Retrofit batteries: How to add storage to your solar panel system

You installed your rooftop solar system a few years ago and are enjoying your disappearing electric bills. But your neighbor just installed a new solar-plus-storage system that couples rooftop solar with a battery storage system. And now you've got a serious case of solar FOMO.  Is it too late to add a battery backup? Did you miss out?

The good news is that it’s entirely possible to add battery storage to an existing solar panel setup. So-called “storage ready” systems are already equipped with an inverter that can easily direct excess power into a battery. But even if your system wasn’t designed with storage in mind, you still have options. 

Let’s explore how easy it is to add a battery to your existing solar setup and what options you have based on your current equipment. Plus, we’ll break down costs and provide tips for finding the right installer if your current one doesn’t install batteries.

You can integrate storage into practically any solar panel system, but some setups are easier than others. The sticking point lies with the type of inverter your system has. 

Best case scenario: You have a storage-ready solar panel system

If your system was designed with storage in mind, or you already have a hybrid inverter (which can manage energy from both solar panels and a battery), adding a battery is relatively easy. In this scenario, a battery storage installation requires minimal additional equipment.

If this isn’t the case for you, don’t worry. While the process might be more complex, adding a battery is still very feasible. You have two primary options: an AC-coupled solution or an inverter replacement.

AC-coupled solution: Easier and cheaper, but less efficient

In an AC-coupled system, electricity from your solar panels is first sent to your home and then stored in the battery. This setup requires multiple conversion steps, which decreases overall system efficiency. Here’s how it works:

1. Your solar panels generate DC electricity.

2. Your solar inverter converts DC to AC and sends it to your home.

3. The AC power is converted back to DC to be stored in your battery.

4. When needed, the stored DC electricity is converted back to AC to power your home.

Each conversion results in a small loss of energy, making AC-coupled systems less efficient.

DC-coupled solution: Higher efficiency but more expensive

DC-coupled systems are more efficient because the power is inverted only once. In this setup, the same inverter handles both your solar panels and battery. The DC electricity generated by your panels is stored directly in the battery and only converted to AC when used in your home.

A DC-coupled retrofit involves replacing your existing inverter with a hybrid inverter that works with both solar panels and batteries.

While DC-coupled systems offer improved efficiency, they'll cost you. Replacing your inverter to accommodate a battery can require a system redesign and rewiring, which can result in additional costs in addition to the new inverter itself.

A DC-coupled system could be a financially smart choice if you're nearing the time for an inverter replacement. Since string inverters typically last around 10 years, upgrading to a hybrid inverter for both solar and storage might make sense if your inverter is already five or more years old.

If you’re looking to retrofit easy-to-install AC-coupled batteries, here are some of the best options:

Best AC-coupled batteries on EnergySage

Batteries for time-of-use rates or partial-home backup power

A single 10 kWh battery can serve multiple purposes, from providing backup power during outages to helping homeowners avoid costly demand charges.

For those in areas with time-of-use (TOU) rates or demand charges, energy storage allows you to use stored energy during peak hours, reducing reliance on the grid and lowering electricity costs.

If your primary goal is minimizing your demand during peak hours or providing backup power to your home during grid outages, you can opt for a smaller battery.

Batteries for whole-home backup power 

To keep your entire home powered during an outage, you'll need a larger capacity battery or multiple batteries working together. The modular design of a battery like HomeGrid's Stack'd Series is ideal for expanding capacity by stacking units, allowing you to create a battery bank tailored to your needs.

Batteries for off-grid use

Most batteries aren't designed to fully disconnect your home from the grid. They generally lack the storage capacity to power your home through extended periods of cloudy, rainy, or snowy weather. If your goal is to go off-grid with solar, you'll need significantly more storage than most common batteries can offer.

On average, installing a battery storage system costs about $13,000 before incentives. However, the final price will vary based on the brand of battery, your location, and the complexity of your installation.

When retrofitting a battery to an existing solar panel system, AC-coupled systems typically cost less upfront because they don't require replacing your existing solar inverter. DC-coupled systems, while more expensive initially due to inverter replacement costs, often offer better efficiency, which may provide greater value over time.

Ultimately, every energy storage project is unique. The best way to understand your options and their costs is by working with a qualified installer. Share the specifics of your system, electricity usage, and storage goals to determine the best solution for your home.

If you’re looking to add a battery to your solar panel system, and your original installer can’t help, don’t worry. EnergySage has partnered with Qmerit to help you connect with a certified electrician to safely add storage to your existing system.