Appendix A: Glossary of Terms & Acronyms

AC (Alternating Current): current that periodically reverses direction; the grid/load standard [Ch 1]. AFCI (Arc-Fault Circuit Interrupter): detects dangerous arcing faults; required on DC PV per NEC 690.11 [Ch 23]. AHJ (Authority Having Jurisdiction): the local body that adopts code, reviews plans, and inspects; final say [Ch 21, 43]. Array: the complete assembly of modules (strings in series, paralleled) [Ch 4]. Azimuth: compass direction a surface faces; true south (N. hemisphere) is the annual optimum [Ch 2, 18]. Band gap: energy an electron must gain to become mobile in a semiconductor; sets usable photons [Ch 3]. Bifacial: module generating from both faces using reflected light [Ch 5]. BMS (Battery Management System): governs a battery pack’s cells, limits, and safety [Ch 9]. BOS (Balance of System): everything besides modules/inverter: conductors, connectors, OCPD, disconnects [Ch 8]. Capacity factor: annual energy ÷ (rated power × 8,760 h); ~13–22% for fixed PV [Ch 14]. Clipping: intentional limiting of rare peak output when DC/AC ratio > 1 [Ch 6, 16]. DC (Direct Current): one-directional current; PV and batteries are natively DC [Ch 1]. Derate factor: multiplier converting DC nameplate to real AC energy (~0.77–0.86) [Ch 14, 19]. DoD (Depth of Discharge): usable fraction of battery capacity [Ch 9, 17]. EGC (Equipment Grounding Conductor): fault-current return path bonding metal parts; sized per NEC 250.122 [Ch 22]. ESIP: NABCEP Energy Storage Installation Professional credential [Ch 44]. FEOC (Foreign Entity of Concern): sourcing-restriction rules affecting tax-credit eligibility (2026+) [Ch 38]. Fill factor: squareness of the I-V curve; a cell-quality indicator [Ch 4]. GEC (Grounding Electrode Conductor): connects system to the grounding electrode; sized per NEC 250.66 [Ch 22]. GFPD (Ground-Fault Protection Device): required for PV circuits ≥30 V or ≥8 A; usually in the inverter [Ch 22]. HJT (Heterojunction): premium n-type cell; highest efficiency/best temperature coefficient [Ch 5]. IBC / IRC: International Building / Residential Code; reference ASCE 7 [Ch 25, 43]. IFC (International Fire Code): governs rooftop access pathways and setbacks [Ch 26, 43]. Insolation / Irradiation: accumulated solar energy per area (kWh/m²/day) [Ch 2]. Irradiance: instantaneous solar power per area (W/m²; ~1,000 at STC) [Ch 2]. ITC (Investment Tax Credit): credit worth a % of system cost to the owner (federal §48E / former §25D) [Ch 38]. I-V curve: current-vs-voltage plot of a module/string; endpoints Voc and Isc, knee at Pmax [Ch 4, 33]. Isc / Imp: short-circuit current / current at max power [Ch 4]. LCOE (Levelized Cost of Energy): lifetime cost ÷ lifetime energy ($/kWh) [Ch 37]. LFP (Lithium Iron Phosphate): safer, cheaper, mainstream storage chemistry [Ch 9]. LID / PID: light- / potential-induced degradation [Ch 5]. LOTO (Lockout/Tagout): hazardous-energy control; note PV DC stays live in light [Ch 28]. MACRS: accelerated depreciation available to business system owners [Ch 38]. MLPE (Module-Level Power Electronics): microinverters/optimizers; provide module-level shutdown [Ch 6, 22]. Module: a framed, laminated assembly of series-wired cells (a “panel”) [Ch 4, 5]. MPPT (Maximum Power Point Tracking): keeps the array at its I-V knee as conditions change [Ch 6]. NABCEP: North American Board of Certified Energy Practitioners; the credential body [Ch 44]. NEC (NFPA 70): National Electrical Code; revised every 3 years, applies as adopted [Ch 21]. NMC: nickel-manganese-cobalt battery chemistry; denser but higher fire risk than LFP [Ch 9]. NOCT / NMOT: nominal operating cell temperature; basis for realistic output estimates [Ch 4]. OCPD (Overcurrent Protection Device): fuse/breaker protecting conductors [Ch 16, 23]. PERC: passivated emitter rear cell; the displaced p-type mainstream [Ch 5]. PFAS (Personal Fall Arrest System): anchor + harness + lanyard/SRL [Ch 27]. Performance Ratio (PR): actual ÷ weather-expected energy; system-health metric (~0.75–0.85+) [Ch 34]. Pmax (Pmp): module maximum power (nameplate watts) = Vmp × Imp [Ch 4]. PPA (Power Purchase Agreement): third-party-owned system; customer pays per kWh [Ch 38]. PSH (Peak Sun Hours): equivalent hours at 1,000 W/m²; numerically equals daily insolation [Ch 2]. PTO (Permission to Operate): utility’s final authorization to energize [Ch 33, 40]. PV (Photovoltaic): direct conversion of light to electricity [Ch 3]. PVA / PVIP: NABCEP PV Associate / PV Installation Professional credentials [Ch 44]. PVHCS (PV Hazard Control System): UL 3741-listed system satisfying rapid shutdown without MLPE [Ch 22]. Rapid shutdown: NEC 690.12 function controlling conductor voltage for firefighters (≤30 V outside / ≤80 V inside the 1-ft array boundary in 30 s) [Ch 22]. SREC: Solar Renewable Energy Certificate, tradable per MWh in some states [Ch 38]. STC (Standard Test Conditions): 1,000 W/m², 25 °C cell, AM1.5; the nameplate basis [Ch 4]. String: modules wired in series [Ch 4, 15]. TOPCon: tunnel-oxide passivated contact; the current mainstream n-type cell [Ch 5]. TPO (Third-Party Ownership): lease/PPA structures where a business owns and claims the credit [Ch 38]. TSRF (Total Solar Resource Fraction): % of ideal annual irradiance after shading [Ch 18]. Voc / Vmp: open-circuit voltage / voltage at max power [Ch 4]. WEEB: washer-type bonding jumper for UL 2703 racking grounding [Ch 22].