The Perfect Solar Battery for Your Solar Panels
As wildfires and extreme weather conditions become more prevalent, solar-plus-storage systems for residential use are increasingly seen as the solution to the problem of frequent power outages. With a solar battery in place, your home can become more power-independent when faced with widespread blackouts that sometimes last for days.
However, connecting a solar battery to your solar system requires some careful thinking because just like the other components of a solar energy system, not all solar batteries are created equal. There are also different types of batteries to choose from, which can prove confusing when you plan to purchase a solar energy storage system for your solar or photovoltaic (PV) installation.
What are Solar Batteries?
Solar batteries are devices that store the excess energy generated by the solar system. In doing so, they help maximize the savings you get from your energy installation. There are different types of solar batteries, each with its set of pros and cons, and you’ll need to look at several factors to determine the kind that will best suit your needs.
Solar batteries are one of the most expensive components of a solar system, with the price ranging between $2,000 and $7,000.
How do Solar Batteries work?
To get a clearer picture of how a solar battery fits into your solar energy installation, you should first understand how a solar power system works. First, the solar panels harness sunlight that falls on their surfaces in order to produce DC electricity. The DC electricity will proceed to the inverter and the inverter turns the DC power into AC electricity to make it compatible with household use.
With solar systems that have no storage capability, the energy produced by the panels should be used immediately. Otherwise, it will go to waste. However, most utilities offer net metering. When you stay connected to the grid, and your solar panel system produces more energy than you use, the surplus goes back to the network. On the other hand, if you consume more electricity than what your solar panels generate, you need to obtain power from the utility grid.
If you have a solar battery in place, the surplus energy coming from your solar system does not flow back into the grid. Instead, the excess electricity goes into the solar battery. This means you have stored electricity in your system, which you can use when your solar panels aren’t generating enough energy. The solar battery can also serve as short-term backup power in case of an outage.
Aside from the solar battery, you’ll need to install another inverter that will work with your solar battery. What type you need will depend on how you integrate the battery into your energy system.
Factors to Consider When Selecting Solar Batteries
The power rating refers to the amount of power the battery can provide. Measured in kilowatts (kW), it helps you determine how many and what type of appliances the solar battery can power.
Usable Storage Capacity
Battery capacity indicates how much energy the battery stores, and it tells you how long your storage system can power your home. However, you won’t be able to use all the energy in the battery, so you’ll need to look for its usable storage capacity, which indicates the amount of electricity you can actually draw from the battery. Typically, this falls between 30% to 80% of the battery’s total capacity.
For example, a battery with a total energy storage capacity of 20kWh and 80% usable capacity will provide you with 16 kilowatt-hours (kWh) of usable energy and 6 kWh at 30% usable capacity.
The round-trip efficiency of a battery measures the amount of energy that can be used relative to the amount of energy it took to store it. Let’s say you store 5 kW of electricity into the battery, and you can only draw 4 kW of power back. This means the battery’s round-trip efficiency is 80%. A battery with a higher round-trip efficiency will give you more value for your money.
In a solar panel system, converting the electricity from direct current to alternating current incurs some losses. The same holds when the electricity goes into the battery and is later drawn out to power your home.
The roundtrip efficiency of battery systems in the market ranges from 70-90%.
Battery Lifetime: Throughput and Cycles
A complete battery cycle means the battery had been charged and discharged once. How long a battery lasts is determined by the number of cycles it has. Some lead-acid batteries can provide 300-700 cycles, while lithium-ion batteries can deliver up to 200 cycles.
Meanwhile, throughput is the amount of energy a battery can store and deliver through its lifetime, and a warranty on this metric is more helpful in determining the best batteries for solar panels.
Depth of Discharge
The Depth of Discharge (DoD) refers to the energy you can draw out from the battery relative to its capacity. Battery life goes down as it is charged and discharged, and the harder the battery works, the sooner it degrades. This means that if you can draw out more power from your solar battery, this high capacity withdrawal will decrease its life expectancy.
You’ll want to know how long the solar battery will provide power in case of an outage or during those times when the panels can’t generate electricity. To determine how long your batteries will last, you’ll need to do a little calculation. Because many factors will affect how long a battery lasts, you’ll have to assume standard conditions to get a rough estimate.
You’ll need the following data:
- The battery’s total capacity (you’ll find this in the manual or label)
- Your circuit’s power (the information is in the electric panel)
Divide the battery’s total capacity by your circuit’s power to get an estimate of the battery’s run time.
A more straightforward way will be to use an online calculator.
Different battery types exist on the market, from the more popular lead-acid and lithium-ion batteries to flow batteries and other experimental battery chemistries, such as saltwater and fluoride batteries. With further advances in solar storage, we can likely expect new additions to the list of best batteries for solar coming from emerging technologies.
