Solar PV Systems
Training Manual

3.1 Types of Electricity

There are two forms of electricity: Alternating Current (AC) and Direct Current (DC).

AC electricity is the type supplied by the national power grid. Its polarity reverses direction 50 times every second (50 Hz). Because of this constant switching, polarity is not a concern in AC systems — but you must never mix AC and DC wiring.

DC electricity flows in one direction only and maintains a fixed polarity. Solar panels and batteries both produce and store DC electricity. For this reason, polarity is critical in solar PV systems. Connecting components in reverse polarity can damage or destroy them.

3.2 Voltage

Voltage is the electrical pressure that pushes current through a circuit. Think of it like water pressure in a pipe — higher pressure means more force to push water through. Higher voltage means more force to push electricity through a wire.

The symbol for voltage is E (or sometimes V). The unit is the Volt (V).

Common solar system voltages: 12V, 24V, and 48V.

3.3 Current

Current is the quantity of electricity actually flowing through a wire at any given moment. Using the water analogy again, if voltage is water pressure, current is the flow rate — how much water is actually moving.

The symbol for current is I. The unit is the Ampere (A), also called amps.

3.4 Resistance

Resistance is how much a material opposes the flow of electricity. A thick wire has less resistance than a thin wire, just as a wide pipe allows more water through than a narrow one. High resistance in wiring causes energy to be lost as heat — which is why the correct wire size matters in solar installations.

The symbol for resistance is R. The unit is the Ohm (Ω).

3.5 Power and Energy

Power is the rate at which electricity does work. It is calculated by multiplying voltage by current. The symbol is P and the unit is the Watt (W).

Energy is power used over time. When an appliance runs for several hours, the total electricity consumed is called energy, measured in Watt-hours (Wh).

3.6 The Laws of Electricity

Electrical circuits follow strict physical laws — Ohm's Law and Kirchhoff's Laws. These laws cannot be violated. Any calculated values that appear to break them are simply wrong. Memorising the formulas is less important than truly understanding what they mean so you can reason through any circuit problem.

3.7 Ohm's Law

Ohm's Law describes the relationship between voltage, current, and resistance in a circuit. When you know any two of these three values, you can always calculate the third.

3.8 The Power Law

The Power Law works the same way as Ohm's Law, relating Power (P), Current (I), and Voltage (E).

3.9 Kirchhoff's Laws

Kirchhoff's two laws govern how current and voltage behave throughout a circuit. They are essential for analysing more complex wiring configurations.

A. Kirchhoff's Current Law (First Law)

At any junction point in a circuit, the total current flowing in must equal the total current flowing out. No current is lost or created at a junction — it simply divides and recombines.

B. Kirchhoff's Voltage Law (Second Law)

In any closed loop of a circuit, the sum of all voltage drops across components equals the source voltage. Voltage used by components always adds up to the supply voltage.

3.10 Series and Parallel Circuits

A. Series Circuits

In a series circuit, components are connected end-to-end in a single path. The same current flows through every component. The total voltage is the sum of all individual voltage drops. The total resistance is the sum of all individual resistances.

B. Parallel Circuits

In a parallel circuit, components are connected across the same two points, creating multiple paths for current to flow. Each component receives the full supply voltage, but the total current is the sum of all branch currents.

4.1 The Role of Solar PV

The purpose of a solar PV system is to convert freely available sunlight into usable electrical energy. Solar panels generate DC electricity during daylight hours. To make this energy useful — especially at night — additional components are needed to store, manage, and sometimes convert that electricity.

4.2 How Solar PV Generates Power

The primary input to any solar PV system is solar radiation — sunlight. Unlike wind turbines that use wind, or hydro systems that use flowing water, solar panels use sunlight directly.

The energy density of sunlight reaching the earth's surface is limited to around 1 kW/m². This means that to get more electricity, you either need to convert it more efficiently or capture more of it using a larger panel area. Both approaches are used in practice.

