generator vs. battery

Backup generators vs. energy storage: do the math

More and more homeowners are looking for ways to improve the resilience of their home’s electricity systems. Historically, many people who wanted backup power for their homes in the event of an emergency–think natural disasters and other outage events–looked to back up generators for that resilience. These days, however, homeowners are increasingly looking to energy storage systems, and solar plus storage systems in particular, for that peace of mind during outages. 

Find out what solar + storage costs in your area in 2022

Despite providing the same benefit of backup power, it can be difficult to compare the two different technologies: backup generators vs. solar + storage installations. With that in mind, earlier this year, we contributed to a report published by Vote Solar, Resilient Clean Energy for California, which includes a section that focuses on the costs and benefits of both technologies. Using that report as a guide, we decided to compare backup generators and solar + storage by doing the math.

The case for backup power

In many parts of the country, the case for purchasing a backup power solution is clear. In California, wildfires and public safety power shutoffs look set to persist for at least the next decade according to scientists and public officials in the state. Each of those can cause prolonged power outages for millions of utility electricity users at homes and businesses across the state. In the Southeast, the increased frequency and severity of hurricanes has led to more outages as well, paired with an increasing demand for backup power solutions. And in the Northeast, many parts of the region experience outages during the winter when strong winds coupled with ice storms lead to snow-laden tree limbs taking down power lines. 

In each of these instances, a backup generator or solar plus storage installation could keep the lights on in homes during the outage itself. And remember, solar panels on their own aren’t enough to provide electricity during an outage. Check out our video on the subject to learn more.

Backup generators vs. energy storage

There are two primary reasons that homeowners have historically opted for backup generators. First, they cost less upfront than other options for providing backup power for your home. Second, in the past, generators have been very easy to find and set up at your home: in fact, you can frequently buy backup generators at home improvement stores, and some might not even need to be installed by an electrician. 

However, backup generators come with a number of downsides. For one, you’ll have to ensure you have the fossil fuel they run on accessible and on hand in anticipation of an outage, which can be tough to do when outages are, you know, unexpected. Next, backup generators are large, loud machines that aren’t meant to be run every day, meaning you only benefit from having them in the event of an outage. Finally, and perhaps most importantly, by burning fossil fuels backup generators cause significant local pollution, not the least of which is carbon monoxide, which has become a large safety risk with fossil fuel powered backup generators. 

Batteries, on the other hand, are more expensive up front and require an electrician to install but solve for all of the issues that can potentially plague backup generators. First, when paired with solar panels, they are powered by the sun, which means the battery can be refilled every day so long as the sun keeps shining. Batteries are very quiet and can provide value to you every single day, especially in places like California where when you have solar, the electricity you pull from the grid when the sun is down can be more expensive than the electricity you put onto the grid when the sun is shining. And, finally, there are no local emission concerns with solar & storage installations–they run entirely on clean, renewable solar power. 

Doing the math: backup generators vs. energy storage

As mentioned above, this section draws heavily on Vote Solar’s Resilient Clean Energy for California report, which EnergySage contributed to for this particular section. At a high level, there are a few key benefits between a solar + storage installation and a backup generator financially. Solar plus storage provides value every day, is fueled by the sun instead of purchased gasoline or diesel, is eligible for tax credits and incentives, requires very little to no maintenance, and is often less expensive than grid power or than purchasing a fossil fuel to use. 

It’s important to consider the overall benefits of solar + storage beyond just providing backup power when comparing backup generators to energy storage systems. As written in Vote Solar’s report in comparing a home with a 5 kilowatt solar panel system & two Tesla Powerwall 2 batteries with a home with a 3.5 kilowatt gasoline backup generator: “The bottom line is that the solar + storage home has a 20-year cost that is more than $22,000 less than the home with the backup generator.” Even without battery incentives, a solar + storage homeowner still saves compared to the backup generator home, in large part due to the energy savings from solar. 

