7 solar installation mistakes to avoid before you buy

Going solar is usually a smart move, both financially and for the planet. But like any home project, a handful of classic mistakes can inflate the bill or leave you disappointed. Here are the 7 traps to avoid, and how to work around each one.

1. Not analysing your consumption before sizing

The number-one mistake: ordering a system without first looking at your meter data. Yet that is the foundation of everything.

What to do instead: pull your last 12 months of consumption (your energy supplier's online portal usually shows it). Work out when you use power, during the day or mostly in the evening. A solar system without a battery does little for you if the house is empty all day.

2. Oversizing without planning for storage

Producing far more than you consume during the day, with no battery, usually means exporting the surplus to the grid at a low feed-in rate, well below the retail price you avoid by self-consuming.

The simple rule: size your system to cover 70 to 90% of your daytime consumption, no more. Add a battery if you want to push self-consumption further.

3. Choosing on price alone

It is the natural temptation: pick the cheapest installer or the bargain panel. But over 25 years, that maths can turn against you.

A panel warranted for 10 years that loses 2% of its output per year can cost far more than a premium model warranted for 25 years degrading at 0.4% per year.

4. Ignoring orientation and shading

Even the best panel on the market will produce very little if your roof faces due north, or if a tree or chimney casts a shadow over it for part of the day.

Check two things:

• The orientation of the target roof plane (south facing is ideal, east or west is acceptable, north is best avoided)
• Cast shadows: simulate them around the equinoxes (March, September) and in winter when the sun sits low

Where partial shading is unavoidable, consider power optimisers (SolarEdge, Tigo) to limit the impact.

5. Forgetting available incentives

Support schemes exist and can be worth several thousand euros. Do not miss them.

Depending on your country, look into:

• Self-consumption or feed-in premiums paid by the grid operator or supplier
• Reduced VAT on qualifying residential installations
• Local and regional grants from your municipality or region
• Energy-saving certificate schemes, often negotiated through your installer

Check the rules before you sign a quote: some incentives carry strict eligibility conditions.

6. Comparing quotes that are not comparable

You receive three quotes and one is 30% cheaper than the rest. Be careful. Quotes do not always compare the same things.

What a complete quote should include:

• The exact make and model of the panels (with datasheets)
• The make and model of the inverter
• The manufacturer warranties and the installer's workmanship warranty
• The grid connection and administrative steps
• Production monitoring

Get at least three quotes from certified installers.

7. Underestimating the inverter

Panels grab the headlines in comparisons, but the inverter is the heart of the system. It converts the panels' DC into usable AC and manages the whole production.

A poor inverter can shave 5 to 10% off your output and fail long before the panels do. Stick to proven brands: Enphase, SMA, Fronius, SolarEdge.

Going further

Before signing anything, take time to compare the panels you are interested in on our comparison tool: efficiency, warranties, temperature coefficient, it is all there.

And if you want a structured selection method, our complete buying guide walks you through it step by step.