Solar energy glossary

Plain-English definitions of the terms you will see on this site and in quotes from installers.

SEG (Smart Export Guarantee)

A UK government scheme that requires licensed energy suppliers to pay you for electricity you export to the grid from renewable sources like solar panels.

Export tariff

The rate your supplier pays for each unit (kWh) of electricity you send back to the grid. Typical rates range from 8p to 15p per kWh.

kWh (kilowatt hour)

A unit of energy. One kWh is the energy used by a 1,000-watt appliance running for one hour. Your electricity bill is priced per kWh.

kWp (kilowatt peak)

The maximum output of a solar panel or system under ideal lab conditions. A 4kWp system has panels rated at 4,000 watts total peak.

Self-consumption

The share of your solar electricity you use directly in your home instead of exporting it. Typically 30-50% without a battery, 60-80% with one.

Grid arbitrage

Using a battery to buy cheap off-peak electricity (around 7p/kWh) and use it during peak hours (around 28p/kWh), profiting from the price difference.

Round-trip efficiency (RTE)

The percentage of electricity you get back out of a battery compared to what you put in. A typical home battery has an RTE of 85-90%.

MCS (Microgeneration Certification Scheme)

An industry quality standard for installers of small-scale renewables. You need an MCS-certified installation to qualify for SEG payments.

RECC (Renewable Energy Consumer Code)

A consumer protection code that sets standards for how renewable energy products are sold. RECC membership means the installer follows fair trading practices.

Smart meter (SMETS2)

A digital meter that sends automatic readings to your supplier, including how much you export. Required for SEG payments based on actual exports.

Irradiance

The amount of solar energy hitting a surface, measured in kWh per square metre per year. Scotland receives roughly 850-1,050 kWh/m2/yr depending on location.

DNO (Distribution Network Operator)

The company that owns and maintains the local electricity cables and poles. You may need DNO approval for solar systems above 3.68kW on a single-phase supply.

G99 application

A formal application to the DNO for connecting a generation system above 3.68kW (single phase) or 11kW (three phase) to the grid.

Deemed export

If you do not have a smart meter, your supplier estimates your exports (typically 50% of generation) rather than measuring them. This usually pays less than actual metered export.

Feed-in Tariff (FiT)

The predecessor to the SEG, closed to new applicants since March 2019. Systems registered under FiT continue to receive their agreed rate for 20-25 years.

Degradation

Solar panels lose a small amount of output each year — typically 0.4-0.5%. After 25 years, most panels still produce over 85% of their original output. Batteries degrade faster, losing roughly 1-2% capacity per year.

TrustMark

A government-endorsed quality mark for tradespeople. TrustMark registration is required for some incentive schemes and shows the installer meets defined standards.

EPC (Energy Performance Certificate)

A rating of your home's energy efficiency (A to G). Solar panels improve your rating. An EPC is required when selling or renting a property.