What Is The Best Battery To Store Energy From Solar Panels?
Solar power has experienced exponential growth over the past two decades, with an average annual increase of 24% since 2000 according to the Solar Energy Industries Association (SEIA). However, solar energy production relies on sunlight, which means energy must be stored for use when the sun isn’t shining. This is where solar batteries come into play.
The most popular battery options for storing solar energy include lead-acid batteries, lithium-ion batteries, saltwater batteries, and flow batteries. Each has its own advantages and disadvantages. Key factors to consider when selecting a solar battery include upfront costs, lifespan, performance, maintenance requirements, safety, and environmental impact. This article provides an overview of the leading solar battery choices and recommendations for residential and commercial installations.
Lead-Acid Batteries
Lead-acid batteries are one of the oldest and most established battery technologies (source). They were invented in 1859 by French physicist Gaston Planté and have been used in a variety of applications like automobiles and backup power supplies. Lead-acid batteries consist of lead electrodes and sulfuric acid electrolyte.
Some pros of lead-acid batteries are that they have a low upfront cost and are readily available. They also have a reasonable energy density and are tolerant to overcharging. On the downside, they have a shorter cycle life compared to lithium-ion batteries, require more maintenance, and are less environmentally friendly due to lead being toxic (source).
Lead-acid batteries work well for solar energy storage when deep discharge is not required. They are a cost-effective solution for small to medium home solar panel systems. However, their limited cycle life makes them less ideal for frequent charge/discharge applications.
Lithium-Ion Batteries
Lithium-ion batteries are currently the most popular type of rechargeable battery for solar energy storage. They have high energy density, low self-discharge, high efficiency, and long lifespans (BloombergNEF, 2022).
There are several common lithium-ion battery types used for solar storage:
- Lithium Nickel Manganese Cobalt Oxide (NMC) – lower energy density but cheaper
- Lithium Iron Phosphate (LFP) – safer chemistry and longer lifespan
- Lithium Nickel Cobalt Aluminum Oxide (NCA) – high energy density but more expensive
Advantages of lithium-ion batteries include:
- High energy density – store lots of energy in a small space
- High efficiency – up to 95% round trip efficiency
- Long lifespan – can last 5-15 years with proper maintenance
- Low self-discharge – only lose 5% charge per month
Disadvantages include:
- Sensitivity to high temperatures
- Risk of thermal runaway if overcharged/damaged
- Degradation over time – lose capacity as they age
- Higher upfront cost than lead-acid
Lithium-ion batteries work well for most home solar storage applications. Their high energy density makes them ideal where space is limited. They can handle frequent charge/discharge cycles from solar panels. LFP chemistry offers the best longevity and safety.
Saltwater Batteries
Saltwater batteries, also known as saline batteries or flow batteries, are a rechargeable battery technology that uses a saline solution as the electrolyte. The saline solution contains sodium and chlorine ions dissolved in water.
The key advantage of saltwater batteries is their use of abundant and low-cost materials compared to alternatives like lithium-ion batteries. The saline solution is non-toxic and non-flammable, making saltwater batteries very safe to operate. Recharging simply requires replacing the discharged saline solution with freshly charged solution, allowing for indefinite reusability. Their modular and scalable design also allows saltwater batteries to be sized for small or large-scale applications.
Some downsides are their low energy density compared to lithium-ion, and the pumping systems required to circulate the saline solution between storage tanks and the battery stack during operation. This makes them less suitable for portable applications. Saltwater batteries also have higher self-discharge rates than other battery chemistries.
Saltwater batteries are ideal for non-mobile applications like storing excess renewable energy or providing backup power for homes, businesses, or microgrids. Their safety, sustainability, and longevity make them well-suited for residential energy storage. Their scalability also allows saltwater batteries to be used for grid-scale energy storage and load-leveling. [1] [2]
Flow Batteries
Flow batteries are a type of rechargeable battery where electrolytes containing one or more dissolved electroactive elements flow through a reactor that converts chemical energy directly to electricity (https://www.powermag.com/flow-batteries-energy-storage-option-for-a-variety-of-uses/). Unlike conventional batteries, the electrolyte is stored externally and flowed through the system as needed.
Flow batteries have some key advantages (https://pubs.acs.org/doi/10.1021/cen-10125-feature1):
- Very long lifespan – able to perform over 20,000 charge-discharge cycles
- The electrolyte liquids can be reused indefinitely
- Energy capacity and power output can be scaled independently
- No degradation over time when idle
However, flow batteries also have some downsides:
- High upfront capital costs
- Low energy density compared to lithium-ion batteries
- Additional balance of plant equipment needed
Flow batteries are ideal for large, stationary energy storage applications like storing solar energy or stabilizing the electrical grid. They are less suitable for small scale or mobile applications due to size and weight constraints. Key use cases are utility-scale energy storage and microgrid storage systems (https://www.powermag.com/flow-batteries-energy-storage-option-for-a-variety-of-uses/).
