This easy guide to off-grid batteries will help you choose the battery storage solution that best works for you. This guide will highlight the various battery technologies available for the off-grid build. Your power usage and generation will determine the requirements for your off-grid batteries and your overall system design.
According to the US Energy Information Agency, in 2018 the average US on-grid household used 914 kWh per month or about 29.5 kilowatt-hours per day. Off-Grid builds often aim to reduce this usage number significantly by relying on using fewer appliances and changing their usage habits. There is a focus on using wood-fired stoves for heating and cooking. Passive solar design to reduce the need for air conditioning or fans.
When living off the grid you will be generating your own power and will need a way to store that energy. Off-grid batteries form a vital role in the energy storage system. This is commonly known as your storage bank. Whether you are generating power via solar or wind you will need to store that energy for use when you are unable to generate power. Most professionals will recommend a minimum of 3 days of storage to combat bad weather conditions.
You will need to consider the power generation and power requirements for your particular needs. This includes your average and peak power usages. Once you know these details it’ll help you to easily determine your storage needs and ultimately which off-grid batteries will work for you.
There are four main battery technologies that are most commonly used in off-grid storage solutions.
- Flooded Lead Acid (FLA)
- Sealed AGM
- Sealed Gel Cell Batteries
Flooded Lead Acid
Flooded lead-acid batteries were the first batteries used for energy storage. First invented by French physicist Gaston Plante in 1859, they have been used in off-grid storage solutions for over a century. Also referred to as wet-cells they are the cheapest batteries for an off-grid solution and are easily recycled. These are also the same batteries you get in golf carts and other electric utility vehicles.
- Good power to weight ratio
- Easy to recycle
- Long lifetime if maintained correctly (5-7 years)
- Require regular maintenance
- Shorter lifespan
- Needs ventilated enclosure
- Spillage possible
- Must be mounted upright
Although these are the cheapest kind of battery you can use for an off-grid storage bank, you will need to ensure regular maintenance and care. You will need to check the battery levels on a monthly basis and top them up as required. These batteries release toxic hydrogen gas when they are charging. These are not a battery you can have stored inside your home. The storage bank will need to have its own enclosure to keep you and the batteries safe.
If you’re on a budget then the flooded lead-acid battery is a viable option. The battery technology is a proven technology that has been around for a very long time. You should only consider this if you need to. There are other options that don’t cost that much more but will provide you with a better storage bank in the long run for your off-grid batteries.
Sealed AGM batteries are a kind of Sealed Lead Acid (SLA) battery. Absorbent Glass Mat (AGM) batteries began wide-spread usage in the early 1980s. These are the most popular type of SLA battery as they can be used in a wide range of applications. These batteries became popular due to the AGM technology which uses a fibreglass mat between the lead plates. They provide low internal resistance, are able to deliver high currents on demand and have a relatively long service life. These require no maintenance and are spill-proof. This is a safer option then the flooded lead-acid batteries mentioned above.
- No maintenance required
- Mounted on any angle
- Charge up to 5 times faster than flooded lead-acid batteries
- Require more batteries for the storage bank
- Must be charged and discharged properly
- Shorter lifespan than flooded lead-acid (3-5 years)
- Need to be ventilated as they may off-gas depending on conditions
Sealed AGM are a great option for your off-grid battery needs. They have a good mix of power capabilities to cost ratio. They are easy to use, install and because they require no maintenance are a good first battery choice. You will still need to pay attention to the charge and discharge rates but for the costs, you can see why these have been used in all kinds of applications over the last 40 years.
Sealed Gel Batteries
Sealed Gel batteries are another kind of Sealed lead-acid (SLA) battery like AGM batteries. Instead of using a fibreglass mat they use a gel for the chemical reaction. The recharge voltages for these batteries are less than for other kinds of batteries. These batteries cost more than AGM batteries but they are good for projects that require a slow discharge. These batteries also perform better in higher temperatures which might need to be considered based on your location and ambient temperatures.
- Perform better in both hot and cold climates
- High resistance to shock and vibrations
- Good lifespan
- Less chance of leakage when damaged
- Require a special charger
- Easily damaged if not charged right
- More expensive than AGM
- Can be mistaken for AGM
- Only good for deep-cycle applications
- More prone to issues due to incorrect charging
- Lower recharge capabilities
Unless you have a specific deep-cycle requirement for your application and high-temperature issues the gel batteries are just not a good option for your off-grid batteries anymore. They are more expensive than AGM and have a lot more disadvantages. Only choose this battery kind if you know your exact requirements.
Lithium batteries can be considered the new kid on the block when it comes to off-grid batteries. Although they have been around since the 1970s in smaller electronics their use in large scale storage solutions is relatively new. The most suitable kind of lithium battery for off-grid applications is Lithium Iron Phosphate or LiFePO4 or LFP. These batteries although they are expensive, have much longer lifespans, can be cycled more often and don’t have to be completely discharged to keep the life cycle.
- Long lifespan (10+ years)
- Faster charging and discharging rates
- High charge cycle counts (3000-5000 cycles)
- No venting
- No maintenance
- A great solution for solar storage
If you have the budget lithium batteries should be your only choice. These are by far the best solution for your off-grid batteries and are able to provide the longest life. More and more solutions are using lithium batteries for storage including the Telsa powerwall or the Huawei home battery. A lot of DIY off-grid builders are using lithium car battery packs to power their off-grid storage solutions. A popular choice is using the Nissan Leaf or the Tesla car power packs.
In this guide, we outlined the four main battery technologies available for you to choose from for your off-grid batteries. The pros and cons of each can give you a better idea on which battery you may purchase for your setup. We will be publishing a buying guide later on in the month that will take the information we have learned here and apply it to an example build including requirements for the power, appliance lists and battery bank specifications. Have any comments or questions about this, feel free to leave them below.