☀️ Renewable Energy Terminology Glossary: 55 Essential Terms Explained

Why These Terms Matter

Renewable energy engineering pulls vocabulary from three formerly separate worlds — electrical code (NEC), utility interconnection standards (IEEE 1547, UL 1741), and project finance (PPAs, ITC, LCOE) — and mashes them together into a discipline where a single project meeting can bounce between "what's your DC-to-AC ratio" and "what's the tax equity structure." Engineers, developers, AHJs, and utility interconnection reviewers all use this vocabulary daily, and a misunderstood term can mean an undersized inverter, a rejected interconnection application, or a system that never qualifies for the incentive it was designed around.

Many of these terms have precise regulatory meanings: "continuous current" drives conductor sizing under NEC 690.8, "rapid shutdown" is a specific life-safety requirement under NEC 690.12, and "ride-through" is a specific grid-support behavior mandated by IEEE 1547-2018. This glossary defines 55 of the most important terms across solar PV, wind, battery storage, and interconnection, organized alphabetically with code and standard references where applicable.

A

AC Coupling — System architecture

An energy storage configuration in which the battery has its own dedicated inverter and connects to the AC side of the system, alongside (rather than behind) the solar inverter. AC-coupled systems are simpler to retrofit onto an existing PV array because the battery inverter is added downstream without re-engineering the DC side, but they incur an extra DC-to-AC-to-DC-to-AC conversion step when storing solar energy, which lowers round-trip efficiency compared to DC coupling.

Ampacity — NEC Article 100, 690.8

The maximum current a conductor can carry continuously without exceeding its temperature rating. In PV systems, NEC 690.8(B) requires conductors and overcurrent devices to be sized for 125% of the calculated continuous current (itself already increased by 125% from the module's short-circuit current in most cases), producing the familiar "1.56x" or "1.25 x 1.25" factor used in solar string and combiner sizing.

Anti-Islanding — UL 1741, IEEE 1547

A protective function built into grid-tied inverters that detects loss of utility voltage and automatically stops the inverter from energizing the line, preventing the inverter from continuing to power a de-energized grid section ("islanding") where utility crews may be working. Anti-islanding is tested and certified under UL 1741 and is a non-negotiable requirement for any inverter interconnected to the utility grid.

Array — NEC Article 690

A mechanically and electrically integrated assembly of PV modules and support structure, including any attached inverters, controllers, or other components, functioning as a single unit. A system may have one array or multiple arrays, each with its own combiner and home run.

Autonomous Time — Battery/off-grid design

Also called "days of autonomy," the number of consecutive days a battery-backed system is expected to supply critical loads with no solar or generator input, sized against the site's worst-case cloudy-day sequence. Off-grid and critical backup designs typically target 1–3 days of autonomy; grid-tied backup systems often target hours, not days, since the grid remains the primary backstop.

B

Balance of System (BOS) — System design

Every PV or storage system component other than the modules/cells and the inverter — racking, conductors, combiners, disconnects, monitoring, and labor. BOS costs have become a larger fraction of total installed cost as module prices have fallen, making BOS optimization (fewer, larger strings; simplified conduit runs) an increasing focus of system design.

Battery Energy Storage System (BESS) — NFPA 855, UL 9540

A system of one or more battery modules, together with the power conversion, monitoring, fire suppression, and thermal management equipment needed to charge and discharge electrical energy on demand. BESS installations are governed by NFPA 855 for fire and life safety (spacing, ventilation, thermal runaway mitigation) and by UL 9540/9540A for equipment listing and thermal runaway propagation testing.

Bifacial Module — PV technology

A solar module that captures light on both its front and rear faces, generating additional energy from light reflected off the ground, roof membrane, or racking ("albedo gain"). Bifacial gain is typically 5–20% depending on ground reflectivity, module height off the ground, and racking configuration, and is increasingly standard in utility-scale and agrivoltaic installations.

