Best Batteries for Off Grid Solar Power Storage

One of the main reasons people set up a solar backup system in their homes is for use in case of an emergency. In many emergencies, the electricity from the power grid is no longer accessible. A backup will ensure you remain relatively comfortable while being able to run basic loads in your home. 

Electricity needs are what we call the load in the setup. An automatic transfer switch will switch your power from the grid to the storage backup in case of a blackout. It is important to note that a solar battery backup may not power your entire home. 

It should however keep your critical loads running like lights or refrigerator running in case of a blackout. During the day the power bank can power your critical loads in case of emergency and during the nighttime, it can power important house loads. In this article, we go through various types of batteries and how each will suit you according to your needs and experience with Solar Systems.

 

Choosing a Solar Battery for your Home

Solar batteries are a key component of any solar energy system. They’re used to store the power generated during the day and release it at night, so your panels won’t be wasted on cloudy days or after sundown.

There are different types of batteries available, each with their own pros and cons. Here are some factors to consider when choosing the right one for your solar system:

Solar Array Size

The first thing to consider is the size of your solar array. The larger the array, the more capacity you need from your battery. If you have a small system, such as a single panel on your roof or in your yard, chances are that all the energy you produce will be used to directly power DC appliances and lighting. So a small battery system may be all you need to store this excess energy for night and on cloudy days.

On the other hand, if your using a big solar panels array to power your home, then you’re going to need a lot more capacity than in order to ensure the power from your solar panels is stored and used to run your home. 

System Voltage

Large systems use small voltages typically 6v while small systems use higher voltages. Most small solar power systems use 12v. Most solar panels are designed to operate at 12V or 24V so this should match the voltage of your battery. 

Cost  

Cost is a huge factor as your budget determines the type of system you can get. A whole-home battery backup like the Tesla Powerwall will cost up to $10,000. However, if you build a small DIY system the costs can be as low as $2000 for the batteries. 

Battery type 

The most common types of batteries include flooded lead-acid and AGM (absorbed glass mat). Flooded lead-acid and AGM are both maintenance-free and have similar energy densities. Flooded lead-acid batteries have the added advantage of being able to be mounted in any position and can be opened up for inspection if needed.

The best batteries for a powering a home are lithium Batteries. They have a higher density in terms of capacity, require little maintenance, and last longer than Lead Acid Batteries. However, in terms of upfront costs, they need you to dig deeper into your pockets. We discuss this later in this article.

 

Sizing a Solar Battery for Your Home 

Battery Capacity or power is measured in Kilowatt hours. In order to get the battery size you need in your home. You need to calculate your daily wattage requirements.

This is a list of essential appliances like a refrigerator for an off-grid home with the Wattage and Daily Watt-hour requirements.

Appliance

Wattage

Daily Watt-Hour Requirements

Refrigerator

200

3200

Lights

40

160

Mini Fan

40

400

Electric Water Heater

1200

300

Laptop

60

300

TV

30

150

Water Pump

60

300

The total wattage requirement for our example above is 2330 watts and the total watt-hour requirement is 4810 Watt-hours.  To calculate watt-hours you simply multiply the wattage by the number of hours you are running the device. 

Battery Rating

Batteries are rated in Ah (amp-hours). This is a measurement of the current output over time. Voltages are fixed but according to the type of battery. However capacity is relative to the type of Battery, this is usually printed on its side.

The capacity of a battery is measured in amp hours (AH), which is the amount of current it can deliver over a period of one hour. For example, an 100AH battery can deliver 5 amps for 20 hours, 20A for 5 hours minutes or 2A continuously for 50 hours before it needs recharging or replacing. The capacity required depends on how much energy you want your battery to supply during peak sunlight hours or when there is no sunlight available at all.

This gives the total storage capacity derived from Voltage and amp hours. Capacity (Watt hours) = Voltage x Ah

Again to get the Amp-hours we will divide the total watt-hours by the voltage. 

4810 Watt-Hours/12v =  400 Ah

So to run all your appliances in a day you’ll need 400 Amp-hours of battery capacity which is a lot in terms of space and price. 

Cycle Life

Every time a battery is discharged and recharged this is called a cycle. Cycle life is the number of times a battery can be charged and discharged. This is used to calculate the life of the battery.

Depth of discharge (DOD)

DOD is measured as a percentage of energy that can be pulled out of Battery during each cycle. Lead acid batteries are recommended to be discharged to 50% of its capacity while Lithium-ion batteries are recommended to be discharged up to 85%. 

Efficiency

Batteries are not 100% efficient; Lithium Batteries have 95-98% efficiency while lead Acid batteries have a 80-85% efficiency rate.

