Module Features

Pallet Size

Figure 14. Pallet Size 

When I shop for solar panels, I often shop for one or two pallets of modules, because that is how to get good module pricing on a residential sized project. Buying just a couple of solar panels isn’t going to get you a good price, unless you call a local installer, let them know your interest, and wait awhile.

Material distributors want you to buy pallets rather than an exact number of panels, and they will treat you as a newcomer with more respect if you make their job easier. I’ll go so far as to design my systems to be one pallet sized which allows material to ship directly to site or otherwise be easily received and handled. 

Manufacturers some have 25, or 27m, or 29, or 30 solar panels in a pallet – it depends on the manufacturer.

Module Warranty 

Figure 15. Module Warranties – Plural

Most installers will say solar has a 25 year warranty but in the same breathe state that they provide a industry standard one year workmanship warranty, so how do you accurately present the 25 year plus life of a solar array? 

Almost all solar panels have a 25 year performance warranty but only a 10 year product warranty. Panels with full 25 year product warranties often cost twice as much as the same panel without one. But even the best panel warranty might only cover lost performance and not replacement labor. It can make sense to skip the premium today and use budget solar modules, rather than paying double for a technology that can become dated the minute it goes on the building. 

The module performance warranty assumes that if nothing is going

wrong with the solar panel itself for 25 years, the cell itself will not substantially degrade or go kaput for 25 years. It’s a warranty of the longevity of the cell quality itself, like providing a warranty on the diamond but not the entire diamond ring. 

What is not covered under the performance warranty is connection point of the cables coming out of the solar module itself, as well as how the frame seals the module glass, cells, and backsheet together, which to be honest is a pretty big deal, except that solar panels do last 25 years if installed properly. It’s that the manufacturer won’t vouch for the quality of the installation unless a much higher premium is paid. 

Figure 16. Claim Procedure 

How the panel is is handled from the time it leaves the factory to

the time it’s put on the roof, including the system design and the array location has an impact on how long a solar array can last. 

Items such as abiding by clamp zones are important and skipping any critical instruction can result in potentially dangerous system failure. Instead, most manufacturers provide a 10 year warranty on solar module workmanship, so you have to watch out how you present the 25 year warranty. If the solar panel itself starts falling apart at year 15, but the cells are proven to still be functioning fine, that is not part of a standard 25 year solar warranty. 

I recently came across a commercial project where the solar modules are facing straight up in the air, such that rain water will pool on top of the modules. It is an interesting design consideration, because pooling water is not good for the panels, although it is arguable that not much advantage is gained with the industry typical  5-10 degree tilt. A perfectly flat array on a flat roof has added structural advantages and could be the right design choice, but the manufacturer will not warranty the water tightness of the standard solar panel for more than 10 years. In normal circumstances this would not be an issue, but it could become a warranty an issue for creative solar projects.

Figure 17. Performance Degradation 

As far as which is better between a bargain solar panel or the very best, I am pretty agnostic with an it’s all good approach. In very high-cost real estate markets or inaccessible surfaces it is worthwhile to go top shelf with an expensive solar panel and full 25 year module workmanship warranty. If real estate is cheap and site access is easy, a lower efficiency module that takes up more space for the same wattage is just fine. 

Better performance warranties are broken out year by year, accounting for a little more degradation in year one than in following years. How that degradation naturally occurs has to do with how the electrons wear into the silicon as they start moving around. But if the installation is done with proper workmanship the expected life of an array is twenty five years or more. At that time, the solar panels should be producing eighty percent of what they do out of the box new, according to their performance warranty. 

The performance warranty sometimes is 97% for year one and then a 0.7% percent decline per year from that. The actual performance loss is a little bit less, such that some warranties track very closely with actual module performance decline each year. 

Another kind of “stair step” production warranty is for 90% of the rated power for 10 years and then 80% percent for the next 15 years. 

This is a cheaper warranty than a “year over year” warranty, but it is often good enough for residential and commercial projects because when modules fail, more than 10% of it goes offline.  The failure that I’ve observed is pretty obvious. 

On commercial projects you can even buy 3rd party warranty insurance because that can be more reliable than trusting the actual manufacturer. My opinion is that if module-level panel electronics like SolarEdge or Enphase are mandated on rooftops, then defective modules are isolated from functioning modules, and so the module warranty matters less than almost any other value-engineered decision on the project. But more expensive modules with full 25 year workmanship warranties are available for the customers who have the budget. 

Bypass Diodes 

Figure 18. Bypass Diodes. 

Let’s assume there is a solar module defect. Maybe it’s a soldered connection that came apart when electricity started to flow through it for the first time in the field. Maybe it arrived that way and the installer only determined during system commissioning. Maybe there are some leaves on the solar panel or some partial shading, but regardless when there is a failure inside the circuitry of a solar panel, there are bypass diodes so that part of the solar module can be damaged but electricity still flows through the other parts.

In that circumstance, the solar production would reduce by 1/3rd if there are three bypass diodes. Module voltage or amperage might read exactly 2/3rds of its neighbors during a failure event. It is very unusual to deal with module performance warranties. They’re usually defects that apply to the 10 or 25 year module workmanship warranty, rather than the 25 year performance warranty.

Shipping and Handling

Figure 19. Module Handling

Most module issues have to do with shipping. 

