Solar Energy Glossary 2026: 70+ Terms Explained for Beginners

If you're new to solar, the terminology can feel overwhelming. Installers quote you in "kWdc," proposals mention "NEM 3.0," and state incentive programs throw around "SREC," "PBI," and "AEC." This glossary cuts through the jargon — plain-English definitions for every solar term you'll encounter, organized A to Z, with links to in-depth guides where available.

Bookmark this page. It's the reference you'll return to throughout your solar research.

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A

AC (Alternating Current) The type of electricity your home uses. Solar panels produce DC electricity, which your inverter converts to AC for household use and grid export. All standard appliances run on AC.

Array The complete collection of solar panels installed on a roof or ground mount. A 10 kW array might consist of 25 panels at 400 W each. The array is the electricity-generating heart of your solar system.

Azimuth The compass direction your panels face, measured in degrees from true north. In the Northern Hemisphere, south-facing panels (azimuth 180°) produce the most energy. East (90°) and west (270°) arrays sacrifice 10–20% of annual production but are common on roofs without south exposure.

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B

Balance of System (BOS) Everything in a solar installation except the panels themselves — wiring, racking, inverter, monitoring hardware, conduit, and disconnect switches. BOS typically represents 25–35% of a residential system's installed cost.

Battery Storage / Energy Storage Electrochemical devices that store excess solar electricity for use at night or during outages. Common in 2026: Tesla Powerwall 3 (13.5 kWh), Enphase IQ 5P (5 kWh), Franklin aGate (13.6 kWh). Qualifies for the 30% federal ITC since 2023. See our home battery storage costs guide for pricing.

Bifacial Panels Solar panels that generate electricity from both the front and back surfaces. The rear side captures reflected (albedo) light from light-colored roofs or ground. Bifacial panels produce 5–25% more energy than monofacial panels in the right conditions; most useful on ground mounts over white gravel or snow.

Bypass Diode A diode built into solar panel junction boxes that allows current to flow around shaded cells. Without bypass diodes, one shaded cell can reduce an entire panel's output to zero. Most quality panels have 3 bypass diodes — one per cell string.

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C

Capacity Factor The ratio of actual annual energy output to the maximum theoretical output if a system ran at full nameplate capacity 24/7. Residential solar arrays typically achieve 15–25% capacity factors (higher in Arizona, lower in Seattle). Useful for comparing locations.

CEC Rating (California Energy Commission) A panel efficiency and power rating measured under real-world conditions (PV USA Test Conditions: 1,000 W/m², 20°C ambient, wind speed 1 m/s). CEC ratings are slightly lower than STC ratings and more accurate for actual production estimates. PVWatts modeling uses CEC ratings.

Cell Efficiency The percentage of sunlight striking a solar cell that is converted to electricity. In 2026, commercial cell efficiencies range from 19% (budget polycrystalline) to 23–24% (premium TOPCon/HJT). Higher efficiency means more power per square foot of panel area. See how solar panels work for the physics.

Community Solar A shared solar installation where subscribers (homeowners, renters, businesses) receive credits on their utility bill for their share of the array's production — without installing panels on their own roof. Available in NY, MA, IL, CT, MN, CO, and growing. See our community solar guide.

C-PACE (Commercial Property Assessed Clean Energy) A financing mechanism for commercial properties that repays solar installation costs through property tax assessments over 10–25 years. The assessment transfers with property ownership, so sellers and buyers share the obligation and benefit. Not available in all states; see our commercial solar guide.

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D

DC (Direct Current) The type of electricity solar panels produce. Electrons flow in one direction (unlike AC). Your inverter converts DC to AC. Battery storage also operates in DC.

Degradation Rate The annual percentage reduction in a panel's power output over time. The industry median is 0.5%/year (NREL). Premium panels (SunPower, Panasonic, REC) degrade at 0.25–0.40%/year; budget panels at 0.7–1.0%/year. Over 25 years, the difference is 10–20% of total production. See our solar panel lifespan guide.

Demand Charge A portion of commercial utility bills based on the highest 15-minute power draw (in kW), not just total energy consumed (kWh). Demand charges can represent 30–60% of commercial electric bills. Solar alone doesn't eliminate demand charges — battery storage paired with solar can reduce demand peaks. See our commercial solar guide.

