How Many Batteries Do I Need?
Choosing the right battery for your application is very critical to ensuring that your solar system operates at peak efficiency, and lasts for as many hours of nighttime or cloudy weather. Whether you need something small, like powering your laptop, or a large battery bank for your new grid-tied or off-grid solar system for your home or office, batteries are one of the critical components of most electrical systems that we use today.
If you are doing small solar applications such as pumping or lighting, generally, a smaller sealed lead acid battery will be about the right size for you.
If you are working on a larger application, such as solar power for your home, office, or large scale remote lighting or power projects, deep cycle batteries are going to be the right choice for you.
To determine how many of which batteries you need…you need to determine how many amps of power you are using…and therefore, how many amps of battery storage you need to provide for your system.
To do this you should determine which appliances or power consuming items will be hooked up to your solar system. Then you need to determine the wattage and voltage of those items (this can generally be found on the label).
Amps= watts/volts
Then determine how many hours you use each of those appliances, multiply the amps for each appliance by the number of hours that it is used.
This gives you the number of amphours (Ah) that you need for each of your appliances.
When you add all those numbers together, you will have a total number of Ah that you need to supply with your Solar System for your appliances to operate as they do with a standard electrical source. This number of Ah is the Ah worth of batteries that you should purchase for your system.
As an example, lets, take an appliance that runs at 1500W. Assuming the Solar Kit we use is running on 24 volts DC, we would see it required 62.5Ah to run for an hour. In order to run it for 6 hours on batteries, you would need 375Ah, so you can have 3 x 125Ah batteriesthat should suffice.
If you are running the same system on 12 volts, the appliance would now require 125Ah to run for an hour. For 6 hours, it would need 750Ah.
Under no circumstances more than 40% of the battery charge should be drained. If you calculate 750Ah of usage for each 6 hours in the example above, we suggest that you have a battery bank of 1875Ah, so only 40% of this is used in 6 hours i.e. 750Ah. If batteries are constantly drained for more than 40%, this repeated drainage can halve the battery life.