4.3 Types of Solar PV Systems

There are two main categories of solar PV systems:

4.4 Off-grid Systems (Stand-alone)

A. Solar Home Systems (SHS)

A Solar Home System is a small, self-contained off-grid solar installation designed to power a single household. SHS units are typically between 20W and 2kW and can supply lighting, phone charging, small TVs, and radios.

SHS systems are the most widely used solar solution in rural Kenya and across Africa. When properly designed and maintained, they are highly reliable. Unfortunately, many SHS systems have failed in the past due to wrong design, poor components, or insufficient maintenance — not because the technology does not work.

Modern SHS systems serve lighting, LCD television, radio/CD players, and mobile phone charging. With an inverter added, AC appliances can also be powered. LED lighting has been a game-changer — consuming far less power than older fluorescent or incandescent bulbs, meaning smaller (and cheaper) solar panels can serve the same lighting needs.

B. Mini-grid Systems (Centralised)

A mini-grid is a larger centralised solar system — typically 10kW to 100kW — installed at a single location and distributing electricity to multiple homes or businesses through a local distribution network. It works similarly to the national grid, but at a smaller, community scale.

Mini-grids offer stable, high-quality power with no interruptions or power surges. However, they are expensive to build and maintain, and the cost of battery replacement is a significant long-term challenge. A mini-grid is only financially viable when government or donor funding covers the battery replacement costs, or when electricity tariffs are set high enough to cover operations.

4.5 Other Applications of Solar PV

A. Solar Water Pumping

Solar water pumping systems use PV modules to power an electric pump that draws water from a well or borehole. Because the pump only needs to operate during daylight hours, a storage tank is used instead of a battery — water is pumped during the day and stored for use at any time.

This makes solar pumping one of the most efficient solar applications, since batteries (the most expensive and short-lived component in most systems) are eliminated. Solar water pumps are used extensively in Kenya for both domestic water supply and irrigation.

B. Solar Refrigeration

Solar-powered fridges are used in health facilities for vaccine storage, in homes, and in businesses. Fridges have specific duty cycle characteristics — they do not run continuously but cycle on and off based on temperature. The ambient temperature in Kenya affects this cycle significantly: higher temperatures mean the compressor runs more often, consuming more energy. System designers must account for this when sizing the PV array and battery.

C. Radio Communication Systems

Remote radio communication towers and base stations — often located in areas far from the grid — are excellent candidates for solar power. These systems typically require continuous reliable power, so they are designed with larger battery banks and redundancy built in.

5.1 Irradiance and Insolation

Two terms are often confused in solar energy: irradiance and insolation. They are related but different.

Irradiance rises from zero at sunrise, reaches its peak around noon, and returns to zero at sunset. When you measure the total area under this daily curve, you get the daily insolation. On a perfectly clear, sunny day in Kenya, daily insolation can reach around 6.2 kWh/m². On a heavily overcast day, it can drop below 1 kWh/m².

5.2 Insolation Data

A. How Weather Affects Insolation

The amount of solar energy received at a location depends heavily on the weather. Cloud cover is the biggest factor. Even a thin layer of clouds can reduce irradiance by 50% or more. When a cloud passes directly over a solar panel, the output power can drop almost instantly to a fraction of its clear-sky value.

B. Daily and Annual Insolation Variation

Solar insolation changes not just day to day, but month to month throughout the year. In the Philippines (used as an example in training data), daily insolation ranges from about 0.1 kWh/m² on the worst rainy days to over 6 kWh/m² on the best sunny days. In Kenya, the annual average for Nairobi is approximately 4.5 kWh/m²/day.

This means that on days with lower-than-average insolation, your system produces less electricity than normal. System designers must size storage and panels to handle these low-insolation periods without cutting off the user's supply.

5.3 Peak Sun Hours

Peak sun hours is one of the most important concepts in solar system design. Because irradiance changes throughout the day, engineers needed a single number to represent how much solar energy a location receives. The solution: "peak sun hours."

