Solar Energy Glossary
Plain-English definitions for every solar term you need to know — from system sizing and inverters to tariffs and battery storage. 55 terms, all written for homeowners.
A
AC vs DC ElectricityDC (direct current) is what solar panels produce; AC (alternating current) is what your home and the grid use — an inverter converts between the two.AzimuthAzimuth is the compass direction your solar panels face, measured in degrees — south-facing (180°) is optimal in the northern hemisphere for maximum energy capture.AC-Coupled vs DC-CoupledAC-coupled and DC-coupled are the two ways a solar battery can be connected to your system — DC coupling (via a hybrid inverter) is more efficient, while AC coupling allows batteries to be added to existing solar systems.
B
Building Regulations Part PBuilding Regulations Part P is the UK electrical safety regulation that applies to solar installations, requiring electrical work to be carried out or certified by a competent person.Battery Capacity (kWh)Battery capacity in kWh measures the total amount of energy a solar battery can store and is the key specification for determining whether a battery can meet your evening electricity needs.Battery Cycle LifeBattery cycle life is the number of charge-discharge cycles a battery can complete before its capacity degrades to a specified level (typically 80% of original), and is the key indicator of battery longevity.Battery DegradationBattery degradation is the gradual reduction in a battery's storage capacity over time due to chemical changes, heat exposure, and repeated charge-discharge cycling.
D
DNO ApplicationA DNO application is the formal notification or permission request sent to your local electricity network operator before connecting a solar system to the grid.Depth of Discharge (DoD)Depth of discharge is the percentage of a battery's total capacity that is actually used before recharging — higher DoD means more usable energy but can reduce battery lifespan if taken too deep.
E
Export RateThe export rate is the price per kWh you are paid for solar electricity you send back to the grid, which is typically much lower than the retail price you pay to import electricity.Electricity TariffAn electricity tariff is the pricing structure your energy supplier uses to charge you for the electricity you use, typically consisting of a unit rate per kWh and a standing charge.Energy ArbitrageEnergy arbitrage in solar means using a battery to buy cheap electricity at off-peak times and use (or sell) it during expensive peak periods, reducing your net electricity costs.Embodied CarbonEmbodied carbon is the total CO₂ emitted during the manufacture, transport, installation, and eventual disposal of a solar panel system, before it generates any clean electricity.Energy Payback TimeEnergy payback time is how long a solar panel takes to generate the same amount of energy that was used to manufacture, install, and eventually recycle it.
F
G
Grid-Connected SystemA grid-connected solar system is connected to the public electricity network, allowing you to draw power from the grid when solar generation is insufficient and export surplus power back to the grid.Grid ExportGrid export is when your solar system generates more electricity than your home is using, and the surplus power flows back into the public electricity network.Generation MeterA generation meter records the total amount of electricity your solar panels produce, and is required to receive payments under the Feed-In Tariff or some SEG contracts.
H
K
kW (Kilowatt)A kilowatt is a unit of power equal to 1,000 watts, used to describe how much electricity a solar system can produce at any given moment.kWh (Kilowatt-hour)A kilowatt-hour is the unit of energy on your electricity bill — it measures how much electricity is actually used or generated over time.
L
Levelised Cost of Energy (LCOE)The Levelised Cost of Energy (LCOE) is the average cost per kWh of electricity generated by your solar system over its entire lifetime, accounting for all upfront and ongoing costs.Lithium-Ion BatteryLithium-ion batteries are the dominant technology used in solar energy storage systems, offering high energy density, long cycle life, and relatively low maintenance compared to older lead-acid batteries.
M
Monocrystalline PanelsMonocrystalline solar panels are made from a single crystal of silicon, making them the most efficient and longest-lasting panel type commonly used in homes.MicroinverterA microinverter is a small inverter fitted to each individual solar panel, converting DC to AC power at the panel itself rather than in a central unit.MCS CertificationMCS (Microgeneration Certification Scheme) is the UK quality standard that solar installers and products must meet for installations to qualify for government incentives and consumer protections.
N
O
P
Polycrystalline PanelsPolycrystalline solar panels are made from multiple silicon crystals melted together, offering a lower-cost alternative to monocrystalline panels with slightly less efficiency.Permitted DevelopmentPermitted Development rights allow most UK homeowners to install solar panels without needing to apply for planning permission, as long as certain conditions are met.Peak Sun HoursPeak sun hours is the number of hours per day when solar irradiance averages 1,000 W/m² — used to estimate how much energy your solar panels will generate.Power Purchase Agreement (PPA)A Power Purchase Agreement is a contract where a solar company installs panels on your roof at no upfront cost, and you agree to buy the electricity they generate at a fixed rate lower than the grid price.
R
Roof Pitch / Tilt AngleRoof pitch (or tilt angle) is the angle of your roof from horizontal — for solar panels, the optimal tilt in the UK is around 30–40°, which matches the angle of the sun's path across the sky.Return on Investment (ROI)Return on investment for solar measures the total financial gain from your solar system over its lifetime, expressed as a percentage of the original installation cost.
