How Many Batteries do I Really Need?

 

As you can see, batteries can get expensive FAST.  But there is a little hope.  

First, we designed this array to provide power during the day with the heaviest utilization of the entire year.  Then we added storage to support 3 of those days in a row.  Those days are in the Summer when the AC is running full tilt.  It is unlikely that we will experience 3 of those high-usage days in a row AND there is no significant sunshine.

Additionally, we designed the battery array to support an entire day without sunshine.  At least initially, we do not need a  battery array that big.  Here's why:

If we want a battery array to just carry us through the night to the next day, we will not need it to hold a full day's energy.  We only need it to hold part of the day.  Suppose, in your region, you get 6 hours of sunlight a day, minimum.  That implies that your battery array only needs to supply 75% of the day's energy.  The solar panels will be able to supply power directly during the day as well as recharge the batteries.  That alone cuts our initial battery array down to 3/4 of its original size, and cost.

It gets even better.  Not only are the batteries only needed to carry us through the night, but we use a lot less energy at night.  So the panels will be supplying our power directly for 6 hours a day AND those six hours are the peak hours of energy use.  

For these reasons, we may be able to get away with half of our original battery array.  This is where it would be advantageous to find out just how much energy you use through the day. 

Don't get too excited just yet.  Remember, we have to scale-up the battery array in order to decreased the depth of discharge.  This scale factor will depend on other actors, but just remember, it can easily DOUBLE the number of batteries you will need.