Solar quotes and datasheets are full of acronyms and technical terms that can be confusing if you’re new to going solar. This glossary covers the terms you’re most likely to encounter, from basic electrical concepts to system components and financing terms.
Electrical Basics
| Term | Definition |
|---|---|
| Voc (Open-Circuit Voltage) | The maximum voltage a panel produces with no current flowing (circuit open) |
| Vmp (Voltage at Max Power) | The voltage at which a panel operates for peak power output |
| Isc (Short-Circuit Current) | The maximum current a panel produces when its terminals are shorted |
| Watt (W) | A unit of power – the rate of energy use or generation at a given moment |
| Watt-hour (Wh) | A unit of energy – power sustained over one hour (used for battery capacity) |
| kW / kWh | Kilowatt (1,000 W) and kilowatt-hour (1,000 Wh) – standard units for solar system size and production |
Testing and Rating Standards
| Term | Definition |
|---|---|
| STC (Standard Test Conditions) | 1,000 W/m² irradiance, 25°C cell temp, AM 1.5 spectrum – the lab conditions panels are rated under |
| NOCT (Nominal Operating Cell Temperature) | A more realistic rating reflecting typical outdoor operating conditions |
| Temperature coefficient | How much a panel’s output drops per degree Celsius above 25°C |
System Components
| Term | Definition |
|---|---|
| Inverter | Converts DC power from panels into AC power usable by your home and the grid |
| String inverter | A single inverter serving a whole series-connected string of panels |
| Microinverter | A small inverter installed on each individual panel |
| Power optimizer | Per-panel device that improves performance without fully replacing the central inverter’s role |
| MPPT (Maximum Power Point Tracking) | The method inverters/charge controllers use to extract maximum available power from panels |
| BMS (Battery Management System) | The circuit that monitors and protects a battery from overcharge, over-discharge, and faults |
Grid and Billing Terms
| Term | Definition |
|---|---|
| Net metering | Billing arrangement crediting you for excess solar power exported to the grid |
| NEM 3.0 | California’s current net metering policy paying a lower avoided-cost rate for exports vs. retail rate |
| Interconnection | The formal utility approval process required before a grid-tied system can operate |
| PTO (Permission to Operate) | Final utility approval allowing your system to legally export power to the grid |
| Anti-islanding | Safety feature that disconnects a grid-tied system during a power outage |
Code and Compliance Terms
| Term | Definition |
|---|---|
| NEC (National Electrical Code) | The code governing electrical installation safety standards, including solar-specific rules (Article 690) |
| Rapid shutdown | NEC 690.12 requirement to de-energize DC wiring quickly for firefighter safety |
| AFCI (Arc-Fault Circuit Interrupter) | Device that detects and interrupts dangerous DC arc faults |
Financing and Incentive Terms
| Term | Definition |
|---|---|
| ITC (Investment Tax Credit) | Federal tax credit for solar – Section 25D (residential) expired Dec 31, 2025; Section 48E (commercial/leased) active through 2027 |
| PPA (Power Purchase Agreement) | You pay for the electricity a system produces rather than owning the equipment |
| MACRS | 5-year accelerated depreciation schedule available to businesses for solar assets |
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Frequently Asked Questions
What does STC mean on a solar panel datasheet?
STC (Standard Test Conditions) refers to the lab conditions – 1,000 W/m² irradiance, 25°C cell temperature – under which a panel’s rated output is measured.
What is the difference between a string inverter and a microinverter?
A string inverter serves an entire series of panels from one central unit; a microinverter is installed on each individual panel.
What does MPPT mean?
MPPT (Maximum Power Point Tracking) is the method inverters and charge controllers use to extract the maximum available power from solar panels.
What is net metering?
Net metering is a billing arrangement that credits you for excess solar power your system sends back to the grid.
What is rapid shutdown and why is it required?
Rapid shutdown, required under NEC 690.12, quickly de-energizes DC wiring for firefighter safety during emergencies.
What’s the difference between Section 25D and Section 48E tax credits?
Section 25D was the residential homeowner credit, which expired December 31, 2025; Section 48E is the commercial/leased-system credit, active through 2027.
What does PPA mean in solar financing?
A Power Purchase Agreement (PPA) means you pay for the electricity a system produces rather than owning the solar equipment yourself.
Summing Up
Understanding these common solar terms can help you read quotes, compare equipment, and make sense of your installer’s proposal with confidence. For personalized answers to your solar questions, call (855) 427-0058 or visit us.solarpanelsnetwork.com.
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