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Panels

Introduction

A solar pv panel (or module) is designed to convert sunlight into electricity. They all share similar properties but are available in different sizes, colours, with different types of cells and produced by different manufacturers.  Selecting a module for a residential or commercial solar system requires an understanding of the different characteristics of each type of panel and the application.  Power classes can increase quickly because of advancements in technology and manufacturing processes. Therefore, when specifying a module, it is wise to select any one of the Silicon Module Super League (SMSL) manufacturers, and use a general power-class rather than a particular output.

Remember, using higher output/better efficiency modules will reduce the number needed to hit your generation goal, and will result in less mounting-kit, install time, and carriage costs.
On this page we explore some of the options and aspects to consider when selecting a solar panel.

Sizes

Solar panels are manufactured in a range of sizes but the industry standard in the UK has been 60 and 72 cell modules. Modules with more cells are becoming more popular as manufacturers release viable options, but larger modules are not better because they are bigger, they will generate the same energy on the same area of roof as smaller panels. i.e. the performance of 5 X 72 cell panels will be identical to 6 X 60 cell ones with the same energy and the same roof area. The choice is about which size of panel will best fit the available roof space.

Colour

Historically, the solar cells do not completely fill the area of the solar panel, there is a small gap around the end of each solar cell. However, with tech advances some manufacturers are maximising surface area by over-lapping cells, or ‘shingling’ their cells. Every panel has a back sheet on which the solar cells are mounted, and this back sheet tends to be white or black. A black back sheet normally looks better as it is closer to the colour of the cells but is slightly more expensive and will cause the solar panel to get warmer, slightly reducing efficiency.

The frame of most solar panels are silver or black. This does not impact on the performance of the solar panel but a black frame tends to be more expensive and preferred for domestic installs whilst the cheaper silver frame is the preferred option for commercial on roof arrays where there is little preference on aesthetics.

Cell Types

A solar panel is made using solar cells. Each cell is about 6 inches, 125mm, square. The cells are made using one of two different materials, monocrystalline or polycrystalline. Polycrystalline is slightly cheaper but is less efficient so a solar panel made with monocrystalline cells will generate more energy than one made using polycrystalline cells. Monocrystalline cells are also darker and so best used when you want a black back sheet for the best-looking solar panels.

Monocrystalline
Monocrystalline or ‘Mono’ cells are manufactured by cutting single sheets from a silicon bar, hence the name. These single crystal cells allow for greater movement of electrons resulting in slightly higher efficiency and the colouration of such cells tends to be black.

Polycrystalline
The Polycyrstalline or ‘Poly’ manufacturing process involves melting fragments of silicon into wafer sheets. This design does not allow the electrons to flow as freely as when on a single sheet due to multiple crystals being present within the cells. The overall difference in efficiency is not significant, usually around 2-3% on most modules of the same rating. Polycrystalline tends to have a more blue colour tinge, and appears less uniform.

PERC
PERC or ‘Passive Emitter and Rear Cell/Contact’ cells are manufactured in a similar process to monocrystalline cells but have an integrated passivation layer. This increases efficiency by allow light refraction through the back of the cell, and by reducing heat absorption and electron recombination. Put simply they offer higher efficiency than standard cells and are likely to perform better for a longer time.

Half Cell
Half Cell modules are a relatively new addition to the market. These modules can be recognised by the busbar running across the centre of the panel. This separates the module and allows for the number of cells to be doubled and made smaller, meaning a 60 cell panel would become a 120 cell module. Smaller cells reduce mechanical strain meaning microcracks occur less frequently. Reducing the impact of microcracks reduces the rate of module degradation over the system life-time. When you take into consideration many Half-Cell modules are using PERC technology these panels are really designed to last.

Bifacial
Bifacial panels are designed to absorb light reflected from behind the panel. To do so they have cells mounted on the front and rear of the module and instead of an opaque backsheet this is transparent or translucent to allow for as much light to pass through as possible. This light is reflected from the roof / ground surface and is then picked up by the cells mounted on the rear of the panel. In order to maximise on this refracted light, it is important to only choose Bifacial when the proper design criteria is met. Bifacial modules should not be mounted flush to a residential tile roof for example, in this scenario the roof tiles are generally dark and will not reflect much light and if the modules are mounted flush to the tiles, light will be blocked by the cells themselves. The best scenario is a flat roof with a light-coloured roofing material, with the panels being mounted at an angle, a fixed distance above the roof itself.

Manufacturers

There are hundreds of solar panel manufacturers in the world all of whom will claim to make top quality panels that will last for 25 years or more. They will all offer a warranty of 10 years or more but it is important to select a manufacturer who you can be confident will still be in business in 10 years to honour that warranty – we call this ‘bankability’.

With major world brands like Canadian Solar, JA Solar, JinkoSolar and others you can be confident they will be around for the long term. We also have panels from world leading manufacturers like LG who offer a 25 year panel warranty!

The top 7 solar panel manufacturers make over 50% of the total panels world-wide and form what is known as the Silicon Module Super League (SMSL). It is highly recommended that you choose one of these brands to give you best the chance of long-term reliability and performance.

 

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