COMPONENTS OF PV SYSTEMS

Vocabulary and core concepts regarding solar photovoltaic system components, radiation principles, electrical properties, and system maintenance.

Stand-alone PV system

An automatic solar system that produces electrical power to charge banks of batteries during the day for use at night when sun energy is unavailable.

Grid-connected system

A solar power system that works with the local utility grid, feeding surplus power into the grid and drawing balance electricity from it when needed.

Solar Constant

The annual mean solar irradiance outside the earth’s atmosphere, measured at $1367 \pm 2\,W/m^2$.

Irradiance

The total specific radiant power per area reaching a receiver surface, measured in $W/m^2$ with the symbol $E$.

Irradiation

The integration of irradiance over a certain time period, measured in $J/m^2$ or $Wh/m^2$ with the symbol $H$.

Illuminance

The quantity analogous to irradiance for visible light, measured in $lm/m^2$ (lumen/$m^2$) or $lx$ (lux).

Direct Irradiance

The component of solar radiation that reaches the earth's surface directly from the solar disk without being scattered.

Diffuse Irradiance

Solar radiation that has been scattered by molecules and particles in the atmosphere but still reaches the surface.

Global Irradiance ($E_g$)

The sum of direct and diffuse irradiance on a horizontal surface, expressed as $E_g = E_{dir} + E_{dif}$.

Angle of Incidence

The angle a ray of sun makes with a line perpendicular to a surface; it is zero when the surface directly faces the sun.

Photovoltaic effect

The direct process by which solar cells convert light energy into electrical energy.

p-n junction

A solid-state electrical interface formed by joining p-type (hole-rich) and n-type (electron-rich) semiconductor materials.

Monocrystalline Silicon

Solar cells made from a single continuous crystal structure, typically produced via the Czochralski method and characterized by high efficiency.

Polycrystalline Silicon

Solar cells made by melting fragments of silicon together, usually appearing blue with visible grain boundaries.

Open-circuit voltage ($V_{oc}$)

The maximum voltage available from a solar cell or array when no load is connected and current is zero.

Short-circuit current ($I_{sc}$)

The maximum current produced by a solar cell or array when the positive and negative leads are connected, resulting in zero voltage.

Maximum Power Point (MPP)

The operating point on the I-V curve where the product of current ($I_{mp}$) and voltage ($V_{mp}$) results in the highest electrical power output.

Fill Factor (FF)

The ratio of the actual maximum power ($I_{mp} \times V_{mp}$) to the theoretical maximum power ($I_{sc} \times V_{oc}$).

Stringing

The process of wiring solar panels together in series or parallel to create a circuit for current flow to an inverter.

Encapsulation

The process of protecting solar cells from the environment, often using Ethylene Vinyl Acetate (EVA) on the front and back of the cells.

PV junction box

An enclosure on the back of a solar module where PV strings are electrically connected and protected from environmental factors.

Hot spot

An area of high temperature on a solar panel caused by localized energy dissipation, often due to shading or cell mismatch.

Blocking Diode

A diode in series with a solar panel that prevents current from flowing backward from the battery to the panel during darkness.

Bypass Diode

A diode that allows current to bypass a shaded or faulty panel in a series string to prevent power loss and hot-spot damage.

Inverter

A device that converts direct current (DC) power from solar arrays or batteries into alternating current (AC) electricity.

Micro Inverter

A small inverter dedicated to a single solar module, allowing for module-level maximum power point tracking (MPPT).

Net Metering

A solar incentive that allows users to send excess electricity to the grid in exchange for credits that offset future energy costs.

Miniature Circuit Breaker (MCB)

An automatic switch that interrupts an electrical circuit during abnormal conditions like overloads or short circuits.

Residual Current Device (RCD)

A safety device designed to quickly break an electrical circuit to prevent fatal electric shock or electrical fires.

Deep Cycle Battery

A lead-acid battery designed with thicker plates to handle repeated deep discharges (typically to 50% depth of discharge).

Sulphation

The buildup of lead sulfate on battery plates, which can crystallize if the battery is not immediately recharged, reducing storage capacity.

Battery Stratification

A condition where acid settles at the bottom of a battery because it is heavier than water, leading to loss of capacity and life.

MPPT Charge Controller

A DC-to-DC converter that monitors the PV array to find the Maximum Power Point and optimizes battery charging efficiency.

Pulse Width Modulation (PWM) Controller

A type of charge controller that regulates voltage to the battery but does not allow the array voltage to exceed battery voltage efficiently.