Solar Glossary

AC cable carries alternating current from the solar inverter output to the AC distribution board, meter and grid. Indian solar installations use PVC, XLPE or PVC-armoured cables sized for current capacity and voltage drop, with copper conductors at 4 to 240 mm² depending on system capacity.

AC coupling is a solar-plus-storage architecture where the PV inverter and the battery inverter are separate units connected through the AC bus. It is the standard topology for retrofitting battery storage onto existing solar PV systems.

Accelerated Depreciation (AD) is the 40 percent first-year tax depreciation allowed for solar PV plants under the Indian Income Tax Act. Provides significant tax benefit for commercial customers, effectively reducing solar capex by 15-25 percent in the first year through tax savings.

Albedo is the fraction of incoming solar radiation reflected by a surface, ranging from 0 (perfect absorber) to 1 (perfect reflector). For bifacial solar plants, ground albedo determines rear-side power generation. Typical Indian conditions: 0.05-0.50.

The Approved List of Models and Manufacturers (ALMM) is the register MNRE maintains of approved solar PV module makers and models (List-I) and solar cell makers (List-II) that projects covered by the ALMM Order must use; MNRE publishes no ALMM list for inverters.

Anti-islanding is the protection function in a grid-tied solar inverter that detects a utility grid outage and disconnects the inverter from the grid within milliseconds. It prevents the inverter from energising a dead grid line and is mandated by IEC 62116 and CEA grid standards in India.

Average Pooled Cost (APPC) or Average Pooled Power Cost is the weighted-average cost at which a DISCOM procures power from all sources (thermal, hydro, renewable). Used as benchmark for excess net metering credits, REC pricing and renewable tariff comparisons. Indian APPC: ₹4-5.5/kWh.

Azimuth angle is the horizontal compass direction a solar panel faces, measured clockwise from north. For northern hemisphere installations including India, panels should face due south (180° azimuth) for maximum annual energy. Deviations cost 1 to 8 percent in yield.

Back sheet is the protective polymer layer on the rear of a solar module that provides electrical insulation, weather protection and mechanical robustness. Traditional materials: PVDF (Kynar/Tedlar), PVF, PET-based composites. Glass-glass bifacial modules replace polymer back sheet with rear glass.

Depth of Discharge (DOD) is the percentage of a battery's capacity that has been discharged from full. Higher DOD per cycle means more usable energy but shorter cycle life. DOD discipline is one of the most important design choices in solar storage.

State of Charge (SOC) is the percentage of remaining usable energy in a battery relative to its full capacity. 100 percent means fully charged, 0 percent means fully discharged. SOC is the most important real-time battery metric for solar storage operation and protection.

BESS (Battery Energy Storage System) is a grid-connected or behind-the-meter battery storage installation, ranging from kWh-scale residential to MWh-scale utility. Indian BESS is growing through the Viability Gap Funding scheme, with 4,000 MWh approved in 2023 and a 30 GWh second tranche announced in 2025, for grid services and renewable firming.

A bidirectional meter records electricity imported from the grid and electricity exported to it in separate registers. The bill treatment depends on the approved metering arrangement and local tariff rules.

A bifacial solar module generates electricity from both its front and rear surfaces. Light hitting the back from reflected ground or surrounding surfaces adds 5 to 25 percent to annual yield over an equivalent monofacial module. Bifacial is now standard in Indian utility solar and increasingly used in C&I rooftops.

BIS certification is the Bureau of Indian Standards' product registration showing that equipment such as solar PV modules and grid-connected inverters meets the applicable Indian Standard, and it is required under India's solar quality control orders before those products can be sold.

A Battery Management System (BMS) is the electronic controller that monitors and protects a battery pack. It manages cell voltage and temperature, balances cells, estimates SOC and SOH, communicates with the inverter and enforces protection limits. Every modern lithium-ion battery has one.

A busbar is a thin metallic strip on the front surface of a solar cell that collects the current generated by the cell and conducts it to the next cell in the string. Modern modules use multi-busbar (MBB) designs with 9-16 thin busbars per cell instead of older 2-3 wider busbars.

C-rate is the charge or discharge current of a battery expressed relative to its rated capacity. 1C means a current that fully charges or discharges the battery in one hour. C/2 is two hours, 2C is half an hour. C-rate affects efficiency, heating and cycle life.

Calendar life is the chronological aging of a battery regardless of cycling. Lithium-ion calendar life: 10-15 years for LFP. Combined with cycle life, calendar life determines total battery service life. Whichever expires first ends usable life.

