Solar photovoltaic (PV) systems are increasingly vital across Kenya’s diverse professional sectors, providing sustainable energy solutions that reduce reliance on grid electricity and fossil fuels. Whether powering a cold store, a printing works, a retail business, or a flower farm packhouse, understanding the components of a solar PV system is essential for effective installation and maintenance. This chapter introduces the main components involved in solar PV systems, focusing on solar panels, charge controllers, and cables, each critical to system performance and longevity.

3.1 Components of Solar System

A solar PV system turns sunlight into electricity that can be used immediately or stored. It does this with a chain of components, each doing one job. The solar panels produce direct current from sunlight. The charge controller manages the energy going into the batteries. The batteries store it. The inverter changes the direct current to alternating current for ordinary appliances. Cables join all of these, and protection devices keep the system safe. An installer must know what each component does, how it works and how it is connected, because the components are installed, tested and repaired one by one. This topic describes the panels, the charge controller, the inverter, the batteries and the cables. The size and rating of each component are worked out in outcome 2 (see size and rating of solar PV system), and the linking of the system to other power sources is covered in integration of solar PV system with other sources of power.

The energy follows this path in a stand-alone system:

Solar panels (DC) → charge controller → battery bank → inverter (AC) → loads

3.1.1 Solar Panels

A solar panel, or PV module, is a set of solar cells joined together and sealed in a frame under glass. Each cell is a thin layer of semiconductor, usually silicon, with a junction inside it. When light falls on the cell, the energy of the light frees electrons in the semiconductor, and the junction pushes them in one direction. This is the photovoltaic effect, and the result is a direct current in the external circuit. A silicon cell gives about 0.5 to 0.6 V, so a panel joins 60 or 72 cells in series to give a usable voltage.

The output of a panel is given on its label at standard test conditions (STC): sunlight of 1,000 W/m², a cell temperature of 25 °C and a standard light spectrum. The main ratings are:

Example: a panel has Vmp = 45 V, Imp = 10 A, Voc = 54 V and Isc = 10.6 A (hypothetical data).

Pmax = 45 × 10 = 450 W

Fill factor = Pmax ÷ (Voc × Isc) = 450 ÷ (54 × 10.6) = 450 ÷ 572.4 = 0.786

If the panel area is 2.2 m², then efficiency = 450 ÷ (1,000 × 2.2) = 0.2045, which is about 20.5 %.

The actual output in the field is lower than the label value, since cell temperature rises above 25 °C, and the sunlight is often weaker than 1,000 W/m².

3.1.1.1 Types of solar panel i.e. Amorphous/thin film, Monocrystalline, Polycrystalline

Panels are grouped by the type of cell.

• Monocrystalline: each cell is cut from a single silicon crystal. These panels have the highest efficiency of the three, usually a dark uniform colour, and need the least space for a given power. They cost more per panel.

Monocrystalline solar panel with connector cable (Source: Wikimedia Commons)

• Polycrystalline: the cells are made of many silicon crystals melted together, and have a blue, speckled look. They are a little less efficient and a little cheaper, and need more area for the same power.
• Thin film: a very thin layer of material, such as amorphous silicon or cadmium telluride, is laid on glass, metal or plastic. These panels are light, can be made flexible and work reasonably in weak light and heat. Amorphous silicon panels have the lowest efficiency and need the largest area; cadmium telluride thin-film modules are more efficient than amorphous silicon.

Flexible thin-film solar panels being installed (Source: Wikimedia Commons)

Panels are also made as bifacial modules, which collect light on both sides, and as building-integrated panels that replace roofing or facade material.

Building facade with integrated photovoltaic panels (Source: Wikimedia Commons)

3.1.1.2 Methods of solar panel connection i.e. parallel, series, etc.

Panels are joined to reach the voltage and current the system needs.

• Series connection: the positive terminal of one panel is joined to the negative terminal of the next. The voltages add and the current stays the same.
• Parallel connection: all positive terminals are joined together and all negative terminals together. The currents add and the voltage stays the same.
• Series-parallel connection: panels are first joined in series to make strings, and the strings are then joined in parallel. This gives the higher voltage and the higher current together.

Example: four panels, each with Vmp = 45 V, Imp = 10 A, Voc = 54 V and Isc = 10.6 A, are connected as two strings of two panels (two in series, two strings in parallel).

Each string: Vmp = 2 × 45 = 90 V, Voc = 2 × 54 = 108 V, current 10 A

Both strings in parallel: Imp = 2 × 10 = 20 A, Isc = 2 × 10.6 = 21.2 A, voltage 90 V

Array power = 90 × 20 = 1,800 W, which equals 4 × 450 W

Points to watch:

• The array voltage, including the open-circuit voltage in cold conditions, must stay within the input limit of the charge controller or inverter.
• Panels in one string must be of the same type and rating, since the weakest panel limits the string current.
• Shading on one panel in a series string reduces the output of the whole string. Bypass diodes in the panel junction box reduce the loss.
• Where three or more strings are joined in parallel, each string is protected by its own fuse, so that a fault in one string is not fed by the others.
• Connectors must be of the same type and fitted correctly, because a loose connector heats up and can cause a fire.

