Solar energy storage systems have become popular among homeowners and businesses seeking greater energy independence and solar backup power during grid outages. The federal investment tax credit (ITC) recently increased to 30% for solar systems and standalone battery storage, further fueling demand for various types of solar storage. In addition, numerous states are now offering battery incentives, including California, Hawaii, Illinois, Maryland, Massachusetts, and Oregon. Thus, 2024 is poised to be a banner year for solar energy storage device adoption across many markets, from residential to utility-scale storage.
“The solar ITC extension is good news for the residential storage industry, preventing a drop in residential solar-plus-storage installations that would have otherwise arrived in 2024. The standalone storage ITC will also boost storage retrofits on homes with existing solar,” said Chloe Holden, research analyst at Wood Mackenzie, in a press release.
Due to the strong demand for solar energy storage, understanding the various options and emerging technologies is helpful when speaking with prospective customers. Knowing the possibilities allows solar contractors to better serve clients by designing and installing photovoltaic (PV) systems with solar energy storage technologies that meet their needs while boosting their return on investment.
What Is Solar Energy Storage?
Because solar energy is an intermittent energy source, it is only available during daytime hours. Solar energy storage systems allow homes and business owners to store energy for later use. For off-grid systems that aren’t connected to the electrical grid, batteries enable properties to have power around the clock. For grid-tied systems, a hybrid solar system with battery storage enables homeowners to have power during blackouts and to use solar electricity when preferable.
In areas with time-of-use rates, renewable energy storage systems allow utility customers to further reduce their electricity bills. They can use stored energy when rates are highest and charge their batteries when rates are lower, reducing the payback period of the photovoltaic solar system.
Some of the most popular solar energy storage systems are the Enphase IQ, Generac PWRcell, LG Chem RESU, Panasonic EverVolt, Sonnen Eco, SunPower SunVault, and Tesla Powerwall 2.
Popular Solar Energy Storage Systems
Solar Battery | Battery Chemistry | Capacity (kWh) | Cycle Life | Inverter Compatibility |
Enphase IQ 10 | Lithium Iron Phosphate (LiFePO4) | 10.1 kWh | 10,000+ cycles | Designed for Enphase microinverters |
Fortress eVault Max | Lithium Iron Phosphate (LiFePO4) | 18.5 kWh | 6,000+ cycles | Compatible with various solar inverters |
Generac PWRcell | Lithium Iron Phosphate (LiFePO4) | Up to 17.1 kWh | Varies | Built-in solar inverter |
LG Chem RESU 10H | Lithium Nickel Manganese Cobalt Oxide (NMC) | 9.6 kWh | 6,000+ cycles | Compatible with various solar inverters |
Panasonic EverVolt | Lithium Nickel Cobalt Manganese Oxide (NCM) | 9, 13.5 or 18 kWh | 6,000+ cycles | Can be paired with various inverters |
Sonnen Eco 10 | Lithium Iron Phosphate (LiFePO4) | 10 kWh | 10,000+ cycles | Integrated inverter |
SunPower SunVault | Lithium Iron Phosphate (LiFePO4) | 13, 19.5, 26, 39, and 52 kWh | 4,000+ cycles | Compatible with SunPower systems |
Tesla Powerwall 2 | Nickel Manganese Cobalt Oxide (NMC) | 13.5 kWh | 4,000+ cycles | Integrated inverter |
*Note: The "Cycle Life" values are approximate estimates
Why Is Solar Energy Storage Important?
An aging utility grid and increasingly common extreme weather events have caused power outages to become more common. For example, some utility companies have been cutting off power during times when threats of wildfires are particularly high. These public safety power shutoffs are designed to help prevent electrical equipment from causing wildfires but result in numerous homes and businesses losing power.
Although backup generators are an option for producing electricity during power outages, they rely on fossil fuels, are noisy, and create carbon emissions. As the cost of solar energy storage falls, solar batteries are becoming an increasingly popular way to keep the lights on during blackouts and store excess energy. These solar energy storage systems can also help with overall grid operation by smoothing out electricity supply and demand.
In some areas, there is so much installed solar capacity that electricity is wasted when solar power production exceeds demand. The duck curve is a graph that shows energy demand and solar energy production and is shaped like a duck. Unfortunately, occasional energy overproduction can lead to waste. However, solar energy storage systems help avoid this by storing energy when demand is low, and making it available when solar production is low and power demand is high.
Types Of Solar Energy Storage
There are many different energy storage technologies at different phases of development. Some are better suited for smaller mobile applications, while some require a lot of space and are better for large-scale applications. Certain technologies can store energy for a few hours, while others are better suited for long-term energy storage.
Electrical Storage
These battery energy systems store energy as electricity. The most common types are lead-acid, such as sealed AGM batteries and lithium-ion batteries. The most popular lithium-ion solar battery storage options are lithium iron phosphate (LFP) and nickel manganese cobalt (NMC).
Chemical Energy Storage Systems
These solar energy storage systems store energy in the form of chemical bonds, not electrical energy. For example, hydrogen gas can be used to store energy in fuel cells for both short and long periods of time. Hydrogen is created from electrolysis, which uses electricity to split hydrogen and oxygen.
Thermal Energy Storage
These energy storage systems use a material, such as water, molten salts, or sand, in an insulated tank to store heat. Then, this energy is either used to generate electricity or is used to provide heat. Thermal storage is useful for concentrated solar thermal power (CSP) plants that focus sunlight to heat a fluid.