CAN (Controller Area Network) bus is a serial communication protocol used between battery BMS and solar inverter, enabling data exchange about SOC, voltage, current, temperature and control commands. Standard for hybrid inverter-battery integration in Indian solar storage.

CAPEX (Capital Expenditure) is the upfront capital cost of designing, procuring, installing and commissioning a solar project. Indian solar capex landed at ₹3.5 to ₹4.5 crore per MW for utility-scale and ₹40,000 to ₹70,000 per kW for residential rooftop in 2026.

The Central Electricity Authority (CEA) is the statutory technical body under the Indian Ministry of Power. It sets grid codes, technical standards for connectivity, smart-meter rules and other technical norms that govern the Indian electricity sector, including solar grid integration.

The Chief Electrical Inspector to Government (CEIG), also called the Electrical Inspectorate, is the state-level statutory authority responsible for electrical safety approval of electrical installations including solar plants above specified capacity thresholds.

Cell balancing is the process of equalising voltages across individual cells in a battery pack. Passive balancing dissipates excess charge through resistors; active balancing transfers energy between cells. Critical for cell longevity and pack capacity utilisation.

A central inverter is a high-capacity solar inverter, typically 500 kW to 5 MW, used in utility-scale solar plants. It processes the combined DC output of a large array through one or two centralised power blocks feeding a step-up transformer.

The Central Electricity Regulatory Commission (CERC) is India's central electricity sector regulator. It sets inter-state transmission tariffs, regulates inter-state trading, sets benchmark renewable tariffs and adjudicates disputes between central generators and DISCOMs.

Clipping loss is the solar energy lost when the DC array would produce more power than the inverter's AC rating. The inverter caps output at rated power, leaving excess DC unused. Typical 1-8 percent of annual generation in DC-oversized plants. Trade-off accepted for higher annual yield from shoulder hours.

A combiner box, also called string combiner or DC junction box, is an enclosure that parallels multiple solar PV strings, provides per-string fuse protection, surge protection and a single DC isolator for the combined output. Standard in utility-scale solar and large C&I rooftop installations.

Commissioning is the formal process of testing, validating and handing over a completed solar plant to the owner or operator. It includes electrical testing, performance verification, DISCOM grid synchronisation, CEIG approval and documentation handover. Marks the Commercial Operation Date (COD) for PPA purposes.

Conduit is a protective tube that houses and routes electrical cables, shielding them from mechanical damage, UV exposure, rodents and water. Indian solar installations use rigid PVC, flexible PVC, GI and HDPE conduits per IS 9537 and IEC 61386.

Capacity Utilisation Factor (CUF) is energy generated during a period divided by the energy a plant would generate if its stated capacity operated continuously for every hour in that period.

Current is the rate of flow of electric charge through a conductor, measured in amperes (A). It is driven by voltage and limited by resistance. Solar PV strings typically carry 10 to 20 A DC, with inverter output currents ranging from a few amperes to thousands of amperes.

Customs duty is the tax charged on solar equipment imported into India: Basic Customs Duty (BCD) on the assessed value, a Social Welfare Surcharge on the BCD, and IGST on the total. Rates differ by tariff line and change with Union Budget notifications, so check the current rate on CBIC.

Cycle life is the number of charge-discharge cycles a battery can deliver before capacity drops to a defined threshold, typically 80 percent of original. It depends strongly on chemistry, depth of discharge, temperature and charge rate.

DC cable, also called PV cable or solar cable, is the specialised cable that carries DC current from solar PV modules to the inverter. Rated for 1000 to 1500 V DC, double-insulated, UV-resistant and rated for 90°C to 120°C operation, it is the foundation of safe and efficient DC connection.

DC coupling is a solar-plus-storage architecture where the PV array and the battery share a common DC bus inside a single hybrid inverter. It is the dominant topology for new residential and small commercial solar-plus-storage systems.

A DC optimiser is a module-level power electronic device that performs per-panel MPPT and reports per-panel telemetry to a centralised string inverter. It provides shade tolerance and panel-level monitoring while retaining the cost advantages of a central string inverter. SolarEdge and Tigo are the major brands.

DC oversizing, also called overpaneling, is the practice of connecting more PV DC capacity than the inverter's AC rating. Typical Indian DC/AC ratios are 115 to 135 percent. The inverter clips at peak noon but captures more energy in shoulder hours, raising annual yield and CUF.

Deep discharge refers to drawing battery to a low state of charge, typically below 20 percent for lithium-ion or below 50 percent for lead acid. Reduces cycle life and potentially damages cells. BMS protection prevents damaging deep discharge in modern lithium systems.