Peak sun hours is the number of hours per day during which the irradiance equals the standard test condition level of 1 kW/m². It is numerically equal to the daily insolation in kWh/m².

5.4 Recommended Tilt Angle in Kenya

In most parts of Kenya, June has the lowest solar insolation of the year — not December as is the case in Northern Hemisphere countries. This is because June is Kenya's overcast/rainy season in many regions.

To optimise solar collection for Kenya's specific conditions, including accounting for the months with lowest energy availability:

5.5 The Purpose of Panel Inclination

A. Why Tilt Matters

Solar panels produce the most electricity when sunlight strikes them at a 90° angle — that is, when the sun is directly perpendicular to the panel surface. By tilting panels toward the direction of the sun's path, we can increase the amount of energy collected over the year.

Tilting panels has two effects on energy production:

• It increases energy collection during the month when the sun is furthest from the panel (e.g., June for North-facing panels in Kenya)
• It decreases energy collection during the month when the sun is closest to the panel (e.g., December)

The goal is to minimise the difference between the best and worst months — this is called optimising, or "flattening," the insolation curve across the year.

B. User Satisfaction

In solar home systems, users notice problems most during the low-insolation months. If a system produces far less electricity in June than in December, users will run out of power regularly during the worst months. Increasing tilt angle raises June output — improving reliability and user satisfaction during the critical low-production period.

C. Practical Rules for Orientation

Different instruments are needed depending on whether you are doing a simple site check, managing a larger centralised system, or running a formal training exercise. The table below summarises what is essential and what is good to have for each situation.

* If the AC-DC clamp meter already includes an AC clamp function, a separate AC power meter is not needed.

What Each Instrument Does

Multimeter

The most essential tool for any solar technician. A multimeter measures DC voltage (panels, batteries), DC current, resistance, and sometimes AC voltage. It is used for virtually every electrical check on a solar system.

AC-DC Clamp Meter

A clamp meter measures current by clamping around a wire — without cutting the wire or breaking the circuit. This makes it ideal for measuring the output current of solar panels and the charging current going into batteries during live operation.

Irradiance Meter

Measures the intensity of sunlight in W/m² at the moment of measurement. Essential for comparing actual panel output against expected output at the measured irradiance level. Used to detect underperforming modules.

Pyranometer

A high-precision instrument for measuring solar irradiance. More accurate than a basic irradiance meter and typically used in centralised monitoring stations to record insolation data continuously throughout the day.

Infrared Thermometer

Used to check the surface temperature of solar panels and batteries without touching them. Hot spots on a panel surface indicate faulty cells, delamination, or shading problems. Battery overheating detected with an IR thermometer is an early warning of failure.

Thermography Camera

A thermal imaging camera produces a full heat-map image of a solar panel, making it easy to identify exactly which cells or connections are overheating. Extremely useful for maintenance of larger PV arrays.

Data Logger

Records electrical parameters (voltage, current, power, temperature, irradiance) over time. The logged data is used to analyse system performance, identify trends, and diagnose problems that only occur under specific conditions.

7.1 Types of Solar PV Modules

Solar PV modules convert solar radiation (sunlight) into DC electricity through the photovoltaic effect. The material used to make the solar cells determines the module type.

A. Crystalline Silicon Modules

Crystalline silicon is the most widely used material for solar cells worldwide, and it is the dominant technology available in Kenya. There are two sub-types:

• Monocrystalline: Made from a single crystal of silicon. These cells are uniform in appearance (usually dark blue or black), slightly more efficient, and have a longer track record. The module lifespan is typically well over 20 years, though the limiting factor is usually the encapsulant resin (EVA) that deteriorates over time.
• Polycrystalline: Made from multiple silicon crystals melted together. Slightly less efficient per unit area, but generally less expensive. The appearance is speckled blue due to the varying crystal orientations. Performance is similar to monocrystalline for most practical applications.

