How to select a Solar Module – A Detailed Guide

Selecting the Correct Solar Module – ensuring you choose the right quality of Module for your needs

By reading this guide you will:

• Understand that cost and efficiency alone are not the sole factors dictating module quality;
• Learn how build quality and component selection affects both solar module lifespan and power production – thus affecting your monetary investment.
• Establish how to ensure a life span of 20 years plus, along with a reliable and high output each and every day.

Background to the Solar Industry 

Many people base their choice of solar energy system purely on cost or how long they can receive solar rebates from the government. Of course, you want to know how long it will be until you will financially break even, but these calculations are often made by assuming there will be no faults or maintenance along the way. However, this is not always the case.

Being a new industry, consumers regularly make their choice by only assessing the level of efficiency and peak price per watt of energy. But when looking at your solar energy choices over the long term, it is necessary to take other points into consideration. A quality module should be able to provide a regular, high quality yield over 20 years or more. The following tells you what you should be looking for before making your final choice.

Module Components

Frame

The frame is an important part of the module, providing it not only with its strength and durability, but also protecting the fragile edges of the glass and the covering film laminate.

 Handy Hint #1 – If viewing in person, assess both the quality and condition of the frame

Anodised aluminium is by far the most superior material for solar panel frames to be constructed from. Coated frames are much more likely to sustain scratches or damage, and any frames which have closed in cavities which could collect water should be avoided. Should this water freeze, it will expand and cause the frame to become misshapen or even to break. You should ensure a flush tapered edge where the frame meets the glass/cells – this will have reduced shading and will allow water to run off and not let frost build up in the winter. Frost can cause damage such as the frame becoming separated from the module. Tapered edges will also prevent a buildup of dust, pollen or other contaminates which would then encourage the growth of moss. If moss grows or lichen happens and covers part of the solar panels, it can reduce the efficiency of the solar output to a great extent.

The frame should exhibit excellent build quality. There should be no sharp edges and most importantly, should be screwed together with special screws designed for this particular job. This ensures that the frame is electrically and mechanically conductive and earthed throughout. Using frames which have blocky, raised sections close to the cells will not provide the most effective output and are therefore not recommended.

Frame parts should be firmly adhered to the laminate. This should be achieved by machined grooves or tracks on the inside edges of the rear of the frame. Whilst silicon can provide adhesion of the frame to the laminate, it is likely to succumb to weather conditions over the years and for this reason is not recommended.

All modules stocked by Greenforce Energy have been designed to satisfy these criteria.

 Cells

A solar module is only as good as the solar cell at its heart. For long and efficient energy production, a very meticulous combination of cells is necessary in order to match the electrical characteristics of the cells within each individual module.

It is customary to find polycrystalline (or multicrystalline) silicon cells  in most large solar pv energy systems worldwide, and this is because their  combination of efficiency and economy is superior to other choices. Poly cells are easy to identify, having uneven crystal-like markings and being square in shape. In recent times, there have been more and more cells made of monocrystalline silcon, and whilst these are more efficient in terms of the cell by itself, the fabrication process means that cells once incorporated into panels typically are found with ‘cropped corners,’ thus resulting in ‘diamond’ shaped white gaps on the panel surface (wasted space). This means that whilst these mono cells on their own are overall more efficient, when combined in a module, they generally don’t perform any better than their polycrystalline cousins.

Handy Hint #2 – Check earthing requirements of the panels

Panels that use thin film, back surface contact, or amorphous silicon (aSi) cells instead of polycrystalline cells may require modifications to the inverter.

Solar Panel Junction box

The junction box moves the electric current from the cells in the module to cables outside the solar panel. It is imperative that this is of a superior design and manufacture, because for poorly fabricated junction boxes the panel’s longevity is reduced and it can even lead to a fire risk under certain circumstances.

 Handy Hint #3 – Make sure the junction box is encased and connections are soldered

Be very cautious of any connections in the junction box which are clamped or plugged together. Only factory soldered and welded connections should be used; others can rust or become loose, causing short circuits and fires. BP, Silex and Suntech panels feature encased junction boxes.

You should also look for flame retardant plastic coating on the junction box.

Diodes

Handy Hint #4 – Bypass diodes provide cell protection under partial shading

The bypass diodes help the cell to remain efficient in times of temporarily adverse conditions. For example, if a solar panel becomes partially covered by anything (leaves for instance) these bypass diodes divert electricity from uncovered cells over the covered one, thus protecting them. If there were no diodes, ‘good’ unshaded cells would try to push energy through the shaded ones, causing the shade cells to heat up. Once the shade source is removed, diodes allow cells to return to their optimal operating status. Whilst protecting the module, the diodes need to be kept cool in order to promote their longevity.  The best modules have many of these bypass diodes, but ensure that each is connected to no more than 20 cells.

To ensure a maintenance free lifespan, the diodes in the junction box should be both thermally isolated from the connection area of the cells. This will guarantee that the diodes will never need replacing. An example of this is BP Solar’s approach to mounting the diodes away from the back of the hot black solar cells.

Glass

Solar glass differs from normal window glass in that is pre-stressed, toughened and extremely transparent. It is also used as stabilizing support for the solar module. Glass on cheaper modules may be as thin as 2.5mm, however the industry leaders are between 3mm and 4mm thickness.