Diffuse Horizontal Irradiance (DHI) is the solar radiation received from the sky on a horizontal surface, excluding the direct beam from the sun. It is the scattered light that creates daylight even on cloudy days. Indian DHI ranges from 600 to 950 kWh/m²/year.

A DISCOM is the electricity distribution company serving a defined area. It manages the local electricity network and customer connection, metering and billing processes under applicable state rules.

Discount rate is the rate used to convert future cash flows to present value in NPV and LCOE calculations. Typically equals WACC for project finance. Indian solar discount rates: 8-12 percent post-tax. Reflects opportunity cost of capital and project risk.

Direct Normal Irradiance (DNI) is the solar radiation arriving on a surface perpendicular to the sun's direct beam, excluding diffuse and reflected components. It is critical for CSP (Concentrated Solar Power), single-axis trackers and bifacial PV gain calculations. Indian annual DNI ranges from 1,400 to 2,400 kWh/m².

Earthing is the deliberate connection of electrical equipment and structures to the ground through a low-resistance conductor. It protects against electric shock, supports overcurrent and surge protection, and is mandatory in Indian solar installations under IS 3043 and CEA Measures Relating to Safety.

The Electricity Act 2003 is India's foundational electricity sector law. It unbundled state electricity boards, created the regulatory commissions CERC and SERC, introduced open access and laid the framework for renewable energy promotion including RPO and net metering.

Encapsulant is the polymer layer that seals solar cells between glass and back sheet, providing electrical insulation, mechanical protection and environmental sealing. EVA (ethylene vinyl acetate) is the traditional choice; POE (polyolefin elastomer) is preferred for premium and bifacial modules.

ESG (Environmental, Social, Governance) is the framework for corporate sustainability reporting. Solar adoption is the most visible E lever for Indian companies, contributing to Scope 2 emissions reduction and net-zero targets. BRSR is the Indian mandatory ESG reporting standard for listed companies.

An EV charger supplies electrical energy to electric vehicle batteries through AC or DC connections. Indian EV charging uses Bharat AC-001 (3.3 kW), Bharat DC-001 (10-15 kW), CCS-2 (DC fast), CHAdeMO and Type 2 AC standards. Solar integration enables zero-emission EV charging.

Fault Ride Through (FRT) is the requirement that grid-tied solar inverters stay connected through brief voltage and frequency disturbances and support the grid during recovery. It includes Low Voltage Ride Through (LVRT) and High Voltage Ride Through (HVRT) profiles defined by grid codes.

A Feed In Tariff (FIT) is a regulated price the utility pays for each kWh of electricity exported by a renewable generator. In Indian solar, FITs are set by state regulators for gross-metered rooftop and small captive solar, and by central tenders for utility-scale projects.

A fuse is a one-time electrical protection device with a metal element that melts when current exceeds its rated value, interrupting the circuit. Solar PV systems use specialised gPV fuses on the DC side for string-level protection, typically rated 10 to 30 A at 1000 to 1500 V DC.

Global Horizontal Irradiance (GHI) is the total solar radiation received on a horizontal surface, equal to the sum of direct, diffuse and ground-reflected components. Measured in W/m² at any instant or kWh/m² over time. Indian GHI annual totals range from 1,200 to 2,200 kWh/m² depending on region.

Green hydrogen is hydrogen produced through electrolysis of water using renewable electricity. It is distinguished from grey hydrogen (from natural gas) and blue hydrogen (gas with CCS). India's National Green Hydrogen Mission targets 5 million tonnes annual green hydrogen production by 2030.

A grid-forming inverter controls an internal voltage reference and can support voltage and frequency formation. A grid-following inverter instead synchronises its current output to an existing voltage reference. Islanded operation, black start and other grid services depend on the complete equipment and control design.

Gross metering is a billing mechanism where the entire solar generation is exported to the DISCOM at a contracted feed-in tariff, while the customer pays separately for all electricity consumed. It uses two unidirectional meters and decouples generation from consumption.

GST (Goods and Services Tax) on solar in India is 5 percent on solar panels and complete solar power generating systems since 22 September 2025, down from 12 percent. Installation services attract 18 percent, so a composite supply is valued 70 percent goods and 30 percent services, about 8.9 percent in total, and business customers can recover the GST through input tax credit.

A half-cut cell module uses cells laser-cut in half along the middle, doubling the cell count and halving the current per cell. The lower current reduces I²R losses, improves efficiency by 1 to 3 percent, and provides better shade tolerance through dual-string architecture.

