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.

Paradigm Shift

Solar arrays consisting of a single module connected into a battery date back to the 1950’s.  A simple setup used by the Telecom companies to provide power in remote locations.  With growing grid instability and preparation for natural disasters, this grass roots design is re-emerging.

Most people are looking for a way to have backup power in the event of a grid outage.  And a simple solar module connected into a battery is a great way to do that.  This grass roots design doesn't require fuel or the utility grid to operate.  With the addition of a battery, you can operate the system at anytime of the day.  Even better, is the quiet peaceful production making it perfect for locations with ordinances.  There is one exception though.  Because most people want a system that can power AC appliances we must introduce one necessary component to our setup.  The modern version of the grass roots design now incorporates an inverter.  This addition greatly increases the versatility of the system.  You can run DC appliances directly off of the battery and AC appliances off of the inverter. 

Choose Solar for your backup generator!