Different Types of Solar Batteries
Different types of solar batteries exist on the market. Some are new technology, while others have been around for a long time. In shopping for a solar battery to pair with your solar panels, you’ll need to look into particular specifications and how they’ll help in maximizing the benefits a solar system brings.
Lead Acid Batteries
Just a few years back, lead-acid batteries are the go-to solution for solar battery storage. Backed by technology that is almost 100 years old, this battery type is still one of the trusted options today.
Sized and installed correctly, lead-acid batteries are safe and reliable and can last for many years. They are still commonly paired with home energy storage systems despite the emergence of newer battery types.
There are two main kinds of lead-acid batteries:
Flooded Lead-acid Batteries
As their name implies, flooded lead-acid batteries should be flooded with liquid so that the battery plates remain submerged. These battery types require a lot of upkeep. They need to be checked regularly and refilled with distilled water to ensure they stay in good operating condition.
Flooded lead-acid batteries should be mounted upright to prevent the liquid from leaking out. They should also be housed in a ventilated enclosure to allow the battery gases to escape.
Failing to maintain this kind of battery properly can impact its lifespan.
Sealed Lead-Acid Batteries
This type of battery is similar to the flooded lead-acid kind. However, a sealed lead-acid battery has no opening where liquid can pass through. The electrolyte is sealed inside upon manufacturing, and there is enough to keep the battery working for a set number of days. As such, you do not need to periodically add distilled water to the battery or vent the gases inside, which means no maintenance tasks for you.
Sealed lead-acid batteries are also sometimes called VRLA (valve-regulated lead-acid) batteries because of the small valve in their enclosure, which allows the gasses that occur during charging to escape.
Sealed lead-acid batteries come in two types, Absorbent Glass Mat (AGM) and Gel, which are pretty similar to each other. Both are spill-proof and require minimal maintenance. Their differences lie in their output, warranty, charge cycles, and discharge rates.
- Proven technology: Lead-acid batteries have been in use since the 1800s.
- Price: Among the existing battery options, lead-acid batteries are the cheapest.
- Life span: With proper maintenance, this solar battery type can last up to 15 years.
- Size: They tend to be big and bulky, so they occupy a lot of space. This could be a problem when there is limited space on the installation site.
- Lower depth of discharge: This battery type’s depth of discharge is around 80% lower compared to newer battery types.
- Number of cycles: This refers to the number of cycles a battery can go through before it fails. Lead-acid batteries have a low cycle life of around 300-500 compared to other battery types that can go through 500-1,500 cycles.
- Temperature sensitivity: Lead-acid batteries are easily affected by heat. High ambient temperatures can cause a drop in their performance and may reduce their lifespan.
Because of their reliability, this battery type is best for off-grid solar systems and for backup power storage for residential PV installations in case of power outages.
Lithium-ion batteries are the power behind almost all rechargeable devices like cellphones, laptops, and even hybrid and fully electric vehicles.
This battery technology typically uses Lithium Iron Phosphate (LFP) cells, although some manufacturers use Nickel Manganese Cobalt (NMC) cells. They have become increasingly popular and are now regarded as the best batteries for solar storage.
- Efficiency: Lithium batteries outpace lead-acid ones in this area as they are more than 95% efficient. In comparison, lead-acid batteries are only 80-85% efficient.
- Higher depth of discharge: Lead-acid batteries can only be discharged up to around 50% of their capacity, while lithium-ion batteries can handle 80% and above discharges in a single cycle.
- Life span: Lithium-ion batteries can go through more cycles than lead-acid batteries, having a warrantied life span of 10 years or 10,000 cycles. In contrast, their lead-acid counterparts only carry 5-year warranties and cycles of around 1,500.
- Less maintenance: You don’t need to vent gases or put water in lithium-ion batteries.
- Cost: Although the price of lithium batteries has fallen through the years, this battery type is still pricier than other battery technologies.
- Fire risks: Thermal runaway, or excessive spikes in temperature inside a lithium solar battery, can cause fires.
- Environmental impact: Extracting lithium from nature wastes significant amounts of resources. It also leads to several forms of environmental degradation.
Lithium batteries are the best option for residential solar systems. Their high depth of discharge means you don’t have to replace them as often as other battery options. Moreover, their higher efficiency means you’ll get to store more solar power, which translates into more savings from your power bills.
Nickel Cadmium Batteries
Although this battery technology emerged way back in the 1800s, it’s not as widely used as lead-acid or lithium-ion batteries.
Nickel-cadmium batteries are made of nickel oxide for the positive electrode and cadmium metal for the negative polarity.
- Durability: These batteries have a long life, usually around 15-20 years, depending on the type and application. Compare that with lithium batteries that last for approximately 10 years.
- Can operate at extreme temperatures: They can operate effectively in temperatures between -20°C and 60ºC.