Harmonics are integer-multiple frequency components present in voltage or current waveforms beyond the fundamental 50 Hz. They are caused by non-linear loads and switching converters, and degrade power quality. Modern solar inverters tightly control output harmonics to meet IEEE 519 and IEC 61000 limits.

HJT (Heterojunction Technology) is a high-efficiency solar cell architecture combining crystalline silicon with thin amorphous silicon passivation layers. It delivers 25 to 26 percent cell efficiency, the lowest temperature coefficient of mainstream cells, and the highest bifaciality factor (90 to 95 percent).

A hot spot is localised excessive heating in a solar cell, typically caused by partial shading or cell defects forcing one cell to act as a load instead of generator. Can reach 100-200°C, damaging encapsulant and back sheet. Modern bypass diodes mitigate but do not eliminate hot spots.

A hybrid inverter is a solar inverter that can simultaneously feed power to the grid, charge a battery, and provide backup AC during outages. It integrates the functions of an on grid inverter, an off grid inverter and a battery charger in one unit.

IBC (Interdigitated Back Contact) is a solar cell architecture with both positive and negative contacts on the rear surface, eliminating front-side shading from busbars. Achieves 23-26 percent cell efficiency. Premium technology associated with SunPower/Maxeon and select premium installations.

IEC 61215 is a series of international standards for design qualification and type approval of terrestrial photovoltaic modules. Passing the tests supports confidence in a module design; it is not a guarantee of a particular service life.

IEC 61730 is the international safety standard for photovoltaic modules covering construction requirements (Part 1) and testing requirements (Part 2). Tests cover electrical, fire, mechanical and material safety. Indian compliance through IS 14286 which references both IEC 61215 and IEC 61730.

IEC 62109 is a series of safety requirements for power converters used in photovoltaic power systems. Part 1 states general requirements; Part 2 addresses particular requirements for inverters.

IEC 62619 specifies safety requirements for secondary lithium cells and batteries used in industrial applications, a scope that can include stationary energy storage.

Inverter efficiency is the ratio of AC output power to DC input power, measured at various load levels. Peak efficiency for modern Indian solar inverters: 97-99 percent. European weighted efficiency (ηEU) and CEC weighted are the bankable figures, typically 96-98 percent.

Internal Rate of Return (IRR) is the discount rate at which the net present value (NPV) of project cash flows equals zero. It is the headline return metric for solar projects, typically 10 to 18 percent for Indian utility solar and 14 to 22 percent for C&I rooftop.

Irradiation is solar energy received per unit area over a period, measured in kWh/m² or MJ/m². Distinct from irradiance (power, W/m²). Daily irradiation in India typically 4.5-6.5 kWh/m²/day. Annual irradiation 1,200-2,200 kWh/m²/year.

An isolator is a manually operated electrical switch that creates a visible disconnect between equipment and its power source for safe maintenance. Solar plants use DC isolators (rated for solar DC) on the PV side and AC isolators on the inverter output, both required by CEA Measures Relating to Safety.

A junction box is a sealed enclosure that houses electrical connections, including PV module junction boxes (containing bypass diodes and MC4 cable exits) and field junction boxes (used for cable transitions, splices and protection device housings) in solar installations.

Kilovolt-ampere (kVA) is a unit of apparent AC power. For sinusoidal single-phase conditions, apparent power in kVA is RMS voltage times RMS current divided by 1,000.

A kilowatt-hour (kWh) is the unit of electrical energy equivalent to one kilowatt of power used for one hour. It is the standard billing unit for electricity in India and the basis for all solar yield and consumption measurements.

Late Payment Surcharge (LPS) Rules 2022 establish escalating penalties on DISCOMs delaying payments to generators. Provides legal mechanism for solar developers to recover delayed PPA payments. Critical for project cash flow and lender comfort.

Levelised Cost of Energy (LCOE) is the per-kWh cost of electricity averaged over the entire lifetime of a solar plant, including capex, opex, financing and degradation. IRENA put India's utility-scale solar LCOE at about USD 0.038 per kWh (roughly ₹3.2) for 2024 projects, while an illustrative 50 kW C&I rooftop plant works out to about ₹4.8 per kWh.

A lead acid battery is a rechargeable electrochemical cell using lead electrodes and sulphuric acid electrolyte. Variants include flooded (tubular), VRLA AGM and VRLA gel. Cheapest battery chemistry, with 500 to 1,500 cycle life. Still used in Indian off-grid solar, UPS and automotive starting applications.

