How to choose the best battery for a solar energy system

When evaluating solar battery options, certain specifications should be used, such as how long the solar battery can last or how much power it can provide. Below, learn about all the standards used to compare home energy storage options and different types of solar batteries.

How to compare your solar storage options

As you consider your solar-plus-storage options, you will come across a lot of complicated product specifications. The most important ones to use during your evaluation are the battery’s capacity & power ratings, depth of discharge (DoD), round-trip efficiency, warranty, and manufacturer.

Capacity & power

Capacity is the total amount of electricity that a solar battery can store in kilowatt-hours (kWh). Most home solar batteries are designed to be “stackable,” which means that you can include multiple batteries with your solar-plus-storage system to get extra capacity. While capacity tells you how big your battery is, it can’t tell you how much electricity a battery can provide at a given moment. To get the full picture, you also need to consider the battery’s power rating. In solar batteries, a power rating is the amount of electricity that a battery can deliver at one time. It is measured in kilowatts (kW).  A battery with high capacity and low power rating will provide a small amount of power for a long time (enough to run some key equipment). Low-capacity and high-power batteries can keep your entire family running, but only for a few hours.

Depth of discharge (DoD)

A battery’s depth of discharge (DoD) indicates the percentage of the battery that has been discharged relative to the overall capacity of the battery. For example, if you have a Tesla Power wall that holds 13.5 kilowatt-hours (kWh) of electricity, and you discharge 13 kWh, the DoD is approximately 96 %.The more frequently a battery is charged and discharged, the shorter its lifespan will be. It’s generally not recommended to discharge a battery entirely, as that dramatically shortens the useful life of the battery. Many battery manufacturers have specified the recommended maximum DoD to achieve the best performance of the battery.

Round-trip efficiency

The round-trip efficiency of a battery represents the percentage of energy that can be used for storage. For example, if you feed 5 kWh of electrical energy into the battery and only get 4 kWh of useful electrical energy, the round-trip efficiency of the battery is 80% (4 kWh / 5 kWh = 80%). Generally speaking, higher round-trip efficiency means that you will get more economic value from the battery.

Battery life & warranty

For most uses of home energy storage, your battery will “cycle” (charge and drain) every day. The battery capacity will gradually decrease as you use it. In this way, the solar battery is just like the battery in a mobile phone-you charge the phone every night to use it during the day, and as the phone gets older, you will start to notice that the battery is low, the same charges as new products. For example, the battery can be guaranteed 5,000 times or 10 years at 70% of the original capacity. This means that at the end of the warranty period, the battery loses no more than 30% of its original stored energy.  Your solar cell will have a guarantee that can guarantee a certain number of cycles and/or service life. Because battery performance naturally degrades over time, most manufacturers will also guarantee that the battery keeps a certain amount of its capacity over the course of the warranty. Therefore, simply answer the following question: “How long my solar battery last?” It depends on the brand of battery you buy and how much capacity will be lost over time.

Manufacturer

Whether the battery you choose is produced by a new gel battery supplier or a manufacturer with a long history depends on your priority. When making a decision, evaluating the warranty associated with each product can provide you with additional guidance.

How long do solar batteries last?

There are two ways to answer this question. The first is to determine how long solar batteries can power your house. In many cases, when solar panels are not producing energy, a fully charged battery can keep your house overnight. To make a more accurate calculation, you’ll need to know a few variables, including how much energy your household consumes in a day, what the capacity and power rating is for your solar battery and whether or not you are connected to the electric grid. To give a simple example, we will determine the size of a battery needed to provide an adequate solar plus storage solution with national average data from the U.S. Energy Information Administration. The average American household will use about 30 kilowatt-hours (kWh) of energy per day and a typical solar battery can deliver some 10 kWh of capacity. Thus a very simple answer would be, if you bought three solar batteries, you could run your home for an entire day with nothing but battery support.In fact, the answer is much more complicated. You will also use the solar panel system to generate electricity during the day, and the system will provide powerful electricity for approximately 6-7 hours of the day during peak sunshine hours. On the other end, most batteries cannot run at maximum capacity and generally peak at a 90% DoD (as explained above). As a result, your 10 kWh battery likely has a useful capacity of 9 kWh.Ultimately, if you are pairing your battery with a solar PV array, one or two batteries can provide enough power at night when no panels are produced. However, if there is no renewable energy solution, it may take 3 or more batteries to power the entire home for 24 hours. In addition, if you want to install home energy storage equipment to disconnect from the grid, you should install a few days of backup power to solve the possible cloudy days.

Solar battery lifespan

The general range of solar cell service life is 5 to 15 years. If you install a solar battery today, you may need to replace it at least once to match the 25 to 30 year lifespan of your PV system. However, just as the lifespan of solar panels has increased significantly in the past decade, it is expected that solar batteries will follow suit as the market for energy storage solutions grows. Proper maintenance can also have a significant effect on the solar battery’s lifespan. Solar batteries are greatly impacted by temperature, so protecting your battery from freezing or sweltering temperatures can extend its life. When a PV battery drops below 30° F, more voltage will be required to reach the maximum charge. When that same battery rises above the 90° F threshold, it will become overheated and require a reduction in charge. To solve this problem, many leading battery manufacturers provide temperature adjustment functions. However, if the battery you purchased does not have it, you will need to consider other solutions like earth-sheltered enclosures. Quality maintenance work will undoubtedly affect the service life of solar batteries.