Derate Factor A multiplier (typically 0.77–0.85) applied to a solar array's nameplate capacity to estimate real-world output, accounting for wiring losses, soiling, temperature effects, shading, and inverter efficiency. PVWatts uses a default system derate of 0.86.

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E

Energy Community (IRS) IRS-designated census tracts with significant fossil fuel employment histories (coal mines, oil and gas, steel mills). Homeowners and businesses in Energy Community tracts qualify for a 40% ITC instead of 30% — a 10-percentage-point bonus worth $2,800–$4,200 extra on a typical residential system. Check eligibility at energycommunities.gov.

Energy Storage System (ESS) See Battery Storage.

Export Rate The price your utility credits you (or pays you) for solar electricity you send to the grid. Under full net metering, the export rate equals your retail electricity rate. Under avoided-cost programs (Alabama Power, Entergy Mississippi, Indiana utilities, TVA), the export rate is $0.03–$0.06/kWh — much less than retail. Export rate is the most important variable for sizing your solar system correctly.

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F

Feed-in Tariff (FiT) A guaranteed long-term payment rate for solar electricity exported to the grid, set by a utility or government agency. Less common in the U.S. than net metering, but used in some markets (Hawaii's former program, some utilities). Generally higher than retail rates in early programs; has been cut in many jurisdictions.

Form 5695 The IRS tax form used to claim the residential solar Investment Tax Credit. Part I calculates your Residential Clean Energy Credit; the total flows to Schedule 3, then to Form 1040 Line 8. See our step-by-step Form 5695 guide.

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G

Grid-Tied System A solar installation connected to the utility grid. The most common configuration for residential solar. Grid-tied systems sell or credit excess production back to the utility and draw from the grid when solar output is insufficient. No battery required (though one can be added). See how solar panels work for system architecture.

Ground Mount A solar array installed on the ground using steel frames rather than on a roof. Ground mounts allow optimal panel orientation (south-facing, optimal tilt angle), easier cleaning, and are common for large residential systems, farms, and commercial installations. Typically cost $0.20–$0.50/W more than roof mounts due to additional racking and concrete.

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H

HJT (Heterojunction Technology) A premium solar cell architecture that sandwiches amorphous silicon layers around a mono-crystalline silicon wafer, achieving very low recombination losses and high efficiency (22–24%+ commercial). HJT panels have excellent temperature coefficients (−0.26%/°C vs. −0.35%/°C for standard PERC). Brands: Panasonic EverVolt, REC Alpha.

Hybrid Inverter An inverter capable of managing both solar generation and battery storage in a single unit. Connects to both the solar array and a battery bank; decides in real-time whether to charge the battery, power the home, or export to the grid. Required for DC-coupled battery systems. Brands: SolarEdge Energy Hub, SMA Sunny Tripower Storage, Victron MultiPlus.

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I

Interconnection Agreement A contract between you and your utility authorizing your solar system to connect to the grid. Required before receiving Permission to Operate (PTO). Interconnection review typically takes 4–12 weeks and is one of the longest steps in the installation timeline. See our installation timeline guide.

Inverter The device that converts solar panels' DC electricity to household AC electricity. Three main types: string inverter (one unit for the whole array), microinverter (one per panel), and string inverter with power optimizers (DC optimization at each panel). See our inverter types guide and microinverters vs. string inverters comparison.

ITC (Investment Tax Credit) The federal solar tax credit — 30% of total installed system cost (40% in Energy Community locations), claimed on IRS Form 5695. The credit reduces federal income tax dollar-for-dollar and carries forward up to 20 years if unused. Applies to residential systems (Section 25D) and commercial systems (Section 48). Locked at 30% through 2032 by the IRA. See our federal ITC guide.

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K

kW (Kilowatt) A unit of power — 1,000 watts. A solar panel rated at 400 W is 0.4 kW. A 10 kW solar system has a nameplate capacity of 10,000 watts (25 × 400 W panels). kW measures rate of electricity production; kWh measures amount.

kWh (Kilowatt-Hour) A unit of energy — one kilowatt of power used or produced for one hour. A 10 kW solar system in a location with 5 peak sun hours/day produces roughly 50 kWh/day (10 kW × 5 hours). The average U.S. home uses 900 kWh/month. Your electricity bill charges you in $/kWh.

kWp (Kilowatt-Peak) The rated output of a solar panel or array under Standard Test Conditions (STC). "Peak" indicates the nameplate rating, measured under ideal lab conditions. A 10 kWp system will rarely produce exactly 10 kW in real-world conditions — actual output is lower due to temperature, soiling, angle, and inverter losses.