LeTID (Light and Elevated Temperature Induced Degradation) is a slower degradation mechanism affecting PERC solar cells under combined light exposure and elevated temperatures (60-90°C). Causes 1-5 percent capacity loss over years. Modern PERC manufacturing controls LeTID through process choices.

LFP (Lithium Iron Phosphate, LiFePO4) is a lithium-ion battery chemistry that uses iron phosphate as the cathode material. It offers superior cycle life (4,000 to 8,000 cycles), high thermal stability and lower cost than NMC, making it the dominant choice for stationary solar storage in India.

LID, Light-Induced Degradation, is the initial loss of efficiency in crystalline silicon solar cells during the first 100 hours of exposure to sunlight. Caused primarily by boron-oxygen defect formation in p-type silicon, LID reduces output by 1 to 2.5 percent and is intrinsic to PERC technology.

A lithium-ion battery is a rechargeable energy storage device that uses lithium ions moving between intercalation electrodes to store and release energy. It is the dominant battery chemistry for modern solar storage, EVs and consumer electronics, with cycle life of 4,000 to 10,000 cycles for stationary applications.

MC4 is the de facto industry-standard photovoltaic DC connector for module-to-module and module-to-inverter connections. Rated for 1000 to 1500 V DC and 30 A, MC4 connectors provide a weatherproof IP67/68 sealed plug-and-socket interface.

A Miniature Circuit Breaker (MCB) is an automatic electrical switch that opens to interrupt current flow when an overcurrent or short circuit is detected. It is the standard protection device in residential and commercial electrical installations, used in solar AC distribution panels.

A micro inverter is a compact solar inverter mounted under each PV module that converts panel-level DC into AC at the module itself. It enables panel-level MPPT, monitoring and shade tolerance, at the cost of higher upfront price than string inverters.

MLPE (Module-Level Power Electronics) is the umbrella term for power electronic devices installed at each PV module: microinverters (full DC-to-AC conversion) and DC optimisers (per-panel MPPT). MLPE provides panel-level performance and monitoring, valuable for shaded rooftops and premium installations.

MNRE, the Ministry of New and Renewable Energy, is the Government of India ministry responsible for policy, programmes and incentives for solar, wind, biomass, small hydro, biogas and other renewables. It administers PM Surya Ghar, PM-KUSUM, ALMM and most central renewable energy schemes.

Modified sine wave (MSW), also called quasi-sine or stepped wave, is a low-cost AC output that approximates sine wave through square-wave steps. THD typically 30-50 percent. Acceptable for resistive loads but damages sensitive electronics, motors and modern appliances. Largely obsolete in modern solar.

Module degradation is the gradual decline in solar PV module output over its operating life, caused by physical, electrochemical and environmental mechanisms. Modern modules degrade 0.30 to 0.55 percent per year, with first-year LID of 1 to 2 percent.

Module efficiency is the percentage of solar irradiance striking a PV module that is converted into electrical output, measured at Standard Test Conditions (1000 W/m², 25°C, AM1.5). Modern crystalline silicon modules achieve 20 to 24 percent efficiency.

A monocrystalline solar panel uses solar cells cut from a single continuous silicon crystal. The uniform structure delivers higher efficiency (20 to 23 percent typical in 2026) and better low-light performance than polycrystalline, and dominates Indian rooftop and utility solar.

A mounting structure is the mechanical framework that supports solar PV modules at the designed tilt and orientation, transferring wind, snow and dead loads to the building roof or ground. Indian solar mounting uses galvanised iron (GI) for cost-sensitive projects and aluminium for premium installations.

MPPT means maximum power point tracking. It adjusts the electrical operating point of a solar array to seek the voltage and current combination that produces the most available power under the present conditions.

N-type silicon is crystalline silicon doped with phosphorus, creating excess electrons as charge carriers. Used in TOPCon, HJT and IBC solar cells. Compared to p-type silicon, n-type eliminates light-induced degradation (LID) and offers higher efficiency potential.

Net metering is a billing mechanism where the utility credits a solar customer for surplus electricity exported to the grid. A bidirectional meter records both import and export, and the customer pays only for net consumption over the billing cycle.

NOCT (Nominal Operating Cell Temperature) is the equilibrium cell temperature of a solar module operating at 800 W/m² irradiance, 20°C ambient and 1 m/s wind speed. Typical modern modules: 42-45°C. Used to estimate realistic operating temperature, distinct from STC's 25°C.