Handy Hint #5 – Look at the surface of the glass

The glass which is used is of huge importance as it can make a big difference to the efficiency and yield of the system. There’s a whole lot of different solar glass available, but the main purpose of all of them is to direct as much sunlight into the unit as possible. Some types of glass, such as those which are very heavily structured, tend to be prone to various pollutants, so decreasing their efficiency over time. In Australia, the best types of glass to use are microstructured glass or glass with a hydrophobic coating. Because of regular rainfall in this part of the world, a self cleaning mode is activated when rained on, preventing a buildup of moss and other contaminants.

Pressure Rating

Handy Hint #6 – Check for a load count of 5400 Pascal for optimum static safety

It is common for modules to be tested only up to 2400 Pa pressure and tensile loads. Whilst this is legal, it these levels do not provide enough strength under extreme weather conditions such as cyclonic winds or snow. It has been known for glass to blow through the cheaper modules during extreme weather events.

Other Important Features to Consider

The physical construction of the panel is one thing to consider, but there are many other user issues which should be assessed before making your choice.

Handy Hint #7 – A low dead weight

For optimum fitting flexibility, you should look for solar panels which are not only lightweight and can therefore be fitted to low bearing weight roofs, but should also be able to be attached by both their long and short sides. The short sides must have approved clamping points to enable them to be fixed in either a crossway or upright way, dependent on the user’s needs.

It is possible to find lightweight modules with a load of less than 90g/Wp. But this should not be at the sacrifice of the pressure and tensile load, as good quality solar panels are both light and strong.

Handy Hint #8 – Optimal output will only be achieved by positive performance tolerances.

Performance tolerances are the way a manufacturer specifies any anomaly to theoretical output. If a minus tolerance is quoted, this means the actual output will be less than the theoretical output which is what you are paying your money for. Look for a guaranteed positive tolerance. This means that you will receive, at the very least, the specified output for which you are paying. With actual use, this yield can often be exceeded by some percent, although beware of overly high positive tolerance values, as these can adversely affect string optimization.

Make sure the positive tolerances quoted are viable and make mathematical sense. If what is quoted would push the module up into the next level of performance then this is not a viable statistic.

Handy Hint #9 – Proof of performance under weak light conditions

Sadly, the sun doesn’t beam down on a daily basis, but when solar panel module performance is tested, it is under these perfect conditions. They are known as ‘standard testing conditions’ or STC. This is 1000 W/m2 irradiation, atmospheric depth AM 1.5 and 25 degrees module temperature. Weak light is conditions of 800 W/m2 irradiation. However, this weak light can also be converted into energy and you should look for a module which has proof of an efficient performance under these conditions.

Handy Hint #10 – Don’t be bamboozled by the array of products on the market

Whilst it may seem that some manufacturers have a seemingly never ending range of products, they all exist to provide one thing – electricity. Do not be blinded by all the options. When selecting a quality module, never forget that these can be installed in a great many different solar panel systems. Some modules are optimized for size, which can be helpful if you are trying to create an improved roof layout.

Handy Hint #11 – Simple installation and safe operation are critical

Modules which are light in weight make moving them around and installation far less of a procedure. Another easy feature is connection cables with screw caps. But ensure that these cables ends are clamped onto the junction box during transportation so they don’t become a hazard which may cause the installer to trip.

Guarantees & Certifications

You should also look for any guarantees offered by the manufacturer which are over and above what they legally need to supply. Various certifications can offer additional security, especially if you live in a coastal region or an agricultural area.

Handy Hint #12 – Be aware of any necessary certifications for the construction of solar energy units in agriculture or in coastal areas.

Because of salt fog which is a problem in any coastal regions, additional regulations come into force. If you live in such an area your solar panels must conform to the standard IEC 61701. This ensures that the unit is resistant against salt corrosion.

Whilst there are no legal extra requirements for agricultural customers, you should check the modules are able to withstand increased airborne loads of various pollutants and chemicals produced from barns full of chicken, cattle and other animals.

Handy Hint #13 – Check warranty periods and any ambiguous wording

At a very minimum, you should expect a warranty for your solar module of at least five years. You may find that your particular manufacturer will offer an extended warranty for a price. However, this can provide you with peace of mind for a system which is of a substantial outlay.

Make sure you understand exactly how the guarantee works; they apply both to the period of time stated and the minimum yield of the module. For example – 20 years at 80% of nominal output.

Because each manufacturer is allowed to specify his own, individual systems scope of performance, you must make sure that your warranty is crystal clear. If there is any failing in the optimum output of the unit, it will be up to you, as the customer, to prove this. If you understand your warranty from the start, then any claims in the future will be far simpler to prove and process.

Handy Hint #14 – Check in which country your warranty provider is situated. Be aware that different countries have different laws.

If you purchase a module which comes under a different country’s jurisdiction, then proving and making any claims may incur high legal fees. You should ensure that you understand this before you sign on the dotted line, and to prevent any difficulties in the future, make sure that your warranty is underwritten by a company that you can reach in Australia (or your country/continent if not in Australasia). BP, Schott, Silex, Conergy and Suntech all have company offices here in Australia.

Handy Hint #15 – Check the environmental standards of the manufacturing facility

For optimal quality and environmental reasons, modules which are certified in accordance with ISO 9001 and ISO 14001 give you the peace of mind that you are buying a solar energy product that is of a high quality and is mindful of the environment as well.