Bypass Diode — Module protection

A diode wired in parallel with a substring of PV cells that provides an alternate current path around a shaded or failed cell, preventing that cell from becoming reverse-biased and overheating (the "hot spot" failure mode). Nearly all modern crystalline-silicon modules embed 3 bypass diodes, one per substring, in the junction box.

C

Capacity Factor — Performance metric

The ratio of a plant's actual energy output over a period to the energy it would produce running at full nameplate capacity for that entire period. Utility-scale solar PV in the US typically runs 20–28% capacity factor; onshore wind runs 30–45%; offshore wind runs 40–55%. Capacity factor is distinct from availability — a plant can be 99% available but still have a modest capacity factor simply because the resource (sun, wind) isn't always at maximum.

Clipping — Inverter operation

The condition where DC power arriving at the inverter exceeds the inverter's rated AC output capacity, forcing the inverter to cap output and "clip" the excess — a deliberate and economical consequence of an oversized DC-to-AC ratio, not a fault. Clipped energy is lost only during the relatively rare hours of peak irradiance; the extra DC capacity boosts output during the much more common partial-sun hours.

Combiner Box — Array wiring

An enclosure where multiple PV source or output circuits (strings) are joined in parallel onto a single set of output conductors, typically with individual overcurrent protection (fuses) for each string. Combiner boxes reduce the number of conductors that must be run to the inverter or disconnect.

Curtailment — Grid operations

The deliberate reduction of a renewable generator's output below its available potential, ordered by the utility or grid operator, usually because transmission capacity is constrained or because supply already exceeds demand (common on the CAISO "duck curve" during high-solar midday hours). Curtailment reduces a project's realized revenue and is an increasingly important variable in project financial modeling in high-renewable-penetration grids.

Continuous Current — NEC 690.8

For PV systems, the maximum current expected under any conditions, calculated per NEC 690.8(A) as 125% of the module's rated short-circuit current (or, for inverter output circuits, 125% of the inverter's continuous output current rating). This value, further multiplied by another 125% under 690.8(B) for conductor and OCPD sizing, produces the standard PV conductor sizing methodology.

D

DC Coupling — System architecture

An energy storage configuration in which the battery connects directly to the DC bus alongside the PV array, sharing a single hybrid inverter for both solar and battery power conversion. DC coupling avoids the extra AC-DC-AC conversion step of AC coupling, improving round-trip efficiency, but requires the storage to be designed in at the outset (or the DC bus re-engineered) rather than simply added later.

DC-to-AC Ratio (ILR) — System sizing

Also called the inverter loading ratio, the ratio of a PV array's DC nameplate capacity (kW-DC) to the inverter's rated AC output capacity (kW-AC). Utility-scale systems are commonly designed with ratios of 1.2–1.4, deliberately oversizing the DC array relative to the inverter to increase energy harvest during low-irradiance hours at the cost of some clipping during peak sun — a decision made on an economic, not a code, basis.

Degradation Rate — Module performance

The annual percentage decline in a PV module's power output over its service life, typically 0.3–0.5%/year for modern crystalline silicon modules after an initial slightly higher first-year "light-induced degradation." Degradation rate is a key input to 25-year energy production estimates and PPA pricing models.

Demand Charge — Utility billing

A charge on a commercial or industrial electric bill based on the customer's highest rate of power draw (kW) during a billing period, separate from the energy (kWh) charge. Behind-the-meter battery storage is frequently deployed specifically to "peak shave" and reduce demand charges, which can represent a large share of a commercial customer's total bill.

Distributed Energy Resource (DER) — IEEE 1547

A source of electric power (generation) or controllable load that is connected to the distribution system rather than the transmission system, including rooftop solar, small wind, behind-the-meter batteries, and demand-response loads. IEEE 1547 is the foundational interconnection and interoperability standard governing how DERs connect to and operate on the utility distribution grid.

Duck Curve — Grid operations

A graph of net electric demand (total demand minus renewable generation) over a day, named for its duck-like silhouette, showing a deep midday belly (as solar output peaks) followed by a steep evening ramp as solar falls off while demand rises. The duck curve illustrates why fast-ramping resources (batteries, gas peakers, demand response) become more valuable as solar penetration increases.

