When installing solar power storage, finding the right number of batteries is a crucial step in designing a system suitable for your home’s energy needs.
Today, home solar batteries come in many different sizes and capabilities, and most high quality products allow you to combine multiple units for increased storage capacity. By installing several solar batteries, you can design an energy system that ensures backup power during local outages, maximizes your electricity bill savings, or both.
Whether you already have panels or are just getting started with renewable power, this guide explains how to determine the number of solar batteries you should install for your unique home energy system.
How many solar batteries do I need for my house?
Finding the number of solar batteries you need for your home is not a one-size-fits-all answer. However, the number of batteries you’ll need can generally be determined by your primary solar energy storage goals.
Today, most homeowners seek out a solar battery installation for one of the following reasons:
- Financial savings
Grid-tied solar batteries configured for self-consumption—but not configured for essential or whole-home backup—can still help you maximize long-term savings on energy bills in California and other parts of the U.S. with net energy metering (NEM). For maximum savings, these batteries can store your daily excess solar electricity production and let you use that stored energy in the evening when utility rates are highest. You could even use that stored energy overnight if you have sufficient storage—so you don’t have to draw and pay for grid power then either. In states with more favorable net metering rates, stored energy may also be exported to the grid during periods of peak demand and peak rates to help your system pay for itself in avoided utility costs.
- Backup for essential systems
When extreme weather or aging utility grids cause local power outages, a solar battery configured for backup can provide electricity for your home’s essential devices. With one or two batteries, a small solar energy storage backup can help power your refrigerator, lights, security systems, and more, whenever grid electricity is unavailable.
- Whole house backup
To back up your entire home with solar energy during grid power outages, you’ll need to install more batteries than would be necessary to run essentials only. Depending on your property’s energy demand, a whole-house backup may consist of anywhere between one and ten premium solar batteries.
- Energy independence
If your goal is to reduce your dependence on grid electricity as much as possible, a whole-home backup system can help power your property with solar energy all day, night, and year. As total energy independence requires the most solar batteries installed, it can also lead to the highest installation expenses and is not always cost-effective when utility electricity is also available.
Although the exact details of your installation depend on several factors, understanding the capabilities of solar power storage systems can help you determine your project goals and get a basic idea of the number of batteries you may need. If you need additional solar energy storage capacity after your initial installation, it may also be possible to incorporate another battery into your storage bank with the right technology and system design.
Factors that influence the number of solar batteries you need
There are several factors to consider when determining the right number of solar batteries for your home. While you should ultimately make your final system design choices with the help of an expert, here are a few primary things to keep in mind.
Energy goals and demand
Whether you intend to only power essential loads or your entire home with a solar backup, the size of your battery bank should be determined by the amount of energy you will need to run your desired systems. Oversizing your storage capacity can also help keep your property prepared for cloudy days with limited solar power generation or prolonged instances without access to grid electricity.
Solar battery specifications
There are several technical solar battery specifications to analyze as you choose your system, including usable energy capacity, peak output, round-trip efficiency, and cycle count.
For example, if two batteries have the same storage capacity but different usable capacities, the amount of actual solar power you can access between the two systems will vary. Likewise, a solar battery with a high cycle count will be able to charge and discharge more lifetime electricity than one with the same storage capacity but a shorter life expectancy.
Property and solar energy system factors
The number of solar batteries you’ll need also depends on the amount of solar energy that’s produced on your property. This is determined by several factors, including the capacity and efficiency of your other energy system components, the average number of peak sunlight hours in your area, and your home’s solar potential.
For instance, if your roof is perfectly suited for efficient solar energy generation, you may be able to install a smaller storage capacity when compared to a property with limited solar power production potential.
How to calculate your ideal solar battery capacity
While the exact calculations may be a bit more detailed, you can use the following steps to estimate the ideal number of solar batteries for your home.
Step 1: Determine your energy storage capacity needs
When backing up only a portion of your property, your storage needs will be the sum of your essentials’ energy demands. For full-home systems, your daily average electricity usage can be found on your utility energy bills.
Step 2: Consider your daily solar production
Your battery’s storage capacity will not need to meet your property's full daily electricity demand, as your home may also be powered by solar or utility energy when available. As a rule of thumb for a cost-effective solution, total battery capacity equal to half of your daily electricity usage is recommended.
Step 3: Divide total storage by the usable capacity of each battery
If you use approximately 30 kilowatt-hours (kWh) of electricity per day, you’ll want to install 15 kWh of solar battery capacity. If your solar batteries have usable capacities of 8 kWh each, this will translate to 1.875 batteries.
Step 4: Round up for extra solar power storage
As it’s impossible to install 1.875 batteries, in this scenario, two batteries would be ideal to ensure you have enough storage capacity to power your home. In the same sense, rounding down can help you lower your installation costs with a smaller battery storage bank.
How to get started
Ultimately, every solar installation is different, and the ideal number of batteries for your home will depend primarily on your goals, budget, and the specifications of your energy system. To design and install your optimal battery bank, we recommend contacting multiple solar professionals in your area for personalized consultations, planning, and contract options.
Solar power storage FAQs
What is depth of discharge (DoD) and why does it matter?
DoD is the percentage of a battery’s energy storage capacity that has been discharged. For example, if your solar battery is full, its DoD would be 0%. In the same sense, a battery discharged halfway would have a 50% DoD. Know your battery’s DoD limits and practice smart charging and discharging habits to help you maximize the lifespan of your system.
How can I reduce the number of solar batteries needed?
You can reduce the number of solar batteries you need by increasing your home’s energy efficiency. There are many ways to do this, including limiting your property’s electricity usage by adopting energy-efficient appliances and improving your home’s building envelope to reduce heating and cooling power consumption.
What are the different types of solar batteries available?
There are a few different types of solar batteries, including those that use lead-acid and lithium-ion battery chemistries. Today, lithium-ion products are the most valuable and common solar energy storage systems for homeowners. With an industry-leading 15-year warranty, Enphase IQ Batteries are powered by Lithium Iron Phosphate (LFP) chemistry, which is the safest home solar battery technology on the market.
