Choosing a solar battery is a fantastic way to transition to a more sustainable lifestyle, but when you decide to make such a significant investment, you’ll want to make sure that your new electricity system is just as reliable as the old. Finding the best solar battery is 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. (Looking for a more detailed guide on how to keep solar lights charged without sun?)
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.
Note: A Brief Technical Explainer
When browsing through the best 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.
Different Types of Solar Battery: Pros and Cons
From lithium to saltwater and lead acid, there are several types of solar power bank 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 batteries for solar charging 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). For smaller devices, like solar grills, you’ll need less power.
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.
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 best batteries for solar power have high coefficients, 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%.
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.
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%.
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 the best batteries for solar 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.
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.
Just like with a solar-powered tent, 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.
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 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. You may also wish to consider a solar battery tester for off-the-grid systems.
- 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. If you’re really keen on protecting your investment, you’ll want to pick up a solar charge controller as well.
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 solar 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.