Solar & Electrical Glossary: 100+ Terms Every Installer Must Know

This glossary defines 90 core terms every solar installer, electrician, and contractor encounters — from datasheet specs to NEC articles, from battery chemistry to utility interconnection. Terms are grouped by category and cross-reference related PES Supply products and our technical articles. Bookmark this page and use the A–Z index above to jump straight to what you need.

Solar Panels

Bifacial gain

Extra energy from rear side; 5–15% over ground, up to 30% over snow/water. Size strings to avoid overvoltage in cold/cloud.

Bifaciality factor

Ratio of rear-side to front-side power output. Typical 0.65–0.85; multiply rear gain by this factor when sizing strings.

Cell efficiency

DC power out vs incident irradiance on cell area. Commercial mono PERC ~21–22%, TOPCon ~22–24%, HJT ~23–25%.

Degradation curve

Power loss over time. Tier-1 warrant ~97.5% at year 1, ~85% at year 25 for PERC; TOPCon ~87–90%.

Fill Factor (FF)

Ratio of max power to product of Voc and Isc. FF > 0.78 indicates a quality cell; lower FF signals resistance losses.

Half-cut cells

Cells halved to halve current, cut resistive losses ~3% and improve shade tolerance.

LeTID (Light and elevated Temperature Induced Degradation)

Long-term loss in PERC/TOPCon at high cell temp; can exceed 5%. Look for LeTID-tested modules.

LID (Light Induced Degradation)

First-year power loss from boron-oxygen defects in p-type PERC; typically 1–2%. N-type cells are LID-free.

MBB (Multi Busbar)

9–16 thin wires vs 5 ribbons; reduces shading and microcrack impact, raises efficiency ~0.5%.

N-type vs P-type

N-type wafer (phosphorus-doped) has no LID, higher efficiency ceiling; p-type (boron) is cheaper but degrades faster.

NMOT (Nominal Module Operating Temperature)

Updated NOCT metric (IEC 61853) using 800 W/m², 20°C, 1 m/s wind, open-circuit. Preferred for modern bifacial/TOPCon modules.

NOCT (Nominal Operating Cell Temperature)

Cell temp at 800 W/m², 20°C ambient, 1 m/s wind. Closer to real-world performance than STC; use NOCT to estimate summer output.

PID (Potential Induced Degradation)

Voltage-leakage loss from sodium ion migration; mitigated by anti-PID inverters and frameless/double-glass designs.

STC (Standard Test Conditions)

Cell temperature 25°C, irradiance 1000 W/m², air mass 1.5 — the factory rating condition. Use STC to compare module nameplate power, but expect 10–15% less in the field.

Temperature coefficient (Pmax)

Power loss per °C above 25°C, e.g. −0.35%/°C. Lower is better; TOPCon (~−0.30%) beats PERC (~−0.37%).

Inverters

AC-coupled

Battery inverter added to existing grid-tied system on the AC side; easiest retrofit.

Anti-islanding

Required shutdown when grid fails (UL 1741 / IEEE 1547) to protect lineworkers.

Clipping

Power loss when DC output exceeds inverter AC capacity at midday; high DC/AC ratio increases it.

DC-coupled

Battery charged directly from PV DC bus; higher round-trip efficiency (~95% vs ~90%).

DC/AC ratio (inverter loading ratio)

Array DC wattage ÷ inverter AC rating. 1.15–1.35 typical; above 1.4 risks clipping losses.

Grid-tied (string) inverter

Synchronizes to grid, no battery. Cheapest; shuts down on outage (anti-islanding).

Hybrid inverter

Grid-tied plus battery charge/discharge ports; supports backup power.

IEEE 1547-2018

Interconnection standard defining smart-inverter reactive power and ride-through requirements.

Microinverter

DC-AC conversion at each panel (e.g. Enphase IQ8). Best for shade/complex roofs; higher cost and more failure points.

MPPT (Maximum Power Point Tracking)

Algorithm that holds the array at its max-power voltage. String inverters have 1–3 MPPTs; more MPPTs handle varied orientations better.

