Glossary

Every acronym, regulation and bit of jargon you'll meet on a solar quote — explained in plain English by working engineers.

Solar PV (15)Battery Storage (12)EV Charging (8)Heat Pumps (8)Grants & Finance (10)Electrical (10)Commercial Terms (7)

Solar PV

kWp (Kilowatt-Peak): Peak power output of a solar array under Standard Test Conditions (STC). A 4kWp domestic install in Scotland's Central Belt typically generates 3,500–3,800 kWh per year.
kWh (Kilowatt-Hour): Unit of energy. The "kilowatt-hours per year" figure tells you how much electricity a system actually produces — far more useful than nameplate kWp.
PVGIS: Photovoltaic Geographical Information System — the EU Joint Research Centre database we use to model yield for any UK postcode, factoring in irradiance and shading.
STC (Standard Test Conditions): 1,000 W/m² irradiance, 25°C cell temperature, 1.5 air-mass. All panel nameplate ratings reference these lab conditions.
MCS Certification: Microgeneration Certification Scheme — the UK industry standard. Required for SEG export tariffs, HES grants and most consumer protection.
SEG (Smart Export Guarantee): UK scheme requiring licensed suppliers to pay for surplus exported renewable electricity. Rates vary by supplier (Octopus Flux pays up to 24p/kWh peak; basic SEG is 5-15p/kWh).
Octopus Flux: Time-of-use tariff from Octopus Energy that pays more for exported electricity during peak hours (16:00-19:00) than off-peak. Battery essential to maximise return.
String Inverter: A single inverter handling multiple panels in series. Lower cost, simpler. Vulnerable to shading affecting whole string.
Microinverter: One inverter per panel. More expensive but each panel optimised independently — better for shaded or split-orientation roofs.
Power Optimiser: Per-panel DC-DC unit that maximises each panel's output before the string inverter (SolarEdge approach). Compromise between string and microinverter cost/benefit.
In-Roof Mount: Panels integrated into the roof tile pattern, replacing tiles. Cleaner look, popular in conservation areas. Slightly more expensive than on-roof.
On-Roof Mount: Standard mount — panels sit on rails above existing tiles. Cheaper, easier to maintain.
Self-Consumption Ratio: Percentage of solar generation used on-site rather than exported. Higher self-consumption = better economics. Battery storage boosts this from ~30% to 70%+.
String Voltage: Total DC voltage of panels in series. Must stay within inverter's MPPT window. Affects how many panels per string.
Bifacial Panel: Solar panel that generates from both front and reflected light on rear face. 5–15% yield boost on suitable mounts (typically ground-mount, car-port).

Battery Storage

BESS (Battery Energy Storage System): Generic term for grid-connected battery storage — domestic or commercial.
AC-Coupled Battery: Battery with its own inverter, connected on the AC side. Easy retrofit to existing solar — no rewiring of original system.
DC-Coupled Battery: Battery shares the solar inverter. Higher efficiency for new installs (one conversion step). Used by Tesla Powerwall 3.
Depth of Discharge (DoD): How much of a battery's capacity is usable. Modern lithium iron phosphate (LFP) batteries are typically 100% DoD; older lead-acid 50%.
Round-Trip Efficiency: Percentage of energy stored that comes back out. Tesla Powerwall: ~90%. LFP batteries: 92-95%.
LFP (Lithium Iron Phosphate): Battery chemistry now dominant in stationary storage. Safer than NMC, longer cycle life (6,000+ cycles), slightly lower energy density.
EPS (Emergency Power Supply): Backup function — battery powers home circuits during grid outages. Tesla Powerwall 3 and Sigenergy include EPS; many EcoFlow variants too.
C-Rate: How fast a battery charges/discharges relative to capacity. C/2 = full charge in 2 hours. Higher C-rate matters for fast EV-charging-from-battery use cases.
Time-of-Use Arbitrage: Charging battery from grid when electricity is cheap, discharging or exporting when expensive. Octopus Flux is the canonical UK example.
Tesla Powerwall 3: Tesla's third-gen residential battery. 13.5kWh, integrated 11.5kW inverter, EPS backup. Premium pricing, best app/ecosystem.
EcoFlow PowerOcean: Modular battery system (5–30kWh). IP65 rated, indoor or outdoor mounting. Strong value vs Tesla.
GivEnergy: UK-engineered battery brand. Strong Octopus Flux integration via GivTCP API. 5–13.5kWh range.

EV Charging

OZEV: Office for Zero Emission Vehicles — the UK government body running EV chargepoint grants and Workplace Charging Scheme.
Workplace Charging Scheme: OZEV grant: £350 per socket × up to 40 sockets for businesses, charities and public sector. Applied for online; approved installers complete the work.
Type 2 (Mennekes): Standard AC charging connector across Europe. All UK home and most workplace AC chargers use Type 2.
CCS (Combined Charging System): DC fast-charging connector standard. Used by virtually every modern EV in the UK except some legacy Nissan/Mitsubishi models (CHAdeMO).
Smart Charger: EV charger that can defer charging to off-peak hours, balance load with solar, and report energy usage. Required under UK EV (Smart Charge Points) Regulations 2021.
Load Balancing: Charger management technique — dynamically reduces individual charger output when total site load approaches grid limit. Avoids expensive supply upgrades.
V2G (Vehicle-to-Grid): Bidirectional charging — the EV battery exports to the grid or home when not driving. Emerging technology, limited UK availability in 2026.
PEN Fault Protection: Required electrical safety feature for outdoor EV chargers — detects and isolates protective-earth-neutral combined supply faults. Built into modern chargers.

