Chapter 5

Introduction

By this stage, we've developed a thorough understanding of the project. We know how much sunlight reaches the site throughout the year. We've found the best location for the solar panels, assessed the roof and identified any potential sources of shading.

The next question seems simple. What equipment should we install?

Walk into any solar supplier and you'll find hundreds of different solar panels, inverters and batteries. They all promise high efficiency, excellent reliability and industry-leading warranties. At the same time, the system must be large enough to meet the customer's energy needs without becoming unnecessarily expensive.

Choosing the equipment therefore isn't simply about buying the highest-rated products. It's about selecting components that work together to create the right system for a particular customer, building and budget. This is where solar engineering becomes an exercise in balancing performance, practicality and long-term value.

There Is No Perfect Solar System

One of the first lessons every solar designer learns is that there is no universally perfect solar system. Every project involves compromise.

A larger system may generate more electricity but cost significantly more to install. A smaller system may have a lower upfront cost but leave the customer purchasing more electricity from the grid.

High-efficiency panels can maximise energy production where roof space is limited, while lower-cost panels may provide better value when space is plentiful. Adding battery storage increases energy independence but also represents one of the largest investments within the entire installation. Even the choice between premium and budget equipment depends entirely on the customer's priorities.

Good solar design is therefore an exercise in optimisation rather than perfection. The goal isn't to design the biggest system or buy the most expensive equipment.

It's to deliver the best overall solution.

Choosing the Solar Panels

At first glance, most solar panels appear almost identical. Beneath the glass, however, they can differ in several important ways.

One of the most significant differences is efficiency. Higher-efficiency panels convert a greater proportion of the available sunlight into electricity, allowing more power to be generated from the same roof area. This becomes particularly valuable when roof space is limited.

Panels also differ in their temperature performance. As we will explore later, solar cells become less efficient as their temperature increases. Manufacturers specify a temperature coefficient, which describes how rapidly a panel's power output falls as the cells become hotter than the standard testing conditions.

In hot climates, selecting a panel with a lower temperature coefficient can noticeably improve annual energy production.

Designers also compare factors such as long-term degradation, warranty length, mechanical strength, appearance and performance under lower light conditions.

No single panel is best for every installation. The right choice depends on the available roof space, climate, budget and the customer's priorities.

Choosing the Inverter

If the solar panels are the heart of the system, the inverter is its brain.

As we learned in Part 4, the inverter converts the direct current (DC) produced by the solar panels into the alternating current (AC) used throughout homes and the electricity grid.

Choosing the correct inverter involves much more than matching the system's power rating.

The inverter must operate efficiently across the expected range of voltages produced by the solar array. It should also provide enough capacity to accommodate the expected power output without unnecessarily increasing the cost of the installation.

Designers also consider whether the customer may wish to install battery storage in the future.

Selecting a hybrid inverter during the initial installation can make future upgrades considerably simpler and less expensive.

The inverter therefore becomes the central component that connects the solar array, battery, home and electricity grid into one coordinated system.

Should the System Include a Battery?

Not every solar installation requires battery storage. Many homeowners are happy to use solar electricity during the day while exporting any surplus energy to the electricity grid. Others want to store excess electricity for use after sunset or maintain power during grid outages.

Whether a battery is worthwhile depends largely on how the customer uses electricity. A household with high evening consumption may benefit significantly from battery storage, whereas a household that consumes most of its electricity during daylight hours may gain relatively little additional value.

When selecting a battery, designers consider its usable capacity, charging and discharging power, efficiency, expected lifespan and compatibility with the chosen inverter.

As with every other component, the largest battery is not necessarily the best choice. The best battery is the one that complements the customer's energy usage and long-term plans.

How Large Should the System Be?

Selecting the equipment and deciding the system size are really the same engineering problem. A designer must balance several competing factors. How much electricity does the household consume? How much suitable roof space is available? What is the customer's budget? Will electricity demand increase in the future through an electric vehicle or heat pump? Would battery storage change the ideal system size? These questions all influence one another.

Installing too few panels may leave significant savings untapped. Installing too many may produce electricity that cannot be used effectively, particularly where export payments are relatively low.

The objective is not to maximise installed capacity. It is to maximise the long-term value delivered by the system.

Designing for the Future

A solar installation is expected to operate for more than twenty-five years. During that time, the customer's energy requirements may change considerably. An electric vehicle may replace the family car. A heat pump could replace a gas boiler. Children may move out, or the household may expand. A battery may be added years after the initial installation.

For this reason, good designers think beyond today's requirements.

Selecting equipment that allows additional panels, battery storage or electric vehicle charging to be added later can significantly reduce future upgrade costs.

Future flexibility is often one of the most valuable features a solar system can provide. Good engineering solves today's problems without limiting tomorrow's opportunities.

Choosing the Right Combination

By now, we've seen that choosing a solar system is about far more than comparing product brochures. The solar panels, inverter, battery and system size must all complement one another.

Each decision influences the next. A limited roof may justify higher-efficiency panels. A battery may change the ideal inverter. Future expansion may influence the equipment selected today.

Successful solar design is therefore about creating a balanced system rather than assembling a collection of individual components.

The best solar system is not the one with the highest specifications. It is the one that best matches the customer's needs while delivering reliable performance for decades.

Looking Ahead

We've now selected the equipment and decided how large the system should be.

But simply choosing the components isn't enough. How many panels should be connected together? How many electrical strings are required? How do the panel voltages determine the inverter selection? And how does electricity actually flow from the roof into the home? These are questions of electrical design rather than equipment selection.

In the next chapter, we'll discover how engineers connect every component together into one safe, efficient solar power system.