More on those shipping defects. Some solar panels come in boxes on pallets and others come outside a box in wrapped stacked bunches.
In particular, the latter can bust pallets if the shipper takes a fast turn. Likewise a forklift can spear a pallet and cause damage.

There are a few things that installers can do to damage a solar panel on a pallet, so its worth pointing them out now. 

Modules can bust by leaning them against a wall for the wind to blow over. More insidiously, modules can break on site or during shipping if tools or other items are stacked on top of stacked modules. 

What installers can do to prevent their end of workmanship defects is not to place heavy objects on the module surface itself. Don’t put elbows or knees, or tool boxes on the panels. If needing to Spider Man

across a solar array to access a particular nut or bolt, the module frame itself can be put to use and anything to distribute your load across the frames rather than the glass, the better.

Scratches and Micro-Cracks

Figure 20. Module Scratching 

It is also easy to leave a noticeable white scratch across the module glass when lifting solar panels up off a pallet, particularly when this is a one person job. If modules must be slid rather than lifted, such as to get a better grip before lifting, care should be taken to slide the modules along their frames, rather than having a frame drag across the glass of a module below. This happens when taking a module off of a pallet.

So don’t scratch the glass and keep your weight on the frame of the panel whenever possible.

This section of the panel can take one inch hail at 40 mph, as well as high evenly distributed loads, but a point load large enough in the wrong spot, such as sitting or leaning against a ground mount after it has been installed, can damage the otherwise robust panels – even in ways which can’t be seen or detected for years to come.

Snail Trails

Figure 21.  Snail Trails

Little micro-cracks can occur within the solar panel which are not obvious and only become problems later. Electricity flowing over these micro cracks like water carving into canyon, can create larger defects by unzipping the silicon cell in these lines called snail trails.

Sometimes these snail trails are problems, and other times not. Sometimes they are caused by manufacturing defects, other times environmental or installation error. 

All-Black Panels

Figure 22. All Black Panels vs. Standard

My favorite solar panel is an all-black panel, with a black frame and black plastic back sheet instead of a white backsheet that hides the individual cells visually, especially from a distance. That look is where most of the value of a residential solar array actually comes from, which is why I almost always use black solar panels on residential jobs. There is a range of all-black panels, the lower end ones having exposed grid lines, the more expensive ones being uniform sheets of black glass, like an infinity pool for your roof.


Figure 23. Frameless

For the sake of variety, these are frameless solar panels. Potentially, frameless solar panels could take over the industry. The module frame itself, being metal, is a weakness. But I would put frameless solar panels well within the experimental category at this point, although they are widespread enough to have racking options available. Most frameless modules today have glass fronts and glass backs, which make them heavy and easy to break. Perhaps a farming environment with heavy ammonia gas or an area with heavy lightning would benefit from a metal-free solar racking system panel.


Figure 24. Bifacial

This solar panel has a glass front and glass back, and is making headlines in the utility-scale sector. This is a glass-on-glass or bi-facial solar panel, and when installed off the ground such as on a utility-scale tracker, they can increase project cost-effectiveness by a whopping 12%, because they can increase production by 35% using similar real estate. Expect to see this market expand in the future, as companies like Dupont have translucent plastic module backsheets which can replace the glass. Again, these products are widely available but small enough to be still considered as novelty. The benefits of adding such modules onto a roof are reduced – I think the glass on glass ones are too heavy for slanted rooftop installation but can have a great building-integrated PV effect.

One easy way to remember the added benefit of these kinds of panels is that the underside of a solar array is by definition shaded. A solar array on an overcast day will generate 10-30% of what the array would do on a sunny day, and a bi-facial solar module will increase performance by roughly that amount, depending on how much space there is between the module and the mounting surface.

Solar Shingles

Figure 25 Solar Shingles

Solar shingles are available, although one of the largest manufacturers of solar shingles (no, it isn’t Tesla but roofing manufacturer CertainTeed) makes solar panels as well as solar shingles, so what does that tell you about the confidence in the product class?

Solar shingles look nice from above, but ugly from the ground. All the problems solar panels have looking good on uneven surfaces are made 10x worse with solar shingles. And even when installed correctly, I do not think they look any better than a well designed traditional array. 

While it is uncertain that a solar shingle array will look better than a traditional array, it is guaranteed to cost substantially more, both in installation and maintenance.

Separating Material + Labor

Figure 26. Distributors

Solar panels, at a minimum, are best bought by the pallet. If seeking to buy just one solar panel, call your local solar installer and sometimes it is convenient for them to sell to you at cost. But when evaluating a residential project, one pallet of solar is a great starting point. 

To get pricing, it is easy enough to find solar distributors online, and if you purchase by the pallet, it is likely they will sell to you, despite being a new customer. Look for newsletters to sign up for, or contractor programs. This is not as rigid a network as in other more established industries such as air conditioning. Anyone can buy solar panels for around the same price as the mainstream installer if they stick to pallet purchasing and do a little bit of material bidding.

Add a bit of design and project management work, combined with some hourly labor, it is a relatively straightforward process to manage a solar project and have it come in 50% less than turnkey installation price. In other words it is useful to get multiple bids and evaluate each for its merits, rather than just focusing on cost.

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Posted July 2, 2020 by John Cromer in category "Material Selection