What Are the Main Types of Solar Batteries? (2023)

Solar batteries store your solar system’s excess energy, providing backup power at night or during emergencies and offsetting periods of high electricity costs to increase your savings. Four types of solar batteries are currently available: lead-acid, lithium-ion, nickel-cadmium, and flow. We’ve researched each type of solar battery and compared their pros and cons, plus provided tips for selecting the best solar battery for your home.

Solar panel systems use four main types of solar batteries: lead-acid, lithium-ion, nickel-cadmium, and flow. Each battery type has different benefits and works for different scenarios.

Lead-Acid Batteries

Lead-acid batteries have the longest history in the solar industry. These batteries are most common because they’re reliable and affordable. Manufacturers classify them as deep-cycle batteries, meaning they can handle regular draining and recharging. However, lead-acid batteries can only safely discharge 50% of their capacity without affecting their life span.

Lead-acid batteries come in two varieties: flooded and sealed. Flooded lead-acid batteries are water-based and require regular maintenance, such as adding distilled water. Sealed lead-acid batteries don’t require any maintenance. Both battery types work with solar power systems, but homeowners prefer sealed options for convenience and safety. 

Lead-acid batteries have a low energy density, meaning they don’t hold much energy within their form. This makes them larger and heavier than other battery options. They also take longer to recharge and have shorter life spans, lasting between three and five years. They contain environmentally harmful chemicals that must be disposed of properly. 

Pros

• More affordable than other battery types
• Reliable technology with decades of history 
• Universal compatibility with most solar systems 

Cons:

• Heavier and bulkier than other batteries
• Limited discharging capabilities 
• Shorter life span of three to five years, requiring more frequent replacement

Best For:

An off-grid system or backup power during power outages. 

Lithium-Ion Batteries

Lithium-ion batteries use newer technology than other options and are becoming more popular for residential solar panel systems. This technology is employed in some of the most popular solar batteries, including the Tesla Powerwall and LG Chem RESU.

Lithium-ion batteries have a higher discharge capacity than lead-acid options. They can discharge up to 80% of their total storage capacity without affecting their life span. Some models can expel 100% of their capacity without sustaining damage, allowing for better energy use and storage. Lithium-ion batteries also take less time to charge. 

Lithium batteries come in two options: lithium nickel manganese cobalt oxide (NMC) and lithium iron phosphate (LFP). NMC batteries are more common and use older but reliable technology. These batteries offer midlevel power ratings and have a lower price point. LFP varieties use a new technology that improves their stored energy retention, making them more efficient. They have a higher power rating but cost more than NMC options. 

Lithium batteries have a high energy density, giving them a lighter and more compact build. They work well in tight spaces and are ideal for smaller homes. Lithium-ion batteries have a life span of up to 10 years and require little to no maintenance. Due to their more advanced technology, lithium-ion batteries are more expensive than lead-acid batteries. 

High temperatures, overcharging, or improper installation can cause lithium-ion batteries to overheat, leading to a condition known as thermal runaway. This results in them catching fire. You can minimize the risk of thermal runaway by ensuring proper installation. 

Pros:

• Have discharging capabilities of 80%–100%
• Use newer technology with better battery capacity and efficiency
• Are smaller, lighter, and longer-lasting than lead-acid batteries

Cons:

• Are more expensive than other battery options
• Require special equipment for installation, limiting their system compatibility
• Are subject to thermal runaway when overcharged or overheated

Best For:

Residential solar installations.

Nickel-Cadmium Batteries

Residential solar systems rarely use nickel-cadmium (Ni-Cd) batteries, as they’re primarily designed for commercial-scale solar installations. However, some manufacturers are testing Ni-Cd models for home solar systems, with the potential for more. 

These batteries can discharge 80%–100% of their capacity. They can handle many charge and discharge cycles, or deep cycling, without affecting their life span. Unfortunately, these batteries have higher self-discharge than other options, meaning they lose charge over time when unused. 

These rechargeable batteries have a lower energy density, making them heavy and bulky. Nickel-cadmium batteries have longer life spans than lead-acid and lithium-ion varieties, lasting up to 20 years or more. They’re low maintenance and work well in extreme temperatures. 

Ni-Cd batteries use very old technology containing toxic materials that can harm the environment when not disposed of properly. Due to their toxicity, several countries, including Canada, Japan, and many American states, have banned their use. These batteries also cost more than lead-acid batteries but less than lithium-ion options. 

Pros:

• Excellent performance in extreme conditions
• Higher discharge capabilities of 80%–100% 
• Life span up to 20 years or longer

Cons:

• Its toxic components make it harmful to the environment
• Lower stored power retention than other battery types
• Not available for residential solar systems

Best For:

Large-scale solar installations and commercial projects. 

Flow Batteries

Flow batteries are another emerging technology. They use water-based electrolytes that flow between two internal chambers, or tanks. The batteries charge and discharge through chemical reactions inside. Adding more tanks can increase their total solar energy storage capacity. Flow batteries are becoming more popular in large facilities but have limited availability to homeowners. 

These batteries have 100% discharge capabilities and excellent efficiency, with little energy lost when charging and discharging. Due to the internal tank size and electrolyte liquid, these batteries have a low energy capacity. They’re quite heavy and require significant space since additional tanks are needed to increase their storage capacity. Flow batteries are also high-maintenance and require frequent refilling and flushing of the electrolyte tanks. They can last 20 years or longer when used properly. 

Flow batteries use nontoxic chemistry and nonflammable electrolyte liquid. However, they’re costly and impractical for residential solar systems, though some manufacturers have begun creating household-friendly flow batteries.