3.1.1.3 Solar Panel Mounting structures and positioning

The mounting structure holds the panels at the right angle and direction and keeps them firm in wind and rain. It is made of galvanised steel or aluminium, which resist corrosion, with stainless steel fixings. The common forms are a roof-mounted frame, a flush mount that follows the roof, a ground-mounted frame and a pole mount.

Positioning means choosing where to put the panels and which way they face:

• Place the panels where there is no shade from trees, buildings and other panels during most of the day.
• Face the panels toward the sun’s path. A site south of the equator faces its panels north, and a site north of the equator faces them south. Near the equator the sun is almost overhead, and the direction matters little at a low tilt.
• Keep the panels reachable, so that they can be cleaned and inspected.
• Leave air space behind the panels, since cooler panels give more power.
• Make the structure strong enough for the wind load and fix it to a sound roof or foundation.

Slanting angle

The slanting angle, or tilt angle, is the angle of the panel from the horizontal. For a fixed panel, a tilt close to the latitude of the site gives the best yearly energy. In Kenya, which lies on the equator, the best tilt is small, but panels are not laid flat. A tilt of about 10° to 15° lets rain wash away the dust and keeps water from standing on the glass.

Example: a panel frame 1.8 m long is tilted at 13°.

Height of the high edge = 1.8 × sin 13° = 1.8 × 0.2250 = 0.40 m

For rows of panels, the shadow of one row must not fall on the next row. The row spacing is the gap on the ground between the back of one row and the front of the next row. With the sun at an elevation of 30° at the design time:

Minimum spacing = 0.40 ÷ tan 30° = 0.40 ÷ 0.5774 = 0.69 m

3.1.2 Types and working principle of

Between the panels and the loads, three devices control, store and convert the energy: the charge controller, the inverter and the battery. Each is described by its types and its working principle.

3.1.2.1 Charge controller

The charge controller sits between the panels and the batteries. It protects the batteries from overcharging when the sun is strong, and from deep discharge when the load is heavy, which prolongs the life of the batteries and keeps the system safe.

Working principle: the controller watches the battery voltage. In the bulk stage the controller passes all the available current into the battery. When the voltage reaches the set value, the absorption stage holds the voltage steady while the current falls. When the battery is full, the float stage keeps a small maintaining voltage. Most controllers also compensate the voltage for temperature, disconnect the loads when the battery is low and stop reverse current at night.

There are two main types:

• PWM (pulse width modulation) controller: it joins the panel to the battery through a switch that opens and closes rapidly. The panel voltage is pulled down to the battery voltage. It is simple and low in cost, and suits small systems where the panel voltage is matched to the battery.
• MPPT (maximum power point tracking) controller: it contains a DC-to-DC converter and a circuit that looks for the voltage at which the panel gives the most power. It converts the extra panel voltage into more charging current. It costs more, and gives more energy, especially with a high-voltage array, cold conditions and a long cable run.

Example (illustrative): a 450 W panel with Vmp = 45 V and Imp = 10 A charges a 24 V battery bank at 27 V.

PWM: the panel works at about 27 V, so power ≈ 27 × 10 = 270 W, which is 60 % of 450 W

MPPT: the panel works at 45 V, and with a converter efficiency of about 97 % the power is about 0.97 × 450 = 436.5 W

The charge controller is chosen to match the battery voltage, the array current and the battery chemistry. The calculation is shown in size and rating of solar PV system.

3.1.2.2 Inverters

The inverter changes the DC from the batteries or the array into AC at the voltage and frequency of the loads, 240 V and 50 Hz in Kenya.

Working principle: electronic switches, usually transistors in a bridge, switch the DC supply on and off in both directions many thousands of times a second. The switching is shaped by pulse width modulation, and a filter smooths the result into an alternating waveform. A transformer or a second converter stage raises the voltage to 240 V.

Types:

• Modified sine wave inverter: gives a stepped waveform. It is low in cost and runs simple loads such as lamps and chargers, but it can make motors and some electronics hot and noisy.
• Pure sine wave inverter: gives a smooth waveform like the grid. It runs all loads, including motors, refrigerators and sensitive electronics.
• Off-grid (stand-alone) inverter: takes its energy from a battery bank.
• Grid-tie inverter: feeds the array output into the grid and shuts down if the grid fails.
• Hybrid inverter: manages the array, the batteries and the grid together.

The main ratings are continuous power, surge power for starting motors, input voltage, output voltage and efficiency.

