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.