Sizing your battery bank for your solar system
How to ensure your solar system will be up and running for years to come
Adding battery storage to your solar installation can be a great way to make sure you have constant, reliable access to power at home or on the road. You can also save thousands on monthly utility bills, become energy independent, and live a green lifestyle. Once you’ve made that decision to add battery storage, it’s time to start thinking about sizing your battery bank. Properly sizing your battery storage is crucial to ensuring you have a long-lasting, safe, and efficient system.
Why battery storage?
As the price of deep cycle batteries continues to drop, more and more people are adopting battery storage for their solar installations. It’s easy to see why. There are some big perks to having battery storage.
You can access power during a blackout: If you’d like to go off-grid or be able to run your solar panels in the case of grid outages, battery storage is a great way to ensure continued energy access.
You’ll reduce your carbon footprint: Relying on renewable energy is a greener, more sustainable way to live and travel.
It makes life on the road much more comfortable. We highly recommend battery storage in your RV or motorhome. This way, your solar panels and batteries can take the place of a gas-powered generator. You’ll be able to keep things running even when your panels aren’t producing energy.
If any of these apply to you, adding storage may be a great option for you:
- I live in a tiny home, cabin, RV, boat, or in an isolated area.
- I want to be energy independent and stop paying money to the utility (or pay less on my monthly bills).
- I live in an area without reliable, steady access to power from the grid.
- I want to live sustainably and lower my carbon-footprint.
- I want to be able to access power during a blackout.
How do solar batteries work?
Solar batteries store the energy that is collected from your solar panels. The higher your battery’s capacity, the more solar energy it can store. In order to use batteries as part of your solar installation, you need solar panels, a charge controller, and an inverter.
When using batteries for solar panels as part of a home solar system, you’re able to store the excess electricity your panels produce instead of sending that energy back into the grid (if you’re tapped into the grid.) Electricity will be sent to the grid if your batteries are fully charged and your panels are still producing energy.
What kind of batteries should I use?
There’s a range of deep cycle battery options available that we’d recommend, such as lead acid, absorbed glass matt, gel, and lithium ion batteries. Lead acid batteries are the most inexpensive option and are available at most big-box and auto stores. Absorbed glass matt batteries store 10 to 15 percent more energy than lead acid batteries and charge up to four times faster. Lithium ion batteries are the most expensive options, but also last four times longer than lead-acid batteries and weigh much less. They also don’t require much maintenance to keep them running strong. For more information about batteries, refer to our blog post on deep cycle batteries.
How do I size my battery bank and why is it important?
It’s very important to properly size your deep cycle battery bank. If your battery bank is undersized, you may not be able to fully meet your energy needs. If your battery bank is oversized, your solar panels may not be able to fully recharge the batteries, which may lead to chronic undercharging, decreased lifespan, and poor performance.
The amount of battery storage you need is based on your energy usage. Energy usage is measured in kilowatt hours. For example, if you need 1,000 watts for 8 hours per day, then your energy usage is 8kWh per day. A battery capacity of 4 to 8 kWh is usually sufficient for an average four-person home. Your energy needs may greatly differ from that. To size a system that will best fit your needs, we recommend making a list of all the devices you plan on running. Get the wattage information, or the amps and volts of the product, and provide an average run time per device. The Renogy solar panel calculator is a great tool that makes it a quick and easy process to help determine your specific needs.
What influences battery bank sizing?
- Temperature: Batteries operate best in a cool environment. If it’s too hot, they may overheat. On the other hand, very cold temperatures also have a negative impact on your batteries because it has to work harder and at a higher voltage to charge.
- Seasonal Variations: You’ll use more power at different times of the year. For example, during the summer months you’ll be producing more power than the winter with those additional hours of sunlight.
- Battery Types: Different battery types have different specifications that will impact how large of a battery bank to have.
- Cycle Life: This specifies the number of discharge and charge cycles a battery can provide before the capacity drops below the rated capacity. This varies sharply from technology to technology and is measured in number of cycles.
- Depth of Discharge: A battery’s depth of discharge refers to the percentage of battery that’s discharged relative to the overall capacity.
- Budget: There’s always a certain level of compromise when it comes to solar installations. You’ll have to come to a decision of what to spend on batteries and may need to investigate back-up power solutions to stay within that budget.
What is the lifespan of solar batteries?
Battery life varies a bit depending on the battery type. For example, many gel batteries typically last 1,100 cycles, absorbed glass batteries 600 cycles, and lithium iron phosphate batteries 7,000 cycles. It’s fair to assume the general range for a solar battery’s lifespan is between 5 and 15 years. Therefore, you may need to replace your batteries at least once within the lifespan of the rest of your solar system.
How to increase the lifespan of your batteries
- Limit the number of batteries in your bank: The more batteries you have in your bank, the higher your chances are of having unequal charging and increased resistance. Therefore, instead of having many batteries of smaller sizes, consider using fewer batteries of larger sizes.
- Keep your batteries charged: Don’t let your partially discharged batteries sit without being recharged for a long period of time. Keep them fully charged and you’ll extend the life of your batteries.
- Adhere to your batteries’ depth of discharge specifications: All batteries specify the recommended depth of discharge. A higher DoD means you can use more of the energy being stored in your battery.The more frequently a battery is charged and discharged, the shorter its lifespan will be.
- Select the right batteries for your system: Not every deep cycle battery is the right battery for you. For example, absorbed glass matt batteries offer a better temperature range than gel batteries, but gel batteries have a greater lifespan than AGM batteries and can be mounted in any orientation. Design a system around your specific needs.
- Use batteries of the same type and amp hour rating: If you go with lithium batteries, all the batteries in your battery bank should be lithium batteries. This will limit any efficiency loss due to having different batteries.
How to maintain your battery bank for best performance
Depending on what batteries you end up using for your system, you’ll want to make sure you keep up with the maintenance of your battery bank. If you’re using flooded lead acid batteries, you need to check water levels with a hydrometer and add water to keep them topped off each month. You’ll also want to make sure your battery terminals are clean and free of corrosion on all battery types.
Charge your batteries fully once a month, in order to equalize the batteries in your bank. If sunshine is not readily available, Renogy has a range of battery chargers available to help you maintain your batteries without overcharging them. You can use an amp hour meter to check to see if the batteries are fully charged.
We also recommend checking to see what your solar system is outputting at least twice a year to make sure you don’t have any underlying issues in your system.
Properly sizing and maintaining your battery bank is key to ensuring you have an efficient and long-lasting system. By taking into consideration battery types, adhering to charging and discharging best practices, and properly sizing your system, you’ll have a well-running system for years to come.