Why Install a Solar Battery?
Today, homeowners who make the switch to solar energy have more options than ever when it comes to their home solar system. Homeowners who want simplicity can opt for a classic grid-tied solar PV system that allows them to benefit from both solar energy and the power grid, while those who are committed to self-sufficiency can opt for an off-grid solar system, and still others may opt for a hybrid system that offers the best of both worlds.
Those who opt for hybrid or off-grid solar systems will need a battery, or often multiple batteries, to ensure proper energy storage. Since solar panels don’t produce energy when the sun isn’t shining, a home solar system needs a backup energy source to provide power at night. With a grid-tied system, the power grid is the backup energy source. With an off-grid system, the battery (or, more often, multiple batteries) are the backup. With a hybrid system, a battery and the power grid both act as backup sources of energy.
A hybrid solar system is essentially a grid-tied solar system that is connected to a backup battery. There are a few reasons to choose a hybrid solar system. A common reason for connecting a backup battery through a hybrid system is the reliability that this type of system offers. With a hybrid solar system, your house will always have power—this is in contrast to a standard grid-tied system, with which your house loses power if the power grid experiences an outage. With a hybrid system, your battery kicks in when the grid goes down, and your home’s electricity continues to run.
Hybrid systems are also attractive to homeowners whose utility companies don’t offer equal credits for net energy metering. Net energy metering is an incentive that most states mandate power companies to offer. Net energy metering allows the utility company to track the excess energy that your solar panels produce and send back to the power grid when it’s sunny and you’re producing more energy than you’re using. Then, the utility company also tracks the energy you use from the power grid when your solar panels aren’t producing power, such as at night. At the end of the month, the utility company subtracts the energy you produced from the energy you used, drastically reducing your power bill.
Typically, net energy metering means you receive one kilowatt hour (kWh) in energy “credits” in exchange for every kilowatt hour your solar panels send to the power grid. However, there is a growing trend in the solar industry, wherein utility companies are changing their crediting system for net energy metering and reducing the value of these solar energy production credits. As a result, homeowners with solar panels are receiving credit for less than the retail market value of the energy they’re sending back to the grid. For homeowners that are tied to power companies that have adopted this unfortunate trend, we recommend opting for a hybrid system. With a hybrid system, excess energy produced by your solar panels gets stored in your battery. When your solar panels aren’t producing power at night, your system will draw from the stored energy in your battery, rather than drawing from the power grid, to power your home. This reduces your power bill and prevents you from giving free energy away to the power company.
Comparing Solar Panel Battery Options
If you’ve decided you want to opt for an off-grid or a hybrid solar system that connects your solar panels to a battery, there are a few things to consider. When you’re evaluating the components of a home solar energy system, the specs and fact sheets often appear complicated. Below, we’ve broken down what to focus on that will help you understand these documents and better assess your solar battery options. You want to look for the battery’s capacity and power ratings, its round-trip efficiency, its depth of discharge (DoD), its warranty, and which company it is manufactured by.
Solar Battery Capacity & Power Ratings
Battery capacity indicates the amount of energy, measured in kWh, that a battery is capable of storing. Typically, the batteries you’ll find for home solar systems are designed to be “stackable,” which means it’s easy to include multiple batteries in your solar system in order to optimize your solar storage capacity. Note, however, that the battery’s capacity only indicates the size of the battery’s storage abilities—it doesn’t actually tell you anything about how much electricity the battery is able to provide in any given moment. You’ll get that information from the battery’s power rating. The power rating indicates the amount of electricity, in kilowatts (kW), that a solar battery can deliver at any given moment in time.
To put it in context: if your battery has a low capacity but has a high power rating, it might be capable of powering your entire home, but only for a short period of time. In contrast, a battery with a high capacity and a low power rating could run a series of appliances in your home for a long period of time.
Solar Battery Round-Trip Efficiency
The round-trip efficiency of a solar battery indicates the amount of energy that can be used in relation to the energy required to store it. As an example, if your battery consumes 10 kWh of energy and you get 7 kWh back, your battery’s round-trip efficiency is 70%. Typically, the higher your battery’s round-trip efficiency, the better the battery’s value.