S
Solar Panel EfficiencySolar panel efficiency is the percentage of sunlight hitting a panel that gets converted into usable electricity.Solar Panel DegradationSolar panel degradation is the gradual reduction in a panel's electricity output over time as its materials slowly deteriorate from exposure to sunlight and weather.Solar Panel WarrantyA solar panel warranty is a manufacturer's guarantee covering both product defects and a minimum level of performance output over the warranty period.Solar Panel OutputSolar panel output is the amount of electricity a panel or system produces, measured in watts (W) at peak conditions or kilowatt-hours (kWh) over a time period.String InverterA string inverter is a single central device that converts DC electricity from multiple solar panels wired together in a series (a "string") into AC electricity for home use.ScaffoldingScaffolding is temporary access structure erected around or on a building to allow safe installation of solar panels on a roof.Solar IrradianceSolar irradiance is the power of sunlight hitting a surface, measured in watts per square metre (W/m²), and is the primary factor determining how much electricity your solar panels can generate.Shading AnalysisA shading analysis is an assessment of how shadows from trees, chimneys, neighbouring buildings, and other obstructions affect your solar panels' output throughout the day and year.Self-ConsumptionSelf-consumption is the proportion of your solar-generated electricity that you use directly in your home, rather than exporting to the grid.Smart Export Guarantee (SEG)The Smart Export Guarantee is the UK scheme that requires energy suppliers with 150,000+ customers to pay solar panel owners for electricity they export to the grid.Solar Payback PeriodThe solar payback period is the number of years it takes for your cumulative energy bill savings and export income to equal the upfront cost of your solar installation.Solar FinancingSolar financing refers to the various ways homeowners can fund a solar installation, including cash purchase, personal loans, green mortgages, and government-backed schemes.Standing ChargeThe standing charge is a fixed daily fee on your electricity bill that covers the cost of being connected to the grid, charged regardless of how much electricity you use.Solar Battery StorageSolar battery storage is a rechargeable battery system installed alongside solar panels to store surplus daytime electricity for use in the evening or during low-generation periods.Solar PVSolar PV (photovoltaic) is the technology that converts sunlight directly into electricity using semiconductor cells, and is what most people mean when they say "solar panels."Solar ThermalSolar thermal systems use sunlight to heat water for domestic use rather than generating electricity, and are a separate technology from solar PV panels.Solar LeaseA solar lease is an arrangement where a company installs solar panels on your roof and you pay a fixed monthly fee to use them, rather than buying the system outright.
T
Thin-Film PanelsThin-film solar panels are made by depositing photovoltaic material in thin layers onto a substrate, making them lightweight and flexible but less efficient than crystalline silicon panels.Time-of-Use TariffA time-of-use tariff charges different electricity prices at different times of day, making it possible to save money by shifting consumption to cheaper periods and by optimising battery charging and discharging.
V
VAT on Solar PanelsIn the UK, solar panel installations are currently zero-rated for VAT (0%), saving homeowners up to £1,500 or more compared to the standard 20% VAT rate.Virtual Power Plant (VPP)A virtual power plant is a network of home solar batteries that are aggregated and controlled together to provide grid services, with participating homeowners receiving payments in return.
Common Solar Questions
What does kWh mean in solar panels?
kWh stands for kilowatt-hour — the unit your electricity bill uses to measure energy consumption. One kWh is the energy used by a 1,000-watt appliance running for one hour. Solar panels are rated in kW (kilowatts) of peak power, but their useful output is measured in kWh generated per day, month, or year.
What is a feed-in tariff?
A feed-in tariff (FIT) was a government scheme that paid solar panel owners a set rate for every unit of electricity their system generated, regardless of whether they used it themselves. The UK FIT closed to new applicants in 2019 and was replaced by the Smart Export Guarantee (SEG), which pays for excess electricity exported to the grid.
What is MCS certification for solar panels?
MCS (Microgeneration Certification Scheme) is a UK quality standard for renewable energy installations. Using an MCS-certified installer is required to claim the Smart Export Guarantee (SEG) payments and to benefit from 0% VAT on residential solar installations. The certification covers both the installer and the equipment used.
What is the payback period for solar panels?
The payback period is the time it takes for cumulative savings from your solar panels to equal the original installation cost. For a typical UK home, this is currently 7–10 years. After payback, the panels generate essentially free electricity for the remaining 15+ years of their lifespan.
What is depth of discharge for a solar battery?
Depth of discharge (DoD) is the percentage of a battery's total capacity that can actually be used without damaging it. A 10 kWh battery with 90% DoD provides 9 kWh of usable storage. Most modern lithium-ion home batteries have a DoD of 80–100%, compared to older lead-acid batteries which typically only allow 50% DoD.
Ready to crunch your solar numbers?
Now you know the terms — use our free calculators to get a personalised estimate for your home.