B. Amorphous Silicon Modules

Amorphous silicon panels are made from a thin layer of silicon deposited on glass or plastic. They are cheaper to produce for small sizes (around 10W) but have significantly lower efficiency — roughly half that of crystalline modules. This means a larger physical area is required to produce the same power. Their efficiency also degrades faster in the long term. Amorphous modules are generally not recommended for permanent installations.

C. Other Technologies

Other PV technologies exist (CIGS, CdTe, perovskite, etc.) but are not yet widely available or cost-effective in the Kenyan market at this time.

7.2 Efficiency and Output Power

Efficiency tells you how much of the incoming solar energy is converted into usable electricity. Module efficiency (η) is defined as:

The input power for a solar module is the solar irradiance multiplied by the module's physical area. At standard irradiance of 1 kW/m², a 0.5m² module receives 500W of solar energy. If it outputs 100W of electricity, its efficiency is 20%.

7.3 Key Characteristics of Solar PV Modules

Solar modules behave very differently from conventional power supplies such as generators or batteries. Understanding this difference is critical for correct system design.

Understanding Key PV Module Terms

7.4 Number of Solar Cells in a Module

A single solar cell produces approximately 0.6V. Since 0.6V is too small to drive any useful appliance, multiple cells are connected in series to add their voltages together and produce a usable output.

For a 12V battery system, the module needs to produce enough voltage to charge the battery even on a warm day (when voltage is reduced by heat). The industry standard is 36 cells connected in series for a nominal 12V module. Larger 150W modules use 54 cells, but both configurations produce the same power per cell.

7.5 The I-V Curve

The I-V curve (Current-Voltage curve) is the most important graph for understanding solar module behaviour. It shows the relationship between the output voltage and output current of a module at a given irradiance and temperature.

Key characteristics of the I-V curve:

• At V = 0 (short circuit), current is at its maximum: Isc
• At I = 0 (open circuit), voltage is at its maximum: Voc
• The Maximum Power Point (MPP) is the "knee" of the curve where power (P = I × V) is greatest, occurring at Vmp and Imp
• When connected to a 12V battery, the module operates within the battery voltage range (approximately 12V–15V), which is close to — but not exactly at — the MPP

The area within the curve represents available power. The power-voltage (P-V) curve derived from the I-V curve shows a clear peak at Vmp — this is the maximum power point. Modern MPPT charge controllers actively track this point to extract maximum energy from the panel throughout the day.

7.6 Effects of Temperature and Irradiance

A. Effect of Temperature

Solar panels operate outdoors in direct sunlight, which means they heat up during the day. Higher temperature has a negative effect on module output — specifically on voltage.

• As temperature rises: voltage decreases (significantly)
• As temperature rises: current increases slightly
• Net result: power decreases at higher temperatures

B. Effect of Irradiance

Irradiance (the intensity of sunlight) has a direct proportional effect on current output:

• When irradiance decreases: current decreases proportionally
• When irradiance decreases: voltage decreases slightly
• Net result: power is reduced significantly on cloudy days

7.7 Effects of Shading

Shading is one of the most serious and underestimated problems in solar PV installations. Even partial shading of a single cell can dramatically reduce the output of an entire module.

Here is why: in a series-connected string of 36 cells, all cells must carry the same current. A shaded cell receives less irradiance, so it can only produce a lower current. Since all cells are in series, the entire string's current is limited to the lowest current of any individual cell — the shaded one.

7.8 Shading and Bypass Diodes

Modern solar modules include built-in bypass diodes to limit the damage caused by shading. A bypass diode allows current to "go around" a shaded group of cells rather than being forced through them.

