What batteries are best for solar storage?

Each type of solar battery serves a unique purpose despite sharing a fundamental function. Selecting a battery with the right chemical composition for your specific application will enhance its reliability and return on investment.

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Some electricity users experience higher kWh rates during particular times of the day or face extra fees for sudden consumption spikes. In these scenarios, batteries that can supply large quantities of power quickly are necessary. While lithium-ion batteries are up to the task, redox flow batteries are not.

No matter your battery choice, understanding the depth of discharge (DoD) is crucial as it impacts the battery's usable capacity. Exceeding the DoD can severely reduce the battery life or even cause permanent damage. For instance, utilizing 70% of stored energy is permissible for a battery rated for 80% DoD but not for a battery rated at 50% DoD.

Lead-Acid Batteries

Commonly utilized in off-grid solar systems, lead-acid batteries are a time-tested technology. Their affordability and well-established supply chain make them an easily accessible option for renewable energy solutions.

However, there are technical limitations:

• Typically, lead-acid batteries offer a lifespan of 500 to 1000 cycles.
• They should be fully recharged after each use to sustain their lifespan.

Absorbed glass mat (AGM) batteries are an advanced form of lead-acid batteries. AGMs charge faster, are spill-proof, and more durable. Deep cycle AGMs are designed for 80% DoD.

Given that lead-acid batteries need suitable charging currents, using them with solar panels necessitates charge controllers to avoid damaging the system.

Lithium-Ion Batteries

Lithium-ion batteries have gained significant popularity due to their compatibility with solar panels and wind turbines. Popular models like the Tesla Powerwall and Enphase IQ are often used in residential solar applications. Brands like Renogy and WindyNation offer portable lithium batteries ideal for DIY solar projects.

Lithium iron phosphate (LFP) batteries are noted for their long service life, offering over 4,000 cycles at 80% DoD, making them perfect for solar systems. Unlike lead-acid batteries, lithium models often include built-in chargers and controls.

Though they come at a high initial cost, impending cost reductions—such as the U.S. Department of Energy’s target of a 90% reduction in energy storage costs by 2030—might make them more affordable. One significant drawback is the possibility of thermal runaway at high temperatures, which can be avoided by purchasing quality batteries and having them installed by professionals.

Nickel-Cadmium Batteries

Known for their durability and tolerance to high temperatures, nickel-cadmium batteries are often used in industrial applications. Despite their advantages, cadmium’s toxicity makes them unfit for household use.

Flow Batteries

Flow batteries utilize stored chemical solutions to release energy upon interaction. These batteries, noted for their reduction-oxidation (redox) reaction, are unfortunately not viable for home use due to their size and cost-efficiency limitations.

They are generally the size of a shipping container, making them impractical for residential solar systems.

Solar battery technology is pivotal in the ongoing shift toward solar power. Reliable batteries ensure that stored solar energy can be used even when there’s no sunlight, offering both dependability and cost savings.

Read more about solar batteries for residences in our guide, Solar Batteries for Home: A Comprehensive Guide.

The Inflation Reduction Act (IRA) now makes battery storage eligible for the Investment Tax Credit (ITC), which stands at 30% until 2032. Even the electric vehicle sector, relying on similar energy storage solutions, drives advancements in solar battery technology and cost reduction.

Are Batteries Worth the Investment?

Investing in a home solar battery can be a sound decision for those seeking to maximize their PV system. Though the initial investment, ranging between $10,000 and $20,000 installed, is steep, the benefits could justify the cost. Additionally, federal and local incentives can bring the price down considerably.

The multifaceted advantages of solar batteries—emergency power generation, long-term energy cost savings, and carbon footprint reduction—make them a worthwhile investment, especially for those planning to stay long-term. The payback period can be as short as five years, depending on system capacity, design, and available incentives.

Tools like Aurora’s Energy Storage tool can help customers visualize the ROI effectively.

Factors to Consider

The rapid evolution of solar battery technology means that newer models frequently enter the market. Options range from traditional lead-acid batteries to modular systems like Tesla PowerWall. These advancements make storage solutions more flexible, easy to install, and maintain.

When planning a solar project, the first step is finding the right battery.

The One-Size-Fits-All Pitfall

Opting for a one-size-fits-all solar battery is often not ideal due to three reasons:

1. The dominant use of lead-acid technology, which isn’t the best available option.
2. Standardized batteries may be bulky with inadequate power storage capacity.
3. These batteries can either be oversized or undersized, affecting their performance.

Solar Battery Specifications

Not all batteries are created equal. Variations in quality control, manufacturing processes, and materials can lead to differences in performance and lifespan, even among batteries with similar specifications.