 Lithium-ion Battery

Lithium batteries are the best option for domestic grid-connected homes. These batteries are commonly used in appliances we use every day from phones to laptops.  Lithium batteries have a higher density of energy compared to Lead Acid batteries. This means that you get more power with a smaller lithium-ion battery than you would with a lead-acid battery of the same size or even bigger.

Lithium batteries can tolerate huge temperature changes and can be used between 320 – 1000 F.   Lithium batteries have a long lifetime can last up to 10 years and do not require maintenance. However, they have higher upfront costs and must use a controller as it poses a slight risk of fire in case of overcharging. 

Advantages of Lithium Batteries

Lithium battery is becoming the battery of choice for many reasons and it is also they are used in portable battery power stations: If you are a Beginner in Solar Setups or looking for a Portable system consider a Power Station that will house a battery, controllers, inverters and more and save you the hassle.

This is because of they add more functionalities to a battery bank to allow it for more than just for home use.

Lighter weight.

When it comes to weight, the Lithium battery wins hands down. It is typically half to one-third lighter than the original lead acid battery weight (for an equivalent run time/capacity lead acid battery bank).

Storing Lithium Batteries for SolarLithium (LFP) Batteries

 

Higher electrical efficiency.

The Lithium battery has a much higher electrical efficiency compared with lead-acid batteries. LiFeP04 lithium batteries are typically 98% charge efficient compared to between 70% and 85% with lead-acid batteries. They also have significantly faster charging times than lead-acid batteries.

What this means is the Lithium battery will charge not only more efficiently, but more quickly than a lead-acid battery. This can be particularly important in situations with limited charging methods available, such as from solar panels. This is also the reason why lithium-ion batteries are used for portable power packs and solar chargers.

For example, camper van owners have reported that their LiFePO4 batteries are fully charged from solar panels by midday compared to 4 to 5 pm using their old lead-acid batteries.

Longer working life.

While good quality Lithium batteries such as C&C Power Supply batteries are far more expensive to buy and set up initially, the actual cost of ownership is considerably cheaper than lead-acid batteries (calculated in terms of cents per charge cycle).

Constant Voltage.

In a lead-acid battery, the voltage will continue to drop over time as the internal circuit within the battery will self-discharge. This forces the connected electrical device to eventually shut down at its minimum operating voltage.

In the Lithium battery, however, voltage tends not to drop under load until the battery is almost depleted. For example, an ignition coil in a motor vehicle will have a consistent spark due to the battery’s ability to deliver a consistent voltage.

This means electrical equipment tends to run more efficiently as they are receiving constant voltage. Ultimately, using Lithium batteries gives electronic equipment a longer working life before failure than the lead-acid battery option.

Faster recharge.

Expect to spend much less time recharging Lithium batteries than lead-acid batteries.

Eco-friendly.

Lithium batteries are the safest batteries for consumers and the environment. Internally, they do not contain corrosive sulfuric acid or any toxic heavy metals such as lead or cadmium which can be environmentally harmful if leaked.

LiFePO4 Battery

A LiFePO4 battery is a lithium-iron-phosphate battery, which is a type of rechargeable battery that has come to replace AGM deep cycle batteries. This is because it has a number of advantages over other types of batteries. 

One advantage is that it has a higher power density, meaning that it can store more energy in a given space than other types of batteries. Another advantage is that it is more stable and safer than other types of batteries. Finally, LiFePO4 batteries can be charged and discharged more times than other types of batteries, making them more durable. 

A 200 Ah LiFePO4 battery can supply as much power as a 400 Ah lead acid battery. As started in the beginning you can actually use 90% capacity of lithium-ion battery. They also charge a lot quicker meaning that any power you use can be easily replenished from your solar power. This adds on an extra capacity to be able to run a system much like from a 400-Ah system.

 

Expert Power 200 Ah LiFePO4 Battery 

 

If you looking to store power for long periods of time for your home without having to worry about something going wrong the ExpertPower battery is the one to go for.  It has a low discharge rate of less than 2% per month meaning you can keep it in storage without losing too much power. But it has safety measures that ensure you can easily leave it on autopilot without much supervision.

A built-in BMS (Battery Management System) protects the battery from overcharging and over-discharging. This means that the battery will shut down if it is discharged to around 10V and if overcharges is higher than 14.4. More or less the BMS circuit shutdowns and to bring it up a small charge must be applied to activate the circuit.