E

Energy Storage System (ESS) — General term

Any system that captures energy for use at a later time — batteries are the dominant technology today, but the term also covers pumped hydro, compressed air, flywheels, and thermal storage. In most current engineering practice "ESS" and "BESS" are used interchangeably to mean battery storage.

EV Supply Equipment (EVSE) — NEC Article 625

The conductors, connectors, enclosures, and equipment installed to deliver energy from a premises wiring system to an electric vehicle, commonly called a "charger" in everyday speech even though the actual charging circuitry is onboard the vehicle. EVSE installations are governed by NEC Article 625, with Level 2 (240V) being the most common residential installation and DC fast charging requiring dedicated utility service and NEC Article 625 Part V provisions.

F

Feed-in Tariff (FIT) — Policy mechanism

A policy under which a utility or government guarantees a fixed price, often above the wholesale market rate, for renewable energy delivered to the grid over a long-term contract, historically used in Germany and parts of Europe to accelerate early solar and wind deployment. FITs have been largely replaced in the US by net metering and PPA structures, though some FIT programs remain for specific project sizes or technologies.

Fill Factor — Cell characterization

The ratio of a PV cell's actual maximum power output to the theoretical maximum obtained by multiplying its open-circuit voltage by its short-circuit current, expressed as a percentage (typically 75–85% for good-quality crystalline silicon cells). Fill factor is a measure of how "square" the cell's I-V curve is and reflects internal resistive and recombination losses.

G

Ground-Fault Protection Device (GFPD/GFDI) — NEC 690.41

A device required in PV DC circuits (with certain exceptions for newer rapid-shutdown-compliant systems) that detects a ground fault, interrupts the fault current path, and in most designs also indicates the fault and may de-energize the array. GFPDs address the risk that a single ground fault in an ungrounded PV array can otherwise go undetected and create fire or shock hazards.

Grid-Forming Inverter — Inverter control mode

An inverter that establishes its own voltage and frequency reference — acting like a synchronous generator — rather than synchronizing to an existing grid voltage waveform, allowing it to operate a microgrid in islanded mode or provide inertia-like support on a weak grid. This is distinct from a conventional "grid-following" inverter, which requires an existing grid signal to synchronize to and cannot start a de-energized system on its own.

Ground-Mount System — Installation type

A PV array supported on racking anchored directly to the ground (via driven piles, ballasted footings, or helical piers) rather than mounted on a building roof, typical of utility-scale and larger commercial solar farms and often paired with single-axis tracking.

H

Hybrid Inverter — Equipment type

An inverter that manages both PV array input and battery charge/discharge through a single unit, enabling DC coupling of storage. Hybrid inverters are increasingly standard in residential solar-plus-storage installations because they reduce equipment count and cost compared to separate solar and battery inverters.

Home Run — Array wiring

The conductors that run from a combiner box, string, or subarray directly back to the inverter or main disconnect without intermediate combining. "Home run" is used informally to describe the wiring layout choice of routing each circuit individually versus combining strings closer to the array.

I

Interconnection Agreement — Utility process

The formal contract between a DER owner and the utility (or grid operator, for larger projects) establishing the technical and operational terms under which the generating system may connect to and operate on the grid, typically following a technical study process (fast-track, supplemental, or full impact study depending on system size and circuit conditions).

Investment Tax Credit (ITC) — Federal incentive, IRC Section 48/48E

A US federal tax credit equal to a percentage of the eligible cost basis of a qualifying renewable energy or storage project, claimed in the year the system is placed in service. The ITC has been the single largest financial driver of US solar and storage deployment and its percentage, eligibility rules (including prevailing wage/apprenticeship and domestic content adders), and technology scope have changed across several legislative cycles — current project economics should always be checked against the version of the code in effect at the time of the project's placed-in-service date.

Islanding — Grid safety

A condition where a portion of the utility distribution system continues to be energized by a distributed generator after it has been disconnected from the main utility source, creating a hazard for utility line workers who expect the section to be de-energized. See Anti-Islanding for the required inverter protection function.

