ASK THE EXPERTS: Adding Backup


My home has a grid-tied batteryless solar-electric array. Can I have it retrofitted with batteries? If so, how is this done and how expensive is it?

Jim Giambrone • via email

Adding batteries to a grid-tied system is possible, but can be expensive. You may not really need it unless you have prolonged or frequent utility outages or have a critical need for energy, such as for medical equipment. Most people do not find it worth the added cost and decreased system efficiency. Generally, PV systems with battery backup cost 1.5 to two times as much as a batteryless grid-tied PV system. Their reduced efficiency (about 10% less) translates to fewer kWh sold to the utility.

You also will need to either replace the inverter with a more expensive one that not only inverts, but also controls grid charging to maintain the batteries, or you could add a battery-based inverter and related equipment that can work with your existing grid-tied inverter on the AC side of the system. You will need a safe battery box and a separate subpanel for backup loads.

If you replace your inverter, you will also need to reconfigure the PV modules for a voltage that is matched to a battery charge controller (another additional component), and you may need to rewire them with larger-gauge wire to avoid wiring energy loss, since system voltages will likely be lower. Chances are, you will need to add to or subtract from the total number of PV modules so that the reconfigured array ends up at the right voltage.

Finally, this is not the kind of project that most grid-tied PV installers have experience with. You will need to find an installer who is expert in battery-based systems.

Please let us know how this project proceeds—be sure to take lots of photos and document the transition for possible future publication.

Michael WelchHome Power senior editor

Comments (3)

Lost's picture

i hope this helps seems it works

royalflushsheri's picture

I have the same siituation as this gentleman. Our solar system was originally supposed to be designed with backup batteries too but wasn't and I am having trouble finding a licensed contractor that will add battery backup to our system. Can you help me find qualified people? How do I find an expert in battery backups? Thanks!

Michael Welch's picture

I am guessing you are near Phoenix, AZ. Here is a list of NABCEP-certified PV system installers. When you call, ask if they have any experience with off-grid or battery backup systems. Experience is crucial.

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