Everything You Need to Know About Batteries for Your Solar System - Speir Solar

Everything You Need to Know About Batteries for Your Solar System

  • April 20, 2020

Solar systems help take a lot of the strain off the grid, especially now that many people are working from home. But are you prepared for a power outage on days your system isn’t producing electricity? A good back-up battery can mean the difference between being in the dark and being the only home in the neighborhood with wifi and a coffee maker! Here’s everything you need to know about batteries for your solar system.

Adding a backup battery to your solar system means your battery gets charged by the power your system generates, and you don’t have to rely on the grid to charge the battery. Whether you already have a solar system in place or are considering one, be sure to factor in the benefits of a backup battery, especially now that technological advances are making them more efficient and more cost-effective.

How Does a Backup Battery Work?

The power from your solar panels powers your household’s energy needs, and any excess is diverted to the grid. At night or on cloudy days, when your system isn’t generating power, you draw power from the grid just like everyone else. If your excess energy is part of a net metering program, this can mean paying next to nothing for electricity, especially if your consumption is outweighed by your production.

A battery lets you “keep” the power you generate by storing it for use when your solar system isn’t generating power: evenings, stormy days, or in the case of power outages or rolling blackouts due to overwhelming demand. Even when your solar panels are generating electricity, if you’re tied to the grid and don’t have a backup battery, you will still lose power.

The trade-off with a battery that is tied to your solar system is that you won’t send as much energy back to the grid (to take advantage of net metering) but you will be guaranteed electricity in any situation.

How to Choose a Backup Battery

There’s no one-size-fits-all solution to home backup batteries. Here’s what to look for, so that you get the best backup for your needs.

Charging Options

The first choice to make is whether you want a battery that’s tied exclusively to your solar system, or one that can also be charged on the grid. If your system generates a lot more power than you actually need during the day, you may want to install a backup that relies exclusively on your solar system; but be aware that if the system isn’t generating power and your backup is running low, you won’t be able to charge it.

Battery Capacity and Power

The next consideration is the capacity and power output of your battery. The total amount of electricity a battery can store is measured in kilowatt-hours (kWh). In most cases, you can “stack” two or more batteries to increase your storage capacity. However, capacity doesn’t always correlate to how much electricity a battery is capable of providing. For example, a high-capacity battery with a low power rating will let you run a few key appliances for a long time, but it won’t power the whole house. A low-capacity battery with a high power rating gives you enough power to run the entire household, but only for a very limited time.

Depth of Discharge

Current technology limits the actual usable energy that you can access from a backup battery. Batteries need to retain some percentage of their charge; completely discharging them significantly shortens their lifespans. The depth of discharge (DoD) refers to the maximum amount of a battery’s power that you can use to keep it running optimally. A higher DoD means you can access more of your battery’s capacity: for example, a 10 kWh battery with a 90 percent DoD means you shouldn’t use more than 9 kWh of its capacity before charging it.


The third consideration is choosing the type of battery: lithium-ion or lead-acid batteries. A few developing technologies are also in the mix (zinc-air and flow); but currently, the best-rated batteries are lithium-ion.

Lithium-ion batteries are recommended because they last a long time, and a high DoD. This makes lithium-ion batteries the best choice if you’re not sure when you’ll be able to charge your battery next, such as emergencies.

Lead-acid batteries are the type that power vehicles. They are often less expensive upfront, but come with significant drawbacks including a shorter lifespan, lower DoD, and more maintenance requirements.

The Best Residential Solar Backup Batteries

When purchasing a backup battery, make sure it’s compatible with your solar system. Many of today’s best batteries are “smart” in that you can view their status on an app, and some are controllable via a smartphone.

Here are three great systems to consider:

Encharge 10 by Enphase

The Enphase Encharge 10™ all-in-one AC-coupled storage system is reliable, smart, simple, and safe. It has a total usable energy capacity of 10.08 kWh and twelve embedded grid-forming microinverters with 3.84 kW power rating. It provides backup capability and installers can quickly design the right system size to meet the needs of both new and retrofit solar customers.

RESU10H by LG Chem

A 9.8 kWh battery that can be piggybacked with another battery for up to 19.6 kWh of storage. This battery comes with a 10 year warranty, gives you installation options for various parts of the home, and it is readily available. The cost does not include installation, and you may also need to purchase a dedicated battery inverter.

Powerwall by Tesla

Synonymous with cutting-edge technology, Tesla has developed a 13.5 kWh battery which can be stacked up to 10 deep, which is perfect for larger or higher-consumption homes. This battery must be installed by a Tesla-certified installer or directly by Tesla technicians. It also features a 10-year warranty, as well as a built-in inverter.

Installation Tips

We recommend having your backup battery professionally installed so that it integrates flawlessly into your solar system and that the installation meets local codes.

Disaster preparedness is always a good idea, especially if you work from home. A backup battery gives you the peace of mind knowing you’ll always have electricity!  Give our experts a call and discover how you can tie a backup battery to your solar system.

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