A relatively widespread application is solar thermal water heaters that use solar collectors to heat water in a storage tank. The hot water can then be used as domestic hot water or to heat buildings through a heat exchanger or a radiant floor heating system. However, researchers at Lawrence Berkeley National Laboratory are investigating how to take this to the next level using next-generation materials and systems.
Determining The Best Type Of Solar Energy Storage
When selecting a battery for a project, it’s critical to consider the power rating, usable storage capacity, roundtrip efficiency, warranties, cost, and battery lifespan. Lead-acid and lithium-ion batteries are the two most common battery technologies used to store solar energy. Although lead-acid batteries have a lower cost, they typically have a shorter lifespan and warranty period. As the price of lithium-ion batteries falls, they have become more popular for most residential and commercial solar applications.
LFP (LiFePO4) Vs. NMC Solar Batteries
There are two types of lithium batteries used in solar PV projects. Lithium iron phosphate batteries contain a lithium iron phosphate cathode, which extends the lifespan of the battery and boosts safety. Nickel manganese cobalt batteries have a cathode made from a combination of nickel, manganese, and cobalt and are commonly found in laptops, cell phones, and electric vehicles. However, many EV manufacturers are switching from NMC to LFP batteries.
Popular LPF and NMC Solar Batteries
NMC batteries are widely used for solar storage, and the Generac PWRcell, LG Chem RESU, Panasonic EverVolt, and Tesla Powerwall 2 are NMC batteries. However, the Enphase IQ, Fortress Power eVault, Sonnen Eco, and SunPower SunVault are LFP batteries.
Advantages of LiFePO4 Solar Energy Storage
Safety: LiFePO4 batteries are known for their excellent safety profile. They are less prone to thermal runaway and are more stable at high temperatures compared to NMC batteries.
Long Cycle Life: LiFePO4 batteries typically have a longer cycle life compared to NMC batteries. They can withstand a higher number of charge and discharge cycles before experiencing significant degradation.
Stability: LiFePO4 chemistry is inherently more stable, which contributes to a reduced risk of thermal runaway and enhances the overall safety of the battery.
High Temperature Performance: LiFePO4 batteries perform well in high-temperature environments, making them suitable for applications where elevated temperatures may be a concern.
Flat Discharge Curve: LiFePO4 batteries exhibit a relatively flat discharge curve, meaning they provide a consistent voltage output over a wide range of states of charge. This can be advantageous for certain applications.
Environmental Impact: LiFePO4 batteries are considered more environmentally friendly than NMC batteries as they contain fewer rare and toxic materials.
Advantages of NMC Solar Energy Storage
Energy Density: NMC batteries generally have a higher energy density than LiFePO4 batteries, meaning they can store more energy in a given volume or weight. This makes them suitable for applications where space or weight is a critical factor.
Cost: NMC batteries can be more cost-effective to manufacture, making them a popular choice for various applications where cost considerations are paramount.
Wider Voltage Range: NMC batteries often have a wider voltage range, providing flexibility in designing battery packs for specific voltage requirements.
Application Flexibility: Due to their higher energy density, NMC batteries are commonly used in electric vehicles and applications where maximizing energy storage in a limited space is crucial.
Which is Better, NMC or LFP Solar Energy Storage Batteries?
Typically, LFP batteries have a longer lifespan and are safer. In contrast, NMC batteries are usually a bit less expensive, have a higher energy density, and can withstand colder temperatures slightly better. However, NMC batteries are not necessarily more cost-effective than LFP batteries because they can have a shorter lifespan.
AC Vs. DC-coupled Solar Energy Storage
When selecting a solar battery, it is also helpful to consider the inverter. Some solar storage batteries are AC coupled, so they have built-in battery inverters. Because AC-coupled solar systems do not require a hybrid inverter, they work with microinverters and string inverters.
If a DC-coupled battery is used, then a hybrid inverter, such as the SolarEdge StorEdge, is needed. The Enphase IQ, Generac PWRcell, Sonnen Eco, SunPower SunVault, and Tesla Powerwall 2 are all AC-coupled batteries.
Considerations | AC-Coupled Solar Batteries | DC-Coupled Solar Batteries |
Efficiency | Generally higher efficiency in energy conversion. | May have lower energy conversion efficiency due to additional steps. |
Flexibility | More flexible in terms of system design and scalability. | Limited flexibility in system design, especially in retrofitting. |
Installation Ease | Simpler installation process, especially for retrofits. | Installation can be more complex, requiring coordination with PV array. |
Battery Compatibility | Compatible with a wide range of batteries. | Compatible with specific battery technologies, usually lead-acid. |
System Monitoring | Enhanced monitoring capabilities for both PV and battery. | Monitoring may be limited, depending on the system configuration. |
System Expansion | Easier to expand the system with additional components. | Expansion may require more intricate planning and adjustments. |
Battery Placement | Batteries can be located at any distance from the PV array. | Batteries need to be located near the PV array for efficiency. |
Cost | Generally more cost-effective for small to medium systems. | Cost may be higher due to additional hardware and complexity. |
Compatibility with Inverters | Compatible with a wide range of inverters. | Requires inverters specifically designed for DC-coupled systems. |
Different Types Of Solar Energy Storage Systems Work Better In Different Applications
Selecting the ideal solar energy storage solution is critical to successful projects. Although many different types of energy storage systems are on the market, some are better suited for specific applications or configurations. Understanding the project goals and budget is critical for choosing the optimum solar energy storage solutions. The GreenLancer team is available to help with all types of solar energy systems.
Work with GreenLancer on your next project to take advantage of our extensive expertise in adding solar energy storage to many different PV projects. We can help with solar permitting, engineering stamps, and utility interconnection applications. Complete the form below to learn more.