Net Present Value (NPV) is the sum of all discounted future cash flows minus the initial investment. Positive NPV means project creates value; negative means it destroys value. Standard investment decision metric, used for solar project go/no-go decisions.

An off grid inverter is a standalone solar inverter that creates its own AC voltage and frequency from a battery bank, with no connection to the utility grid. It powers homes, farms, telecom towers and remote sites that have either no grid access or unreliable supply.

An on grid inverter is a grid-tied solar inverter that converts DC from PV modules into AC and feeds it directly into the utility grid. It cannot run without grid voltage, has no battery, and shuts down during grid outages for safety. It is the most common inverter used in Indian rooftop solar.

Open Circuit Voltage (Voc) is the voltage of a solar module when no current is flowing (no load connected). Maximum voltage the module produces. Used for string sizing: cold-temperature Voc must not exceed inverter maximum DC input. Typical: 41-50 V per modern module.

OPEX (Operating Expenditure) is the recurring cost of running a solar plant over its life, including O&M, insurance, land lease, replacement parts and overheads. Under CERC's 2024 renewable tariff rules, O&M for solar PV is assessed project by project rather than at a fixed national benchmark.

P-type silicon is crystalline silicon doped with boron, creating a deficit of electrons (holes) as charge carriers. Used in PERC, BSF and older solar cells. Lower cost than n-type but susceptible to boron-oxygen LID. Dominated solar from 2000s to early 2020s.

P50 is a solar-energy estimate with a 50% probability of being exceeded under its stated model; P90 is a lower estimate with a 90% probability of being exceeded under the same stated assumptions and period.

Payback period is the time required for cumulative cash flows from a solar project to recover the original investment. Indian residential payback under PM Surya Ghar typically ranges from 2.5 to 5 years; C&I rooftop 3 to 6 years; utility solar 6 to 10 years.

Peak Sun Hours (PSH) is the number of hours per day during which solar irradiance averages 1,000 W/m² (1 kW/m²). It is a simplified measure of daily solar resource. Indian PSH ranges from 4.0 to 6.5 hours/day depending on location and season.

PERC (Passivated Emitter and Rear Contact) is a solar cell architecture that adds a passivated rear contact layer to capture light that would otherwise pass through. It raised crystalline silicon efficiency by 1 to 2 percentage points and was the dominant cell technology for solar modules from 2017 to 2024.

Performance Ratio (PR) is the ratio of actual energy generated by a solar plant to the energy it would have generated under ideal conditions for the same incident solar irradiance. PR isolates plant quality from weather and location, with typical Indian values of 75 to 82 percent.

Perovskite is an emerging solar cell technology based on hybrid organic-inorganic perovskite materials. Lab efficiencies exceed 26 percent single-junction and 33 percent in perovskite-silicon tandems. Commercial production is pre-commercial; tandem cells expected to enter market by 2026-2028.

Plane of Array (POA) irradiance is the solar radiation hitting the actual tilted surface of PV modules, expressed in W/m². Calculated from GHI, DNI, DHI and ground-reflected components through sky models. POA is the direct input to PV yield calculation, distinct from horizontal GHI.

PM Surya Ghar Muft Bijli Yojana is the Government of India's central rooftop solar subsidy scheme launched in February 2024. It aims to install rooftop solar at 10 million Indian homes by 2027, with central subsidies of up to ₹78,000 for a 3 kW system.

PM-KUSUM (Pradhan Mantri Kisan Urja Suraksha evam Utthaan Mahabhiyan) is India's flagship scheme for agricultural solar, launched in 2019. It targets 35 GW of solar capacity in agriculture by 2026 across three components: A (decentralised solar plants), B (standalone solar pumps), C (grid-connected solar pumps).

A polycrystalline (multi-crystalline) solar panel uses cells cast from molten silicon that solidifies as multiple small crystals. Less efficient (17 to 19 percent) than monocrystalline but historically cheaper. Now largely displaced by mono in new Indian installations.

Power factor is the ratio of active power to apparent power at a stated point and operating condition. It indicates how much of the apparent AC power is active power.

A Power Purchase Agreement (PPA) is a long-term contract between a solar generator and an electricity buyer (DISCOM, C&I customer or open access trader) for the sale of generated electricity at a fixed or formula-based tariff for the contract period, typically 25 years.

Pure sine wave is a smooth sinusoidal AC output waveform identical in shape to grid power. All modern grid-tie, hybrid and quality off-grid inverters produce pure sine wave. Compatible with all AC loads including motors, electronics and sensitive equipment.

