Solar Energy Glossary

Definitions for 50+ solar energy terms used in SolarScope and the solar industry.

A B C D E G I L M N P R S T U

A

  • Albedo — Albedo is the reflectivity of a surface, expressed as a fraction from 0 to 1. High albedo ground surfaces increase energy production from bifacial solar panels.
  • Azimuth — Azimuth is the compass direction solar panels face, measured in degrees from north. South-facing (180°) is optimal for northern hemisphere solar installations.

B

  • Balance of System (BOS) — Balance of system (BOS) refers to all solar PV system components except the panels themselves — including inverters, racking, wiring, monitoring, and installation labor.
  • Battery Storage — Solar battery storage systems store excess solar energy for use when panels aren't producing. Lithium-ion batteries are now standard for residential and commercial applications.
  • Bifacial Solar Panel — Bifacial solar panels capture sunlight on both front and rear surfaces, generating additional energy from reflected light (albedo). Now standard for utility-scale projects.

C

  • Capacity Degradation — Capacity degradation is the long-term reduction in a solar panel's power output over its operating life, typically 0.5% per year for modern crystalline silicon.
  • Capacity Factor — Capacity factor is the ratio of actual energy output to maximum possible output if a solar system ran at full power continuously. Typically 15-25% for solar PV.

D

  • DC/AC Ratio — DC/AC ratio is the ratio of a solar system's DC capacity to the inverter's AC rating. Typically 1.1–1.3 for optimal system economics and performance.
  • DHI (Diffuse Horizontal Irradiance) — DHI is the scattered solar radiation arriving from all sky directions on a horizontal surface. Important for evaluating solar potential in cloudy climates.
  • DNI (Direct Normal Irradiance) — DNI is the solar radiation received on a surface perpendicular to the sun. Key metric for concentrating solar and tracking PV systems.
  • Degradation Rate — Solar panel degradation rate is the annual decrease in power output due to aging. Typically 0.5-0.7% per year for modern monocrystalline panels.

E

  • Energy Yield — Solar energy yield is the annual electricity production of a solar PV system, typically expressed in kWh/year or kWh/kWp/year (specific yield).

G

  • GHI (Global Horizontal Irradiance) — GHI is the total solar irradiance received on a horizontal surface, combining direct and diffuse components. The primary metric for evaluating PV sites.
  • Ground Coverage Ratio (GCR) — Ground Coverage Ratio (GCR) is the fraction of ground area covered by solar panels. Higher GCR means more panels per acre but more self-shading between rows.

I

  • Interconnection — Solar interconnection is the process of connecting a solar PV system to the utility grid, requiring utility approval, technical review, and metering installation.
  • Inverter — A solar inverter converts DC electricity from solar panels to AC electricity compatible with the grid and building loads. Types include string, microinverters, and power optimizers.
  • Investment Tax Credit (ITC) — The federal solar Investment Tax Credit (ITC) allows solar system owners to deduct 30% of installation costs from federal taxes. Available through 2032 under the Inflation Reduction Act.

L

  • LCOE (Levelized Cost of Energy) — LCOE is the average cost per kWh of electricity over a power plant's lifetime, including capital, operating, and fuel costs. Used to compare energy generation technologies.

M

  • Maximum Power Point (MPP) — The maximum power point (MPP) is the combination of voltage and current at which a solar panel produces maximum power. MPPT is the technology that tracks this point continuously.
  • Microinverter — A microinverter is a small solar inverter mounted on each individual panel. Enables panel-level optimization, monitoring, and independence from shading effects.

N

  • Net Metering — Net metering is a billing policy that allows solar customers to send excess electricity to the grid and receive credit against future electricity consumption.

P

  • Peak Sun Hours — Peak sun hours (PSH) is the number of hours per day when solar irradiance averages 1,000 W/m². Used to estimate daily solar energy production.
  • Performance Ratio — Performance ratio (PR) is the ratio of actual solar PV system output to theoretical maximum output, accounting for all real-world losses. Typically 75-85% for well-designed systems.
  • Photovoltaic (PV) — Photovoltaic (PV) technology converts sunlight directly into electricity using semiconductor materials. The dominant solar technology for rooftop and utility-scale power generation.
  • Power Purchase Agreement (PPA) — A Power Purchase Agreement (PPA) is a contract where a solar developer installs and owns a system on a host site and sells the electricity to the host at a fixed rate.

R

  • Racking — Solar racking (mounting) is the structural system that attaches solar panels to a roof, ground, or other surface at the correct tilt angle and orientation.

S

  • Shade Analysis — Shade analysis evaluates the impact of obstructions (trees, buildings, chimneys) on solar panel production. Critical for accurate energy yield assessment.
  • Single-Axis Tracker — A single-axis solar tracker rotates panels on a north-south axis to follow the sun from east to west, increasing energy production by 15-25% vs. fixed-tilt.
  • Soiling Losses — Soiling losses in solar panels are caused by dust, pollen, bird droppings, and other contaminants blocking light. Typically 1-5% annually but can exceed 20% in arid regions.
  • Solar Array — A solar array is a group of solar panels connected together electrically and mechanically to form a single power-generating unit. Arrays can range from a few kW to hundreds of MW.
  • Solar Irradiance — Solar irradiance is the power per unit area received from the Sun, measured in watts per square meter (W/m²).
  • Solar Module — A solar module (solar panel) is the basic unit of solar energy collection, consisting of solar cells encapsulated in a weatherproof package. Typically 300-650W for residential and commercial.
  • Solar Panel Efficiency — Solar panel efficiency is the percentage of sunlight converted to electricity. Standard panels achieve 18-22%; premium panels reach 22-24%.
  • Specific Yield — Specific yield (also called specific production) is solar energy output per kW of installed capacity, measured in kWh/kWp/year. Used to compare solar resource quality across locations.
  • Standard Test Conditions (STC) — Standard Test Conditions (STC) are the controlled laboratory conditions under which solar panels are rated: 1,000 W/m² irradiance, 25°C cell temperature, AM 1.5 spectrum.
  • String Inverter — A string inverter connects a series of solar panels (a string) and converts their combined DC output to AC. Cost-effective for unshaded, uniform arrays.

T

  • TMY (Typical Meteorological Year) — A Typical Meteorological Year (TMY) is a synthetic dataset of hourly weather data representing average conditions at a location, used for energy system simulation.
  • Tilt Angle — Tilt angle is the angle of solar panels from horizontal. Optimal tilt for fixed systems is approximately equal to the site latitude for maximum annual production.

U

  • Utility-Scale Solar — Utility-scale solar refers to large solar PV plants of 1 MW or more that sell electricity wholesale to the grid. The lowest-cost source of new electricity generation in most markets.