A
AC (Alternating Current)
The type of electrical current used in UK homes and the National Grid. Solar panels produce DC power, which inverters convert to AC for home use.
Array
A group of solar panels connected together. A residential 'array' typically consists of 10-20 panels working as a single system.
Azimuth
The compass direction your roof faces. In the UK, south-facing (180° azimuth) is optimal for solar, though east (90°) and west (270°) work well too.
B
Battery Storage
A battery system that stores excess solar electricity for later use, typically during evenings or at night when panels aren't generating.
Bifacial Panels
Solar panels that can generate electricity from both sides. They capture reflected light from the ground or roof, increasing total output by 5-20%.
C
Clipping
When the inverter limits output because panels are producing more power than the inverter can handle. Minor clipping is normal and often intentional.
D
DC (Direct Current)
The type of electrical current produced by solar panels and stored in batteries. Must be converted to AC for home appliances.
Degradation
The gradual reduction in panel output over time. Modern panels typically degrade 0.3-0.5% per year, producing 80-90% of original output after 25 years.
DNO (Distribution Network Operator)
The company responsible for the electricity distribution network in your area. They must be notified of solar installations over 3.68kW.
E
EPC (Energy Performance Certificate)
A rating from A to G showing how energy efficient a property is. Solar panels can improve your EPC rating, increasing property value.
Export
Electricity generated by your solar panels that flows back to the National Grid when you're producing more than you use.
Export Limiting
A device or setting that limits how much electricity is exported to the grid, sometimes required by the DNO for larger systems.
F
Feed-in Tariff (FIT)
A previous government scheme (closed 2019) that paid homeowners for generating and exporting solar electricity. Replaced by the Smart Export Guarantee.
G
G98/G99
Grid connection standards. G98 allows systems up to 3.68kW to connect with simple notification. Larger systems need G99 approval from the DNO.
Generation Meter
A meter that records how much electricity your solar panels generate in total, regardless of how it's used.
Grid-Tied
A solar system connected to the National Grid, allowing you to import when needed and export surplus. The most common residential setup.
H
Hybrid Inverter
An inverter that manages both solar panels and battery storage in one unit, handling solar generation, battery charging, and grid interaction.
I
Import
Electricity drawn from the National Grid when your solar panels aren't generating enough for your needs.
Inverter
The device that converts DC electricity from solar panels into AC electricity for home use. Often called the 'brain' of the solar system.
Irradiance
The amount of solar radiation hitting a surface, measured in W/m². The UK averages around 100-120 W/m² annually.
K
kW (Kilowatt)
A unit of power (1,000 watts). Used to describe the capacity of solar systems. A typical UK home system is 3-5kW.
kWh (Kilowatt-hour)
A unit of energy. One kWh is using 1kW of power for one hour. Your electricity bill is charged per kWh.
kWp (Kilowatt-peak)
The maximum power output of a solar system under ideal test conditions (25°C, 1000W/m² irradiance). Used to compare system sizes.
L
LFP (Lithium Iron Phosphate)
A type of lithium battery chemistry. Safer and longer-lasting than NMC but slightly lower energy density. Used by Tesla, BYD, and others.
Load Shifting
Running appliances during peak solar generation hours (typically 10am-3pm) to use more of your free solar electricity directly.
M
MCS (Microgeneration Certification Scheme)
The quality assurance scheme for renewable energy installations in the UK. MCS certification is required for SEG payments and some incentives.
Microinverter
A small inverter attached to each individual panel. Optimises each panel independently, ideal for complex roofs or partial shading.
Monocrystalline
Solar cells made from a single silicon crystal. More efficient and space-efficient than polycrystalline, with a distinctive black appearance.
MPPT (Maximum Power Point Tracking)
Technology in inverters that constantly adjusts to extract maximum power from panels as conditions change throughout the day.
N
NMC (Nickel Manganese Cobalt)
A type of lithium battery chemistry. Higher energy density than LFP but shorter lifespan. Used in some home battery systems.
O
Off-Grid
A solar system not connected to the National Grid, relying entirely on solar and batteries. Uncommon in the UK but used for remote locations.
Optimiser
A device attached to each panel that maximises its individual output. Used with string inverters to provide panel-level optimisation.
P
Payback Period
The time it takes for energy bill savings to equal the initial cost of a solar system. Typically 8-12 years in the UK.
Peak Sun Hours
The equivalent hours of 1000W/m² irradiance per day. The UK averages 2.5-4 peak sun hours daily, higher in summer, lower in winter.
Polycrystalline
Solar cells made from multiple silicon crystals. Less efficient than monocrystalline but cheaper. Recognisable by their blue, speckled appearance.
Power Purchase Agreement (PPA)
An arrangement where a company installs solar for free and you buy the electricity at a fixed rate. Can be good value but read the terms carefully.
PV (Photovoltaic)
The technology that converts light directly into electricity. 'Solar PV' refers to solar panels as opposed to solar thermal (hot water) systems.
R
Retrofit
Adding solar panels to an existing building, as opposed to including them in new construction.
ROI (Return on Investment)
The percentage return from your solar investment. UK residential solar typically offers 8-15% annual ROI over its lifetime.
S
Self-Consumption
The percentage of solar electricity you use directly rather than exporting. Higher self-consumption = greater savings.
SEG (Smart Export Guarantee)
The current government scheme requiring energy suppliers to pay for exported solar electricity. Rates typically 4-15p per kWh.
Shading
When shadows fall on panels, reducing output. Even partial shading can significantly impact a string inverter system; optimisers or microinverters help.
Smart Meter
A digital meter that records import and export readings automatically. Required for SEG payments and time-of-use tariffs.
Solar Irradiance
The power of sunlight reaching a surface, measured in watts per square metre (W/m²). Varies by location, time of day, and weather.
Solar Thermal
A system using the sun's heat to warm water (not electricity). Different from solar PV. Less common in UK new installations.
String
A series of solar panels wired together. Performance is limited by the weakest panel in the string.
String Inverter
A central inverter that converts DC from a string of panels to AC. The most common and cost-effective inverter type.
T
Temperature Coefficient
How much panel efficiency decreases as temperature rises. Lower is better. Panels work better in cool, sunny conditions than hot ones.
Tilt Angle
The angle at which panels are mounted relative to horizontal. In the UK, 30-40° is optimal, roughly matching typical roof pitches.
Time-of-Use Tariff
An electricity tariff where prices vary by time of day. Useful with solar and batteries to minimise costs and maximise export income.
V
VAT
Currently 0% on residential solar installations (until 2027). Previously 5%, and before that 20%, making solar more affordable than ever.
W
Watt (W)
The basic unit of power. A typical solar panel produces 350-450W. 1000 watts = 1 kilowatt (kW).
Z
Zero Export
A system setting that prevents any electricity from being exported to the grid. Sometimes required by DNOs or in specific circumstances.