We’ve reproduced a table from the Vote Solar report below that compares the 20 year cost for backup generators vs. solar plus storage. Though the solar plus storage installation has higher upfront costs, it more than makes up that difference over 20 years in bill savings, as well as in avoided maintenance and fuel costs.

ca residential customer cost table

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About Spencer Fields

Spencer is the Manager of Market Strategy & Intelligence at EnergySage, where he's able to showcase his expertise around all things energy. Prior to joining EnergySage, he spent five years at Synapse Energy Economics, providing environmental, economic and policy analysis for public interest groups. Spencer has degrees in Environmental Studies and Hispanic Studies from Brown University, meaning when he's not in the office you can find him outside or traveling somewhere to work on his Spanish.

6 thoughts on “Backup generators vs. energy storage: do the math

  1. Kelvin Smith

    This is comparing apples and oranges, or maybe I should say apples vs. a fruit salad. The backup generator should more appropriately be compared with the cost of the battery storage system, not the entire system; that’s the math I did when deciding against adding a battery to my solar panel system. There may be benefits from storing solar-generated power during low-value times and using that during high-value times, which will reduce the effective cost of battery storage, but the battery is much less likely to last the length of the power outage, especially if the outage has the bad manners to happen on or immediately following a cloudy day (like a rainstorm/hurricane).

    Perhaps the biggest benefit of having a battery is simply the ability to use your panels when the grid is down, since I’m not otherwise allowed to shunt the power I generate into my house’s wires, to protect against backfeed into the power company lines while workers are repairing them.

    Let the panels stand on their own as a cost-effective investment; I’m looking at an 11-year payback on my system, which I’m very happy about. But batteries are still a long way from being cost-effective absent unusual circumstances (like being off the grid).

  2. Shawn Bennett

    Agree with previous poster here. I work in the energy industry on energy resilience solutions, and the cost assumptions don’t appear to provide an apples-to-apples comparison on performance of the back-up generator versus battery storage.

    Once the cost assumptions are normalized for performance, a hybrid approach (solar plus storage plus generator) may in some instances be most cost-effective.

  3. Paul Tanenbaum

    I have a different problem in Ohio where we can have net metering to sell excess power generated back to the electric utility company. We cannot have the solar running if there is a power outage because it will backfeed power into the lines and be a danger to anyone working on the lines in a power outage. You would think that it would be possible to set it up to run and not backfeed but it can’t at this point. I have checked on this with my solar installer. The way around this is to have a backup battery if you want to rely on solar. Instead we installed a whole house backup generator a couple of years before the solar array.

    1. Nick Lucchese

      Greetings Paul. The ability to keep your solar running without backfeeding into the utility during an outage can absolutely be done. Many of us have been doing it for nearly two decades however the most recent 5 years it’s become a much easier feat. Maybe your installer is overwhelmed by understanding the additional equipment and logic but quite a few of the battery based inverter manufacturers now offer kits to make it a bit easier. Not trying to dog on your installer, but have him/her look into AC coupling or perhaps speak with another solar professional in your area to see what it would take. Some are easier than others but it’s absolutely doable to still benefit from your PV system when the utility is down. Start with some of this information from Outback but be sure whoever it is you purchase from works with the manufacturer they have the most experience and comfort working with since the systems can often be overwhelming for some especially if it’s a new brand they don’t have years of experience with.

  4. Michael Moffitt

    I am all for solar when it makes sense, but I question the “fuel” costs you have stated for a back up generator and the overall costs as well. First, and foremost, most people do NOT purchase gasoline powered generators when they want to power most of their home’s electricity needs in an emergency. In my neighborhood, here in Montana, most of us have emergency generators installed and they all use Propane which we store in 1000 gallon tanks. These are all connected to our homes with an automatic transfer switch as well. The generator sizes range from 12 KW to 20KW, which are able to power most to all of a home’s electrical requirements. BTW: My current cost for propane is $1.42/gallon in MT.
    How much would the cost be for a Solar Panel-Power Wall system that can duplicate this amount of back up power? And how long can a battery provide power during an outage–some of which can last for more than 24 hours? Our other challenge here in Montana is that our roofs are totally snow covered perhaps 4 months out of the year, which can significantly limit the amount of solar energy that panels can produce. And it is precisely during the winter, with our occasional snowstorms, that our need for emergency power is the highest.


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