All solar batteries have the same basic function, but each type is suited for different applications. Your solar battery will offer higher reliability and return on investment when its chemistry is suitable for the application at hand.
For example, some electricity consumers are subject to higher kWh prices at certain times of the day, or additional charges for sudden peaks in consumption. In this case, you need a battery bank capable of delivering large amounts of electricity in a short time. Lithium-ion batteries are suitable for this task, but not redox flow batteries.
Regardless of the battery type, you also need to consider the depth of discharge (DoD), which indicates a battery&#;s usable capacity. The service life of a battery can be drastically shortened if you exceed the DoD, or you can even cause permanent damage. For example, using 70% of the stored energy is acceptable with a solar battery rated for 80% DoD, but not a 50% DoD battery.
Lead-acid batteries are an established technology, commonly used by off-grid solar energy systems in remote locations. Lead-acid batteries are affordable and have a well-established supply chain due to their popularity, so you can easily find vendors and technical support.
In spite of their low cost, lead-acid batteries have some technical limitations you should consider:
An absorbed glass mat or AGM battery is an improved version of the traditional lead-acid battery. They can charge faster while having a spill-proof design and more durability. You can also find AGM deep cycle batteries that are designed for 80% DoD.
Using lead-acid batteries along with solar panels requires charge controllers to sustain a suitable charging current. These batteries should not be wired directly to your solar array, or your system may be damaged by excessive current.
Lithium-ion batteries have become very popular in recent years since they can achieve synergy with solar panels and wind turbines. For example, the Tesla Powerwall and Enphase IQ are two types of lithium-ion batteries commonly used in home solar applications. You can also find smaller lithium batteries from brands like Renogy and WindyNation, which are portable and better suited for DIY solar projects.
Lithium iron phosphate or LFP batteries are a subtype of lithium batteries, characterized by a superior service life. The best LFP batteries offer a service life of over 4,000 cycles at 80% DoD, which means they can last for over 10 years on a daily charging cycle. This makes LFP batteries the ideal complement to solar installations. Unlike lead-acid batteries, which need separate charge controllers, many of the lithium battery models that are commercially available come with built-in chargers and controls.
The main drawback of lithium-ion batteries is the high price, but this could change in the near future &#; the U.S. Department of Energy is targeting a 90% energy storage cost reduction by . Lithium batteries can also suffer a phenomenon called thermal runaway when used at high temperatures, which causes them to catch fire. You can prevent thermal runaway by making sure your batteries are high-quality and installed by qualified electricians.
Nickel-cadmium batteries are characterized by their durability, tolerance to high temperatures and simple maintenance needs. Thanks to these performance features, nickel-cadmium batteries are popular in industrial and utility applications. Unfortunately, cadmium is highly toxic to humans, so nickel-cadmium batteries are not recommended in homes.
Flow batteries store energy by separating positive and negative electrical charges in chemical solutions, which are stored in separate tanks. When these two solutions interact, they undergo a reduction-oxidation reaction (redox) and the battery releases energy. This battery technology is also referred to as &#;redox flow&#; for this reason.
The main disadvantage of redox flow batteries is their space requirement, and they are not cost-effective for small-scale projects. Even a small redox flow battery system can be the size of a shipping container, so using flow batteries in home solar systems is not viable.
Like solar panels, batteries need an inverter to convert their stored DC electricity into usable AC electricity. Different types of inverters exist, depending on whether your battery system is AC- or DC-coupled. DC-coupled batteries often come with an integrated hybrid inverter for both solar and storage. AC-coupled batteries sometimes come with an integrated storage inverter, which only works with storage, meaning you'll need a separate solar inverter. Some batteries don't come with an inverter, so you must pair it with a separate, third-party inverter.
You may be able to save on equipment costs with a hybrid inverter, but you could have higher installation costs if retrofitting to an existing solar system, and you could miss out on some incentives, as we previously described.
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There are two ways to measure the output you'll get from your battery: usable capacity and power rating. Usable capacity is measured in kWh and describes the maximum amount of electricity your battery can store on a full charge. The higher the usable capacity, the longer your battery's runtime. When comparing the usable capacity of different batteries, you'll also want to consider how many batteries you can stack in parallel; even if the usable capacity of one battery is low, if you can connect multiple batteries to one inverter, it may allow you to customize your system to meet your energy needs better.