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L

LFP (Lithium Iron Phosphate) The dominant battery chemistry for residential energy storage in 2026. More thermally stable (no thermal runaway risk), longer cycle life (3,000–6,000 cycles vs. 1,500–2,000 for NMC), and environmentally benign compared to NMC or cobalt-based chemistries. Used in Tesla Powerwall 3, Franklin aGate, Enphase IQ 5P, and many others.

LCOE (Levelized Cost of Energy) The average cost per kWh of solar electricity over a system's 25–30 year life, including upfront cost, maintenance, and financing costs. A typical residential solar system in 2026 achieves an LCOE of $0.06–$0.10/kWh — well below grid rates in most states, especially after 2026 utility rate inflation projections.

Load Your household's electricity consumption. "Load shifting" means moving energy-intensive activities (EV charging, dishwasher, laundry) to times when solar production is highest, maximizing self-consumption and minimizing grid draw.

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M

MACRS (Modified Accelerated Cost Recovery System) The IRS depreciation schedule for commercial solar assets. Solar qualifies for 5-year MACRS, allowing commercial owners to depreciate 60% of system cost in years 1–2 under current bonus depreciation rules. Combined with the Section 48 ITC, commercial owners can recover 50–60% of system cost in year one — a major financial advantage over residential buyers. See our commercial solar guide.

Microinverter An inverter installed on each individual solar panel, converting DC to AC at the panel level. Advantages: panel-level monitoring, no single point of failure, no DC wiring on the roof. Disadvantage: higher upfront cost ($0.20–$0.25/W more than string). Best for shaded roofs or complex roof configurations. See our microinverters vs. string inverters guide.

Monocrystalline Solar cells cut from a single silicon crystal — the most efficient and most common cell type in 2026. Characterized by uniform dark blue or black color. All premium cell technologies (PERC, TOPCon, HJT, IBC) are monocrystalline.

MPPT (Maximum Power Point Tracking) The electronic algorithm used by inverters to continuously adjust electrical load to extract maximum power from solar panels as conditions (sun angle, temperature, partial shading) change. Modern inverters include MPPT as standard; it's responsible for recovering 2–10% more energy than a fixed-load inverter.

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N

Nameplate Capacity The rated output of a solar panel or system under STC (Standard Test Conditions). A "10 kW system" has a nameplate capacity of 10 kW. Real-world output is typically 75–85% of nameplate due to temperature effects, soiling, wiring losses, and inverter efficiency.

Net Metering (NEM) A billing mechanism where your utility credits you at the retail electricity rate for solar electricity you export to the grid, then deducts those credits from your import bill. Under net metering, 1 kWh exported = 1 kWh of credit. The most favorable export structure for solar economics. Available in most states; see our net metering guide and solar ROI by state comparison.

NEM 3.0 (California) California's third-generation net metering tariff, effective April 2023 for NEM 3.0 applicants. Export rates dropped 75% vs. NEM 2.0 (from retail rate to ~$0.03–$0.08/kWh). Systems approved before April 2023 are grandfathered on NEM 2.0 for 20 years. NEM 3.0 makes battery storage essential for CA solar economics. See our California solar guide.

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O

Off-Grid System A solar installation completely disconnected from the utility grid. Requires battery storage sized for multiple days of consumption (backup autonomy) and a backup generator for extended cloudy periods. Common in rural areas without grid access and for homeowners seeking full energy independence. Higher upfront cost but no utility bills. See our off-grid solar guide.

On-Grid / Grid-Tied See Grid-Tied System.

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P

Payback Period The time required for a solar system's cumulative energy savings to equal its net purchase price (after incentives). National median in 2026: 8–12 years. Ranges from 3–5 years in CT/MA/RI/HI (high rates + strong incentives) to 14–18 years in TN/MS/ID (low rates, limited net metering). After payback, the system generates pure savings for 15–20 more years. Calculate yours with our solar payback period calculator.

