Chapter 3

Introduction

Imagine placing the same solar panel in two different positions on the same roof.

One receives direct sunlight for most of the day. The other faces a less favourable direction, sits beneath the shadow of a chimney and receives only a few hours of strong sunlight.

Although the panels are identical, they will not produce the same amount of electricity.

Where a solar panel is installed has a major influence on how well it performs. Its direction, angle and exposure to sunlight determine how much solar energy reaches its surface throughout the day and across the seasons. The available roof space, condition of the building and strength of the mounting structure also determine whether the installation is practical and safe.

Choosing the best location is therefore about much more than finding an empty section of roof.

A successful design must identify where the panels can capture the most useful sunlight while remaining secure, accessible and reliable for decades.

Which Direction Should the Panels Face?

The direction a solar panel faces is known as its orientation, or sometimes its azimuth.

Orientation affects when the panel receives the strongest sunlight and how much energy it generates throughout the year.

In the Southern Hemisphere, the Sun spends most of the day across the northern part of the sky. For this reason, north-facing panels generally receive the greatest amount of sunlight over the course of a year and often produce the highest annual energy output.

In the Northern Hemisphere, the opposite is true. South-facing panels usually receive the most annual sunlight.

However, the direction that produces the greatest total energy is not always the direction that provides the greatest value to the customer.

East-facing panels receive more sunlight during the morning, while west-facing panels continue generating later into the afternoon. A household that uses large amounts of electricity after returning from work may therefore benefit from west-facing panels, even if their total annual output is slightly lower than a north-facing system.

Some installations deliberately divide panels across east- and west-facing roof sections. This creates a broader generation profile, with electricity production beginning earlier in the morning and continuing later into the afternoon.

Good solar design does not simply ask: Which direction produces the most electricity? It also asks: When will that electricity be most useful?

Finding the Right Tilt

The angle between a solar panel and the horizontal ground is known as its tilt angle. Tilt matters because solar panels receive the greatest amount of energy when sunlight strikes their surface as directly as possible.

A simple analogy is holding a sheet of paper beneath a torch. When the paper faces the beam directly, the light is concentrated over a relatively small area. As the paper is tilted away, the same light spreads across a larger surface and becomes less intense.

Solar panels behave in much the same way.

The ideal tilt angle varies with location and with the objective of the system. For maximum annual energy production, the preferred angle is often broadly related to the site's latitude. Steeper angles can favour winter production, when the Sun remains lower in the sky, while shallower angles may favour summer production.

In practice, most residential solar panels are mounted parallel to the existing roof. This is usually cheaper, simpler and more visually appealing than constructing a separate frame to achieve the theoretical optimum angle. The small amount of energy gained by adjusting the tilt may not justify the additional materials, wind loading or installation cost.

As with orientation, the best tilt is not always the mathematically perfect one. It is the angle that provides the best overall balance between energy production and practical design.

Making the Most of the Available Space

The total size of a roof is not the same as its usable solar area. A large roof may still provide only a limited amount of suitable installation space.

Chimneys, skylights, roof vents, antennas and air-conditioning equipment can all interrupt the panel layout. Designers may also need to leave clear space around roof edges, ridgelines and access routes to meet safety requirements and allow future maintenance.

The dimensions of the panels themselves also matter. Modern solar modules are large rectangular objects that cannot always be arranged neatly around complex roof features. A roof may appear capable of holding twelve panels, only for detailed measurements to show that ten panels fit safely without overhanging edges or blocking access.

This makes panel layout similar to solving a large jigsaw puzzle.

Designers use roof measurements, aerial imagery and specialist software to test different arrangements before choosing the final layout. The aim is not simply to fit the greatest possible number of panels, but to use the available space effectively without compromising safety, appearance or maintainability.

On buildings with several roof sections, panels may be divided across different orientations. When this happens, the electrical design must later account for the different conditions experienced by each group.

Identifying Potential Shading

Even a well-oriented roof can perform poorly if the panels spend part of the day in shadow.

Trees, chimneys, antennas, neighbouring buildings and surrounding terrain can all block sunlight from reaching the panels. These shadows also move as the Sun travels across the sky and changes position throughout the year. A roof that appears completely unshaded at midday in summer may experience significant shading during winter mornings or late afternoons.

For this reason, designers assess more than the conditions visible during a single site visit. They consider the path of the Sun throughout the day and across the seasons to predict where shadows are likely to fall.

Sometimes the solution is simple. Panels can be moved away from a chimney, placed on a different roof section or arranged to avoid the shadow of a nearby tree. In other cases, shading may influence the type of inverter technology selected or the way panels are divided into electrical groups.