A standard 36-cell module for 12V systems has two bypass diodes, each protecting a sub-module of 18 cells. When one of those 18-cell groups is shaded:

• The bypass diode for that group activates
• Current bypasses the shaded 18-cell group entirely
• The module's output drops to roughly half its normal value (from 18 unshaded cells)
• Without bypass diodes, the output would collapse to near zero

7.9 Bypass Diodes and Blocking Diodes — Deep Dive

These two diode types are routinely confused, even by experienced technicians. They look similar and are both found in solar PV systems — but they perform completely different jobs at completely different points in the system. Understanding both is critical for correct installation and fault diagnosis.

What Is a Diode?

A diode is a simple electronic component that allows current to flow in one direction only, like a one-way valve for electricity. When current tries to flow the wrong way, the diode blocks it. This property is what makes diodes so useful in solar PV systems, where current direction matters enormously.

A. Bypass Diodes — In Detail

Bypass diodes are located inside the junction box on the back of every quality solar module. They are placed in parallel across groups of solar cells (sub-modules) within the module — not in series with them.

Under normal unshaded conditions, bypass diodes are completely inactive. Current flows through the solar cells as normal, and the bypass diode's reverse-blocking behaviour means it plays no role whatsoever.

When one group of cells becomes shaded or faulty, two things happen simultaneously:

• The shaded cells' output drops dramatically — they can no longer carry the full string current
• Because the string current exceeds what the shaded cells can produce, those cells are forced into reverse — they become a load, dissipating power as heat (a "hot spot")

The bypass diode activates at this point: it opens a parallel path around the shaded group, allowing current to flow around it instead of through it. The shaded cells are bypassed, eliminating the hot spot risk and recovering most of the module output.

B. Blocking Diodes — In Detail

Blocking diodes serve an entirely different purpose. They are connected in series with each string of modules, between the string's positive terminal and the charge controller or battery bus. Their job is to prevent reverse current flow.

Two scenarios make blocking diodes necessary:

• Night-time reverse current: At night, the battery voltage is higher than the (zero) panel voltage. Without a blocking diode, current would flow backwards from the battery through the panels, slowly draining the battery overnight.
• Parallel string imbalance: When two or more strings are connected in parallel and one string produces less voltage than the other (due to shading or a faulty module), current from the higher-voltage string can flow backwards into the lower-voltage string. A blocking diode in each string prevents this cross-current.

7.10 Wiring Solar Modules — Series and Parallel Connections

When a single solar module cannot provide the required voltage or current, multiple modules are connected together to form an array. When multiple modules are connected in a single series chain, that chain is called a string.

Series Connection — Increases Voltage

Connect the positive terminal of one module to the negative terminal of the next. The total voltage adds up; current stays the same.

Parallel Connection — Increases Current

Connect all positive terminals together and all negative terminals together. Current adds up; voltage stays the same.

7.11 Technical Specifications — Reading a Module Datasheet

Every legitimate solar module comes with a specification label on the back and a formal datasheet. Knowing how to read these is an essential skill for procurement and quality checking.

8.1 The Role of a Battery in a Solar PV System

A solar module only generates electricity while sunlight is available. Most household electrical demand, however, occurs in the evening — exactly when the sun is down. A battery solves this mismatch by storing electricity generated during the day for use at night or on cloudy days.

Rechargeable batteries serve two primary functions in a solar system:

• Charging: Converting electrical energy from the PV modules into chemical energy for storage
• Discharging: Converting stored chemical energy back into electrical energy to supply loads

A secondary benefit of the battery is that it stabilises the system output voltage. Without a battery, the voltage from the solar panel fluctuates throughout the day with changing irradiance. The battery acts as a voltage buffer, providing steady, reliable power to connected loads.

8.2 Types of Lead-Acid Batteries

Lead-acid batteries are by far the most common battery type used in solar PV systems in Kenya and across Africa. They are available in a wide range of capacities and are well understood by most technicians. There are two main types of lead-acid batteries:

A. Automotive (Starter) Batteries

Automotive batteries — also called SLI batteries (Starting, Lighting, Ignition) — are designed to deliver a very large burst of current for a very short time to start an engine. After starting, the alternator immediately recharges them, so they are almost never deeply discharged in normal use.

