Lesson 101 batteries

How much energy storage do you need?

Determining how many batteries you need is the most important part of your purchase. If you don’t have enough battery capacity, you will run out of energy and run out of power which you want to avoid and can avoid with us.

Sizing solar batteries is one of the first steps in designing your off-grid system. The amount of battery storage you need depends on your energy consumption. Energy consumption is measured in kilowatt-hours (kWh) over a period of time.

Example: 1000 watts x 8 hours per day = 8 kWh per day.

After estimating the daily consumption, we will determine the type of battery that will work best, as they have unique performance characteristics and are sized differently.

The two main categories are lithium and lead acid.

  1. Lithium batteries are more efficient, weigh less, lose less energy in the charge/discharge process, and have the highest power density. [Batteries in this category are Lithium-Ion, LiFePO4, and NMC batteries.]
  2. Lead-acid batteries are less efficient, heavier, lose more energy during the charge/discharge process, and have a lower power density. [Batteries in this category are flooded, sealed, AGM, gel, and deep cycle leads acid batteries].

People used to buy “lead acid” batteries because they were cheap; we now offer “lithium batteries” at the same price per usable kWh that last 3 times as long and require no maintenance. Lead acid batteries have a limited usable capacity and can be discharged to 50%.

Due to better efficiency and deeper discharge, lithium batteries should only be HALF the size of a comparable lead acid battery! Lead-acid batteries are sensitive and need to be fully recharged every day, whereas lithium batteries can stay at a partial charge without any negative effects!

PWREnergy was created to make lithium batteries affordable for everyone. The lifespan is 3 times longer and requires no maintenance. Lithium batteries are clearly the better solution while being more efficient and cost-effective.

Calculations needed for your battery pack

The exact calculation of the size of your battery system is based on your daily energy consumption and the type of battery.

Based on a usage of 8 kWh per day, here are some examples.

Lithium sizing

8 kWh x 1.2 (for 80% deep discharge) x 1.05 (inefficiency factor) = 10.08 kWh

Battery capacity is specified in either kilowatt-hours or amp-hours.

Example: 24kWh = 500Ah at 48V → 500Ah x 48V = 24kWh

It’s usually a good idea to round up to help cover inverter inefficiencies, voltage drops, and other losses. Think of this as the minimum battery pack size for your typical usage. Based on this example, you may want to consider a capacity of 600 to 800 amp hours, depending on your budget and other factors.

Battery packs are typically wired for 12, 24 or 48 volts, depending on the size of the system. Here are examples of battery packs for lithium, based on an off-grid home using 10 kWh per day.

FOR LITHIUM, 12 kWh IS EQUIVALENT TO:

  • 1050 Ah at 12V
  • 525 Ah at 24V
  • 262.5 Ah at 48V

Other factors that influence battery sizing:

Ambient temperature – heat or cold has a significant impact on battery performance and capacity.

Seasonal factors – energy consumption varies throughout the year depending on a few factors. For example, the sun produces more energy in summer than in winter.

Budget – the size of the battery bank is often a compromise between what you want to spend on batteries and how often you will need to run your backup generator.

Finding the right supply voltage needed

The Voltage of Lithium Ion Battery Packs

Voltage is a measurement you can use to find the perfect lithium-ion battery pack. Here you can look at our batteries by the voltage to find the best battery for your application based on the voltage power needed. Our selection ranges from 12V to 12KWH lithium batteries.

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