Bypass Diodes

Imagine you are driving down the highway.  All the sudden, all traffic comes to a stop.  There is an accident ahead.  Luckily, there is a secondary road you can take and keep moving forward.  Without this secondary pathway, you would be stuck on the highway.  Solar modules function in the same way as above.  If there is even a little bit of shade, the flow of electricity is blocked.  By adding bypass diodes, a solar module now has multiple pathways.  This allows for the electricity to flow even if there is a blockage.

Typical solar modules will have at least three bypass diodes.  These three diodes separate the solar module into three sections.  In other words, your solar module has three pathways for electrical production.  If one section of the module is shaded from the Sun, the other two sections will still produce electricity.  This does mean the module will be reduced to 2/3 of its normal production.  However, without the bypass diodes, the production would be zero.

The question now is how these sections are created.  If you look at your solar module, you will notice silver tabs at the bottom.  And typically, there will be three separate silver tabs.  This tells you how the module is divided into sections (See figure 1).  Because of the bypass diodes, each of these sections can function independently of the other two.

What does this mean for your solar array?  If you have a location for your solar array that has some shading issues, you can still optimize that array.  Let us look at two examples:

Figure 1

Example one:  You have morning shade that affects the Eastern edge of your array.

In this example, it would make sense to mount your modules in portrait.  This is just like when you print a piece of paper.  The longer side of the module faces North-South.  By mounting the solar module this way, we are allowing the bypass diode to do its work.  If the Eastern edge of the array is shaded, we may lose a few sections in our modules, but the remaining sections will still produce electricity. 

Example two:  You have morning shade that will cover the bottom edge of the array.

In this example, if we mounted our array in portrait like above, we would have zero production.  This is because we have blocked every bypass diode.  Mounting the modules in landscape would be a better idea.  By doing this, you will lose roughly 1/3 of your electrical production during the shade.  But the bypass diodes still work, and you get 2/3 production.

Remember, when it comes to off-grid arrays, our goal is maximum production.  This allows us to have a more reliable off-grid array.  And that reliability will also translate into a longer lasting system.

Choosing the Right Module

Most of you familiar with gas generators know the need for gas.  No gas means the generator cannot run.  And that means there is no electricity to be had.  Well, a similar thing happens with any off-grid array.  At the heart of the off-grid array is the solar module.  This module is the fuel (gas) for the array.  The solar module collects energy from the sun and converts it into electricity.  The problem becomes choosing the right solar module.  And today we are going to tackle that question.

There are three major types of solar modules: Monocrystalline, Polycrystalline, and Thin Film.

Monocrystalline – if you are limited on space, this is the module for you.  Monocrystalline panels have higher efficiencies.  And the higher efficiency means that the panel provides more electricity per square foot.  This is due to their cells coming from a single crystal of pure silicon.    Typically, these modules will have solar cells that appear very dark in color.  For some, this is more pleasing to look at.  Just be warned, this panel does come with a higher price as well.

Polycrystalline – if you want a good cost module that still performs, this is the one for you.  Although these panels are not as efficient as monocrystalline, they are not far behind.  Their solar cells are made from pieces of crystal silicon.  This makes their solar cells typically appear bluer in color.  Polycrystalline is a great all-around module at a fair price.

Thin film – if you need a portable or flexible module, this is the one for you.  We are talking amorphous thin film here.  This module still uses silicon, just not in a wafer form.  Instead, the silicon is spread on a flexible material like plastic.  This allows the module to follow curved structures.  It also means that the module is less likely to get damaged due to movement.  Thin film modules work great for mobile applications.  But, of the three types, they typically have the least efficiency.

As you can see, each solar module has its place in off-grid arrays.  And selecting them comes down to us clearly defining our goals for the off-grid array.  Remember, the goal is to create an off-grid array that best fits our individual needs. 

Ground Fault Protection

What is ground fault protection and do you really need it?  A ground fault is an abnormal condition in which current is traveling along the ground wire, which is normally a non-current carrying conductor.  This means that something in the Solar Array is shorting out, causing the current to flow into the ground wire.  If the condition is left to remain, the point where the short is happening will eventually fail causing a fire.  This can be seen in two recent devastating fires caused by Solar Array Ground faults. (Bakersfield, CA and Delanco, New Jersey)

Now is where the question arises, doesn't a circuit breaker of fuse remove the ground fault?  In a ground fault, a circuit breaker of fuse may not open clearing the ground fault.  The reason behind this is that in order for a circuit breaker or fuse to trip, the current flowing through that device must be higher than the devices rating.  For example, a 20 ampere circuit breaker needs over 20 amperes to trip.  In a ground fault there may not be enough current flow to trip the breaker.

The problem with ground faults is that not all of the current is flowing into the ground wire.  There is always a certain amount of resistance that happens in a ground fault that reduces the amount of possible current.  This means that even though there is a fault, it is not high enough to trip the circuit breaker of fuse that is normally in the system.  Therefore, ground fault protection is added to the circuit.  In general, a ground fault protective device is set to trip as low as 1 ampere.

A ground fault protection device will disconnect any loads on the Solar Array.  By disconnecting the loads, there is no longer a flow of current stopping the short circuit from persisting.  Now the Solar Array is brought to a safer condition until the short can be removed from the system.

Now for the million dollar question, do you need one?  If you are planning on putting solar panels on your dwelling, the answer is yes.  A ground fault protective device will help prevent your house from catching fire due to a ground fault.  Remember, ground faults generally do not trip your normal circuit breakers or fuses.  On the other hand, if your solar panels are going to be ground mounted, this isn’t a requirement, but still a good idea.

Having a ground fault protection device installed in your Solar Array is like having insurance.