It also has a low-temperature cut-off that will stop discharge on the batteries at temperatures lower than -4 degrees Fahrenheit. This is because discharging lithium batteries below this temperature will destroy your batteries. This adds another layer of protection to your batteries. Although not entirely waterproof it is sealed to provide some level of protection but it is best to keep the battery away from water.

The best thing about this lithium battery is that you won’t have to worry about exceeding 50% depth of discharge as you have with deep-cycle lead-acid batteries. You can get the full 100ah or 200ah from the battery. But remember the recommended depth of discharge is 80% for longer life.

Also while recharging a lead-acid with 50 amps can damage the battery this is safe with LifePO4 batteries meaning you can get them from zero to 100% in just over 2 hours. This can be around 5-6 hours with a 200 Watt panel on a good day.

 

Lead Acid Battery

Lead Acid batteries are the common types of batteries we find in cars, tractors and submarines. There are two types; Flooded Lead Acid batteries and Sealed Lead Acid batteries. 

Flooded Lead Acid Batteries

Flooded Lead Acid batteries are old-school deep cycle batteries. They are high maintenance and need to be stored in a place with good ventilation as they emit gas. They are referred to as flooded as because it needs to be submerged in distilled water regularly.   It is an economical option for off-grid systems but needs hands-on maintenance.

Lead Acid Battery Bank

Gel Batteries

Sealed Lead Acid batteries are the better option if you don’t intend to do regular maintenance.  While the liquid inside the standard flooded battery looks like water, the liquid in a gelled deep cycle battery looks like jello and they’re sealed.

The whole concept of spilling, a hazard, is removed so that’s really nice in addition to the no maintenance. But, a disadvantage of these is that a regular automotive type charge could easily damage them. The charging current has to go by the manufacturer’s recommendations.

Too much current too fast will damage the battery. If you see yourself putting a nice pump-up charge on your battery before (or even during) your battery use “solar season” or some intermittent charging over the off-season, this could be an added hassle factor.  These batteries also typically cost more.

AGM Batteries

AGM batteries, or Absorbed Glass Mat, are the non-spill type that you find (normally) as small 10 amp-hour alarm system backup batteries. They are also sometimes called “dry” or “starved electrolyte”.

There’s a fine fiber between the plates holding the acid. They’re sealed, maintenance-free, more efficient, can’t spill, and don’t freeze easily – lots of great qualities. Some applications need these features.

This type of battery is also available in larger capacities for solar applications, and has advantages, such as a bit more available energy per pound of battery, and are safer because there is no electrolyte (battery acid) to deal with, there are also disadvantages such as cost, and, for some, the fact that they are ‘maintenance free’ means that once they are done, there is not much you can do.

These can be great for an off-grid system that you don’t visit regularly and battery banks for grid-tied systems.

Using a Car Battery for Solar

The WORST type of battery you can use for alternative energy applications is the standard car battery. They will ‘work’, and some will argue that given the cost and availability, they are the best for someone just starting out, and in some limited way, I agree.

You may have an extra/old car battery you’re thinking of using. Just know if you use a ‘starting’ battery like you would a Deep Cycle battery (repeated discharges) it could fail after not too long, as few as 30 discharges, depending on its condition. Starting batteries are not designed for repeated deep discharge – doesn’t mean you can’t use one as long as you understand it’s limitations.

car battery

This however does not mean you can’t use a Car Battery with Solar. A trickle charger can be used to maintain a car battery charge so that it does not go flat. This setup does not include a load.

For someone in a garage that just wants to tinker with a 100-watt inverter to run a couple of lights and that’s all they will ever want out of their system, I would say yes, grab any battery (A deep cycle if you can get you’re hands on one), a cheap inverter and panel hooked into a controller (usually available as a set) will do just fine, and for a couple hundred bucks, you have a working system.

 Why you need a Deep Cycle Battery

For example, when you’re starting your car you only need that short burst of power to get the motor running and once it’s running the alternator takes over from there and gives the motor all the power it needs.

‘Starting’ batteries have thin “plates” to provide lots of surface area for that initial cranking oomph. Deep Cycle batteries have thicker plates. Less initial oomph, but better long-term cycling capabilities (a cycle means a discharge with subsequent charge).

There are many kinds of Deep cycle Batteries and, many are not ‘True Deep Cycle batteries”. And more than that, it’s hard to tell. Some of the lower-end ones are called Deep Cycle Marine Batteries. A more accurate term for them might be ‘hybrids’. They’re sort of a ‘Deep Cycle – Starting’ combination.

But they’re less expensive and they work, especially on smaller systems. You can pretty much assume that if a battery is on the lower-end expense wise it’s probably a hybrid of some sort whether it’s mentioned or not. But that’s not a horrible thing.