At this stage, the important principle is straightforward: A good location must provide reliable access to sunlight, not merely enough physical space for the panels.

In the next chapter, we will explore why shading can have such a significant electrical effect and how designers reduce its impact.

Assessing the Roof

Before panels can be installed, the roof itself must be suitable.

Solar modules are expected to remain in place for more than 25 years. Installing them on a roof that is damaged, heavily corroded or approaching the end of its life can create expensive problems later.

If the roof requires replacement only a few years after the solar system is installed, the panels may need to be removed and reinstalled, increasing cost and creating unnecessary risk. Designers therefore assess the roof covering as well as the underlying structure.

They consider:

• The age and condition of the roof

• The type of roofing material

• The strength and spacing of the supporting structure

• Existing damage, leaks or corrosion

• Whether the roof can safely carry the additional load

• Whether suitable fixing points are available

Solar panels are relatively lightweight when their load is spread across a roof, but the complete system also includes mounting rails, brackets, cables and other equipment.

The mounting structure must support this weight while also resisting forces created by wind.

During severe weather, wind flowing around a building can create powerful uplift forces that attempt to pull panels away from the roof. These forces are often greatest near roof edges and corners.

The mounting system must therefore be designed for the building, roof type and local wind conditions rather than treated as a universal set of brackets. A reliable solar system begins with a sound structure beneath it.

Choosing the Mounting Location

Rooftops are the most familiar place to install solar panels, but they are not the only option. Where roof space is unsuitable or insufficient, panels may be installed on a ground-mounted structure, carport, canopy or purpose-built frame.

Each location presents different advantages and constraints.

Rooftop systems make use of otherwise unused space and usually require no additional land. The roof can also position the panels above many nearby sources of shade. However, rooftop systems are limited by the shape, direction and condition of the building. Installation and maintenance may also be more difficult because technicians must work at height.

Ground-mounted arrays allow greater freedom over orientation, tilt and panel spacing. They are often easier to access for inspection, cleaning and repair. However, they require suitable land and may need additional foundations, fencing or planning approval. Vegetation growth and shading from nearby objects must also be managed.

Solar carports and canopies combine electricity generation with another practical function. They can provide shade and weather protection for vehicles while creating space for electric vehicle charging. Their structures must be designed specifically to support the panels and withstand environmental loads, making them more complex and expensive than placing panels on an existing roof.

There is no single mounting location that is best for every project. The right choice depends on the available space, cost, customer priorities and the physical conditions of the site.

Designing for Access and the Future

A solar system must remain accessible after installation. Over its lifetime, the panels, cables and mounting equipment may need to be inspected, cleaned, tested or repaired. Technicians must be able to reach important components without unnecessarily dismantling the entire array. Designers therefore consider:

• Safe access onto and across the roof

• Space around electrical equipment

• Routes for DC and AC cables

• Access to junction boxes and connectors

• Drainage and the movement of rainwater

• Whether individual panels can be removed or replaced

• Space for possible future expansion

These details may appear minor compared with panel efficiency or inverter size, but they can have a major effect on the long-term cost and reliability of the system. A layout that maximises the number of panels while leaving no safe access may perform well on paper but create serious difficulties during installation and maintenance.

Good solar design does not end when the panels begin generating electricity. It considers the entire lifetime of the system.

Finding the Best Overall Position

The best location for a solar panel is not determined by one factor alone. A perfectly oriented roof may be heavily shaded. An unshaded roof may be too small. A large roof may be structurally unsuitable. A ground-mounted system may offer excellent performance but require land the customer cannot spare. The designer must therefore bring orientation, tilt, sunlight, space, structure, access and cost together before selecting the final position.

This is another example of optimisation rather than perfection. The goal is not necessarily to find the roof section with the highest theoretical output. It is to find the location that delivers the best combination of:

• Energy production

• Structural safety

• Installation practicality

• Long-term reliability

• Accessibility

• Cost

Choosing where the panels go is one of the most important decisions in the entire design process. Once installed, that location will influence the system's performance every day for decades.

Looking Ahead

We now understand how orientation, tilt, roof space and mounting location influence the performance of a solar system.

But one issue deserves a closer look.

A nearby tree may shade only a small corner of one panel. A chimney may cast a narrow shadow for only an hour each afternoon.

Surely such small shadows can only cause small losses. Unfortunately, the electrical behaviour of solar panels makes shading far more significant than it first appears.

In the next chapter, we will explore how shade affects series-connected solar cells, why shaded cells can become dangerously hot and how bypass diodes, microinverters and power optimisers help reduce the damage.