Off-grid inverter

Standalone, no grid connection; requires battery and charge controller sizing.

Power optimizer

DC-DC per-panel MPPT that feeds a central string inverter (e.g. SolarEdge). Shade resilience at lower cost than microinverters.

Rapid shutdown (NEC 690.12)

PV conductors must drop to <30V or <240VA within 30s (1- and 2-family dwellings) of the array boundary.

Rule 21

California grid-code for smart-inverter functions: volt-VAR, frequency-watt, ride-through.

String inverter

One inverter for a series string of panels. Lowest $/W, best for unshaded roofs; add optimizers for partial shade.

Transformerless inverter

No galvanic isolation transformer; lighter, higher efficiency (~98%), requires functional grounding per NEC 690.43.

Batteries & Storage

AC-coupled battery

Self-contained battery+inverter (Tesla Powerwall, Enphase IQ Battery); easiest retrofit.

Backup vs self-consumption

Backup = reserve for outage; self-consumption = maximize daily cycling. Hybrid inverters support both.

BMS (Battery Management System)

Monitors cell voltage, temperature, current; balances cells and disconnects on fault. Mandatory for lithium.

C-rate

Charge/discharge rate relative to capacity. 1C = full discharge in 1 hr. Most home LFP is 0.25–0.5C.

Cycle life

Number of charge/discharge cycles to 70–80% capacity. LFP 4,000–6,000; lead-acid 500–1,500.

DoD (Depth of Discharge)

Percentage of capacity used. LFP allows 80–95% DoD; lead-acid only 50% for cycle life.

LFP (LiFePO4)

Lithium iron phosphate chemistry — safer (no thermal runaway at normal temps), 4,000–6,000 cycles, slightly lower energy density than NMC.

NMC (Nickel Manganese Cobalt)

Higher energy density, ~2,000–3,000 cycles, more thermal-runaway risk than LFP; common in EVs and some home batteries.

Round-trip efficiency

AC energy out ÷ AC energy in. LFP ~90–95%, lead-acid ~75–80%, flow ~70–80%.

Stacking

Multiple battery modules on one inverter to scale capacity (e.g. EG4, Fortress).

Sulfation

Lead-acid failure mode from chronic undercharging; lithium does not sulfate.

Thermal runaway

Uncontrolled self-heating in NMC/lithium-cobalt cells; LFP is far more resistant. Fire codes (NFPA 855) govern lithium ESS.

Time-of-use (TOU) shifting

Charge battery at cheap off-peak, discharge at peak — primary economic driver in CA, NY, MA.

Usable capacity

Nameplate × DoD. A 10 kWh LFP at 90% DoD gives 9 kWh usable.

NEC & Electrical

AHJ (Authority Having Jurisdiction)

Local building/electrical inspector who approves the permit. Always confirm AHJ-specific requirements.

Ampacity

Current-carrying capacity, derated for temperature and conduit fill (NEC 310.15).

Arc-fault protection (690.11)

DC arc-fault detection required for PV >240W on dwellings.

Article 240

Overcurrent Protection — breaker/fuse sizing at 125% of continuous current.

Article 250

Grounding and Bonding — EGC, GEC, grounding electrode system.

Article 310

Conductors for General Wiring — ampacity tables, insulation types (THWN-2, PV wire).

Article 625

Electric Vehicle Power Transfer System — EVSE, branch circuit sizing.

Article 690

NEC section for Solar PV Systems — array, inverter, conductors, grounding.

Article 705

Interconnected Electric Power Production Sources — grid tie, point of connection, anti-islanding.

Continuous load

Expected to run 3+ hours; PV output counts as continuous — size OCPD and conductors at 125%.

EGC (Equipment Grounding Conductor)

Bonds non-current-carrying metal; sized per Table 250.122.

GEC (Grounding Electrode Conductor)

Connects system to grounding electrode (rod/ufer); sized per Table 250.66.