PBI (Performance-Based Incentive) An ongoing payment per kWh of solar electricity produced (rather than a one-time rebate on system cost). Examples: Massachusetts SMART ($0.15–$0.22/kWh for 10 years), Minnesota Solar*Rewards ($0.02–$0.035/kWh for 10 years), Illinois Shines (15-year REC contracts). PBI rewards system performance over time; higher-efficiency panels and better siting earn more income.

Peak Sun Hours (PSH) The number of equivalent hours per day when sunlight intensity reaches 1,000 W/m² (full peak sun). Phoenix: 6.0 PSH/day. Atlanta: 5.0 PSH/day. Seattle: 3.8 PSH/day. Boston: 4.2 PSH/day. A 10 kW array in Phoenix produces ~60 kWh/day (10 kW × 6.0 PSH); in Seattle, ~38 kWh/day. PSH is the key variable for sizing solar systems.

PERC (Passivated Emitter Rear Cell) The most widely deployed solar cell technology from 2018–2024, now being superseded by TOPCon. PERC adds a passivation layer on the rear of the cell to reduce electron recombination, achieving 20–22% efficiency. Still widely available in mid-range panels from Canadian Solar, Jinko, Trina, and Silfab.

Performance Ratio A dimensionless metric indicating how efficiently a solar system converts available sunlight to usable electricity, accounting for all real-world losses. Formula: Actual output (kWh) ÷ Theoretical output at STC (kWh). Healthy residential systems achieve 0.70–0.85. Ratios below 0.70 indicate underperformance worth investigating. See our solar monitoring guide.

PPA (Power Purchase Agreement) A financing structure where a solar company installs panels on your roof at no cost and sells you the electricity they produce at a fixed rate ($/kWh) for 20–25 years. The company owns the system and claims the ITC. Advantages: $0 upfront; disadvantages: no ITC benefit, escalator clauses raise your rate annually, complicates home sale. See our solar lease vs. purchase guide.

PTO (Permission to Operate) Written authorization from your utility allowing your solar system to connect to the grid and begin producing power. Issued after the utility inspects the interconnection. The date you receive PTO — not the installation date — determines which tax year you file your ITC claim. See our installation timeline guide.

PVWatts NREL's free online solar production modeling tool (pvwatts.nrel.gov). Enter system size, location, tilt, azimuth, and losses to get a monthly and annual energy production estimate. Used by most installers to generate production estimates. You can run your own numbers to sanity-check a proposal.

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R

Racking The mounting hardware that attaches solar panels to a roof or ground frame. Must be rated for your local wind and snow loads (per structural engineering standards). Common roof-mount brands: IronRidge, SnapNrack, Unirac, Ecofasten. Ground-mount systems use steel posts driven into the ground.

Rapid Shutdown (NEC 690.12) A U.S. National Electrical Code requirement (2017 and later) that solar systems must de-energize DC wiring on the roof within 30 seconds of activation, for firefighter safety. Complied with using module-level electronics (microinverters, power optimizers) or rapid shutdown transmitter/receiver sets. Required by virtually all U.S. jurisdictions.

REC (Renewable Energy Certificate) A tradeable certificate representing 1 MWh of electricity generated from renewable sources. RECs can be bought and sold separately from the electricity itself. SRECs (Solar Renewable Energy Certificates) are RECs specifically from solar generation. See our SREC guide.

REAP (Rural Energy for America Program) A USDA grant program providing up to 50% of renewable energy project costs (including solar) for agricultural producers and rural small businesses. Funded with $2 billion under the IRA. Stacks with the 30% federal ITC. Farm payback periods of 3–7 years are achievable with REAP + ITC. See our USDA REAP guide.

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S

Specific Yield Solar production per kW of installed capacity, expressed in kWh/kW/year. A 10 kW system in Phoenix producing 16,000 kWh/year has a specific yield of 1,600 kWh/kW/year. Healthy residential systems range from 1,100–1,300 kWh/kW/year in the Northeast to 1,700–2,200 kWh/kW/year in the Desert Southwest.

SREC (Solar Renewable Energy Certificate) A tradeable certificate representing 1 MWh of solar electricity generation, issued to system owners in states with solar carve-outs in their Renewable Portfolio Standards. Active SREC markets: New Jersey ($185–$270/MWh), Maryland ($60–$90/MWh), Pennsylvania ($25–$50/MWh), Illinois ($65–$80/MWh under Shines). SRECs are additional income on top of energy savings. See our SREC guide.