Solar Battery Depth of Discharge
Generally, it’s best for batteries to retain some of their charge, rather than discharging all of their energy every time they are used. This is due to the way batteries are composed chemically—use and wear naturally degrades batteries and using a battery’s entire charge will more quickly reduce its ability to store energy. With this in mind, depth of discharge refers to the amount a solar battery’s charge should be emptied, relative to its overall storage capacity. For example, if you purchase a 10 kWh solar battery with a DoD of 80%, you should not use more than 8 kWh before recharging the battery. It’s important to pay attention to this number. If a battery is discharged beyond its recommended DoD, the value of the battery may be significantly impacted by the resulting degradation. This is a key consideration to factor in when shopping for a solar battery.
A lower DoD reduces the cost per kWh stored, but it also reduces the usable kWh per week. Lead-acid batteries are most susceptible to highly specific DoD specs. There are other types of batteries, such as flow batteries and saltwater-based AHI batteries that, theoretically, offer nearly 100% DoD. The Tesla Powerwall is an excellent option that offers a remarkable 100% DoD as well.
Solar Battery Warranties
Home solar batteries typically cycle on a daily basis, which just means your solar battery will charge and then drain each day. Regardless of the DoD factors mentioned above, all batteries’ ability to hold a charge lessens gradually over time. You’ve probably noticed this with your phone—as it gets older, a full charge lasts for less and less time.
To help you understand how your battery’s useful life will change over time, your battery’s warranty should guarantee the battery’s degradation rate over a specified number of years. For lead-acid batteries, which degrade more quickly, a typical warranty will be 5 years, whereas lithium-ion batteries often have longer warranties, often up to 10 years. Some manufacturers will go further by providing a warranty that guarantees your battery’s integrity for a specified number of cycles. For example, a battery that’s warranted for 5,000 cycles at 80% of its original capacity should still be able to provide no less than 20% of its original energy storage capabilities at the end of its “useful life” (which, in this case, is after 5,000 cycles). Lithium-ion batteries can typically withstand more cycles than lead-acid batteries and will be warranted accordingly.
Solar Battery Manufacturers
There are a wide range of companies developing, manufacturing, and selling solar batteries, from tech companies like Tesla to more traditional electronics manufacturers and solar-specific hardware brands. It can be hard to decide between an older, institutional company with a robust history of delivering value in comparison to a tech startup that’s pioneering incredible innovation. If you’re having a hard time deciding, we suggest closely comparing each company’s warranties to help make the decision.
Because home solar systems and electric vehicles share similar technologies by using batteries to create sustainability, efficiency, and eliminate greenhouse gases, it makes sense that automotive manufacturers are getting into the solar battery business. Companies like Tesla, BMW, and Mercedes-Benz have invested a great deal of their research and development into their energy storage batteries, and they’re using those resources to develop innovative solar batteries for homeowners. At Smart Solar Energy Co., we are big fans of the Tesla Powerwall, but each of these companies offer unique benefits depending on your unique situation.
How Long Will a Solar Battery Last?
To determine how long a solar battery will last, we will look at two distinct indicators. First, how many hours can a solar battery power your home? And second, what is the lifespan of a solar battery?
How Many Hours Can a Solar Battery Power a Home?
There are some cases in which a fully charged solar battery can power your entire home overnight when your solar panels aren’t producing power. To find the definitive answer, your solar representative would need to delve deeper. First, we would determine how much power your home requires in a single day. Then, we’ll look at your solar battery’s capacity and power rating. Finally, whether your system is a hybrid, grid-tied solar system or an off-grid solar system will make a big difference in your battery needs.
