Is it worth getting a solar battery? Ask yourself what value your household places on having reliable electricity when the power is out, and consider using all the energy you produce and selling none of it back to the utility company.
Welcome to our series answering reader questions and concerns about how to cut the utility-company cord.
I’ve used a 9.35-kilowatt solar-photovoltaic system for nine years without any problems. The system feeds my house and even sends excess electricity back to the grid. However, when our power goes out, I’m left without electricity, so I’ve been thinking about energy storage. My solar company tells me that adding batteries won’t be an economically sound investment. Should I stay storage-free or spend more to keep the lights on?
-John W. Gibson
I believe you can make batteries pay for themselves. Converting an existing solar photovoltaic system to a battery-backup system can be both practical and economical. With your current system, you’re most of the way there. I’m not surprised with the answer your solar installer gave you. Many solar installers shy away from battery systems, because they aren’t trained in the technically advanced aspects of off-grid or battery-backup systems; plus, in the early years, it was expensive to install battery systems. The way to think about the economics of batteries is by asking yourself, “What value does my household place on having reliable electricity – and, by extension, food storage and possibly heat and pumped water – at all times?” My own family is willing to pay a premium for energy security, which changes the math.
Because you have a grid-tied system, your inverter is designed to shut down when the utility grid goes. This is a mandatory safety feature to protect utility workers from electricity back-feeding through the power lines. If you want to have backup electricity from solar when the grid goes down, you’ll need a “hybrid” inverter that’ll work with both batteries and your existing solar panels.
Batteries can be expensive, but because you want to use the system for backup instead of off-grid, 24-hour-a-day electricity, you don’t need a lot of them. You only need a bare-minimum-sized battery bank to cover your essential loads (it’ll be easy to add more batteries later if you want more).
A few other features will give you the backup power without costing an arm and a leg: Add a standard auto-start generator to your system that’s controlled by your battery-backup hybrid inverter. When outages are short-term, batteries can carry your household, so you won’t burn fuel or add wear and tear to your generator. If you have a long-term outage, you can still operate with your solar, batteries, and generator until you run out of fuel. So long as the sun is shining, the fuel you do have will last a lot longer. You can also separate out your most important loads – your refrigerator, a few lights, and a well – to be the only items in use during an outage. This would allow you to have a smaller generator and fewer batteries. Another feature on most hybrid systems is the ability to have “nice-to-have” items (like a TV or computer) powered up for a while, and then automatically disconnected when your batteries drain below a certain level and before your generator kicks in.
Today, you can find newer inverters available that combine off-grid and grid-tied functions into a single economical unit. Lithium-ion batteries have warranties of 10 to 15 years. They’ll give you up to three times the energy storage of old lead-acid batteries.
Finally, you mentioned you sometimes produce more electricity than you use, so that goes back into the power company’s grid. Utility companies resell electricity at full retail, passing taxes and fees on to the end users (you and your neighbors). You, on the other hand, only get a credit for the excess solar production at the wholesale rate. It’s to your advantage to use all the electricity you make and sell none of it back to the utility company. Modern hybrid inverters allow you to prioritize your system even when you’re connected to the grid.
With some planning – and using better math – you can design a battery-backup system that meets emergency needs economically for years to come.
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May all your days be filled with sunshine – even when it rains!
Hoss Boyd is founder, president, and CEO of TeraVolt Energy and a recognized solar and energy-storage expert.
