Batteries for Solar Off Grid or Hybrid System

OK everyone, we have covered solar panels, a solar array, and charge controllers, so the logical next step is for us to discuss batteries.  Over the lifetime of your system, Batteries will be the most expensive part because the ones that are cost effective when starting a system don't last very long and the ones that last a relatively long time are prohibitively expensive.   Batteries are the center cog of any system because they store the excess energy produces by your source(solar array, generator, or even the grid) and then distribute that energy when generation falls below need.

Here are a few things to remember when considering a battery bank:

How many days of autonomy do you want?  So if your panels stop producing, how long do you want your battery bank to be able to provide energy to the house?

What climate will the batteries be stored in?  Batteries are rated for about 80 degrees, if they are stored at below freezing conditions, you may need 50% more capacity to meet your needs.  A cruel fact is that when its cold you normally have less sunlight as well.

What voltage will your battery bank be?  12v systems are easy but when you start drawing a lot of current it makes sense to step up to 24v or even 48v to reduce the wire size and reduce the number of parallel strings.

 How committed to maintenance will you be?  If you want plug and play batteries that you rarely need to visit, expect to pay more than for minimalist flooded lead acid batteries that require regular measurement and maintenance.

We are going to discuss the main categories that batteries fall into and how to use them.

Flooded Lead Acid Batteries for Solar such as golf cart batteries are the most common off grid battery bank component.  They are the lowest cost option, last between 4 and 7 years depending on how well they are cared for and what depth of discharge you normally take them to, and will work pretty well even if you dont religiously equalize and fill them.

Sealed Batteries for offer some advantages over Flooded Lead Acid because they are relatively maintenance free.  They only require a regular full charge.  They dont spill or leak fluid, they can be installed in any orientation because you dont need to get to the tops to fill the electrolyte.  They are expected to last around 8 years when protected from overcharging.

Lithium Ion Batteries are the wave of the future, offering 2x the average lifespan of a lead acid battery with higher Depth of Discharge, smaller space and about half as heavy per kWh of storage.  The problem with them is that the current charge technology in the market hasn't caught up with Lithium Ion and they are very picky when it comes to overcharging.  Currently I would not recommend Lithium Ion batteries for solar until more research and development is done.  The Powerwall may be a solution for grid connected hybrid systems but that's a specific niche that would require its own article.

Nickel Iron Batteries are the most expensive but also the most bulletproof batteries for solar systems on the market.  They can take 11000 cycles at 80% depth of discharge, with a wide range of operating temperatures and resistance to both over and under-charge conditions.  Unfortunately they are very expensive.  If you are looking for a battery that will last as long as your solar array, with low maintenance and have the financial means to utilize Nickel Iron this is the battery choice for you.

Well i hope you learned something today, bear with me as I continue to convert the blog to a podcast.  I am self teaching as I go and watching a ton of youtube videos and reading a bunch of articles, but implementation will be hit or miss.