Solar PV basics

Energy One Ltd

By Mathy Mpassy Isinki

Off Grid Energy Solutions Business andTechnical Sales Professional

Heat andlight

The sun delivers its energy in two mainforms:

Solar electric systems convertthe sun’s light energy intoelectricity using photovoltaiccells.

Grid connected (or grid tied) and Off grid (or stand alone)

Types of PV systems:

Grid connected solar PV systems exportexcess energy to the grid;

Off grid solar PV systems store excessenergy into batteries.

Grid connected solar PV systemsbenefit from grid's energy while;Off grid solar PV systems benefit fromenergy stored into batteries.

When the sun is not available:

Photovoltaic (PV) cells are made oflight sensitive semiconductor materialsusing photons to dislodge electrons anddrive an electric current.

Mono-crystalline silicon;Poly- crystalline;Thin films

There are three main type of PV cellstechnology in use:

Crystalline silicon is made from ultrapure silicon material such as the one usedfor semiconductor chips;

Thin films is made by depositing layers ofsemiconductors material onto glass orstainless steel substrate.

Mono-crystalline silicon: 12.5-15%Poly-crystalline silicon: 11-14%Copper Indium Gallium Selenide (CIGS): 10-13%Cadmium Telluride (CdTe): 9-12%Amorphous Silicon (a-Si): 5-7%

Solar cells conversion efficiency:

Crystalline silicon: -0.4 to -0.5CIGS: -0.32 to -0.36CdTe: -0.25a-Si: -0.21

Solar cells temperature coefficient:

Effect of temperature:

PV cells performance declines astemperature rises

Solar PV modules are made of theaggregation of solar cells.

Solar power terms:

Pmax: The maximum power a solarmodule can produce.Vpmax: The voltage at whichmaximum power is produced.Ipmax: The current at which maximumpower is produced.

Voc: The maximum possible voltageacross the solar module when current iszero.Isc: The maximum possible currentflowing through the solar panel whenno load is connected and voltage iszero.

Standard Test Conditions (STC):

Temperature of the cell – 25°C.Solar Irradiance – 1000 Watts persquare meter.

PV modules are connected in series into PVstrings;

PV arrays are formed by the parallelaggregation of PV strings.

Cables that can withstand environmentalconditions are used to interconnect PVstrings and arrays.

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