K

Kilowatt-Peak (kWp / kW-DC) — Rating convention

The DC power rating of a PV array measured under Standard Test Conditions (STC: 1000 W/m² irradiance, 25°C cell temperature, AM1.5 spectrum), used as the nameplate capacity for modules and arrays. Real-world output is almost always lower than the kWp rating because field conditions (higher cell temperature, soiling, non-ideal irradiance angle) rarely match STC exactly — this gap is part of what the derate factor accounts for.

L

Levelized Cost of Energy (LCOE) — Economic metric

The average total cost (capital, financing, operations, and maintenance) to build and operate a power-generating asset over its life divided by the total energy it is expected to produce over that life, expressed in dollars per megawatt-hour. LCOE allows apples-to-apples comparison of generation technologies with very different cost structures (high upfront capital and near-zero fuel cost for solar/wind versus lower capital but ongoing fuel cost for gas), though it does not by itself capture time-of-day value or grid reliability contribution.

Levelized Cost of Storage (LCOS) — Economic metric

The storage-system analog of LCOE — the total lifetime cost of a storage asset divided by the total energy it discharges over its life, factoring in round-trip efficiency losses, degradation, and augmentation/replacement costs as the battery ages.

M

Maximum Power Point (MPP) — I-V curve

The point on a PV cell or module's current-voltage (I-V) curve at which the product of current and voltage — and therefore power output — is maximized. The MPP shifts continuously with changes in irradiance and temperature, which is why inverters must actively track it rather than operating at a fixed voltage.

Maximum Power Point Tracking (MPPT) — Inverter/charge controller function

The control algorithm, built into inverters and solar charge controllers, that continuously adjusts the electrical operating point of the PV array to keep it at its maximum power point as sunlight and temperature conditions change. Multiple MPPT inputs on a single inverter allow independent tracking of subarrays facing different directions or experiencing different shading, improving harvest compared to a single shared MPPT.

Microgrid — System architecture

A localized group of interconnected generation, storage, and loads that can operate connected to the main utility grid or disconnect and operate autonomously in "island mode," typically requiring a grid-forming inverter or synchronous generator to establish voltage/frequency reference when islanded.

Microinverter — Equipment type

A small inverter mounted at each individual PV module that converts that module's DC output to AC at the module level, rather than one central (string) inverter converting the combined DC output of many modules. Microinverters eliminate string mismatch losses from partial shading and allow module-level monitoring and rapid-shutdown compliance by design, at a higher per-watt equipment cost than string inverters.

N

Net Energy Metering (NEM) — Utility billing/policy

A billing arrangement in which a customer-generator's exported solar energy is credited against their consumption, typically on a kWh-for-kWh basis (traditional NEM) or at an avoided-cost/time-varying export rate (as under California's NEM 3.0 and similar successor tariffs). NEM policy design — the credit rate, whether it's kWh-based or value-based, and whether it varies by time of export — is one of the single biggest drivers of residential solar-plus-storage economics.

Nameplate Capacity — Rating convention

The manufacturer-rated maximum power output of a generating unit or system under specified reference conditions, printed on the equipment's rating label. For PV, this is the STC DC rating on the module label; for an inverter, it's the rated continuous AC output.

O

Offtaker — Project finance

The party that purchases the electricity (and/or associated renewable energy certificates) generated by a project, typically under a long-term Power Purchase Agreement. Offtakers range from utilities (utility-scale PPAs) to corporations (corporate PPAs) to individual homeowners (residential solar leases/PPAs).

Open-Circuit Voltage (Voc) — Module rating

The voltage across a PV module's terminals when no current is flowing (an open circuit), measured under STC and printed on the module label. Voc is temperature-dependent (rising in cold weather) and is the value used, together with the low-temperature correction factor, to calculate maximum string voltage under NEC 690.7 — a critical check to avoid exceeding equipment voltage ratings on cold mornings.