These batteries are NOT suitable for solar PV applications. In a solar system, the battery is regularly discharged to 50% or lower capacity (called deep cycling). Automotive batteries are not designed for this and their plates will deteriorate rapidly, reducing their lifespan to just a few months of solar use.

B. Deep Cycle Batteries

Deep cycle batteries are specifically designed for applications where the battery is regularly discharged by 50% or more before being recharged. Their internal construction — thicker, denser plates — allows them to withstand hundreds to thousands of charge-discharge cycles.

Within deep cycle batteries, there are two common formats:

• Flooded (wet cell): The most common and affordable type. The electrolyte (diluted sulphuric acid) is liquid and can be accessed. These batteries require regular maintenance — specifically, topping up with distilled water to keep the electrolyte level correct.
• Maintenance-free (VRLA): Sealed batteries that do not require water top-ups. The electrolyte is either absorbed in a glass mat (AGM) or formed into a gel (Gel battery). These cost more but require significantly less maintenance and can be installed in any orientation.

9.1 What a Charge Controller Does

A solar panel, left uncontrolled, will continue pushing current into a battery even after it is fully charged. This leads to overcharging — a serious condition that causes batteries to overheat, lose electrolyte, and deteriorate rapidly, sometimes dangerously.

The charge controller solves this by monitoring battery voltage continuously and reducing or stopping the charging current when the battery reaches full charge. It also prevents the battery from being discharged too deeply — a condition that permanently damages lead-acid batteries.

There are two main technologies used in solar charge controllers: PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking). Understanding the difference — and when to use each — is one of the most important decisions in solar system design.

9.2 PWM Charge Controllers

PWM stands for Pulse Width Modulation. A PWM controller works by connecting the solar panel directly to the battery through a switch that opens and closes rapidly. When the battery is low, the switch is closed more often (longer pulses) to let more current through. As the battery approaches full charge, the pulses become shorter and less frequent, reducing the charging current until the battery is fully charged.

How PWM Handles Voltage

This is the key limitation of PWM: when a PWM controller connects the panel to the battery, it forces the panel to operate at battery voltage — not at the panel's optimal Vmp. A 12V battery charges at around 14V. But the panel's Vmp might be 17.2V. The PWM controller discards the voltage difference between 17.2V and 14V — wasting energy that could have been harvested.

9.3 MPPT Charge Controllers

MPPT stands for Maximum Power Point Tracking. An MPPT controller is a sophisticated electronic converter that continuously searches for — and locks onto — the panel's Maximum Power Point (Vmp × Imp), regardless of what the battery voltage is at that moment.

Rather than connecting the panel directly to the battery like PWM does, an MPPT controller uses a DC-DC converter to accept the panel's higher voltage at its MPP, convert it to the lower battery charging voltage, and deliver the equivalent power as a higher current at battery voltage. No energy is wasted in the voltage conversion — the converter is typically 93–97% efficient.

9.4 PWM vs MPPT — The Critical Role of Temperature

Temperature is the deciding factor that determines how much advantage MPPT has over PWM in any given installation. This is one of the most misunderstood topics in solar PV design, and getting it right can save customers significant money.

How Temperature Affects Panel Voltage

As we saw in Chapter 7, increasing panel temperature decreases voltage significantly. The Vmp of a crystalline silicon panel drops by approximately 0.4–0.5% per °C above 25°C. In Kenya, panels regularly reach 55°C–65°C in direct sunlight.

This is the key insight: when the panel is hot, its Vmp drops close to battery charging voltage. When Vmp ≈ Vbat, PWM can extract nearly as much power as MPPT — because there is very little "wasted" voltage difference left to recover.

