How Many Batteries Do I Need For My Solar System?

solar system batteries

If you’re a residential solar user, you’ve probably considered investing in a battery. Although you can spend between $25,000 to $35,000 for your solar system, solar batteries offer a better ROI by maximizing your usage potential.


Whether you’re grid-tied or off the grid, you can surely benefit from a solar battery.


Before you take the plunge, you must consider several factors, including how many solar batteries you will need to supplement your residential solar set-up.

Do You Need Solar Batteries?

If you’re a grid-tied solar user, not really.


A standard solar arrangement is enough to power your home with the energy your array produces and send the excess to the grid of your utility provider. You can draw power from the grid at night or on days when your set-up does not produce enough solar energy for your needs.


In this case, your utility provider’s grid acts as a makeshift battery.


You can even earn credits if you sign up for a local net metering plan, although the regulations vary from state to state. You can save up to 30% on your utility bills if you go for solar batteries.


If you’re an off-the-grid solar user, you should get solar batteries. Solar is your only energy source, and you need to store it for future use. The battery will be critical at night and on cloudy days.


That’s just the short of it. The long of it is much more complex.


Purchasing solar batteries will help maximize your long-term return on investment. You should go for one if:


  • Your area experiences frequent power outages
  • You don’t have a profitable net metering policy in your state, such as NEM 3.0 in California
  • You are a grid-tied user, and your utility provider charges high Time of Use (TOU) rates
  • You want to be as energy-efficient and independent as possible


A reliable solar battery setup enables you to use solar efficiently and sustainably, giving you the ultimate freedom to do as you please.


Let’s move on to the next big question.

How Many Solar Batteries Do You Need?

This depends mainly on your household’s power consumption, plus a few other important contributing factors.


Let’s consider the Energy Information Administration (EIA)’s estimates for simplicity’s sake. Per the EIA, an average American home consumes 30kW of power a day. A 7kW solar system is more than enough to provide this, as it can produce 21 to 49kWh of power daily in ideal settings.


Keeping these factors in mind, you will need to have a solar battery set up to connect to your 7kW system and back up as much power as it can.


Solar batteries come in multiple varieties and capacities. While a Sonnen EcoLinx 30 can hold up to 30kWh of power, a Tesla Powewall 2 can only hold 13.5kWh. So, you might need to purchase more than one battery to maintain sufficient power backup for your home.


To determine how many batteries you need, consider the following:


This one’s obvious: you need a battery with the ideal capacity, especially if you are an off-the-grid solar user or want to maximize your savings on utility bills. A durable, high-capacity battery will drastically reduce your dependence on the grid if you’re a grid-tied user. Similarly, you can use it to transition out of the grid, if that’s your end goal.


If you want to consistently power your entire household, just one battery may not suffice. You will need multiple batteries stacked together to get reliable performance for all your needs. This is why most solar manufacturers have built batteries to be stackable.


But if the purpose of the battery is for backup power during emergencies, a medium-capacity battery is all you need.

Power Rating

A solar battery’s power rating indicates how much power it can provide and, therefore, how many appliances you can run at any given time.


On average, household solar batteries can deliver 5kW of continuous power. This means you have an uninterrupted supply of 5kW for all of your appliances.


But there’s more to a power rating than that. All solar batteries have two kinds of power ratings: peak and continuous.


The peak power rating tells you how much power you can get for a short burst of a few minutes. It can help you jumpstart appliances that need lots of energy to operate, like a snow plow. Peak power also gives your solar setup the capacity to handle load spikes and safeguards your grid against potential overloads.


Continuous power rating measures how much uninterrupted usable power it can deliver over an extended period. So if you want to keep your home warm and well-lit during a snowstorm, go for a battery with the best possible continuous power rating.

Depth of Discharge (DOD)

Another critical factor in terms of solar batteries is the depth of discharge. This tells you how much stored power you can use without harming or draining the battery.


A high DOD of 70% to 90% means you will need fewer batteries to fulfill your requirements. If your solar battery has a low to medium DOD, you will need several of them to power your home continuously and for hours or days at a time.


However, irrespective of DOD, it’s best to go for solar batteries that are stackable. This future-proofs your setup, so you can combine multiple to increase your backup capacity anytime to accommodate the changing energy requirements of your home.

Roundtrip Efficiency

Another crucial metric you must consider before investing in a solar battery is its roundtrip efficiency. This tells you how much power you can use for every unit of power your battery stores.


So, if you have a 10kW battery with a roundtrip efficiency of 90%, it means you will be able to use 9kW of the energy it stores.


The higher the roundtrip efficiency, the better your battery’s performance in the long term. This will help you calculate the number of batteries you need to power your household needs.

Type of Battery

There are three types of solar batteries that you can choose from, depending on the unique advantage each offers. These include:


  • Traditional Lead Acid Batteries – These are not too expensive yet effective. They only have 50% depth of discharge and are quite bulky. They are an excellent choice if you prioritize cost-efficiency and affordable backup power from your battery.
  • Lithium Ion Batteries – Also known as Li-ion batteries, they are highly efficient and long-lasting, with 80% to 100% depth of discharge.
  • Flow batteries – These are relatively new to the market and boast excellent efficiency with a 100% depth of discharge. However, they are quite large and expensive.


Based on their efficiency, you may need more lead acid batteries than li-ion and flow options. Consider your household’s energy needs, available space, and budget before taking your pick.

Your Need Underpins Your Solar Battery Requirement

Experts highly recommend investing in a solar plus storage set-up if you’re choosing to take the renewable energy route. You will make good on your investment with immediate effect.


The number of solar batteries you need is specific to your immediate requirements and long-term goals. It’s best to consult a solar expert to get an overview of the options available to you and make an informed decision. Solar batteries are not cheap, and you must do your due financial and technical diligence before investing in them.

Authored by Ryan Douglas

Authored by Ryan Douglas

NRG Clean Power's resident writer and solar enthusiast, Ryan Douglas covers all things related to the clean energy industry.