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.

Pairing Modules with Batteries-A lost Art

Before charge controllers hit the market, you would need to pair your solar modules properly with your batteries.  System designs required finesse to make them work properly, not a piece of equipment.  Pairing seems to be an art that is slowly disappearing.  But the importance of proper pairing cannot be overstated.

What is pairing?  In simple terms, it is matching the solar production with the batteries capacity.  By properly pairing your solar modules with your batteries capacity, you are maximizing the efficiency.  Remember, there are only so many hours of sunlight per day.  Higher efficiency equates to more production, which in turn means you have more electrical energy at your disposal.

While there are many considerations in pairing, here are a few key points to follow:

1)      Understand the Solar Window

All solar production is based upon the solar window.  The solar window is considered the time when maximum energy harvest is possible.  In general, this is from the hours of 9am to 3pm.  With that in mind, you should design your array assuming that you will only have 6 hours of solar module production max.  You could get better results on some days; conversely, you may also get fewer hours on others.

2)      Solar Module Production needs to be greater than the Depth of Discharge

The best way to insure your batteries will receive a full charge is to match you solar module production to the depth of discharge you plan on using.  Remember, we use a DOD of 50% to 70% of the batteries rated capacity.  If your solar module production is slightly more than the DOD of the battery, the battery can be fully recharged and will last longer.  If your solar module production is slightly lower than the DOD, you will be deficit cycling your batteries effectively reducing its lifespan. We learned about deficit cycling in this article: http://www.solarunplugged.com/blog/2014/5/3/deficit-cycling-dead-batteries.

3)      Solar Module Voltage must be slightly higher than the Battery Bank

In order to charge a battery bank properly, you must provide a higher voltage than the battery bank nominal voltage.  Even in the last charging cycle (Float), the voltage going into the batteries will be higher than the battery bank.  This allows the batteries to remain topped off at all times.  More importantly is the equalization charging cycle.  During equalization, the voltage going into the battery is much higher than normal.  This allows for the electrolyte to boil and clean the battery plates.  Having a voltage that is too low will not allow for the batteries to be properly maintained. Again, reducing the longevity of your batteries.

Advanced charge controllers involved or not, there is one sure-fire way to get the most out of your solar array.  Take the time to understand the necessity in pairing solar modules with your battery bank and then further implementing them into your own system design to maximize the lifespan and production of your solar array.

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.