When MPPT Genuinely Outperforms PWM

• High-voltage panels on low-voltage batteries: A 60-cell panel (Vmp ~30V) charging a 12V battery — PWM wastes over 50% of potential power; MPPT recovers most of it
• Long wire runs with voltage rise: If panel wiring raises open-circuit voltage significantly, MPPT handles the higher input voltage safely; PWM controllers have strict max input voltage limits
• Cold climate or high-altitude installations: Cool panels have much higher Vmp, maximising MPPT advantage
• Systems where efficiency is critical: When the panel array is sized tightly and every watt matters

9.5 Sizing a Charge Controller

A charge controller must be sized to handle the maximum current that the solar array can produce. Undersizing a charge controller will cause it to overheat and fail.

Step 1 — Calculate Array Short Circuit Current (Isc)

The maximum current a panel array can ever produce is its short-circuit current (Isc), which occurs under very high irradiance. Use the datasheet Isc value for your panel. For parallel strings, add the Isc values together.

Step 2 — Apply a 25% Safety Factor

Always add a 25% safety margin to account for irradiance spikes (e.g., cloud-edge effect where irradiance briefly exceeds 1 kW/m²) and controller heating:

9.6 Charge Controller Settings and Battery Protection

Most quality charge controllers allow you to programme or adjust key voltage thresholds. Setting these correctly for your specific battery type is essential for long battery life.

10.1 The Design Process Overview

Solar system design follows a logical five-step sequence. Each step feeds into the next. Never skip a step — even a seemingly small error at Step 1 compounds into a significantly wrong system by Step 4.

10.2 Step 1 — Load Assessment

The load assessment is the foundation of the entire design. It determines how much energy the system must produce every day. If this step is wrong, everything that follows will also be wrong.

For each electrical appliance the customer wants to run, record:

• The power rating in Watts (check the label on the appliance)
• The daily usage time in hours
• The number of units

Then multiply: Watts × Hours × Quantity = Daily Watt-hours (Wh) for that appliance. Sum all appliances to get the total daily energy demand.

10.3 Step 2 — Battery Sizing

The battery must store enough energy to supply the load for the required number of "autonomy days" — consecutive cloudy days when the solar panels produce little or no energy. In Kenya, using 2–3 autonomy days is standard for most SHS designs.

Lead-acid batteries must never be discharged below a safe depth. The Depth of Discharge (DoD) limit for flooded lead-acid batteries is typically 50% — meaning you can only use half the rated capacity. VRLA (AGM/Gel) batteries typically allow up to 70–80% DoD. Exceeding these limits dramatically shortens battery life.

10.4 Step 3 — PV Array Sizing

The solar array must generate enough energy each day to replace what the battery supplies to the loads, plus overcome system losses. System efficiency accounts for battery charging/discharging losses, wiring losses, and controller losses. A realistic overall system efficiency for a basic SHS is 70–80%.

10.5 Step 4 — Charge Controller Sizing

Use the method described in Chapter 9. Calculate total array Isc, multiply by 1.25, and select the next standard size above that value.

10.6 Step 5 — Wiring and Fusing

Correct wire sizing is critical for both safety and efficiency. Undersized wires:

• Cause voltage drop — reducing available power at the load
• Overheat — creating a fire risk
• Degrade faster — causing high-resistance connections over time

Calculating Voltage Drop

The resistance of a copper wire depends on its cross-sectional area and length. The cable resistance of 1mm² copper cable is approximately 0.02Ω per metre. For a 4mm² cable, it is 0.02 ÷ 4 = 0.005Ω per metre.

The factor of 2 accounts for both the positive and negative conductors (current flows down one wire and returns through the other).

Acceptable voltage drop limits:

• Between panel and charge controller: ≤ 3%
• Between battery and loads: ≤ 3%
• Between battery and charge controller: ≤ 1%

Fuse Sizing

Every circuit in a solar system must be protected by a fuse or circuit breaker, placed as close to the battery positive terminal as possible. The fuse protects the wiring — not the load — so it should be rated for the wire's maximum safe current, not the load current.

