Renewable Energy Glossary
Plain-English definitions of 77+ heat pump, solar, battery, EV and UK regulation terms. Whether you're decoding a quote or understanding a grant, you'll find it here.
Battery StorageEV ChargingElectricalGeneralGrants & FinanceHeat PumpsHeatingHot WaterRegulationsSolar PV
Battery Storage
AC Coupling
A battery topology where the battery has its own inverter and connects to the household AC bus, alongside (rather than through) the solar inverter.
DC Coupling
A battery topology where solar panels and battery share a hybrid inverter, communicating in DC for higher round-trip efficiency.
EV Charging
Bidirectional Charging
Charging hardware that lets an EV's battery push power back out to your home (V2H) or to the grid (V2G), turning the car into mobile storage.
Mode 3 charging
IEC 61851-1 charging mode covering AC charging via a dedicated EV chargepoint with full safety signalling — the standard for UK home and workplace charging.
OCPP
Open Charge Point Protocol — the open standard for communication between EV chargers and back-office management software, key for commercial chargepoint operators.
Octopus Go
An off-peak EV-focused tariff offering a 5-hour cheap overnight window (typically 23:30-05:30) at around 7p/kWh.
OZEV EV Chargepoint Grant
A £350 (75% up to £350) UK grant toward the cost of a home EV chargepoint, available to flat-dwellers and those without dedicated off-street parking via cross-pavement solutions.
Tethered (EV charger)
An EV charger with a permanently attached cable, typically 5-7m long, terminating in a Type 2 plug.
Type 2 Connector
The standard 7-pin AC charging connector used by all EVs sold in Europe, supporting 3.6kW to 22kW AC charging.
Untethered (EV charger)
An EV charger with a Type 2 socket but no captive cable — you bring your own cable from the car boot for each charge.
Vehicle-to-Grid (V2G)
A bidirectional charging mode where the EV battery exports power to the public grid in response to smart tariff signals or DNO demand response.
Vehicle-to-Home (V2H)
A bidirectional charging mode where the EV battery powers the household, useful for backup during a power cut or for self-consumption optimisation.
Workplace Charging Scheme (WCS)
OZEV grant covering up to £350 per socket (max 40 sockets) toward EV charger installation at business or charity premises.
Electrical
Standing Charge
A daily fixed charge on your electricity and gas bills covering grid connection, metering and supplier overheads — payable even if you use zero energy.
Time-of-Use Tariff
An electricity tariff with different unit rates at different times of day, designed to reward off-peak usage and penalise peak demand.
General
Grants & Finance
Boiler Upgrade Scheme (BUS)
The UK government grant offering £7,500 toward an air or ground source heat pump installation in England and Wales, running until March 2028.
ECO4
The Energy Company Obligation (Phase 4) — a supplier-funded scheme covering whole-house retrofit including heat pumps for low-income and vulnerable households.
Public Sector Decarbonisation Scheme (PSDS)
A UK government grant programme funding low-carbon heat and energy efficiency upgrades in public sector buildings, administered by Salix Finance.
Renewable Heat Incentive (RHI) — legacy
The closed-to-new-applicants tariff scheme (2014-2022) that paid quarterly payments over 7 years for renewable heating installations.
Warm Homes Local Grant
Local authority funding (formerly HUG2) covering insulation, low-carbon heat and solar for off-gas-grid, low-income households.
Heat Pumps
Air Source Heat Pump (ASHP)
A low-carbon heating system that extracts thermal energy from outdoor air and upgrades it to useful heat for radiators, underfloor heating and hot water.
Coefficient of Performance (COP)
The instantaneous ratio of heat output to electrical input for a heat pump, measured at a single operating point.
Ground Source Heat Pump (GSHP)
A heat pump that draws stable, year-round thermal energy from buried ground loops or boreholes, typically delivering higher efficiency than air source.
Hybrid Heat Pump
A system pairing a heat pump with a gas or oil boiler that automatically switches to whichever fuel is cheapest or most efficient at any given moment.
Octopus Cosy
Octopus's heat-pump-specific time-of-use tariff with three cheap windows per day designed to align with heat pump duty cycles.
Refrigerant R290 (Propane)
Propane refrigerant with a Global Warming Potential of just 3 and excellent high-temperature performance, increasingly the default in new ASHP ranges.
Refrigerant R32
A single-component HFC refrigerant with GWP 675, widely used in mid-range air source heat pumps as a lower-impact replacement for R410A.
Refrigerant R410A
A legacy HFC refrigerant blend with GWP 2,088, now being phased out under F-Gas regulations and rare in new heat pump installations.
Seasonal Coefficient of Performance (SCOP)
A weighted-average efficiency rating that reflects a heat pump's real-world performance over a full heating season.
Seasonal Performance Factor (SPF)
The measured (not modelled) seasonal efficiency of a heat pump installation, including ancillary loads like circulation pumps and immersion top-up.
Heating
BTU
British Thermal Unit — an imperial energy unit (1 BTU ≈ 1,055 J) still occasionally used for radiator and boiler ratings. 1 kW ≈ 3,412 BTU/hr.
Buffer Tank
A small thermal store (typically 25-100L) that decouples a heat pump from emitters, providing cycle protection and defrost reserve.
Combi Boiler
A combination boiler that provides both central heating and instantaneous hot water without a separate cylinder, taking up minimal space.
Heat-Only Boiler
Also called a "regular" or "conventional" boiler — a heat-only unit feeding a hot water cylinder via a vented header tank in the loft.
Low-Loss Header
A vertical hydraulic separation device that decouples primary and secondary circuit flows in a heating system, often used with system boilers and heat pumps.
