Best Solar Battery – Which Is Good for Storage?

Last Updated: 5 March, 2019 by Alin Sparkle

Best Solar Battery – Which Is Good for Storage?

Going solar is a fantastic way to transition into a more sustainable lifestyle, but when you decide to make such a significant investment, you want to make sure that your new electricity system is just as reliable as the old. Choosing the best solar battery is therefore essential.

Solar energy is intermittent, which means that when your solar panels are not exposed to sunlight, the system cannot generate electricity. During the night and during cloudy days, the reliability of the system rests in the quality of its storage units – the batteries. To ensure a smooth renewable energy ecosystem for your household, it’s a good idea to invest in high-quality batteries for solar panels.

What exactly is the best deep cycle battery for solar? How can you recognize a good battery from the bulk? What is the best solar battery for your specific solar power system? Read on for more details.

What Is a Solar Battery?

Conventional electricity systems do not require storage units because they can produce energy on the spot, at any time of the day. This is not the case with solar power systems, which can only convert sunlight into electricity when the sun is up in the sky. During the night, this is not possible for obvious reasons, while cloudy or otherwise bad weather days can reduce the effectiveness of the solar panels and decrease the energy output of the entire system.

This is why batteries for solar panels are necessary. It is likely that, during the day, your solar energy system produces more electricity than you actually use. You can choose to feed this electricity back into the grid for modest compensation from the state you live in or you can install solar batteries to store it and make it available during the night or during low-sunlight days. Many homeowners now prefer the latter alternative.

Together with solar panels, a charge controller, an inverter, and all the necessary cables to connect these components, a solar battery can ensure your energy independence. Differently put, if you own a solar power system with storage units, you can rely primarily on solar energy (even during a blackout) and draw much less conventional electricity from the grid. 

3 Reasons Why a Solar Battery is Worth It

If the solar energy system works without a battery, why change it? Actually, whether you’re new to solar energy or you’re just upgrading an older system, there are a few good reasons to consider adding one or several batteries. Below are three of the most relevant.

Sustainability

Including a solar panel battery in your solar power system can further decrease the amount of conventional electricity you draw from the grid. This, in turn, means that less fossil fuel is burned for the production of electricity for your household and that your carbon footprint is even lower. Of course, you might think that one household going full solar will not make a tremendous difference. You are right to believe this. However, if the majority of homes undergo these changes together, the impact can be considerable. Ultimately, this is the aim of solar power. 

Savings

Some argue that the greatest disadvantage of going solar is the cost. Certainly, an initial investment is necessary and can amount to a significant sum even after the federal tax incentive is applied. This is only half of the story though. When you switch your household to solar energy and if you use batteries to store any excess electricity you produce, you begin to consume little to no electricity from the grid, which means your monthly bills are much lower. In fact, the average solar power system pays for itself in monthly savings in no longer than 7 years. Given that the lifespan of the system is expected to extend well into 20 years or more, you’ll actually be able to make a profit in the long run.

Energy independence

Many people who go solar choose to do so because they want to become energy independent. In short, either because they disagree with the policy of their providers, they are worried by the recent increases in the cost of electricity, or they simply do not support the industry altogether, these people want to generate, store, and consume their own renewable energy. Batteries for solar panels go a long way in making this possible because they ensure households can manage their own electricity needs without depending on the grid.

Different Types of Solar Battery: Pros and Cons

From lithium to saltwater and lead acid, there are several types of solar battery you can choose from when installing your solar system. Below is a list of the most common batteries for solar panels ordered from the longest lifespan to the shortest. Several new technologies are currently in development and experimentation phase, but their prices are, at present, not suitable for widespread commercialization.

Lithium batteries for solar panels

Lithium or lithium-ion is widely considered to be the best solar battery currently available on the market. The name is an umbrella term that covers about six types of battery chemistry that primarily relies on lithium. As a lighter and more compact version to lead acid, the main advantages of lithium are a lifespan that goes well beyond 10 years (around 10,000 cycles), and a high depth of discharge, which ranges from 80% to 90%. Moreover, lithium batteries have an excellent resilience to thermal changes, they can easily handle high current ratings, and are also tolerant to abuse. Their production, commercialization, and technology were greatly improved by Tesla’s entry to the renewable market for vehicles and energy.

Saltwater batteries for solar

Instead of using flammable substances or heavy metal compounds that are difficult to recycle, Aquion Energy came up with a way to store power using water and a type of salt (manganese). With the highest depth of discharge currently available for a solar panel battery, 100%, a thermal resilience that ranges from -5°C (23 F) to 50°C (122 F), and an average lifespan of about 5 years or 5,000 cycles, saltwater is a strong alternative to lithium. More importantly, this is the only solar battery that is safe to touch, transport, and store, which makes them ideal for public institutions frequented by children.

