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Battery Bank Sizing

How to choose the right size battery bank for your solar system.

What is Solar Battery Sizing

Solar battery sizing (otherwise known as battery bank sizing) is one of the most important considerations when choosing the specifics of your solar electric system.

The main objective when sizing a battery bank is to get one that can handle the load coming from your PV panel array and provide enough stored power for your needs without having to regularly discharge to an unhealthy point.

By wiring multiple batteries together in different wiring arrangements you can design a battery bank that's right for your solar power system and thus correctly perform solar battery sizing.

Factors Affecting Battery Bank Sizing

The number of batteries you use in your solar system depends on the following factors:

Basically, the bigger your batteries are and the more batteries you have, the more convenient it is for you and the better it is for your batteries' health. This is due to the fact that with more batteries / storage capacity you will have more power available, plus you will be discharging your battery bank in smaller (more shallow) cycles and thus increasing it's overall lifespan.

Therefore, as a general rule in solar battery sizing, it's always better to have more batteries in your battery bank and only discharge them 30-50% of the way down - than to have less batteries and discharge them more. Use a battery bank sizer calculator that can help automate the process for you.

Determining a Battery's Storage Capacity

An important part of solar battery sizing is determining the storage capacity, so you know how long you can use it for.

Sizing a Battery Bank - Watt Hours

Let's say you go out and buy a battery for your solar system that is 12 volts (push) and 105 amp hours (storage capacity).

You could find out approximately how much energy this battery will store / provide by calculating the watt hours. To do this, just multiply the volts (V) x the amp hours (AH) and divide by 100.

Volts x Amp Hours / 100 = Watt Hours

12V x 105AH = 1260 / 100 = 12.6 Watt Hours

What this means is that you can power a 100 watt appliance for 12.6 hours on a fully charged battery.

Make sure you find out what the specs on your batteries are before buying them. By knowing what to look for and what each spec means, you can insure your solar project's battery bank operates smoothly, efficiently and free of costly "battery bank sizing" mistakes.

Battery Life Expectancy

One thing you want to pay close attention to when solar battery sizing is how long the batteries you buy will last. The life expectancy of a sealed lead acid battery is rated using the number of cycles that battery can perform.

The "number of cycles" refers to the number of times the battery can be charged and discharged before it's dead.

So if your battery is a 3000 cycle battery, this means it can be charged and discharged 3000 times before it dies, that is providing it is consistently charged correctly and not discharged past acceptable levels. Batteries are considered to be at the end of their lifespan when 20% of their original capacity is gone.

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