P

Peak Sun Hours — Solar resource metric

The number of hours per day during which solar irradiance would need to average 1000 W/m² to deliver the same total daily energy (in kWh/m²) actually received at a location — a normalization that lets designers use a single daily number (typically 3–6+ depending on location and season) instead of a full irradiance curve for first-pass sizing.

Performance Ratio (PR) — System performance metric

The ratio of a PV system's actual measured energy output to the theoretical output it would produce if it always operated at its rated STC efficiency with no losses, capturing the combined effect of temperature, soiling, wiring, inverter, and availability losses. Well-designed, well-maintained systems typically achieve PRs of 0.75–0.85.

Power Optimizer — Equipment type

A DC-to-DC converter installed at each module (similar in placement to a microinverter) that performs module-level MPPT but still sends DC power to a central string inverter for the final DC-to-AC conversion, combining most of the shading-mismatch and monitoring benefits of microinverters with the lower per-watt cost of a central inverter.

Power Purchase Agreement (PPA) — Project finance

A long-term contract under which a renewable energy project owner sells the electricity generated (and often the environmental attributes) to an offtaker at an agreed price structure, providing the revenue certainty that underpins most project debt and equity financing.

Production Tax Credit (PTC) — Federal incentive, IRC Section 45/45Y

A US federal tax credit paid per kilowatt-hour of qualifying electricity actually generated and sold over the first ten years of a project's operation, historically the primary incentive mechanism for wind projects (as an alternative to the ITC, which developers can elect instead in many cases).

R

Rapid Shutdown — NEC 690.12

A life-safety requirement that PV system conductors within the array boundary be reduced to a low voltage (30V or less) within 30 seconds of initiation, protecting firefighters who may need to cut into a roof or contact array wiring during a fire. Compliance is typically achieved with module-level rapid-shutdown devices (built into microinverters, power optimizers, or dedicated shutdown units) that communicate over the DC wiring itself, activated by a manually operated or automatic initiating device.

Renewable Energy Certificate (REC) — Environmental attribute

A tradable certificate representing the environmental, social, and other non-power attributes of one megawatt-hour of renewable generation, which can be sold separately from the underlying electricity itself. RECs allow a project's environmental value to be monetized independently and are the mechanism behind most corporate "100% renewable" and green power claims.

Ride-Through — IEEE 1547

The requirement, under IEEE 1547-2018, that a DER remain connected and continue operating through specified momentary grid voltage and frequency disturbances rather than tripping offline, improving overall grid stability as DER penetration increases and reducing the risk of a large simultaneous loss of generation during a minor grid disturbance.

Round-Trip Efficiency — Storage performance metric

The ratio of energy delivered by a battery on discharge to the energy required to charge it, capturing conversion, internal resistance, and thermal management losses. Modern lithium-ion BESS typically achieve 85–95% round-trip efficiency (AC-to-AC), with DC-coupled systems generally at the higher end of that range due to fewer conversion stages.

S

Short-Circuit Current (Isc) — Module rating

The current through a PV module's terminals when they are shorted together (zero voltage), measured under STC and printed on the module label. Isc is the basis for the continuous-current calculation under NEC 690.8(A) and rises slightly with irradiance and temperature above STC, which is why the code applies safety multipliers rather than using the nameplate value directly.

Single-Axis Tracker — Racking system

A mounting system that rotates PV modules about a single horizontal (typically north-south) axis to follow the sun's daily east-to-west path, increasing energy capture roughly 15–25% over a fixed-tilt array in most locations, at added mechanical complexity and cost. It is the dominant racking choice for utility-scale ground-mount projects in most of the US.

Solar Access — Site assessment

The measure of how much of a site's available solar resource actually reaches a proposed array location after accounting for shading from trees, adjacent structures, and terrain, usually quantified as a percentage of unshaded, unobstructed sun exposure across a full year using tools like a solar pathfinder or shading analysis software.

State of Charge (SOC) — Battery management

The current available capacity of a battery expressed as a percentage of its full rated capacity, analogous to a fuel gauge. Battery management systems use SOC, along with state of health, to manage charge/discharge cycling and protect against damaging over-discharge or overcharge.