STC (Standard Test Conditions) The laboratory conditions under which solar panel nameplate wattage is rated: 1,000 W/m² irradiance, 25°C cell temperature, air mass 1.5. Real-world conditions rarely match STC; panels typically perform at 80–90% of STC rating in the field.

String Inverter A traditional inverter that converts DC power from a series ("string") of multiple panels into AC. One inverter handles the whole array. Advantages: lower cost, simpler maintenance. Disadvantages: the weakest panel in the string limits the whole string's output; no panel-level monitoring. See our inverter types guide.

System Size The nameplate capacity of a solar installation, measured in kilowatts DC (kWdc). Most residential systems range from 6–15 kW. Sizing is based on annual kWh usage, roof space, peak sun hours, and target offset percentage. Our how-many-solar-panels calculator guide walks through the sizing formula.

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T

Temperature Coefficient The rate at which a solar panel's output decreases as panel temperature rises above 25°C (the STC reference). Expressed as %/°C. Premium panels: −0.26%/°C (HJT). Standard panels: −0.35%/°C (PERC). TOPCon: −0.30%/°C. In Phoenix summers (70°C panel temperature), a standard panel loses 15.75% of rated output to heat; a premium HJT panel loses 11.7%.

TOPCon (Tunnel Oxide Passivated Contact) The leading solar cell technology in 2026, displacing PERC as the mainstream standard. Efficiency: 22–24%. Achieved by adding a thin tunnel oxide passivation layer and doped polysilicon contacts. Better temperature coefficient than PERC (−0.30%/°C vs. −0.35%/°C). Brands: Jinko Tiger Neo, LONGi Hi-MO 6, Canadian Solar HiHero, Trina Vertex S+. See our solar technology guide.

TOU (Time-of-Use) Rates A utility pricing structure where electricity rates vary by time of day — typically higher in late afternoon/evening (peak demand) and lower overnight or midday. Solar systems paired with TOU rates can shift consumption to off-peak times, maximizing the value of solar production. Critical for California NEM 3.0 economics. See our TOU rates and solar guide.

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U

Utility Interconnection The process of connecting a solar system to the utility grid, requiring an interconnection application, engineering review, and Permission to Operate (PTO). Timeline varies by utility: SolarAPP+ jurisdictions can permit in days; some utilities take 4–12 weeks for interconnection review. See our installation timeline guide.

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V

Virtual Net Metering (VNM) A net metering mechanism that allows solar electricity credits from a shared installation (community solar, multifamily building) to be applied to subscriber utility accounts at different locations. Used for community solar programs in NY, MA, CA, MD, NJ, and others. See our community solar guide.

VPP (Virtual Power Plant) A network of distributed home batteries aggregated and controlled by a utility or energy company to provide grid services (frequency regulation, demand response) in exchange for bill credits or payments to homeowners. Examples: Tesla Virtual Power Plant (TX, CA, VT), Sunrun Shift (CA), Green Mountain Power program (VT). Batteries enrolled in VPP programs earn ongoing income on top of self-consumption savings.

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W

Watt (W) The basic unit of electric power. A 400 W solar panel produces 400 watts under STC conditions. 1,000 W = 1 kW.

Watt-Peak (Wp) Equivalent to a panel's nameplate wattage under STC. A 400 Wp panel is rated at 400 watts under Standard Test Conditions. See STC.

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Next Steps

Understanding solar terminology is the first step. Once you're fluent in the language, you're ready to:

1. Calculate your system size: How Many Solar Panels Do I Need?
2. Understand total installed cost: Solar Panel Installation Cost 2026
3. Calculate your payback period: Solar Payback Period Calculator
4. Find your state's incentives: Solar Incentives by State — All 50 States
5. Claim your tax credit: IRS Form 5695 Step-by-Step Guide
6. Design your system: Solar System Designer Tool

Want to compare equipment options? See our solar panel brands guide, inverter types explained, and microinverters vs. string inverters comparison.

For the full financial picture, our solar vs. grid electricity cost comparison and solar ROI by state provide 25-year financial models for every major market.