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.

Fully Charge your Batteries for Max Life

As you may have noticed, several of our articles state to always fully recharge your batteries.  In this article, we are going to explain why this process is critical to battery maintenance.   

During normal discharging, soft lead sulfate crystals form on the lead plates inside a lead-acid battery.  As the battery is recharged, these soft lead sulfate crystals are removed from the lead plates.  If a battery is left in a discharged condition or simply being undercharged, the soft lead sulfate crystallizes into hard lead sulfate.  Unfortunately, hard lead sulfate cannot be removed during recharging.  Thus, the surface area of the lead plates becomes reduced.

The storage capacity of a battery is based on the available surface area of the lead plates.  As that surface area reduces, so does the storage capacity.  Eventually, the surface area can become so reduced, that a battery will no longer accept a charge, rendering it lifeless.

Failing to fully recharge a lead acid battery is estimated to cause approximately 85% of deep cycle lead-acid battery failures.  When it comes to battery maintenance, this is a priority.

As always, take care of your off-grid array and it will serve you well for years.

The Power of Batteries

When it comes to batteries, a common problem is a misunderstanding of the actual power available from the battery.  Unfortunately, clever marketing can perpetuate misleading information.  Before you invest in an off grid array let’s take a minute to discuss the real power of batteries.

All batteries are generally rated by their maximum capacity.  For example, a battery with a voltage of 12 and an ampere-hour (Ah) rating of 100 will be listed as having 1.2kWh (kilowatt-hours) worth of capacity.  This is the accepted practice to standardize the way in which batteries are rated.  However, this rating doesn’t mean that this is the capacity available for use.

Depending on the battery type we choose, our battery will not be able to produce its maximum rated capacity.  Let’s use a lead-acid battery for off-grid solar as an example.  Remember from our earlier article, “Top 5 Battery Mistakes” we do not want to go below 50% depth of discharge. We do this in order to insure our batteries last as long as possible. Therefore, using our battery example above, using a 50% depth of discharge we have roughly 600Wh (watt-hours) worth of capacity available for use.

Here is where most off-grid designs fall short.  Even though we aren’t overtaxing the batteries on paper, we have left out a very important detail.  That detail is how we plan on consuming the power from the battery.  It is true that our battery from above has a rated capacity of 1.2kWh.  But, what we must realize is that the rating is based on a C/20 rate or 20 hour charge rate.  In simple terms, this means that we have 1.2kWh if we consume that capacity over the course of 20 hours. That gives us roughly 60Wh worth of power each hour for 20 hours.

This nuance of batteries generally catches people off guard.  If we consume more than 60Wh each hour, the available capacity of the battery reduces.  We have to remember that batteries use chemical reactions to produce and store energy.  When we speed up the chemical process, we reduce the efficiency of the reactions.  This means our battery’s true capacity will be reduced during higher power draws.  If we consume our power over the course of 10 hours, the battery capacity will reduce down to around 90% of its rated capacity.  In our case, our 1.2kWh battery is now a 1.1kWh battery.

The biggest change we will see in a battery’s capacity is when we consume the bulk of our power in a single hour.  When a battery is required to give the bulk of its energy stores in one hour, its capacity will reduce to around 60% of its stated rating.  This is a significant change in the battery’s capacity.  The same 1.2kWh battery from above is now an 864Wh battery.  Remember, we still do not want to consume more than 50% of the available battery capacity.  Therefore, we have now effectively dropped our consumable power from 600Wh down to 432Wh.

By better understanding how batteries capacity is affected by our energy consumption, we can prolong the life of the battery.  Most early battery failures are the result of over-discharge.  Take care of your batteries and they will reward you with long lasting life.