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What do the main battery and tariff terms mean?
This glossary explains battery and energy terms in plain English, from arbitrage, spread and round-trip efficiency to G98, G99, SEG, VPP and the Scottish network operators. If a surveyor, installer or energy supplier uses a word you do not recognise, look it up here before you compare quotes or tariffs for your home.
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- Arbitrage
- Buying energy cheaply and using or selling it when prices are higher.
- BESS
- Battery Energy Storage System. A large-scale battery installation, typically above 1MWh.
- DNO
- Distribution Network Operator. The company that manages the local electricity grid. In Scotland: SP Energy Networks (central/south) or SSEN (north/Highlands/islands).
- G98
- The grid connection notification process for small-scale generation (up to 16A per phase, typically under 3.68kW).
- G99
- The grid connection notification process for larger generation above the G98 threshold.
- kWp
- Kilowatt peak. The maximum output of a solar panel under standard test conditions.
- kWh
- Kilowatt hour. A unit of energy. One kWh powers a 1kW appliance for one hour.
- MCS
- Microgeneration Certification Scheme. The UK quality mark for renewable installers. An MCS-certified installation is required to receive SEG export payments.
- EPC
- Energy Performance Certificate. A rating of a property's energy efficiency from A (best) to G (worst).
- SEG
- Smart Export Guarantee. A UK scheme requiring energy suppliers to pay for exported renewable electricity. Published flat rates ran roughly 1p to 25p per kWh in 2026.
- RTE
- Round-Trip Efficiency. The percentage of energy recovered from a battery after charging losses. Typically about 88% for AC-coupled systems.
- VPP
- Virtual Power Plant. A network of distributed batteries and other assets aggregated and controlled as a single flexible resource.
- Octopus Agile
- A variable time-of-use tariff with half-hourly pricing. Widely used for battery arbitrage because prices change every half hour.
- Intelligent Octopus Go
- An Octopus tariff with a fixed cheap overnight window, designed around a compatible electric vehicle or charger.
- Spread
- The gap between the cheapest and most expensive electricity prices in a day. A wider spread gives a battery more to work with.
- Peak and off-peak
- Peak is when electricity is most expensive, usually late afternoon to early evening. Off-peak is when it is cheapest, usually overnight.
- Inverter
- The unit that converts the battery's direct current into the alternating current your home uses, and back again when charging.
- AC-coupled and DC-coupled
- AC-coupled batteries have their own inverter and are easy to add to an existing home or solar system. DC-coupled batteries share a hybrid inverter with solar panels.
- SP Energy Networks
- The network operator for central and southern Scotland, including Glasgow, Edinburgh, Fife, the Borders and Dumfries and Galloway.
- SSEN
- Scottish and Southern Electricity Networks. The network operator for the north of Scotland, including the Highlands, Aberdeenshire, Moray and the islands.
- Tenement
- A traditional Scottish block of flats, usually sandstone or granite, sharing a close and stair. Batteries here often run on grid arbitrage without solar.
- Harling
- A rough lime or cement render common on Scottish houses. It affects how wall-mounted equipment and cable routes are fixed.
- Off-gas home
- A property not connected to the mains gas network, typically heated by oil, LPG or electricity. Common in rural Scotland and on the islands.
- Outgoing Octopus
- An export tariff paying a flat 12p/kWh for exported solar/battery energy from 1 March 2026.
- LiFePO4
- Lithium iron phosphate. A battery chemistry known for safety, long cycle life, and thermal stability.
- TrustMark
- The government-backed quality mark for trades. Provides dispute resolution and consumer protection.
- eBuildingStandards
- The Scottish online portal for building warrant applications.
- Triad
- The three highest half-hourly demand periods on the UK grid between November and February. Commercial batteries can avoid peak charges by discharging during Triads.