- Toxicity: Cadmium is highly toxic. In fact, several countries have banned its use. This makes nickel-cadmium batteries a threat to the environment.
- Memory effect: This term refers to a battery’s ability to hold a charge. Crystal formations in the electrode of Nickel-cadmium batteries sometimes lead to this issue, lowering the battery capacity as the device ages.
Because of their durability, nickel-cadmium is the best battery for solar storage on a utility scale.
Flow batteries are part of the latest additions in the battery storage options. Unlike other battery technologies, the aqueous electrolyte solution in flow batteries is encased in separate tanks and doesn’t mix with the positive and negative electrodes. Instead, the active materials flow through a cell membrane. Charging the electrons in the solution leads to chemical reactions, which allow the energy to be stored and discharged.
- Depth of discharge: This battery technology has a 100% depth of discharge, meaning that you can use all the stored energy in the battery without impacting its life span.
- Long life: Flow batteries can last up to 30 years.
- Zero fire risk: The electrolyte solution inside the battery acts as a fire retardant, thus eliminating thermal runaway.
- Low energy density: Flow batteries require large electrolyte storage tanks to provide the same amount of power coming from smaller-sized lithium-ion batteries.
- Cost: This battery option costs more than other solar batteries.
Flow batteries are best paired with large-scale solar installations.
Best Solar Batteries in 2022
Undoubtedly one of the most popular solar batteries on the market, the Tesla Powerwall comes with innovations that help make using backup power a breeze. However, you can only purchase a Powerwall along with Tesla solar panels, which solar consumers consider a major drawback to this solar storage solution.
Capacity: 13.5 kWh
Cost: $8,500, before installation
This is a modular battery storage system, which means it’s composed of small battery packs. This feature makes it easier to customize the size of the battery according to your needs. Compared to modular battery brands, the Generac PWRcell is readily available and easier to install.
Cost: $20,000 before installation
Although Delta is better known for their inverter line, they’ve also ventured into battery storage. The Delta BX6.3 is protected by a four-layered protective steel casing and has been subjected to intensive impact and fire testing.
Capacity: 6.3 kWh
Cost: $7,400 before installation
A long-lasting battery with a warrantied battery life of 10,000 cycles, this affordable battery will help you maximize your savings in going solar. Aside from the attractive purchase price, the Sonnen ECO uses lithium-iron-phosphate, the safest lithium battery technology. It’s also sold in 2.5 kWh capacities so you can customize your installation’s battery size.
Capacity: 5 kWh (two batteries of 2.5 kWh each)
Cost: $6,100 before installation
Considered an excellent alternative to the Tesla Powerwall, this battery type is ideal for both on and off-grid solar panel installations. Compared to the Sonnen ECO, its closest competitor, the LG RESU is lighter and more compact.
Capacity: 6.5 kWh, 9.8 kWh, 13 kWh, and 16 kWh
Cost: $6,400 and $7,200 before installation depending on capacity
Can I use normal battery in solar inverter?
Solar batteries, also called deep cycle batteries, are different from standard batteries. Unlike car batteries, for instance, that give short bursts of power, solar batteries can produce electricity for long periods.
Because acquiring a solar panel system involves a sizeable chunk of money, it’s best to use equipment and accessories specifically designed for solar energy use. With so many solar batteries on the market, you won’t run out of options
Why won’t my solar panel charge my battery?
There are several reasons why your battery isn’t charging even if the solar panels are under direct sunlight. These include:
• A loose connection between the battery and the solar installation.
• Wrong wiring system
• A blown fuse
• Problems with the solar charge controller settings
• Solar panel issues
How long will a 100 watt solar panel take to charge a 12V battery?
For a 100-watt solar panel that generates 1 amp of electric current, charging a 12V battery to full capacity will require around 5-8 hours.
What size battery do I need for my solar?
The size you’ll need for your solar system will depend on several factors, including your electricity consumption and the size of your energy system. On average, a 5 kW solar panel system will need a battery with a capacity of 10 kWh at the very least, while a 13 kWh one will be the better option.
Solar Batteries: Is it Worth it or not?
So, are solar batteries worth the extra expense? Many factors come into play when you’re deciding whether it makes financial sense to pair your solar system with battery storage. How much electricity you need compared to the amount of energy your panels generate, your goals for switching to solar energy, and your utility’s billing system are just some of them.
One crucial consideration associated with solar energy storage in today’s changing climate is the increasing frequency of power outages caused by extreme weather events.
Solar batteries are handy during prolonged outages caused by storms, which leave most homes, even those using solar power, in the dark. Pairing your energy installation with a solar battery can significantly ease the uncomfortable living conditions during blackouts. Thus, having solar storage is an excellent means to achieve energy security during these changing times when the power supply is becoming more and more unreliable.