Lead acid batteries for solar panels

Although they have a shorter lifespan and a lower depth of discharge than other batteries for solar panels, lead acid batteries are still used in many industries. Lead acid is actually the oldest type of rechargeable battery, dating back to the 1860s, but also cheapest, which is why they have become the staple battery for the automotive industry. The more recent AGM (absorbent glass mat) technology greatly improved their lifespan, recharging time, and thermal resilience by comparison to regular, acid flooded batteries. This turned them into a relatively viable option as batteries for solar technology systems.

How to Accurately Assess any Solar Panel Battery

Depending on how you intend to use your solar power system, as well as on the environmental characteristics of the region where you live, certain batteries for solar panels might be better than others. Beyond this, some customers search for the best solar battery in terms of price, others emphasize capacity because they want to be independent from the grid, while others still would rather opt for the most environmentally safe option.

Size or capacity

Capacity in a solar battery indicates how much energy the battery can store at a given time. Higher capacity does not necessarily equal higher efficiency, since the depth of discharge will have a definite and often sizeable impact on long-term usage. Nominal capacity is normally used to refer to the total amount of energy a battery can hold, while usable capacity also factors in the depth of discharge, basically telling you how much you can use safely. The size is usually measured in kilowatt-hours (kWh), although some manufacturers opt for watt-hours (Wh) or amp-hours (Ah).

Power rating

The power rating of a battery is just as important as its capacity, since it dictates how much energy you can draw from the unit at a given time. If you plan to use the battery in a household that has a fridge, TV, and washer/dryer, then maximum kW should be a focal point. As with capacity, there are two types of power. Peak power (maximum kW or peak surge power) is the absolute top limit the battery can provide for a short amount of time, whereas continuous power refers to the amount of energy you can continuously extract from the battery.

Round-trip efficiency

The round-trip efficiency of a battery indicates the maximum amount of energy that can be extracted from it as a percentage of the energy that was needed to charge it. For instance, if a battery takes 10kW to charge up to maximum and is able to provide you with 8.8kW before recharging, it has a round-trip efficiency of 88%. Round-trip efficiency can save you a lot of money if you want to stay off the grid during nighttime or overcast days. The higher the coefficient, the more value you’ll be getting from your solar battery.

Depth of Discharge (or DoD)

Because of various chemical interactions, some batteries have a higher depth of discharge than others. The DoD is the optimum amount of battery charge that you should use. De-charging a battery beyond its DoD will affect its lifespan and performance. For instance, Lithium has a DoD of 80% to 90%, which means you can safely use it down to 20% or 10% of its power before having to recharge it. Lead acid batteries, on the other hand, are known to have lesser DoDs, such as 50% or even 60%.

Lifespan or cycle life

Whether in years or cycles, the lifespan expresses the amount of time that the battery is expected to work within acceptable parameters. Most manufacturers specify the likely performance and the end of their solar panel battery’s life. Generally speaking, batteries are expected to last anywhere between 5000 and 10000 cycles (5 to 15 years), while their performance is expected to remain above 60%.

Temperature range

Operating and storage temperature increase in importance with the variation in year-round temperature that your area is subject to. Because of their chemistry, certain batteries for solar panels loose more efficiency and even shut down when it’s freezing cold or incredibly hot. As an example, lithium ion’s performance is optimal between 10°C (50 F) and 60° C (140 F).

Manufacturer, Warranty, and Cost

Depending on organizational goals, some manufacturers may offer newer solar battery technology than others. As a rule, automotive companies will focus on providing the most reliable and cost-effective solutions, while tech start-ups will likely emphasize delivering high-tech, environmentally-friendly products. Regardless of what manufacturers you’re considering, the warranty is a focal point of your purchase. Using a battery for a home PV system usually means it will have to charge and drain on a daily basis. Because each cycle slightly decreases the overall performance, it is crucial for you to pay attention to the amount of cycles that are guaranteed by the manufacturer. After 5 years of usage, you can expect your battery’s efficiency and capacity to be visibly lower than when you initially bought it (around 10-15% for lithium), so if you’re looking to save money through renewable means, look for the best deep cycle battery for solar energy.

The more the initial purchase cost, the more you’ll need to save in order to compensate for your expense. Lithium is a good long-term investment that will cover its costs and make a good profit over a two-decade period. Although it has gotten cheaper in the past ten years, however, it can still be a bit too expensive for some homeowners. Lead acid can be a handy, short-term solution until lithium stabilizes at a more affordable rate or a better solar panel battery solution presents itself.