Heat Pumps

ASHP (Air Source Heat Pump): Heat pump extracting energy from outside air. Most common UK heat pump type. Works down to -15°C with modern units.
GSHP (Ground Source Heat Pump): Heat pump using ground-loop heat exchange. More efficient than ASHP but much higher install cost (boreholes or trenches).
COP (Coefficient of Performance): Ratio of heat output to electricity input. Modern ASHPs deliver COP 3-4 — i.e. 3-4kWh of heat per kWh of electricity.
SCOP (Seasonal COP): Average COP across a heating season — more realistic than peak COP. UK average SCOP for ASHPs is around 3.0-3.5.
Flow Temperature: Hot-water temperature delivered to radiators or underfloor heating. ASHPs run best at lower flow temperatures (45-55°C) — may require radiator upsizing.
Heat Loss Calculation: MCS-required calculation of a building's peak heating demand. Determines correct heat pump sizing.
MCS 020: MCS planning standard for heat pumps — covers noise emissions and minimum distances from boundaries.
BUS (Boiler Upgrade Scheme): England-only grant (Scotland uses HES). £7,500 toward ASHP. Mentioned here because cross-border properties sometimes qualify.

Grants & Finance

Home Energy Scotland (HES): Scottish Government scheme delivering grants and interest-free loans for domestic renewables and energy efficiency.
HES Grant: Up to £7,500 (£9,000 rural) for heat pumps and other measures. Combined with HES loan for up to £24,500 of total support.
HES Loan: Interest-free loan up to £15,000 from the Scottish Government via the HES scheme. Repayment 7-12 years depending on amount.
ECO4: Energy Company Obligation Phase 4 (2022-2026) — supplier-funded scheme that can fully fund solar, ASHP and insulation for qualifying low-income households.
Warmer Homes Scotland: Scottish Government-funded scheme for older or vulnerable households. Delivered by Warmworks (the contracted delivery partner).
GBIS (Great British Insulation Scheme): UK-wide insulation grant scheme — sits alongside ECO4 for households not qualifying on income but living in low-EPC homes.
Capital Allowances: Tax relief for business solar and BESS — 50% first-year allowance for special-rate plant in 2026, plus continuing super-deduction debate.
Green Mortgage: Mortgage product with preferential rates for energy-efficient properties or for adding renewables. Several UK lenders offer them.
Ideal4Finance: FCA-regulated credit broker (FRN 703401) — Ecoaim partners for 0% finance options on domestic installs.
EPC (Energy Performance Certificate): Property energy rating A–G. Required for property transactions and many grant applications.

Electrical

DNO (Distribution Network Operator): Company that operates the local electricity grid. In Central Belt Scotland: SP Energy Networks for most areas, SSEN for Stirling and Clackmannanshire.
G98: Engineering Recommendation for connecting small generation (≤16A/phase, ≤3.68kW single-phase) — notification only, no pre-approval.
G99: Engineering Recommendation for larger generation requiring DNO pre-approval. All commercial solar > 3.68kW and most domestic > 5kW falls under G99.
G100: Active Network Management — used when DNO capacity is constrained. Allows install with output curtailed to safe levels.
Phase (Single vs Three): Domestic UK supplies are usually single-phase. Larger commercial and farm sites have three-phase — allows bigger inverters and chargers.
Consumer Unit: The fusebox/breaker panel. Many older units require upgrade before solar or EV charger install to meet 18th Edition wiring regs.
RCD (Residual Current Device): Safety device that trips on earth-leakage faults. EV chargers require Type-A or Type-F (or built-in) RCDs.
Earthing System (TT/TN-S/TN-C-S): How the property is earthed — affects safety device selection for EV chargers and outdoor solar.
AC Isolator: External lockable isolator switch for safe isolation of solar/battery systems. MCS-required.
DC Isolator: Per-string DC switch on the panel side of the inverter. MCS-required for safe maintenance.

Commercial Terms

PPA (Power Purchase Agreement): Third party owns and operates the solar asset; the host buys the electricity at a fixed lower rate. Zero CapEx route.
CapEx: Capital expenditure — outright purchase of the asset. Best long-term IRR for businesses with cash and tax appetite.
IRR (Internal Rate of Return): Effective annual return on investment. Typical commercial solar IRR in 2026: 12-22% post-tax depending on tariffs and self-consumption.
Payback Period: Years to recoup CapEx from energy savings + export. Scottish commercial solar typically 4-7 years in 2026.
LCOE (Levelised Cost of Energy): Lifetime cost ÷ lifetime energy yield. Useful for comparing solar to grid prices on a like-for-like basis.
Half-Hourly Metering: Commercial metering granularity. Lets you model solar self-consumption properly against actual load shape.
Embodied Carbon: CO₂e emitted to manufacture and install the system. UK solar pays back its embodied carbon in 1-2 years.

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