Solar panels: what you are actually buying

By the IsaKiel team · Lagos · Updated 16 August 2026 · 8 min read

Panels are the part of a solar system everyone pictures, and often the part people worry about most. In practice, they are the most straightforward component. They have no moving parts, last a long time and are priced fairly consistently across the market.

The real issues are very specific and come down to three questions: what the wattage on the label actually represents, whether the panel is truly what it claims to be and what happens after it is installed on your roof.

New to this? Start with So you want solar for an explanation of how the whole system fits together. Panels are one part of four.

What the watt rating means

A 600W panel produces 600 watts under test conditions: bright, direct light at a set temperature. That is a laboratory figure, not a promise about Tuesday afternoon in Ikeja.

In practice, the output will be lower. That is expected. Heat will be the main reason for this drop off. Panels lose efficiency as they get hotter, and a rooftop in Lagos gets very hot. Dust, cloud, the angle of installation and resistance in the cable reduce the output further.

This is why sizing is not simply "daily usage divided by panel wattage". We size around 4.5 peak sun hours for Lagos. This is industry jargon for treating the day's total sunlight as if it arrived during 4.5 hours of perfect conditions.

A 6kW array is therefore planned around roughly 27kWh on a good day, not the 72kWh you would get by multiplying 6kW by 12 hours of daylight.

If an installer's projection assumes anything close to 8 to 10 productive hours, ask how they got to this figure.

Mono, poly and bifacial

Monocrystalline is what you should expect to be offered. It is also what nearly everything in the market now is. It is more efficient per square metre, which matters when roof space is limited.

Polycrystalline is older technology. It is slightly cheaper per watt and slightly less efficient. It is still around, mostly in smaller or older stock.

Bifacial panels generate electricity from the back as well as the front. They can pick up light reflected from the surface beneath them. They are increasingly common in Nigeria, often at prices close to standard mono panels.

If a bifacial panel costs about the same as a standard one, it may be worth considering. Do not pay a premium for a benefit most installations will not get.

How many panels

The calculation is simple. An array is specified in kilowatts. A panel is rated in watts. Divide the array size by the panel wattage.

• A 5kW array using 600W panels needs about 8 panels.
• A 10kW array using 600W panels needs about 17 panels.

Two practical points are easy to miss.

Roof space. A modern panel is roughly 2.3 metres by 1.1 metres. Eight panels therefore need about 20 square metres of unshaded roof, before allowing space to walk and mount them. Many roofs have less usable area than they appear to once you subtract vents, tanks and sections that fall into shade.

Matching. Panels in the same string should be the same model and wattage. Mixing a 550W panel with a 600W panel in one string can pull the whole string towards the weaker panel. This is why a quote should not mix wattages without explaining why.

Orientation, tilt and shade

Nigeria sits close to the equator, so the sun passes much closer to overhead than it does in Europe. Orientation matters less here than is often suggested. A roof with a broadly suitable orientation and a modest tilt can perform well.

Tilt matters for another reason. Rain and dust need somewhere to go. A panel laid completely flat collects standing water and dust that may not wash off easily. That layer affects output. A small amount of tilt helps rain move across the surface and carry some of the dust with it.

Shade is different. It can reduce output far more than its size suggests. Panels are wired in strings, so a shaded panel can drag down the performance of the whole string rather than simply losing its own share.

A dish, aerial, water tank or neighbour's tree can therefore cost more output than you might expect. Before installation, look at the roof in the morning and again in the late afternoon, not just at noon.

Brands, tiers and fakes

A panel can be difficult to assess by appearance alone. A laminated sheet of glass can look much like another laminated sheet of glass.

Names that come up repeatedly in the market include Jinko, JA Solar, Trina and Longi. These are the brands worth asking about.

Around ₦180 to ₦210 per watt was the range seen across the Alaba market in July 2026. That puts a 600W panel at roughly ₦110,000 to ₦125,000.

Here is what to check:

• Get the brand, model and wattage in writing on the quote. "Solar panels" is not a specification.
• On delivery, check the serial numbers on the panels themselves. Make sure they match the brand and model quoted. The serial numbers come with the product and are used for warranty registration.
• Look at the glass and frame. Scratches, scuffed frames and weather-marked backsheets can indicate used stock.
• Check the junction box on the back. It should be sealed and undamaged.
• Be careful with a price well below the market. It may be genuine competition. It may also mean second-hand stock or a lower wattage than claimed.

Warranties, and what they really cover

Two different things are often called "the warranty".

A performance warranty, often covering up to 25 years, promises that the panel will still produce a stated percentage of its rating after a given number of years.

A product warranty is usually much shorter. It covers manufacturing defects in the panel itself.

Both come from the manufacturer rather than the installer. They are only useful if the panels are genuine and the warranty terms can be used.

Ask what the manufacturer covers, for how long and whether the installer will register the panels for you.

Mounting, the part that can leak

Panels can last a long time, but a poor mounting job can create problems much sooner.

Nigerian homes commonly have long-span aluminium, stone-coated steel or concrete roofs. Each requires a mounting method suited to the roof.

When a solar installation causes trouble, the problem is often not the panel itself. A roof penetration that was not sealed properly may only become obvious during the next heavy rain.

Ask any installer:

• What are you fixing into, and how will you seal it?
• Is the mounting structure aluminium or treated steel? Untreated steel rusts.
• How will you route the DC cable into the building, and how will you seal that entry?
• Can the panels be reached for cleaning without walking on them?

Living with them

Panels ask for very little from you, which is why they are easy to neglect.

• Rinse them. Quarterly is enough for most of the year. Clean them more often when dust builds up quickly. Dust is a common reason a system produces less than expected.
• Clean them early in the morning or in the evening. Do not put cold water on hot glass in the middle of the day.
• Do not use abrasives or a pressure washer. Do not climb onto a wet roof.
• Watch for new shade. A dish, aerial or growing tree can quietly reduce output that was there the year before.

Related reading

• So you want solar, the overview, if you have not read it
• How much does solar cost in Lagos in 2026?, current prices for panels, batteries, inverters and installation