PWM stands for Pulse Width Modulation, a switching technique where a transistor is rapidly turned on and off to control average voltage or current. In solar, PWM refers to the charge controller topology that connects panel to battery directly through a switch, without DC-DC conversion.

Rapid shutdown is a safety function that de-energises rooftop solar PV conductors to a safe voltage within a defined time when triggered by emergency switch or AC removal. Mandatory under US NEC 690.12; voluntary in India. Implemented through microinverters, DC optimisers or dedicated rapid shutdown devices.

A Residual Current Circuit Breaker (RCCB), also called Residual Current Device (RCD) or Earth Leakage Circuit Breaker (ELCB), detects imbalance between line and neutral currents and trips to prevent electric shock. Standard sensitivity is 30 mA for personal protection.

Reactive power, measured in kVAR, is the component of AC power that oscillates between source and load without doing useful work. It maintains voltage and supports magnetic fields in motors and transformers. Modern solar inverters can inject or absorb reactive power on demand.

A Renewable Energy Certificate (REC) is a tradable certificate representing 1 MWh of renewable energy generation. RECs allow renewable energy generators to monetise the green attribute separately from electricity. Indian RECs are issued by CERC and traded on power exchanges to fulfil RPO obligations.

RESCO (Renewable Energy Service Company) is a solar deployment model where a third-party developer installs, owns and operates the solar system on a customer's premises, and sells the generated electricity to the customer at a discounted PPA tariff. The customer pays no upfront capex.

Round-trip efficiency (RTE) is the ratio of energy retrieved from a battery to the energy stored in it. For LFP: 92-95 percent at cell level, 85-92 percent at system level (including PCS losses). Critical metric for storage economics and Indian solar storage system design.

Renewable Purchase Obligation (RPO) is the percentage of total electricity purchase that distribution licensees, open access consumers and captive power producers must source from renewable energy. Indian RPO trajectories set by SERCs target 43.33 percent renewable share by 2029-30.

Second-life batteries are EV batteries retired from automotive service (at 70-80 percent SOH) but suitable for less-demanding stationary storage applications. Lower cost than new cells. Indian market emerging as EV adoption grows. 5-10 year additional service typical.

A State Electricity Regulatory Commission (SERC) is the state-level electricity regulator that sets retail tariffs, governs intra-state DISCOMs and notifies net metering and gross metering regulations for distributed solar within the state.

Shading analysis is the process of quantifying solar yield loss from obstructions like trees, buildings, parapets and inter-row shadows. It uses sun-path geometry, site obstruction mapping and software tools like PVsyst, Helioscope, Pathfinder or SunEye. Critical for rooftop and complex-terrain solar plants.

A sine wave inverter converts DC into AC with a smooth sine-shaped waveform, the same shape as grid power, so that motors, electronics and grid-tied systems run properly on its output.

A single line diagram (SLD) is a simplified electrical drawing that shows the main components, connections and protection of a power system without drawing every conductor separately.

A site survey is the systematic assessment of a proposed solar installation site, evaluating roof or land condition, electrical infrastructure, shading, structural load capacity, accessibility and regulatory feasibility. It is the foundation for accurate design and quotation.

A smart inverter is a grid-tied solar inverter with advanced functions beyond basic DC-to-AC conversion, including volt-var control, frequency-watt response, fault ride-through, reactive power dispatch and remote configuration. Required for utility-scale solar under CEA Grid Code and increasingly for C&I.

A smart meter is an electricity meter with two-way digital communication, time-of-day registers, remote disconnect and tamper detection. It enables AMI, automated billing, distributed generation and demand-response programmes.

Soiling is the accumulation of dust, pollen, bird droppings and other particulates on solar module surfaces, reducing light transmission and power output. Indian soiling rates are among the highest globally, with cumulative annual losses of 5-25 percent without cleaning. Regular cleaning is critical for Indian solar plants.

A solar inverter is the electronic device that converts the direct current (DC) produced by solar PV modules into alternating current (AC) compatible with home appliances and the utility grid. It also performs MPPT, protection, monitoring and grid synchronisation, making it the brain of every solar PV system.

Solar yield, or specific yield, is the annual energy generated per kilowatt of installed solar capacity, expressed in kWh per kWp per year. Indian solar yield typically ranges from 1,200 to 1,900 kWh/kWp depending on location, technology and plant quality.

A Surge Protection Device (SPD) limits transient overvoltages from lightning or switching events by diverting surge current to earth. SPDs are mandatory on both DC and AC sides of solar installations in Indian thunderstorm zones.

