Solar panels and inverters: what to know

Most quotes list a panel model and an inverter type. You don't need to be an engineer to compare them, but knowing a few basics will help you spot a sensible design and ask the right questions.

Panel types

Almost all residential panels sold today are monocrystalline silicon. Within that, you will see a few cell technologies:

• Mono PERC has been the mainstream technology for years. It is proven and widely available.
• TOPCon is a newer design that is becoming common. It generally offers slightly higher efficiency and somewhat better performance over time.
• Other designs, such as heterojunction, also appear on some quotes, often at a higher price.

For most homes, the differences between reputable panels are modest. Installation quality, shading and roof layout usually matter more than the exact cell technology.

Panel wattage

Typical residential panels today are roughly 400 to 480 W each. Higher wattage means more power from the same panel size, which helps on smaller roofs.

A 7 kW system might use around 16 panels at 440 W each. Check that the quote's total system size matches the panel count multiplied by the panel wattage.

Warranties

Panels usually come with two separate warranties.

Also ask about the installer's workmanship warranty, which covers roof penetrations, wiring and installation. A manufacturer warranty is only as useful as the company standing behind it, so established brands with a Canadian presence are a safer choice.

Degradation

All panels slowly lose output over time. Quality modern panels typically degrade around 0.4 to 0.5% per year after the first year.

At 0.5% per year, a panel would still produce roughly 88% of its original output after 25 years. A good savings estimate includes degradation, and SolarMyBill does.

Inverter types

The inverter converts DC power from the panels into AC power for your home. There are three common approaches.

String inverters

Panels are wired together in series, called a string, and connected to one central inverter, usually mounted near your electrical panel. This is the simplest and often the lowest-cost option.

The downside is that the string is only as strong as its weakest panel. Shade on one panel can pull down output across the string. Monitoring is usually at the system level, not panel by panel.

String inverters typically need replacing after roughly 10 to 15 years, so budget for one replacement over the life of the system.

Microinverters

A small inverter sits under each panel. Every panel works independently, so shade or snow on one panel does not drag down the others. You also get panel-level monitoring.

Microinverters cost more upfront, and there are more components on the roof. They usually come with long warranties, often 20 years or more.

Power optimizers

Optimizers are small devices under each panel that condition the DC power before sending it to a central inverter. They reduce shading losses and offer panel-level monitoring, while keeping a central inverter. The central inverter still has a shorter life than the panels.

Which setup suits your roof

None of these is always best. A shaded roof often benefits from panel-level electronics, while an open south-facing roof may not need them.

Questions to ask about equipment

• What is the panel wattage, and does the total system size add up?
• What are the product and performance warranty terms, in writing?
• What type of inverter is proposed, and why for this roof?
• How long is the inverter warranty, and what is the replacement plan?
• Will the system work with a battery if I add one later?

Next step

See what size of system fits your roof: check your roof.