How Long Will a Solar Battery Last?

There are two things to consider when it comes to the lifespan of your solar panel battery. The first has to do with how long a fully-charged battery can power your home. The answer depends on a number of variables, including the quality of the battery, its size, and the amount of electricity required by your household.

Assuming that, like most US households, you consume an average of 30kWh per day, you’ll need three 10kWh solar batteries to power your home for one day. Remember that your solar power system produces electricity each day and constantly recharges your batteries. Still, it is ideal to own additional storage units for emergency situations during blackouts, but also for days when your solar panels will be less effective due to cloudy or overall bad weather.

In addition, there’s the question of how long your batteries for solar panels will last over the years. Depending on the quality of each storage unit and how well they are maintained, you can expect your batteries to last anywhere between five to fifteen years. Given that the average lifespan of a solar power system ranges from 25 to 30 years, you’ll probably have to change each solar battery once or twice. 

What Is a Deep Cycle Battery?

The best deep cycle battery for solar power systems is a type of battery that features a high DoD (or depth of discharge). In other words, these batteries can provide sustained energy for long periods of time without becoming deteriorated as a result.

Generally, a battery is considered to be “deep cycle” if its DoD is at least 80%, which is to say that up to 80% of its capacity can be used before the battery must be recharged. Some batteries for solar panels have DoDs as high as 90%, but manufacturers will often recommend that you do not discharge them below 45% of their capacity to extend their lifespan.

For a solar power system to work during the night and during cloudy days, a great deal of electricity must be stored in one or several batteries. The latter are sometimes used for up to 12 hours before solar panels are once again able to convert sunlight into electricity, which means that they are nearly depleted on a regular basis. This is why it is essential to own the best deep cycle battery for solar power systems as opposed to batteries that can only provide short bursts of energy at a time.

Technical conversions: Watt vs. Watt-hours vs. Amp-hours

When browsing through batteries for solar panels, you’ll notice that different manufacturers describe their products using different units. This can be confusing, especially since it is essential that you ensure the solar battery you buy can store enough electricity to power your entire household.

To make things easier, you can use the following conversions to approximate the capacity and power of your battery of choice:

  • 1kW (or kilowatt) = 1000W (watt)
  • 1200kWh (or kilowatt-hours) = 1Ah (or amp-hours), for a 12V battery
  • 2400kWh = 1Ah, for a 24V battery
  • 4800kWh = 1Ah, for a 48V battery

As a general rule, the capacity of a solar panel battery is expressed in kWh or Ah, while the power of the battery is expressed in W or A. You’ll find that the energy requirements for most home appliances are expressed in kWh and W, which is why it’s helpful to convert the specs of different solar batteries to these units.

The Right DC Voltage for Your Solar Battery

Battery voltage is very difficult to alter once your solar power system is built and installed, so it’s essential to choose the right voltage for your storage unit in order to match the rest of the system. The most common DC voltages for solar batteries include 12V, 24V, and 48V:

  • A 12V solar battery is ideal for small solar power systems that include up to 500W in solar modules.
  • A 24V solar battery is recommended for any system above 500W that is still connected to the conventional power grid.
  • A 48V solar battery is the best solution for your solar power system if you intend to disconnect the household from the power grid entirely.

There are two advantages to higher DC voltages that recommend the latter for larger solar panel arrays. The first is that a higher DC voltage will be less expensive for the entire system. The second is that a higher voltage system can achieve the same amount of power for lower current. For example, a 2000W system at 12V will require 166A, while the same system at 48V will only need 41.5A to function. In turn, this means you can use smaller-gauge wires for the installation, thereby lowering your costs even further.

How to Choose the Best Deep Cycle Battery for Solar Systems

Like with most components of a solar power system, there is no one best deep cycle battery for solar applications. Instead, choosing the best solar battery largely depends on your specific household needs. To make an optimal purchase, consider:

  • Whether your system will be off-grid or tied into the grid, since you’ll likely require bigger, more powerful batteries and a higher voltage for an off-grid solar power system.
  • How much electricity your household needs on average, as well as the output of your solar power system, both of which can determine what battery size and power are most suitable for you.
  • The type of outdoor environment the battery will be exposed to, which can dictate the importance of weather-proof features or protective closures.
  • How much you are willing to spend on the battery, since this will help you narrow your search to certain manufacturers that sell products in your budget range.

Overall, it is true that if you choose to install a DIY solar power system, you have to be a little tech savvy to choose the right battery. You shouldn’t let this intimidate you, though. Just by reading this article, you’ve already become familiar with the basics of batteries for solar panels, while additional reviews from experts and customers alike can help you make an even better purchase.