State of Health (SOH) is the percentage of original capacity remaining in a battery, measuring long-term degradation. 100 percent when new, dropping over years to end of life (typically 80 percent). Distinct from SOC (immediate charge level).

STC (Standard Test Conditions) is the laboratory reference condition for rating solar module electrical parameters: 1000 W/m² irradiance, 25°C cell temperature, AM1.5G solar spectrum. Module nameplate watts (Wp = peak watts) refers to STC output. Real-world operation differs significantly from STC.

A string inverter is a centralised solar inverter that processes the combined DC output of one or more series-connected strings of PV modules into grid-quality AC. It is the dominant form factor in Indian residential, commercial and utility solar.

String sizing is the process of determining the optimal number of solar modules connected in series within a string, bounded by the inverter's MPPT voltage window at hot maximum and cold minimum temperatures. Correct string sizing maximises yield and avoids inverter damage.

A tandem solar cell stacks two or more semiconductor materials with different bandgaps to capture a broader portion of the solar spectrum. Perovskite-silicon tandems exceed 33 percent lab efficiency. III-V tandems used in space; perovskite-silicon entering terrestrial commercial production.

Tariff is the per-unit price of electricity, in ₹/kWh. Indian electricity tariffs include retail (consumer-facing, varying by slab and category), wholesale (PPA-based), feed-in tariff (FIT for solar export), and time-of-day (ToD) variants. Set by SERCs and CERC.

Temperature coefficient is the percentage change in solar module electrical parameters (Pmax, Voc, Vmp, Isc) per degree Celsius rise above STC (25°C). Pmax coefficient typically -0.26 to -0.37 percent/°C. Critical for Indian climates where module temperatures regularly reach 60-80°C.

Thermal runaway is uncontrolled self-heating of a battery cell, where temperature increases trigger more heat-releasing reactions, leading to fire or explosion. LFP highly resistant (270°C threshold). NMC more vulnerable (150-180°C). Critical safety concern in lithium-ion storage.

Tilt angle is the inclination of a solar panel from the horizontal plane, measured in degrees. The optimum annual tilt approximately equals the site latitude. For India this ranges from 8° (Kerala) to 32° (Kashmir), with most installations using fixed tilts of 10° to 25°.

TOPCon (Tunnel Oxide Passivated Contact) is a crystalline silicon solar cell architecture that uses an ultra-thin tunnel oxide and doped polysilicon layer to achieve passivated contacts. It delivers 24 to 25 percent cell efficiency and is the dominant new-build cell technology from 2024 onward, replacing PERC.

Total Harmonic Distortion (THD) is the RMS magnitude of the harmonic components of a voltage or current waveform divided by the RMS magnitude of its fundamental component, usually expressed as a percentage.

A transformerless inverter is a solar inverter that omits the galvanic isolation transformer, using high-frequency PWM and an LCL output filter to interface directly with the grid. This raises peak efficiency to 97-98.6 percent and reduces weight and cost. Dominant topology in modern Indian residential and C&I solar.

UPS (Uninterruptible Power Supply) provides continuous backup power during grid outages, using battery storage and inverter. Common types: offline, line-interactive, online double-conversion. Increasingly integrated with solar in hybrid configurations for combined backup and solar self-consumption.

Viability Gap Funding (VGF) is a capital subsidy mechanism providing one-time grant to bridge the gap between commercial viability and project cost. In Indian solar, VGF supports battery energy storage systems (BESS) with budgetary support of ₹3,760 crore for 4,000 MWh approved in 2023 (up to 40 percent of capital cost) and a second tranche in 2025 at ₹18 lakh per MWh.

Virtual Net Metering (VNM) is a billing arrangement that distributes solar export credits from one PV plant across multiple electricity accounts of the same customer or group, even when the consumption points are physically separated.

Voltage is the electrical potential difference between two points in a circuit, measured in volts (V). It drives the flow of current. Indian solar systems use DC voltages from 12 V to 1500 V and AC voltages of 230 V single-phase, 415 V three-phase, and higher for transmission.

WACC (Weighted Average Cost of Capital) is the blended cost of a project's debt and equity financing, weighted by their respective shares. Indian solar WACC: 8-10 percent for utility projects, higher for residential. Used as discount rate in LCOE and project NPV calculations.

Zero export is an operating arrangement that controls a solar system so it does not intentionally send surplus power to the utility grid. It requires compatible inverter settings and an approved measurement/control arrangement; it does not make a grid connection unregulated.