10.7 Complete Worked Example — Full SHS Design

11.1 Why End-User Education Matters

When a solar system is handed over to a customer, the installer's job is only half done. The system will be used daily by people who have little or no technical background. Their decisions — how long they leave the TV on, whether they add a new load, how they check the battery — will determine whether the system lasts 2 years or 10 years.

Common user behaviours that destroy systems prematurely:

• Connecting additional loads not included in the original design (overloading)
• Ignoring the Low Voltage Disconnect warning and trying to bypass it
• Using ordinary tap water instead of distilled water to top up batteries
• Allowing battery acid to remain on battery terminals without neutralising and cleaning
• Blocking ventilation around batteries (causing dangerous heat and gas build-up)
• Pointing the solar panel at a wall or under a tree shade
• Using the system as a charging hub for neighbours' phones (overloading)

11.2 How to Operate the System

During handover, walk through every aspect of normal operation with the user. Do not assume they know anything — explain everything clearly, demonstrate it, then ask them to repeat it back to you.

Starting the System

• The system is always "on" during the day — panels charge the battery automatically through the controller
• There is no on/off switch for charging — it is automatic
• Loads are controlled through the switches provided on the distribution board
• The charge controller LED indicators show system status — show the user what each colour means

Understanding the Charge Controller Indicator Lights

Normal Daily Pattern

Help users understand the natural rhythm of a solar system:

• Morning: Battery may be low after overnight use. Charging begins at sunrise. Avoid heavy loads early morning.
• Midday: Battery is near full. Full power available for all approved loads.
• Evening (6pm onwards): No more solar input. Battery discharges as loads run. Use only what is needed.
• Night: Minimise loads to preserve battery for morning. Switch off TV and lights when sleeping.
• After cloudy days: Battery may be lower than usual. Reduce loads until the next sunny day fully recharges the battery.

11.3 What Users Must Never Do

11.4 Daily and Monthly Maintenance Checks

Simple, consistent maintenance by the user extends system life dramatically. Teach users to perform these checks as part of their routine.

Daily Checks (Takes 2 Minutes)

• Glance at the charge controller indicator — is the solar charging light showing during the day?
• Are all lights and appliances working normally?
• Is there anything different from yesterday? (unusual smells, sounds, or indicator colours)

Weekly Checks

• Inspect the solar panel surface — wipe off dust and bird droppings with a soft damp cloth
• Check that nothing is casting a shadow on the panel (new tree growth, moving objects)
• Check all visible wiring for damage, rodent chewing, or loose connections

Monthly Checks (Flooded Batteries Only)

• Check battery electrolyte level — should be 10–15mm above the plates
• If low: top up with distilled water only — never above the maximum fill line
• Inspect battery terminals for corrosion (white or blue powder) — clean with a mixture of baking soda and water, then dry and apply petroleum jelly
• Check that all battery terminal connections are tight
• Verify that the battery is in a ventilated location and the area is free of clutter

Annual Checks (Installer to Perform)

• Measure battery specific gravity with a hydrometer (for flooded batteries) to assess battery health
• Check all cable connections for corrosion and retighten if necessary
• Test all fuses
• Inspect panel mounting — check that bolts are tight and the frame has not shifted
• Verify charge controller settings have not been changed
• Measure and record actual system performance vs. expected output

11.5 Warning Signs and How to Respond

Train users to recognise warning signs early. Early detection prevents a small issue from becoming a costly failure.

11.6 User Training Handover Checklist

Use this checklist during every system handover. Both the installer and the user (or household representative) should sign it. Keep one copy with the system documentation.

You have now completed the Diaspora Solar Solar PV Training Manual Volume 1. This manual has taken you from the fundamentals of DC electricity all the way through to complete system design and professional user handover. These are the essential competencies of a qualified solar PV technician.