Comparison of Options
When selecting the best battery type for storing solar energy, it’s important to compare the key factors like upfront costs, lifespan, efficiency, maintenance requirements, and safety. Here is an overview of how the main battery options stack up against each other:
| Battery Type | Upfront Cost | Lifespan | Efficiency | Maintenance | Safety |
|---|---|---|---|---|---|
| Lead-Acid | Low | 2-5 years | Moderate | High | Moderate |
| Lithium-Ion | Moderate | 5-15 years | High | Low | Moderate |
| Saltwater | Low | 5-10 years | Moderate | Low | High |
| Flow | High | 10-20 years | High | Low | Moderate |
As you can see, lithium-ion and flow batteries tend to have the longest lifespan and highest efficiency, but have higher upfront costs. Lead-acid is inexpensive upfront but requires more maintenance. And saltwater offers a good balance of efficiency, lifespan and safety. Choosing the right option depends on your budget and needs.
Factors to Consider
When choosing a battery for solar energy storage, there are several important factors to consider:
Climate and Temperature
The climate and temperature where the solar battery system is located will impact performance and longevity. In very hot climates, lithium-ion batteries can experience reduced lifespan and capacity. Lead-acid batteries also don’t function optimally in high heat. Cold temperatures can also degrade battery performance. Carefully consider the typical ambient temperatures for the battery installation location.
Installation Considerations
The battery bank size, wiring, and connections must be properly sized for the solar system. Batteries are heavy, so the location and structural support must accommodate weight loads. Ventilation and temperature control are also installation factors, especially for enclosed battery bank areas. Any local building codes must be followed.
Maintenance and Monitoring
Regular maintenance and monitoring is crucial for solar batteries to ensure proper operation and maximize lifespan. This includes checking battery voltage and connections, cleaning corroded terminals, equalizing charges for lead-acid batteries, and monitoring cell balance and health data. Advanced monitoring systems can provide automatic alerts and diagnostics. Hands-on maintenance is required at regular intervals.
Recommendations
Based on the factors and options discussed, the best overall battery for storing energy from solar panels is the LG Chem RESU10H lithium-ion battery (https://www.lgessbattery.com/us/home-battery/lg-resu10h.lg). LG Chem’s lithium-ion batteries offer high efficiency ratings up to 95%, 10 year warranties, a slim and wall-mountable design, and integrated software for monitoring and control. With high depth of discharge and 4,000-10,000 charge cycles, the LG Chem RESU10H provides longevity and optimal storage for solar power.
When pairing a battery with solar panels, the LG Chem RESU10H lithium-ion battery aligns well for small to medium home solar needs (3-8kW systems), while the larger RESU16H scales up to 12kW systems. Flow batteries like the CellCube FB 10-100kW also pair well for large scale solar storage. Lead-acid batteries like the Trojan T105 are most cost-effective for smaller 1-2kW solar systems. The battery size, energy capacity, voltage, and maximum discharge rate should match the solar array’s energy production.
Installation and Maintenance
The process for installing a solar battery bank consists of several key steps. First, a site assessment and energy audit should be conducted to determine the proper size and placement of the system (https://sistinesolar.com/solar-battery-storage-installation/). Next, any necessary electrical upgrades are completed and permits acquired. The battery bank is then mounted, wired, and connected to the solar panels and inverter. Most experts recommend hiring a qualified solar installer for complex battery bank installations (https://www.beyondsolar.com.au/wp-content/uploads/2018/11/guide-to-installing-a-household-battery-storage-system.pdf).
Proper maintenance is crucial for solar batteries to operate safely and efficiently long-term. Batteries should be visually inspected monthly for any corrosion or damage. Cables and connections should also be checked for wear. Most manufacturers recommend a full maintenance check 1-2 times per year, which may include cleaning terminals, testing voltages and connections, and verifying proper ventilation and temperature. Battery electrolyte levels may need to be checked for certain battery types. Following the manufacturer’s maintenance schedule and guidelines can extend the battery bank lifetime.
Conclusion
When choosing the best battery for an off-grid solar energy system, the main options are lead-acid, lithium-ion, saltwater, and flow batteries. Lead-acid batteries are the most affordable option, but have a shorter lifespan. Lithium-ion batteries are lighter, more efficient, and last longer, but are more expensive. Saltwater batteries using abundant raw materials, but currently have limitations around energy density. Flow batteries have very long lifespans, can discharge 100% without damage, and are scalable, but have high upfront costs.
The optimal solar battery depends on your budget, energy needs, climate, and how much maintenance you are willing to do. Lead-acid batteries can work well for smaller systems in warmer climates if replaced every 5-8 years. Lithium-ion is best for larger systems and colder weather, despite the higher price tag. Weigh longevity, capacity, efficiency, maintenance and costs to choose the right technology for your solar installation. With improvements in battery tech continuing, it’s an exciting time to go solar.