Based on data from the US Energy Information Administration, the average household uses about 28.9 kWh of energy each day. For simplicity’s sake, we’ll call this 30 kWh per day. Then, let’s assume your solar panels produce power for 6 hours of the day, and you’ll be drawing from your solar battery during the other 18 hours of the day. We’ll assume your solar battery has a capacity of 10 kWh—but its DoD is 90%, meaning it will actually produce 9 kWh. In this case, one to two solar batteries would likely be enough to supplement your solar panels and keep your home fully powered throughout the day. However, if you are working with an off-grid solar system, you’ll likely need even more solar batteries to ensure you have enough backup energy to get through several dark, cloudy days without running out of power.
What is the Lifespan of Solar Batteries?
Typically, the useful life of a solar battery will be somewhere between five to 15 years. Your solar panels, in contrast, are more likely to be warranted for 25 years, which means most homeowners need to replace their solar batteries at least once before their solar panels’ warranty ends. Caring for your batteries will boost their useful life, as well. It’s important to keep your batteries in temperatures above 30 degrees and below 90 degrees Fahrenheit. When batteries are exposed to extreme temperatures, they don’t work as efficiently. If your battery comes with temperature monitoring, you won’t have to worry about this—but if your battery doesn’t have a temperature monitoring system, it’s important that you find a way to ensure they’re within the appropriate temperature range to extend the life of your solar batteries. Additionally, solar technology has improved massively in recent years, and we expect that it will continue to do so. As more manufacturers invest in renewable energy solutions, more and better options for solar energy storage will continue to become available to homeowners.
Comparing Solar Battery Types
There are several key types of batteries that you’ll see most often when you’re shopping for solar: lithium ion batteries, lead-acid batteries, and saltwater batteries. Lead-acid batteries tend to be the least expensive, while lithium ion batteries are typically the highest quality (and can also be the costliest).
Lead-Acid Batteries
Lead-acid batteries have been around for a long time, and they tend to be the least expensive up-front solar battery option. Their cost per amp hour and cost per cycle tends to be relatively low. The downside of lead-acid batteries is the amount of maintenance they require and their shorter lifespans. Lead-acid batteries are a common choice for homeowners who wish to go completely off-grid and are comfortable taking on the significant maintenance requirements for these batteries. Because lead-acid batteries have shorter warranties and cycle guarantees, they also have to be replaced more frequently than other types of solar batteries. Lead-acid batteries typically come with a DoD of 50%, which means you may need to install a greater number of batteries in order to meet your energy storage needs.
Lithium-Ion Batteries
Most new solar battery technologies are made lithium-ion batteries, making these the most popular battery type. Lithium-ion batteries are much smaller and lighter than lead-acid batteries, tend to last much longer, and are generally more efficient. These batteries can typically be used at 80% DoD and offer longer warranties. While lithium batteries are the more expensive upfront option, they often provide more long-term value per kWh than other options. Lithium-ion batteries also don’t require cleaning or maintenance to perform well.
Saltwater Batteries
Saltwater batteries are the newest solar battery technology, and these batteries offer unique benefits. Saltwater batteries are safer than other battery types, because they don’t use toxic substances or heavy metals and pose no risk of flammability. Saltwater batteries have the longest lifespan of all the battery options and they are also recyclable—unlike lithium-ion and lead-acid batteries, which require special disposal processes. For the many solar converts who are passionate about sustainability, these features make saltwater batteries an attractive option. However, because saltwater batteries are such a new technology, they’re still relatively expensive to manufacture, and that cost gets passed along to the consumer. Saltwater batteries are also less energy-dense than lithium-ion batteries and require significantly more storage space to provide the same amount of energy.
When you’re thinking about going solar, battery types are just one of the considerations to factor into the decision process. Navigating solar panel costs and benefits can be complex—we know! To help you navigate the process, Smart Solar Energy Co. offers free solar audits, which can be done onsite at your home or virtually.
When you get a solar audit, you’ll get the full picture of whether your home qualifies for solar, how much you might save with a solar PV system, and a full cost breakdown for a grid-tied, hybrid, and/or off-grid solar system, depending on your preference. We’ll help you choose the best options when it comes to solar batteries and solar panels, and we’ll help you find your utility company’s net energy metering policy to determine whether you’ll benefit financially from a battery backup that stores your system’s excess energy.