State of Health (SOH) — Battery management

A measure of a battery's current capacity and performance relative to its original, as-new specification, declining over the battery's life due to cycling, calendar aging, and temperature exposure. SOH is the primary metric used to plan battery augmentation or replacement schedules over a storage project's contracted life.

String — Array wiring

A series-connected group of PV modules whose voltages add together to reach the operating voltage window of the inverter or charge controller. String sizing (the number of modules per string) is governed by staying within the equipment's maximum input voltage at the coldest expected temperature and its minimum MPPT voltage at the hottest expected temperature.

String Inverter — Equipment type

A central inverter that converts the combined DC output of one or more series-connected module strings to AC, the traditional and still most common inverter architecture for residential and commercial rooftop and ground-mount systems, offering the lowest per-watt cost but with output vulnerable to the worst-shaded module in each string (unless paired with power optimizers).

Supply-Side Connection — NEC 705.11

An interconnection method in which the PV or storage system's output connects to the service conductors ahead of (upstream of) the main service disconnect, rather than through a breaker in the existing panel — one of the two primary interconnection methods addressed by NEC 705.11/705.12, often used when there is insufficient busbar capacity in the existing panel for a load-side (backfed breaker) connection.

T

Temperature Coefficient — Module rating

The percentage change in a PV module's power output (or voltage) per degree Celsius change in cell temperature relative to the 25°C STC reference, typically around -0.3% to -0.5% per °C for power. Because cell temperature in the field commonly runs 20–30°C above ambient air temperature, this coefficient explains why real-world PV output on a hot summer afternoon is meaningfully lower than the STC nameplate rating would suggest.

Thermal Runaway — Battery safety

A self-sustaining, escalating chain reaction inside a lithium-ion cell in which internal heating triggers further exothermic chemical reactions, generating more heat, off-gassing, and potentially fire or explosion, which can then propagate cell-to-cell or module-to-module if not contained. UL 9540A testing evaluates a specific BESS's propagation behavior and informs the spacing, ventilation, and suppression requirements applied under NFPA 855.

Time-of-Use (TOU) Rate — Utility billing

An electricity rate structure in which the price per kWh varies by the time of day (and often season) it is consumed or exported, typically charging more during afternoon/evening peak periods. TOU rate structures are a major driver of the economic case for pairing solar with battery storage, since stored midday solar energy can be discharged during the expensive evening peak period instead of exported at a lower rate.

Total Harmonic Distortion (THD) — Power quality

A measure of how much a voltage or current waveform deviates from a pure sine wave due to harmonic components, expressed as a percentage. IEEE 1547 and UL 1741 limit inverter output current THD (typically to 5% or less) to protect power quality on the distribution grid.

U

Utility Interconnection — Grid connection process

The overall technical and contractual process by which a generating system is connected to the utility distribution or transmission grid, encompassing the application, technical review/impact study, equipment certification, metering, and the eventual Interconnection Agreement and permission-to-operate approval.

V

Volt-Ampere Reactive (VAR) Support — Grid support function

The ability of a smart inverter to absorb or supply reactive power (independent of the real power it is generating) to help regulate local grid voltage, a grid-support function increasingly required by utility interconnection standards for larger DER installations as a condition of interconnection approval under IEEE 1547-2018's expanded ride-through and volt-VAR functional requirements.

W

Wind Turbine Capacity Factor — Performance metric

See Capacity Factor; specific to wind, this is heavily influenced by hub height, rotor diameter relative to nameplate rating, and site wind resource class, which is why modern wind turbine design trends toward larger rotors and taller towers on lower-wind-speed sites to raise capacity factor economically.

Wind Resource Class — Site assessment

A classification of a site's average wind power density and speed at a reference height, used to screen sites for wind project feasibility before detailed met-tower measurement campaigns; higher classes indicate stronger, more economically attractive wind resources.

