.

The exact process depends on the system design, inverter capacity and local network requirements.

MPAN – Meter Point Administration Number

An MPAN is the unique reference number used to identify an electricity supply point.

It is sometimes called the electricity supply number and can normally be found on an electricity bill.

MCS – Microgeneration Certification Scheme

MCS is the UK quality mark for small-scale renewable energy products and installations, including solar PV and battery storage.

An MCS-certified installation is designed, installed and commissioned in line with applicable MCS standards using appropriately certified products.

MCS Certificate

An MCS certificate provides evidence that an eligible installation has been designed, installed and commissioned to the relevant MCS requirements.

It may be required when applying for certain export tariffs or consumer-protection arrangements.

Commissioning

Commissioning is the final process of checking, testing and activating a solar panel or battery system after installation.

This may include electrical safety testing, inverter setup, system monitoring configuration and completion of the required documentation.

Single-Line Diagram

A single-line diagram is a simplified electrical drawing showing how the solar panels, inverter, battery, consumer unit, meter and grid connection are linked.

Consumer Unit

The consumer unit, sometimes called a fuse box, distributes electricity around the property and contains protective devices for the electrical circuits.

An assessment may be required to confirm that the existing consumer unit and electrical installation are suitable for the proposed solar and battery system.

Generation Meter

A generation meter records the total amount of electricity produced by a solar PV system.

This is separate from the electricity import and export measurements taken by the property’s main meter.

Solar System Performance

Efficiency

Solar panel efficiency describes how much of the solar energy reaching a panel is converted into electricity.

A higher-efficiency panel can generate more power from a smaller roof area, although efficiency is only one factor to consider when selecting a system.

Degradation

Solar panel degradation is the gradual reduction in panel output over time.

Manufacturers commonly provide a performance warranty stating the minimum expected output after a specified number of years.

Performance Warranty

A performance warranty relates to the expected power output of a solar panel over time.

It is different from a product warranty, which relates to faults in the physical panel or its materials.

Product Warranty

A product warranty covers manufacturing faults or specified product failures for a defined period and subject to the manufacturer’s terms.

Solar panels, inverters and batteries may each have different warranty periods and conditions.

Workmanship Guarantee

A workmanship guarantee covers specified aspects of the installer’s work for the period stated in the installation agreement.

It should be checked separately from the equipment manufacturer’s warranties.

Monitoring Portal

A monitoring portal or mobile app allows homeowners to view information such as solar generation, household consumption, battery charge level, grid import and grid export.

The information shown will depend on the installed inverter, battery and monitoring equipment.

Payback Period

The payback period is an estimate of how long it may take for potential energy-bill savings and export income to equal the original cost of the system.

It is not guaranteed and can change according to electricity prices, export tariffs, household usage, system performance, maintenance costs and other assumptions.

Self-Sufficiency

Self-sufficiency describes the percentage of a household’s electricity demand supplied by its solar panels and battery rather than imported from the grid.

A property can have high solar self-consumption without being completely self-sufficient throughout the year.

Need Help Understanding a Solar Quotation?

A professional solar quotation should clearly explain the proposed system size, estimated annual generation, panel and inverter specifications, battery capacity, warranties and expected installation arrangements.

Solar Panel Scotland is a trading name of Arctic Improvements Ltd. You can request an initial guide price and discuss the solar panel and battery storage options available for your property.

Any generation, savings or payback figures provided are estimates rather than guarantees. The final system design and price will depend on the property survey, technical requirements and products selected.