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How Many Batteries Do You Need?

Shannon Higgins

June 2022

wilson_generac photoIf you've been looking into solar, chances are good that you've also thought about a battery - or at least come across an ad or two for energy storage. While not everyone wants a or needs a battery, the combination of solar and battery together allows you to maximize the use of the solar power you generate even when the sun isn't shining above. The story gets even more compelling when you look at the financial benefits.

Storing your unused solar energy for use at night or when the grid goes down further reduces your need to purchase expensive and dirty utility power. In short,  this combination brings you one significant step closer to true energy independence.

Those interested in batteries are typically most curious about which appliances can be supported with a battery addition and how many batteries they'll need to meet their specific goals. Knowing which battery to buy and how many is not always black and white since energy demands vary widely between users and devices. A 20-year-old air conditioner on a 2,500-square-foot home will consume dramatically more energy than a new, energy-efficient unit on a small, single-story residence.

Let's take a quick look at some of the key considerations when shopping for energy storage.

 

Battery Capacity

Each battery offers a different potential for energy storage. Some can even be expanded with modules as your energy needs grow. At Sun Valley Solar Solutions, we are a Tesla Powerwall Certified Installer, and we also carry Generac PWRCell batteries. Each of these handles capacity in different ways.

A Tesla Powerwall is a sealed unit with a fixed capacity of 13.5 kilowatt-hours. In contrast, Generac PWRCell has anywhere between 9-18 kilowatt-hours of capacity, depending on the number of modules integrated into the design. The PWRCell allows you to add modules as your energy needs grow. With Tesla, you need to purchase additional Powerwalls if more storage is required down the road.

 

AC Coupled vs. DC Coupled Batteries 

Tesla and Generac differ in another critical way. Tesla is an AC-coupled solution, whereas the Generac PWRCell is DC-coupled. To fully understand this distinction between the two, check out our blog that discusses AC vs. DC-coupled batteries in greater detail.

For the sake of this article, it's best to think of DC vs. AC coupling in the context of your starting point. In short, DC-coupled batteries like the Generac PWRCell are the best option if you are installing solar and batteries at the same time. If you are adding a battery to an existing solar array, an AC-coupled solution like the Tesla Powerwall is the best approach.

 

What loads do you want to be backed up?

One of the first questions a qualified battery installer will ask is which appliances you want to be connected to the battery to ensure constant power, even when the power is out. Naturally, this consideration will affect the number of batteries you need to plan for. There are two main ways to configure a battery and the loads you'll want to have backup power: whole-home backup and critical loads only backup.

 

Critical Loads Backup

A battery backup system will run your most critical loads – or a designated room – during a grid failure or at night. Batteries are charged by your panels during the day and discharged to keep critical devices or rooms powered. This configuration typically requires fewer batteries than a whole home backup.

 

Whole-Home Backup

With a whole-home backup system, you can add just enough batteries to offset the most expensive on-peak utility hours or add more to keep your house operational longer during an outage. Since you're powering more of your home with batteries, this type of setup requires more battery capacity (or multiple batteries)  than a critical loads-only design.

 

How long do you want backup power?

Determining how many batteries you'll need also depends on how long you'd like to access backup power. Are you looking for energy storage to help offset just the expensive "on-peak" hours? Or are you looking to have backup power in a prolonged grid outage? Or are your goals to be completely off-grid and independent from your local utility? The longer your desired amount of time, and the more appliances you wish to have connected, are directly related to the amount of energy storage you need.

 

What is your household energy usage profile?

Your energy usage habits are unique to you. Another family living in the same house might use dramatically more or less energy than yours. If your household draws a large amount of power over the course of the day and into late evening hours, you'll need more energy storage capacity. Think of your batteries as cups of water, and the energy your house uses drains that cup. Having more cups or a larger cup will ensure your energy demands and goals are met.

 

Will your battery be paired with solar?

Installing a battery with solar allows you to store the clean solar energy you generate during the day for use after the sun goes down or to help offset costly on-peak utility rates. Without solar, you're simply buying dirty utility power to store. Also, keep in mind that blackouts will become more and more common as our energy infrastructure continues to age. A battery paired with solar empowers you with a personal micro-utility in times of crisis.

If you're interested in a battery, a solar energy system, or both, don't hesitate to reach out to our team. Our education-first sales approach ensures you have all the necessary knowledge to make the right decision for your home and family. Click the button below to request a free, no-obligation quote.

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