Quick Reference Table — 55 Renewable Energy Terms

Term	Primary Reference	Key Point
AC Coupling	System architecture	Battery inverter added on AC side
Ampacity	NEC 690.8	Conductor sized at 125% of continuous current
Anti-Islanding	UL 1741, IEEE 1547	Trips inverter offline when grid is dead
Array	NEC Article 690	Integrated assembly of modules + support
Autonomous Time	Off-grid design	Days battery covers loads with no sun
Balance of System (BOS)	System design	Everything except modules and inverter
BESS	NFPA 855, UL 9540	Battery + management + fire safety systems
Bifacial Module	PV technology	Captures light on both faces
Bypass Diode	Module protection	Routes around shaded/failed cells
Capacity Factor	Performance metric	Actual output ÷ theoretical max output
Clipping	Inverter operation	DC power capped at inverter AC rating
Combiner Box	Array wiring	Parallels strings before inverter
Curtailment	Grid operations	Utility-ordered output reduction
Continuous Current	NEC 690.8(A)	125% of Isc for sizing basis
DC Coupling	System architecture	Battery shares DC bus with PV
DC-to-AC Ratio (ILR)	System sizing	DC nameplate ÷ AC inverter rating
Degradation Rate	Module performance	~0.3–0.5%/year output decline
Demand Charge	Utility billing	Charge based on peak kW draw
DER	IEEE 1547	Distribution-connected generation/load
Duck Curve	Grid operations	Midday solar dip, evening ramp
ESS	General term	Umbrella term including BESS
EVSE	NEC Article 625	EV charging equipment/wiring
Feed-in Tariff	Policy mechanism	Fixed long-term export price
Fill Factor	Cell characterization	Actual Pmax ÷ Voc x Isc
GFPD/GFDI	NEC 690.41	Detects and interrupts DC ground faults
Grid-Forming Inverter	Inverter control mode	Sets its own voltage/frequency reference
Ground-Mount	Installation type	Racking anchored to ground, not roof
Hybrid Inverter	Equipment type	Manages PV + battery in one unit
Home Run	Array wiring	Direct conductor run to inverter/disconnect
Interconnection Agreement	Utility process	Formal grid-connection contract
ITC	IRC Section 48/48E	Federal tax credit on eligible cost basis
Islanding	Grid safety	DER energizing a de-energized grid section
kWp / kW-DC	Rating convention	Nameplate rating under STC
LCOE	Economic metric	Lifetime cost ÷ lifetime energy
LCOS	Economic metric	LCOE analog for storage
MPP	I-V curve	Point of maximum power on I-V curve
MPPT	Inverter/charge controller function	Tracks maximum power point continuously
Microgrid	System architecture	Can island and operate autonomously
Microinverter	Equipment type	Module-level DC-to-AC conversion
NEM	Utility billing/policy	Credits exported solar energy
Nameplate Capacity	Rating convention	Manufacturer max-rated output
Offtaker	Project finance	Buyer of PPA power/RECs
Voc	Module rating	Voltage at zero current; rises when cold
Peak Sun Hours	Solar resource metric	Normalized daily irradiance measure
Performance Ratio (PR)	System performance metric	Actual ÷ theoretical STC output
Power Optimizer	Equipment type	Module-level MPPT, central inverter
PPA	Project finance	Long-term power sale contract
PTC	IRC Section 45/45Y	Per-kWh federal tax credit
Rapid Shutdown	NEC 690.12	30V/30 sec array de-energization
REC	Environmental attribute	Tradable renewable attribute per MWh
Ride-Through	IEEE 1547-2018	Stay connected through brief disturbances
Round-Trip Efficiency	Storage performance metric	Discharge energy ÷ charge energy
Isc	Module rating	Current at zero voltage (shorted)
Single-Axis Tracker	Racking system	Follows sun east-to-west
SOC / SOH	Battery management	Charge level / capacity health
String / String Inverter	Array wiring / equipment type	Series modules / central converter
Supply-Side Connection	NEC 705.11	Connects ahead of main disconnect
Temperature Coefficient	Module rating	~-0.3 to -0.5%/°C power change
Thermal Runaway	Battery safety	Self-sustaining overheat chain reaction
THD	Power quality	Waveform distortion from pure sine