Your battery will come with two power ratings, both measured in kW. Its peak power rating measures the amount of power your battery can output in a short period. It's important to have a battery with a high peak power rating if you need it to run appliances that require a lot of energy to start, like an air conditioner or a sump pump. Your battery's continuous power rating measures the amount of power your battery can output consistently. The higher its continuous power rating, the more appliances you can run at once.
Ultimately, the amount of capacity and battery backup power you need depends on how much of your house you plan to power with your battery&#;and for how long.
Two primary metrics differentiate batteries in terms of performance. Depth of discharge (DoD) indicates the percentage of the battery that can be discharged relative to its overall capacity. In other words, it's the amount of your battery's capacity you can use in one cycle for optimal battery performance: The higher the DoD, the more you'll get out of your battery.
Roundtrip efficiency measures the electrical losses involved with charging and discharging a battery. Batteries with higher roundtrip efficiencies better convert incoming electricity into stored electricity and back to usable electricity; they're considered higher-performance batteries.
Every time you charge and discharge your battery, it slightly reduces its ability to hold a full charge. A battery system is a big investment, so you'll want to ensure it lasts. The best way to feel confident that your battery will continue working efficiently is to choose one with a strong warranty. Battery warranties include many different components and clauses, which all impact the assurance you can feel when choosing a long-lasting battery.
Your battery's warranty period is measured in years and covers the integrity and output of your system&#;typically, battery companies offer 10-year warranties. Most battery warranties also include an end-of-warranty capacity guarantee, which states that by the end of the warranty period, the battery will still maintain a certain percentage of its original usable capacity. Batteries also often come with a cycles clause (a specified number of times you can drain and charge your battery under warranty) and/or a throughput clause (the total amount of energy the manufacturer expects the battery to deliver throughout its lifetime). Similar to how many car warranties come with a time and/or mileage component (i.e., ten years, 100,000 miles), if you hit your warranted cycle life or throughput before your battery reaches the end of its warranty period, it could end your warranty term.
You'll also want to look at other warranty information, like if labor and shipping costs are covered for repairs and replacements; batteries are considered hazardous waste, which means that these costs can be extremely high in some cases if you need to send the battery back to the manufacturer for diagnostics.
Energy or load management systems enable you to both monitor and control your energy consumption, typically at the circuit level. In most cases, if you're installing a battery, you'll need to install a critical load panel, which protects your appliances and battery from unintended electrical failures and enables you to power only your most essential devices during power outages.
Energy management systems replace the need for a critical load panel by providing real-time flexibility, allowing you to turn circuits on and off remotely. They can replace your main electrical panel, serve as a sub-electrical panel (similar to a critical loan panel), or be installed along individual circuit lines for a more modular approach. Most importantly, these systems allow you to get more out of your battery during power outages by only powering the most important loads at a given time. One of the most prominent energy management system brands, Span, claims that their smart home panel provides 40% longer backup than battery-only systems.
Some battery companies are now manufacturing their own energy management systems, while others are compatible with third-party systems like Span and Lumin. Not all batteries are compatible with all energy management systems, so make sure to pick a battery compatible with the energy management system you prefer.
You'll want to get the most bang for your buck when purchasing a home battery. Battery cost comes down to two key factors: the equipment and installation time. Some batteries are more expensive due to factors like their chemistry or supply chain strength, while others may be bulky and large and, therefore, more difficult (and expensive) to install.
Thousands of homeowners request battery quotes through our Marketplace every year, providing us with unparalleled insight into the cost of different battery brands. Based on our latest Solar & Storage Marketplace Report, there's an extensive range in battery prices: HomeGrid offers the lowest cost batteries at $480/kWh, likely in large part due to their flexible configuration, which makes them easy to transport and quickly install, while Sonnen offers the highest cost batteries at $1,570/kWh, likely due to their extremely strong warranty. The most quoted battery company on the EnergySage Marketplace is Enphase, which surprisingly is the second most expensive battery brand at $1,490/kWh.
While there are many great battery companies, a few stand out above the rest. Depending on what you're looking for in a battery system, Duracell, HomeGrid, and Villara Energy Systems offer some of the best solar batteries today.
If you want to learn more, please visit our website battery storage solutions.