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.

Deficit Cycling equals Dead Batteries

In the last article, we mentioned the term deficit cycling.  But what is deficit cycling?  And more important, how does it affect you and your solar array?

Deficit cycling refers to a situation where the consumption of the batteries stored energy exceeds the energy production of the solar module.  This will cause the batteries capacity to slowly drain down towards zero.  Once that happens, you have a dead battery on your hands.

Here is how it works.  When you first get your battery, it is boosted to full capacity.  Let’s say this battery capacity is 200Ah for this example.  At a 50% Depth of Discharge, your available battery capacity for use is 100Ah.  With that in mind, you go ahead and use 100Ah.  Now, lets assume your solar module can only replace 90Ah worth of energy in a day.  This leaves your battery at a 10% deficit for that day (based on Depth of Discharge only).  The next day, you use 100Ah of battery capacity.  Again, the solar module can only replace 90Ah.  At the end of the day, your battery is at a 20% deficit.  In two more cycles, your batteries will be at a full 40% deficit.  A few more beyond that and the battery will begin to drastically reduce in performance and reliability.

An easy way to think about deficit cycling is like your bank account.  If you withdraw more funds than you are putting in, eventually you will have a zero balance.  The problem with batteries is that a zero balance means you finished off the battery and will need a new one.