NEC (National Electrical Code, NFPA 70)

U.S. electrical safety standard, updated every 3 years. NEC 2026 effective adoption rolling through states.

Rapid shutdown (690.12)

Controlled array boundary de-energization within 30s.

SCCR (Short-Circuit Current Rating)

Equipment's withstand rating; PV combiner SCCR must exceed available fault current.

Supplemental electrode

If a single ground rod reads >25Ω, drive a second rod (250.53).

Ungrounded array

No grounded current-carrying conductor; transformerless inverters require ungrounded conductors, often purple/pink per NEC 200.6.

Working space (110.26)

Clearance around equipment: 3 ft front, 6.5 ft height minimum.

Mounting & Racking

Bonding

Electrical continuity between rail, clamps, and frames to ground the array (NEC 690.43).

End clamp / Mid clamp

Hold module edges to rail; sized to module frame height.

Flashing

Roof-boot or shingle-integrated seal around penetrations; required by most roofing warranties.

Flat-roof ballast

Non-penetrating mount weighted by pavers/blocks; designed for wind uplift per ASCE 7.

Ground mount

Freestanding structure (pole, table, or pile-driven) for open land.

L-foot

Connects rail to roof attachment (lag bolt to rafter or standoff).

Rail

Aluminum extrusion (IronRidge XR100, Unirac SM) that supports modules; span, load, and cantilever sized per ASCE 7.

Roof load capacity

Structural limit (psf) the roof assembly (dead + live + snow + PV) must not exceed — engineer sign-off often required.

Sealant vs flashing

Flashing is primary waterproofing; sealant (mastic, butyl tape) is secondary.

Snow load

Downward force from accumulated snow; ASCE 7 + local AHJ determines psf.

Splice bar

Joins rail sections for longer arrays; placed at expansion gap or mid-span per manufacturer.

Standoff

Roof-penetrating mount with flashing; raises rail off roof for ventilation.

Tracker

Single/dual-axis mount that follows the sun; adds 15–35% yield, higher maintenance.

Wind uplift

Upward suction force; ballasted and anchored systems must resist per ASCE 7.

Grid & Utility

Anti-islanding

See Inverters; protects lineworkers during outage.

Demand charge

Commercial $/kW for peak demand; battery peak-shaving reduces it.

FIT (Feed-in Tariff)

Fixed long-term price per exported kWh; rare in U.S. now, common historically.

Frequency-watt

Smart-inverter reduces output when grid frequency rises above 60.2 Hz.

Import / export meter

Bi-directional meter measuring grid flows separately for net billing.

Interconnection agreement

Utility contract allowing grid-tied generation; application + fee + one-line diagram.

Net billing

Export compensated at a lower avoided-cost rate, not retail (e.g. NEM 3.0 California).

Net metering

Utility credits exported kWh at retail or near-retail rate. Policies vary widely by state.

PBI (Performance Based Incentive)

Per-kWh payment for verified production (common with SRECs).

SREC (Solar Renewable Energy Certificate)

1 MWh of solar generation = 1 credit; traded in compliance markets (NJ, MA, PA, OH, DC, MD).

Time-of-use (TOU)

Rate that varies by hour; peak 4–9 pm in most utilities — battery shifting targets this.

Virtual net metering

Shared system credit allocated to multiple accounts (community solar).

Voltage ride-through

Smart-inverter stays connected through brief voltage sags (IEEE 1547).

Shop the Relevant Gear

PES Supply stocks the panels, inverters, batteries, breakers, wire, and racking referenced throughout this glossary. Standard delivery is 7–10 business days.

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Deeper Reading

• Microinverters vs. String Inverters: Which Is Better for Your Solar Array?
• String Inverter Sizing Guide: How to Match Inverters to Your Solar Array
• Solar Market Outlook H2 2026: Panel Prices, Supply Chain, and Demand Trends
• Solar Panel Efficiency Explained: Monocrystalline vs. Polycrystalline vs. Bifacial (2026)
• How Many Solar Panels Do I Need? System Sizing Guide with Calculator