Open Therm
A communication protocol between modulating boilers/heat pumps and smart thermostats, enabling load-modulating control rather than simple on/off.
S-Plan
A central heating control architecture using two motorised zone valves to independently control space heating and hot water from a system or heat-only boiler.
System Boiler
A boiler that heats radiators and a separate unvented or vented hot water cylinder, with most components (pump, expansion vessel) built into the boiler casing.
Underfloor Heating Manifold
The brass distribution unit that splits a heat pump or boiler flow into multiple underfloor heating zones, each independently controlled.
Volumiser
A small (12-25L) inline thermal vessel used as a lightweight alternative to a full buffer tank where minimum heat pump system volume is the only concern.
Weather Compensation
A control strategy that adjusts heating flow temperature based on outdoor temperature, raising efficiency by running emitters as cool as possible.
Y-Plan
An older central heating control architecture using a single 3-port mid-position diverter valve to share boiler flow between heating and hot water.
Hot Water
Mixergy Cylinder
A smart hot water cylinder that heats only the volume of water you need on demand, with thermal stratification monitoring and grid-flexibility integration.
Unvented Cylinder
A pressurised hot water cylinder fed directly from the mains, delivering balanced mains-pressure hot water to all outlets without a loft tank.
Vented Cylinder
A hot water cylinder fed by gravity from a cold water tank in the loft, delivering low-pressure hot water without G3 regulation.
Regulations
Article 4 Direction
A local planning measure withdrawing specific permitted development rights from a defined area, requiring full planning permission for works normally exempt.
Climate Emergency DPD
Cornwall Council's Development Plan Document (adopted 2023) setting out policies to support net-zero, including stronger backing for renewable energy proposals.
Conservation Area
A designated area of architectural or historic interest where permitted development rights are restricted to protect the area's character.
Cornwall Local Plan
Cornwall Council's statutory development plan (current 2010-2030, review under way) setting out planning policies for new development including renewable energy.
Energy Performance Certificate (EPC)
A document rating a property's energy efficiency from A (best) to G (worst), legally required for sales, lets and most retrofit grant applications.
EPC C 2028
The proposed UK regulation requiring all new private tenancies to achieve EPC band C from April 2028 and all existing tenancies from 2030.
Future Homes Standard
The 2025 Building Regulations update mandating that new-build homes in England produce 75-80% lower CO2 than 2013 standards, effectively ending fossil-fuel heating in new builds.
G3 Qualification
The Building Regulations Part G3 qualification required to install or service unvented hot water cylinders over 15L.
Gas Safe Register
The official UK register of qualified gas engineers, replacing CORGI in 2009. Mandatory for any gas appliance work.
HIES
Home Insulation & Energy Systems Contractors Scheme — a consumer protection body for renewable energy installers, alongside RECC.
Insurance-Backed Guarantee (IBG)
A third-party insurance policy that honours an installer's workmanship guarantee if the installer ceases to trade.
Listed Building Consent
Statutory permission required from the local planning authority before any internal or external alteration to a listed building.
MCS Certification
The Microgeneration Certification Scheme — the UK quality standard required for installers of grant-funded renewable systems including heat pumps and solar PV.
MCS Installer Number
A unique identifier issued by the Microgeneration Certification Scheme to every certified installer, used on all certificates and grant claims.
MEES
Minimum Energy Efficiency Standards — the regulation requiring rented properties in England and Wales to meet at least EPC band E (rising to C from 2028).
NICEIC / STROMA Notification
The Building Regulations Part P notification of electrical work in dwellings, made by a registered competent person via NICEIC, STROMA, NAPIT or ELECSA.
OFTEC
The Oil Firing Technical Association — registers engineers competent to install and service oil-fired boilers, AGAs and tanks. Critical in off-gas-grid Cornwall.
Permitted Development
Planning rules allowing certain works (including most ASHP and solar installations) without a full planning application, subject to size and siting limits.
RECC
Renewable Energy Consumer Code — the alternative consumer protection body to HIES, sponsored by RenewableUK and approved by the Trading Standards Institute.
TrustMark
The UK government-endorsed quality scheme for tradespeople, mandatory for ECO4 and Warm Homes Local Grant work.
Solar PV
Feed-in Tariff (FiT) — legacy
The closed-to-new-applicants generation tariff that paid solar owners between 2010 and 2019 for every kWh generated, regardless of use.
Inverter
The device that converts DC power from solar panels (or a battery) into 230V AC power compatible with the grid and your home.
kWp
Kilowatt-peak — the rated maximum DC power output of a solar PV array under standard test conditions (1,000W/m², 25°C cell temp).
Microinverter
A small inverter mounted directly behind each solar panel, converting DC to AC at the panel rather than at a single central unit.
MPPT
Maximum Power Point Tracking — the inverter algorithm that constantly adjusts voltage to extract the most power from a solar string under changing conditions.
n-Type TOPCon
The dominant 2026 solar cell technology, using n-type silicon with a tunnel oxide passivated contact for higher efficiency and lower degradation than older PERC cells.
Octopus Intelligent Flux
A smart import/export tariff from Octopus that automatically charges and discharges your home battery to maximise export earnings and minimise import costs.
Optimiser
A DC-DC device fitted behind each solar panel to perform per-panel MPPT before sending power to a central string inverter.
p-Type PERC
The previous-generation solar cell technology using p-type silicon and Passivated Emitter Rear Cell architecture, now being phased out by n-type TOPCon.
Smart Export Guarantee (SEG)
The current UK scheme requiring large electricity suppliers to pay solar owners for surplus power exported to the grid.