Battery Capacity

The capacity of batteries is measured in amp-hours, indicating how much electric energy it can store and deliver. To select the right battery, estimate peak power requirements in amp-hours.

Lifespan and Charge/Discharge Cycles

Key factors affecting battery longevity include:

• Depth of Discharge (DoD): This is the proportion of the battery's capacity that is used. Exceeding the DoD can shorten the battery’s lifespan.
• Cyclic Life: The number of charge and discharge cycles a battery can handle.
• Temperature: Higher temperatures increase chemical activity in batteries. It's best to install them in a temperature-controlled environment.

Flooded vs. Sealed Batteries

Batteries can be either flooded or sealed:

• Flooded batteries: Standard lead-acid batteries, used in vehicles and off-grid systems. They produce hydrogen gas and require regular maintenance.
• Sealed batteries: Also known as VRLA (valve regulated lead acid), they are maintenance-free and do not emit gases.

Peak Power Output

Measured in kilowatts peak (kWp), this indicates the maximum power output under ideal conditions. Higher kWp ratings suggest better performance.

Round-Trip Efficiency

This measures how much energy the battery outputs compared to the energy put in. A higher efficiency means the battery is more economical.

Ambient Working Temperature

This is the temperature range within which the battery operates efficiently. This factor is important for those living in areas with extreme temperatures.

Brand and Warranty

Choose a brand that offers a longer warranty and has a reputable history. This ensures reliability and quality.

Cost

Costs vary widely, with solar batteries ranging from $200 to $750 per kWh. Lead-acid batteries average around $260 per kWh, while lithium-ion batteries cost around $271 per kWh. Always consider available incentives like the Federal Investment Tax Credit (ITC) to reduce costs.

Types of Solar Batteries

Your budget and requirements should guide your choice of battery type.

Lead-Acid Batteries

A long-standing technology, lead-acid batteries are affordable and reliable. They include both flooded and sealed varieties and are suitable for off-grid systems and emergency backups.

Pros

Affordable and reliable, with a stable supply chain.

Cons

Bulky, heavy, and with a limited lifespan and depth of discharge.

Lithium-Ion Batteries

High in energy density and requiring minimal maintenance, lithium-ion batteries are becoming popular. Models like the Tesla Powerwall exemplify their potential.

Pros

Minimal maintenance, high energy density, and long lifespan.

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Cons

Expensive and require stabilizing circuits.

Flow Batteries

These scalable batteries have a long cycle life and fast recharge rates. However, they're bulky and expensive, making them suitable for large-scale projects rather than home use.

Sodium-Nickel Chloride Batteries

These are safe, reliable, and recyclable, but their high cost and limited lifespan make them suitable for large installations rather than residential projects.

Comparing Battery Types

Lead-Acid

• Cheapest option.
• Reliable and easy to maintain.
• Bulky with a short lifespan.
• Best for off-grid and emergency backups.

Lithium-Ion

• High energy density and long life.
• Minimal maintenance required.
• Expensive and fragile.
• Ideal for electric vehicles and remote devices.

Flow Battery

• Long cycle life and fast recharge rates.
• Expensive and non-recyclable.
• Ideal for large installations.

Sodium-Nickel Chloride

• Safe and recyclable.
• Short lifespan and expensive.
• Suitable for large-scale uses.

Conclusion

The best battery for your needs depends on specific power requirements. Most new buyers recommend using a solar battery storage tool for accurate estimates. Lithium-ion batteries are highly recommended for both industrial and residential installations due to their evolving technology and decreasing costs. For budget-conscious projects, lead-acid batteries remain a viable choice, considering environmental factors and expected usage.

Schedule a personalized demo to learn more about how Aurora can help you add battery storage to your offerings.

FAQs

Do solar panels have batteries?

Solar panels do not contain batteries. They generate electricity from solar energy, which can be stored in external batteries for later use.

What type of battery backups do solar systems use?

Common battery types in solar systems include:

• Lead-acid
• Lithium-ion
• Flow batteries
• Sodium-nickel chloride

What is the best way to choose a battery system?

Two key factors to consider are:

1. Storage needs: Batteries for brief power outages will differ from those for prolonged usage.
2. Budget: Balancing power requirements with budget constraints may require trade-offs.

Which type of batteries last the longest?

Lithium-ion batteries offer the longest lifespan and best performance.

Which battery chemistry is safest?

Lithium iron phosphate (LFP) batteries are among the safest available today.

How many solar batteries are needed for my home?

Calculate your daily energy requirements and multiply by the number of days you need storage. For example, a 30 kWh home needing two days of power would require six 10 kWh batteries.

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