How to choose a solar panel in 2026: the complete guide

Choosing a solar panel can quickly turn into a headache. Between peak power in watt-peak, efficiency, cell types, warranties and quality labels, it is easy to get lost. This guide gets straight to the point: the criteria that genuinely matter, in the order you should look at them.

1. Start with your roof, not the panels

Before comparing datasheets, ask yourself two fundamental questions:

• How much exposed area do you have? A square metre of south-facing roof produces roughly 150 to 200 kWh per year. Count your usable square metres.
• How much consumption do you want to cover? A four-person household uses between 4,000 and 8,000 kWh per year.

These two figures define the total power to install (in kWp) before you even look at panels.

2. Peak power (Wp): how much each panel produces

Peak power is the output under standardised lab conditions (STC: 1,000 W/m², 25 °C, AM1.5 spectrum). In 2026, good residential models sit between 420 and 500 Wp.

What it means for you:

• The higher the power, the fewer panels you need to hit your target
• A 440 Wp panel takes about 1.7 m², so check it fits your roof dimensions

3. Efficiency (%): how well it uses the area

Efficiency measures the share of sunlight converted into power. 22% efficiency means 22 watts of electricity for every 100 watts of sunlight hitting one square metre.

Reference figures in 2026:

• Monocrystalline PERC: 19.5 to 21.5%
• TOPCon: 21.5 to 23%
• HJT (heterojunction): 22 to 24%

4. Cell type: PERC, TOPCon or HJT?

This is the most asked question. Here is a simple summary:

Monocrystalline PERC, the proven benchmark

• Good value, durability proven over 10 to 15 years
• Efficiency 19 to 21.5%, suited to large roofs
• Favour it if budget is tight or roof area is generous

TOPCon, the new residential standard

• Higher efficiency (21.5 to 23%), better heat tolerance
• Lower degradation over time
• The 5 to 15% premium is justified for limited roofs or hot regions

HJT (heterojunction), the high end

• Record efficiency (22 to 24%), excellent temperature coefficient
• Higher price, suited to premium projects

5. Warranties: what protects your investment

A solar panel is an investment over 25 to 30 years, so warranties are essential.

Two warranties to tell apart:

Product warranty (manufacturing defects)

• Acceptable minimum: 12 years
• Good level: 15 years
• Excellent: 25 years (Maxeon, REC, LONGi Hi-MO X10 and similar)

Performance warranty (output over time)

• The panel must retain a percentage of its original output after X years
• Check the linear curve or step structure: a good panel keeps 87 to 90% after 25 years
• Be wary of "stepped" warranties with large early drops

6. Temperature coefficient: crucial in hot regions

All solar panels lose efficiency as they heat up, it is unavoidable. The temperature coefficient measures this loss in %/°C above 25 °C.

• Standard PERC: around -0.34 to -0.36%/°C
• Good TOPCon: -0.29 to -0.32%/°C
• HJT: -0.24 to -0.27%/°C (the best)

In summer in the south of Europe, a panel can reach 65 to 70 °C. The gap between a -0.27% and a -0.35% coefficient can amount to several hundred kWh over a season.

7. Brand and certifications: judging reliability

Not all brands are equal. Here is how to assess them:

Minimum certifications to require:

• IEC 61215 (qualification test)
• IEC 61730 (safety)
• MCS or TÜV (depending on the country)

Advanced quality signals:

• RETC reliability scorecards: check the brand is not on a black list
• Bloomberg Tier 1 (financially solid manufacturers)

Recommended brands in 2026: LONGi, JinkoSolar, Trina Solar, Qcells, Canadian Solar, REC Group, Maxeon, Aiko, each with its own strengths.

Recap: the 5 criteria in order

1. Power (Wp), matched to your available area
2. Efficiency (%), crucial if space is limited
3. Temperature coefficient, important in hot regions
4. Warranties, product 15 years or more, linear performance over 25 years
5. Total price, cost per kWh produced, not just the purchase price

Ready to compare?

With these criteria in mind, the best next step is to compare real models against your profile. Our solar panel comparison tool lets you filter by technology, power, budget and warranty.

FAQ

How many panels do you need for a house? Between 6 and 20 panels depending on the size of your home and your self-consumption goals. A 3 kWp system (6 to 8 panels) covers 30 to 50% of an average home's needs.

More cheap panels or fewer premium ones? It depends on your area. If you can fit 12, PERC is often more cost effective. If you only have room for 8, TOPCon or HJT maximise your output.

Are bifacial panels worth it on a residential roof? Rarely on a tilted roof, since the rear sees little reflected light. They mainly pay off ground mounted on a light surface (white gravel, concrete) or on a pergola with reflectors.