Pros:

• Ability to add tanks makes storage capacity customizable
• Excellent efficiency and life span of 20 years or longer
• Nontoxic and nonflammable components for improved safety

Cons:

• Too expensive for residential use 
• Low power density due to internal tanks’ size and weight
• High-maintenance

Best For:

Large-scale installations. There is currently no residential version available at an affordable price.

Consider the following factors when selecting the right solar battery storage solution.

Battery Capacity

Battery capacity, represented in kilowatt-hours (kWh), is the amount of power a solar battery stores. You’ll find batteries listed with two capacities: storage capacity and usable capacity. Storage capacity represents the battery’s full storage capacity. Usable capacity is how much energy the battery provides minus the amount needed to run it.

Battery capacity should align with your solar system’s energy production. High-efficiency solar panels generate more power than needed, making it easier to store the excess energy for later use. Installing a battery smaller than your system’s capabilities will waste energy, while a battery that’s too big for your system will never charge to its full capacity. 

Depth of Discharge

Depth of discharge (DoD) determines the amount of storage capacity a battery can use before requiring recharging. The industry standard is 50% for lead-acid batteries and 80%–100% for lithium-ion options. 

Solar battery manufacturers include DoD limits to preserve a battery’s life span. Repeated deep discharge cycles will significantly damage the battery and shorten its life span. Lithium-ion batteries have a better DoD than lead-acid options and provide more usable energy.

Life Span

Solar batteries with longer life spans add more value to your system and require fewer replacements, helping reduce your total investment. Battery life span varies based on battery chemistry, depth of discharge, and quality. Batteries with shorter life spans also create more waste and have a higher environmental impact. 

Batteries generally last between five and 15 years, depending on the type. Lead-acid batteries last five years, while lithium-ion batteries last 10 years or more. 

Price

Solar battery pricing varies based on the battery’s chemistry, capacity, efficiency, and brand. Choose a battery that balances affordability with durability. Lead-acid batteries are cheaper but will require replacement after three to five years. Lithium-ion batteries last longer but are more expensive up-front.

Homeowners should consider using solar incentives and credits to lower overall system costs. The federal solar credit provides a tax credit equal to 30% of your installation costs. This credit helps reduce or eliminate your owed federal taxes during tax time. As of January 2023, homeowners can also receive 30% off the cost of a stand-alone solar battery. This means homeowners with existing solar systems can use this credit to add energy storage more affordably. 

Additional state and local solar incentives may reward you for adding a solar battery to your system. We recommend checking the Database of State Incentives for Renewables and Efficiency (DSIRE) for local incentives. 

Round-Trip Efficiency

Round-trip efficiency indicates how well a battery can store and retrieve energy, and how efficiently a battery operates once it’s charged. Inefficient batteries drop in energy levels after charging, reducing the available stored energy. According to the U.S. Energy Information Association (EIA), the industry standard for round-trip efficiency is around 80%.

Batteries with a higher round-trip efficiency will convert power from your solar panels with minimal energy loss. Pairing an efficient solar battery with high-quality solar panels will produce better energy and store more energy for future use. 

Warranty

Most solar batteries have a standard warranty of 10 years. Some manufacturers include additional clauses that may end the warranty before the published end date. For example, some companies add a cycle clause that designates a specific number of charge and discharge cycles a battery will reach during its lifetime. One cycle includes a full battery charge and discharge. If your batteries reach this cycle clause before the warranty period, your warranty will end early. If the cycle clause is 3,000 cycles, your battery might reach this threshold before the end of 10 years. 

Warranties also include details on projected capacity. The industry standard for end-of-warranty capacity is 60%. Any batteries that meet or exceed that threshold are excellent options.

Solar batteries have several benefits, including better energy savings, a reduced carbon footprint, and greater energy independence. We’ll review some highlights below. 

Extend Energy Independence

Solar batteries let homeowners store excess solar energy generated during the day to power their homes during low-sunlight days or overnight. You’ll reduce your reliance on grid-tied power and gain greater energy independence.  

Improved Energy Efficiency

Top solar companies build systems that meet or exceed your home energy needs. Installing a solar battery allows you to use that extra energy in the future, extending your system’s efficiency. 

Increased Cost Savings

Solar batteries improve your savings by putting your excess energy to good use. If your utility company offers time-of-use (TOU) rates, you can avoid periods of high electricity rates by tapping into your stored energy. When rates drop, your solar battery will activate and charge, saving you money on your electricity bills. 

Provide Backup Power

Solar batteries power your home during blackouts without additional backup generators. Homeowners can direct power to the whole household or major appliances, helping conserve their backup power. 

Reduce Carbon Footprint

Batteries help reduce your environmental impact and carbon footprint. By storing more solar energy, you’ll improve your clean energy benefits and further reduce fossil fuel reliance.

Solar batteries can boost your energy savings, improve your solar system’s efficiency, and reduce your dependency on grid-tied power. Lead-acid and lithium-ion batteries are the best solar batteries for homeowners. Lead-acid batteries work best in off-grid installations, while lithium-ion options are ideal for standard residential solar systems. Other battery options, such as flow and nickel-cadmium batteries, are used in commercial and large-scale projects but aren’t currently available for residential use.

Consider a battery’s DoD, round-trip efficiency, and power capacity when choosing the right one for your home. Solar battery installation is complex, and we don’t recommend it as a do-it-yourself (DIY) project. Work with professional solar installers to add a battery to your home system. Many installers have certifications for specific battery brands to ensure a safe and reliable installation.

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