Example: a 500 W load is run from a 24 V battery through an inverter of 92 % efficiency.

Input power = 500 ÷ 0.92 = 543.5 W

Battery current = 543.5 ÷ 24 = 22.6 A

3.1.2.3 Solar batteries

Solar batteries store the energy produced during the day for use at night and in cloudy weather. Batteries for solar use are deep-cycle batteries, made to be discharged repeatedly and deeply, unlike a car starting battery, which gives a short heavy current.

Types:

• Flooded lead-acid: low in cost and long-lived with care. They need regular topping up with distilled water, and they give off hydrogen when charging, so the room must be ventilated.
• Sealed lead-acid (AGM and gel): need no topping up, and most sealed lead-acid batteries can be mounted on their side, but follow the maker's instructions; they cost more and are sensitive to overcharging.
• Lithium iron phosphate (LiFePO4): light, with a long cycle life, a deep usable discharge and high efficiency. They cost more at the start and require a compatible controller.

Capacity is given in ampere-hours (Ah). The stored energy in watt-hours is the capacity times the voltage. Batteries are joined in series to raise the voltage and in parallel to raise the capacity.

Example: 12 V, 100 Ah batteries.

Two in series: 24 V, 100 Ah, energy 24 × 100 = 2,400 Wh

Two in parallel: 12 V, 200 Ah, energy 12 × 200 = 2,400 Wh

With a 50 % depth of discharge limit for lead-acid, the usable energy in each case is 2,400 × 0.5 = 1,200 Wh.

Safety points: wear eye protection and gloves, avoid short-circuiting the terminals with tools, connect the correct polarity, keep the batteries cool and dry, and use only batteries of the same type, age and capacity in one bank.

3.1.3 Cables

Cables carry the current between panels, controller, batteries, inverter and loads. A cable that is too small heats up, wastes energy and can start a fire, and one that is the wrong type fails in sunlight.

Types of cables:

• Photovoltaic (PV) cable: UV-resistant and weatherproof, with double insulation, used for the outdoor wiring from the panels.
• Copper conductors: preferred for their high conductivity and flexibility.

Copper conductors inside insulated electrical cable (Source: Wikimedia Commons)

• Aluminium conductors: lighter and cheaper but of lower conductivity, so a larger size is needed. They are used mostly on long, large runs.

Cross-section of aluminium conductor cable (Source: Wikimedia Commons)

• Twin core cables: carry the positive and negative conductors together, for the DC connections between panels and controller.

Close-up of twin core electrical cable (Source: Wikipedia (Twin and earth))

• Multi-core cables: used on the AC side, from the inverter to the loads or the grid.

Cable sizing depends on the current to be carried without overheating, the length of the run, the voltage drop allowed, the ambient temperature and the way the cable is installed. A voltage drop of 3 % or less is a common target for DC circuits.

Voltage drop (two-conductor circuit) = 2 × L × I × ρ ÷ A

Here L is the one-way length in metres, I the current in amperes, ρ the resistivity of copper (1.68 × 10⁻⁸ Ω·m, which is 0.0168 Ω·mm²/m) and A the cross-section in mm².

Example: a 12 V circuit of 8 m one way carries 15 A on a 10 mm² copper cable.

Voltage drop = 2 × 8 × 15 × 0.0168 ÷ 10 = 4.032 ÷ 10 = 0.403 V, which is 0.403 ÷ 12 = 3.4 %

This is more than 3 %, so a 16 mm² cable is chosen:

Voltage drop = 4.032 ÷ 16 = 0.252 V, which is 2.1 % of 12 V

Installation practices:

• Use conduit or trunking: protects the cables from mechanical damage and sunlight.
• Fix the cables securely: prevents sagging and strain on the terminals.
• Colour code the conductors: red for positive and black for negative on the DC side makes the polarity clear.
• Keep to the bending radius: a sharp bend damages the conductor and insulation.
• Earth the metal parts: the frames and enclosures are connected to the earthing system.
• Make firm connections: use proper lugs and connectors, since loose terminals cause heating and sparks.

Cables are inspected regularly for cracks, rodent damage and heat marks, and any damaged length is replaced.

Chapter Summary

This chapter provided a detailed overview of the components that make up a solar photovoltaic system, beginning with solar panels, their various types, and the different methods used to connect them. It also covered the importance of solar panel mounting structures and proper positioning to maximize energy capture. The discussion then moved to key system elements such as charger controllers, inverters, and solar batteries, explaining their types and operating principles. Attention was given to the role of cables in ensuring efficient and safe electrical connections within the system. The chapter further explored how solar PV systems can be integrated with other power sources to enhance reliability and performance. Proper care and maintenance practices for solar PV components were emphasized to ensure longevity and optimal functionality. Finally, the preparation of as-built drawings was highlighted as an essential step for documentation and future reference during system operation and maintenance.