Battery Bank Sizing for Off-grid Systems
In an ideal world a solar energy battery bank would be very simple to design. On the surface it seems to be simple. However, it is not…
Here are the basics to be considered when choosing solar battery type and design.
What Types of Battery Should I Use?
There are two main types of solar battery, Lithium or Lead Acid. Both come as flooded or sealed. Flooded batteries use distilled water which needs to be maintained regularly. Sealed are just that and need no maintenance. Flooded are the cheapest and have a longer lifespan but require maintenance to remain healthy. Sealed are more expensive but requires zero maintenance.
Our battery sizing calculator can help design the perfect solar system for your needs. Try it now!
Lithium Solar Batteries
The best battery differs from site to site and system to system. Lithium batteries are the first product to be hailed as the best. While this is true in some cases, they are not idea for all scenarios.
Lithium battery pros:
- Light weight
- Good cycle life
- Hard to damage day to day
- Typical off grid usage of 80%
Lithium battery cons:
- Don’t work well in cold below 14 degrees. Some will not function at all below zero degrees
- Usually have a low current ability. Lithium is usually restricted to 50A or 70A so additional blocks may be required
- Requires regular recharging
In short, Lithium batteries are good where space and weight are at a premium. They also offer a good warranty and life expectancy.
They are not so good where larger inverters and small battery banks are used. They also cost over twice that of a good AGM bank with similar capacity. Finally, they may not be great in uninsulated installations.
AGM Solar Batteries
AGM is a type of lead acid battery that performs very well in off-grid situations. With increased use of AGM technology in vehicles with start-stop functionality the price is now very competitive.
AGM battery pros:
- AGM batteries can be used with large currents
- They charge quickly and efficiently
- Have around 70% DOD (depth of discharge) usable power
- They are maintenance free
AGM battery cons:
- They can lose around 30% usable power in cold conditions
- When charging with a generator they require 4 hours more charge time to reach 100% capacity
How Large Should the Battery Be?
The battery storage capacity should slightly exceed the power generation potential of your system to ensure batteries are not stressed too much.
Ideally the battery should store enough usable power to supply energy for one full 24 hour period. The next day there should be a power source to fully recharge it. The battery bank should be large enough to support the power and load maximum requirement safely and without damaging or shortening the life.
For more in-depth information on battery sizing, read ‘How to size an off-grid solar power system’. It will help you decide how much energy you are likely to need in your off-grid solar power installation.
Our solar battery calculator will help you specify a suitable system.
If a system is fully off-grid and without a backup power source such as a generator, then the usable battery capacity is usually tripled to allow for overcast days. If it is possible to increase the solar to ensure the worst case is covered then this is not necessarily true.
- Lithium is best for homes and larger applications where generators are used regularly or in winter.
- AGM is ideal for fully off grid power supplies, usually smaller projects.
If you would like to know more about solar battery bank sizing or anything to do with off-grid power generation, the Sunstore team of solar experts would be happy to help!
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