You only compare price and power? What to ask your installer before buying solar.

Many homeowners begin their solar journey by doing what seems logical: comparing offers by price and power output. Yet those two numbers only tell part of the story. What truly defines the long-term value of your solar system are the factors that often stay hidden in the fine print: longevity, reliability, and sustained performance over decades, long-term energy yield, and, of course, the looks.

A system that costs slightly less upfront but degrades faster or uses less durable components can end up being far more expensive in the long run – and additionally low-yielding. Likewise, differences in shading analysis, low-light performance, climate resistance or warranty coverage can add or subtract thousands of kilowatt-hours over time.

Before signing any contract, it’s worth asking your installer the right. These insights not only help you compare offers fairly, they protect your investment and ensure your solar system performs as promised for years to come.

Knowing what to ask your installer won’t just help you find the best module, it can save you years of frustration.

1. Does the portfolio of the installer include high-efficiency modules with back contact technology?

Not all solar panels are the same. High-efficiency modules based on back contact (BC) technology represent the latest generation of solar innovation. By moving all electrical contacts to the back of the cell, these panels expose more surface area to sunlight, reducing losses and increasing power output per square meter.

If your installer offers back contact options, it’s a good sign they stay up to date with the most advanced and durable products on the market. For homes with limited roof space, BC modules deliver more energy from the same area and often perform better in low light. Ask your installer whether they are experienced in working with such systems.

2. Can my roof carry the load reliably?

That’s one of the most common and important questions homeowners ask and for good reason. Every roof is different, and knowing its load-bearing capacity is essential for a safe and durable solar installation.

The good news is that most residential roofs in Europe can easily handle the additional weight of solar panels. A typical module weighs between 18 and 25 kilograms and covers about two square meters, which translates to roughly 10–12 kg/m². This is much less than what most roofs are designed to carry. In fact, a layer of snow in winter can add far more weight.

Still, older roofs or those in poor condition may need closer inspection. The actual capacity depends on rafter spacing, roof age, and structural materials. A professional installer should assess these factors and, if needed, involve a structural engineer before installation.

Asking this question early helps your installer choose the best mounting method and ensures your roof will safely carry your solar system for decades.

3. Can your installer assess and minimize shading?

Shading is one of the most common causes of performance loss in rooftop systems. Even small obstructions, like a chimney or nearby tree, can noticeably reduce energy yield if not considered in planning. A professional installer should therefore assess how shadows move across your roof throughout the year. Using digital tools or on-site measurements, they can model the shading impact and suggest the best layout, the best solar technology dealing with shades, string configuration, or microinverter solution to minimize losses.

4. Are the solar panels compact with a high watt per square meter (W/m²)?

When comparing panels, most people focus on total power, for example, 400 W or 500 W. But what really matters for homes is how efficiently a module uses your available roof space. This is measured in power density, expressed in watts per square meter (W/m²).

A compact, high-efficiency panel delivers more power from the same area, which is especially important for smaller or complex roofs. For example, a 500 W module that measures around 2 m² achieves a density of roughly 250 W/m², meaning it converts more sunlight into usable energy from each square meter of roof.

Larger modules, which are also used in commercial projects, may also have 500 W or 600 and even more W, but they achieve it by being physically bigger (often over 2.2 meters long). Such panels are heavier, harder to handle, and not ideal for residential roofs. They also experience higher mechanical stress, which makes them more prone to microcracks or damage from wind, snow, or thermal expansion over time.

That’s why it’s worth asking your installer if the panels they recommend are compact, residential-grade modules with a high W/m² ratio. Back contact technologies, like LONGi’s EcoLife Series, achieve excellent power density through higher efficiency rather than larger size - delivering around 250 W per square meter, which is considered a very strong ratio for residential systems. It means you get more energy and a cleaner look without overloading the roof.

5. What performance and yield can you realistically expect?

Ask for a clear estimate of the system’s expected annual yield (kWh/year) and the assumptions behind it: sunlight hours, roof orientation, system size, solar technology and related performance in low-light conditions. Comparing this number with publicly available tools such as PVGIS helps you verify if the estimate is realistic.

If you’re considering different technologies, ask how lifetime output compares between them. Back contact modules, for instance, maintain higher performance over time and perform better in low light, increasing your overall energy yield.

6. How do the panels perform in heavy or cloudy weather?

A well-designed solar system should deliver reliable performance in all kinds of weather, from strong winds and snow to heat and hail. Quality modules are tested according to international standards (IEC) for mechanical load, temperature resistance, and hail impact to ensure long-term safety and durability.

Selected modules from the EcoLife Series are certified to withstand snow loads of up to 5,400 Pa, equivalent to the pressure of around four meters of fresh snow or the weight of an adult standing on each panel without causing damage. They also endure wind pressures of 2,400–3,600 Pa, comparable to storm- or hurricane-level gusts found along European coastlines. This means they stay safely in place even during severe winter storms or heavy snowfalls.

The frame design, glass thickness, and cell structure all influence how well a panel handles mechanical stress.

High-quality back contact modules, for example, maintain performance in both icy winters and hot summers, while also performing better in low light and high temperature conditions than conventional panels. The result is a more stable energy output throughout the year - whatever the weather.

7. How does the warranty work in practice?

Most premium solar panels today come with long performance warranties of 25–30 years. But it’s equally important to check who handles the claim process. A trustworthy installer will act as your first point of contact and coordinate directly with the manufacturer if needed. Also check the installation warranty on the installation itself. This is a guarantee provided by the installer, not by the manufacturer. It covers the quality of the installation work itself - how the solar panels, cables, inverters, and mounting systems were fitted to your home.

If something goes wrong later because of how the system was installed (for example, a leaking roof penetration, loose wiring, or a poorly mounted bracket), the installation warranty ensures the installer will fix it at no cost to you.

8. What is the expected payback period and what assumptions were made?

The payback time tells you how long it takes for your solar investment to “pay for itself” through electricity savings. In other words, it’s the number of years until the money you’ve saved on energy bills equals the cost of the system.

For example, if your system costs €9,000 and saves around €1,200 per year on electricity, your payback time is roughly 7.5 years. After that, the electricity you generate is effectively free.

However, this figure depends on several assumptions such as local electricity prices, how much of your solar energy you use directly (self-consumption), your system’s performance, and any future changes in tariffs or incentives. That’s why it’s worth asking your installer to show different payback scenarios rather than just a single optimistic one. For example, how the calculation changes if energy prices fall or your electricity use increases due to an EV or heat pump.

A good installer should be transparent about these variables, not just present a single optimistic number.

9. What happens after installation?

A solar system runs for decades. And ideally, so should your relationship with the installer. Once the panels are up and running, your installer should help you set up the monitoring tool so you can track production, consumption, and savings. This allows you to verify that your system performs as expected and quickly spot irregularities.

Ask if they provide a handover report with all relevant information, such as the system layout, inverter settings, warranty certificates, and maintenance recommendations.

Technically, PV systems require very little routine maintenance. The panels are static, and most inverters automatically report issues. But periodic checks every few years, or whenever you notice a drop in production, are smart. They can catch small issues early, like loose connectors, aging cables, or shading changes from growing trees, before they cause significant yield losses.

Some installers also offer optional service or maintenance packages, including annual inspections or remote performance checks. Smaller installers often provide on-demand service, meaning they step in whenever maintenance or troubleshooting is needed.

Reliable after-sales support not only gives peace of mind but also keeps your solar system performing at its best for decades, protecting the long-term value of your investment.

‍