Hybrid Solar System: Adding a Backup Battery to an Existing Grid-Tied Solar System

Hybrid Solar System: Adding a Backup Battery to an Existing Grid-Tied Solar System

renogys blog Sep 17th 2021

As time goes by, it’s becoming more and more clear that solar power is inevitably going to take over. Many of us have anticipated the usefulness of solar power years ago, creating  off-grid solar systems and grid-tied solar systems to supplement our power needs. Hybrid solar systems are becoming a true game-changer to ensure your safety and comfort at home and reduce reliance on the grid.

However, when it comes to power, efficiency is the name of the game. Any power generated in excess is power wasted. So, to capture that excess for backup power, we turned to batteries. Unfortunately, batteries came with two significant caveats back in the day一high upfront cost and low efficiency. That has changed.

Today, batteries are declining in cost and jumping in efficiency, making them viable options for power storage for those of us with grid-tied solar systems. Now, we can rely on hybrid solar systems, which combine the advantages of solar panel kits with the existing power grid.

how do hybrid solar systems work?

Your solar panels draw energy from natural sunlight, collecting it and converting it into DC electricity. Once collected, this power is sent through an inverter, which converts your DC power into AC power, the lifeblood of every home and business in the United States. Excess power stores in your installed battery. Together with your connection to the grid, this forms your hybrid solar system.

As your hybrid solar system generates power, you can tap it as a resource for your various devices, lights, appliances, and more. But, let’s say something happens. Maybe a transformer blows down the street, or there’s a failure in the grid. Ultimately, you lose power from the grid, and everything is dark. When that happens, you can rely on your battery to power essentials until the sun comes back up or the grid gets restored.

Essentially, a solar battery is much like a generator, except without all the noise, maintenance, and fuel needs. It simply collects power from your existing solar system when you need it most.

What Solar Batteries Are Compatible with My Panels?

Solar batteries are essential to every hybrid solar system, but finding the right one might seem daunting at first. Thankfully, most batteries designed for small-scale applications will be compatible with your existing panels.

However, keep in mind that these batteries won’t take your home or business off the grid for extended periods on the scale of several days. Most batteries will have enough solar energy stored to keep your critical loads up and running for a few hours. To rack up more up-time for your critical loads, you can stack multiple batteries to boost your bank of available power.

For a few hours of backup power when you need it, you should consider a larger battery for your hybrid solar system. If you’re hoping to avoid periods of high energy rates from your utility, smaller batteries will help.

As for battery chemistry, many people choose lead-acid batteries for their reliability, safety, and low upfront cost. However, lead-acid batteries are bulky and subject to corrosion over time. Also, they need regular maintenance, need to be oriented upright to prevent leakage, and you need to keep them in a well-ventilated space. Your other option for your hybrid solar system will be lithium-ion batteries, which are smaller, lighter, and last a long time.

What Is a Hybrid Solar Systems?

A hybrid solar system is one of the best ways to mitigate grid consumption while preparing your home for power outages. A hybrid solar system will combine the solar energy produced by your home’s solar panels and the power imported from your grid. Energy from your solar panels will travel through a solar inverter, where it will convert into usable electricity. This electricity will be used to power your home, charge your battery, or go into the grid.

When inclement weather or an unstable grid results in a power outage, you can rely on your backup battery to power your home, so you never have to worry about entirely losing power. Alternatively, you can depend on your solar panels and battery to help reduce grid consumption. When the sun goes down, and your battery dries up, you can switch to grid power instead.

Adding batteries to existing solar system

Can you add batteries to an existing solar system? The answer is YES. When it comes to long-term power outages, backup power is king. However, relying on generators can be a noisy and environmentally harmful affair that requires regular maintenance and fuel. Instead, it would be a lot more helpful to rely on your own hybrid solar system to keep your home up and running when your power is out. With backup batteries, you can do exactly that.

A battery, or multiple batteries, can be tied into your existing solar system to store solar power overtime for when you need it most. But first, you will need to decide how you want your battery coupled with your solar system. There are currently three primary ways of doing this: a solar buffer, AC coupling, and DC coupling.

In terms of cost, adding a battery to your existing solar system isn’t on the level of a major home upgrade. Depending on the rates of your local electrician or solar installers, you can expect the labor cost of the project to be around $1000. If you’re replacing your inverter as part of the installation, you must account for the increased cost.

Solar Buffer Battery

A solar buffer is a battery management strategy that determines where generated power goes and how your home will consume energy. When generating power with your solar panels, your solar buffer will decide where that power goes in order of priority.

First, power will go to your appliances, lights, devices, and whatever may be consuming energy in your home at the moment. The excess will go directly to your backup battery. Once your battery can no longer store any more power, the remainder will export to the grid.

When using your power, a solar buffer will decide where that power comes from. Your solar panels will have top priority, typically followed by your backup battery. When neither is available, power will come from the grid.

The most significant advantage of a solar buffer is its efficiency. There are no new conversions from AC to DC, or vice versa, minimizing power loss and minimizing costs. The greatest disadvantage is getting the right equipment. If you don’t get the right equipment to form your solar buffer, you may not have backup power available at all, and your solar panels won’t know how to bypass the battery when it is fully charged.

To get around this, you can use something like the Tesla Powerwall, a 7 kilowatt-hour home energy storage system designed as a solar home buffer. It recharges as you generate solar energy and can keep your home powered during an outage.

AC Coupling

An AC-coupled system will connect your solar panels to a solar inverter, which connects to your switchboard and meter, which then connects to a second inverter that charges your battery. With an AC-coupled system, power will flow from your panels to your building, then to your battery when excess power is available, and finally to the grid when your battery is fully charged.

AC coupling is a lower-cost option than DC coupling and enjoys a more straightforward installation process. The trade-off is efficiency. While your home and the grid will use AC power, your batteries will store DC power. When you need to use power from your battery, that power will need to be converted to AC, losing some energy in the process.

DC Coupling

A DC-coupled system will connect your solar panels directly to a hybrid inverter, which connects to both your battery and your switchboard and meter. The hybrid inverter will convert the DC power generated by your panels into AC power, which your home and grid can use. Energy stored in your battery will be DC power, but you get to use more of your overall generated solar energy because fewer total conversions are happening.

DC-coupled systems are more challenging to install, take more time to install, and have a higher upfront cost. Because of this, if cost is an issue, it’s best to consider a DC-coupled system if your current inverter is approaching the end of life.

Is a Hybrid Solar System Right For You?

If you have a grid-tied solar system, you don’t necessarily need a battery backup, but having one can make a difference. With a labor cost of around $1000, a hybrid solar system isn’t prohibitively expensive and will only help save you money in the long term. With a hybrid solar system, you will not only take further advantage of your existing solar system, but you will increase your safety and comfort at home during events that would cause extended power outages. Or, you can rely on your battery to help reduce the cost of using your utility when rates are exceptionally high. If you have a good budget, adding battery backup to existing solar system can be a very smart decision.