Solar & Energy Glossary

Quotes for solar, battery and heat pump installs are full of abbreviations nobody explains up front. Here’s what the ones you’ll actually run into on this site mean, without the technical manual version.

kW (kilowatt)

A measure of how fast something is using or generating electricity right now, not how much it's used in total. A 3kW kettle pulls power three times as fast as a 1kW one. Your solar system's inverter and your car charger are both usually described in kW.

kWh (kilowatt-hour)

The actual amount of electricity used or generated, and the unit your bill is charged in. Run a 1kW appliance for an hour and you've used 1 kWh. A typical UK home gets through somewhere between 1,800 and 4,100 kWh a year depending on its size, according to Ofgem's typical consumption figures.

kWp (kilowatt peak)

How solar panel systems are sized, it's the maximum output the panels can produce under ideal lab conditions (full sun, no shading, cool panels). Real-world output is lower most of the time since the sun isn't always at its strongest, but kWp is still the standard way installers describe system size, for example a "4kWp system."

Unit rate

The price you pay per kWh of electricity, in pence. It's the number that actually determines your bill once you know how many kWh you've used, and it's set by your supplier or capped by Ofgem's price cap.

Standing charge

A fixed daily fee on your electricity bill that you pay regardless of how much you use, on top of the unit rate. It covers the cost of keeping you connected to the grid. Solar and battery storage reduce your unit-rate spend but not this fixed charge.

SEG (Smart Export Guarantee)

A scheme that requires licensed electricity suppliers to pay you for solar electricity you export to the grid instead of using yourself. Rates vary a fair amount between suppliers, so it's worth comparing rather than assuming your own supplier's SEG tariff is the best one available.

Self-consumption (self-use)

The share of the electricity your panels generate that you use in your own home, rather than exporting to the grid. Higher self-consumption means bigger savings, because electricity you use yourself offsets your unit rate, while exported electricity earns the usually-lower SEG rate. A battery raises self-consumption by storing daytime surplus for use after dark.

Payback period

How long it takes for the money you save on bills (plus any SEG income) to add up to what you paid for the system. UK solar payback is typically somewhere in the 6 to 12 year range, with panels usually still producing well after that point.

MCS certification

MCS (Microgeneration Certification Scheme) certifies that an installer and the equipment they fit meet a recognised quality standard. It matters beyond reputation too, you generally need an MCS-certified installation to qualify for SEG payments or 0% VAT on the install.

G98 / G99 (grid connection)

The technical approval process for connecting a generator, like solar panels, to the UK electricity grid. G98 covers smaller systems that your installer can usually register after the fact; G99 covers larger ones and needs approval from your network operator before installation. Most home solar systems fall under G98.

Battery cycle life

How many times a home battery can be fully charged and discharged before its storage capacity noticeably drops. Most home batteries are rated for several thousand cycles, which at one cycle a day works out to well over a decade of daily use.

Degradation rate

How much a solar panel's output drops each year as it ages. It's gradual, typically around 0.3 to 0.5% a year, not a cliff edge, and most manufacturer warranties guarantee at least 80% of original output after 25 years.

EPC (Energy Performance Certificate)

A rating from A to G showing how energy-efficient a property is, required whenever a home is built, sold or rented. It's worth checking yours before a solar or heat pump quote, since it can flag insulation gaps worth fixing alongside (or before) any new install.

Inverter

The box that converts the DC electricity your solar panels produce into the AC electricity your home's sockets and appliances actually run on. It's also usually where a battery connects in, and its own kW rating is what limits how fast your system can deliver power.

Still stuck on a term that isn’t here, or want to see how one of these plays out on your own bill? Our quote form matches you with installers who can walk through the specifics for your home.