Solar with Battery Backup Vs Generator, Advantages & Disadvantages 

battery backup versus generator california


There are all kinds of options to serve your backup power needs in the event of a power outage. They can serve either a portion of your electrical circuits through a subpanel as covered in a previous article, or your entire building.  We’ll review the advantages and disadvantages of the “larger options” below. Other options can include things you might plug just a single item or small power strip into, such as a UPS (uninterruptible power supply) or portable battery units like those made by Goal Zero (www.goalzero.com) and other companies.

Grid-tied solar system with battery backup

There are three major types of solar systems. Grid-tied (connected to a utility like PG&E) make up close to 100% of the systems being installed these days. For safety reasons , grid-tied solar systems do not provide power to the home even when the sun is still shining. If they didn’t disconnect they could harm utility workers trying to fix power lines, which they need de-energized to work on safely.

The second type is an off-grid system, with no connection to the utility grid. They use different equipment and include batteries to supply the power needed when there’s not enough sun available or at night.

The third type is a grid-tied solar system with battery backup.

With those fine points out of the way, here are some advantages and disadvantages to battery backup systems.


  • No interruption of service, your system switches to batteries automatically.

Power can be available for 3 – 5 days during extended cloudy weather, depending on power use and battery size. A generator may be required if the need for power exceeds what the sun can provide.

  • The Investment Tax Credit (Federal Solar Tax Credit) of 30% helps reduce the total cost.
  • An automatic generator start unit can be used in conjunction with a generator to help reduce the size and cost of the batteries needed. If the batteries get too low it automatically fires up the generator.



  • Compared to the common grid-tied system their efficiency is a little lower. This means less savings which, along with a higher installation cost, reduces the economic benefits.
  • The batteries & battery box requires additional space and may need to be vented to the outdoors, which is part of the added cost.

– Lead-acid batteries – “Flooded” lead acid batteries – the ones with caps that allow you to periodically add distilled water – require monthly to bi-monthly attention to maintain the water level. “Sealed” lead-acid (no-maintenance) batteries cost roughly twice as much, and lithium ion batteries can be roughly four times the cost for the same storage capacity.

  • Battery warranties are typically one year, but for larger more expensive “industrial” batteries or lithium ion batteries it’s up to 10 years. It should also be noted that lithium ion batteries can cycle (charge and discharge) hundreds of times more than lead-acid batteries before needing to be replaced, which is part of the justification for their higher price. They are also more efficient, losing less energy when cycling.
  • A “critical load subpanel” must be installed and this adds cost. This panel is powered by the batteries when the power goes out. Given the cost of batteries it often excludes non-critical loads such as air conditioning and electric clothes dryers. Including them would require larger (more expensive) batteries, a larger inverter and possibly more solar panels to charge the batteries to achieve the same amount of backup time. While it’s possible to provide backup power for everything in the house, having a few circuits that aren’t backed up lets you know when there’s an outage. These non-powered circuits help inform you the power is out which signals you to conserve more energy, extending the time your batteries will last (unless you also have a generator, this is covered below).
  • In addition to extra space and venting for the batteries, more space is required for the equipment, the inverter and the power distribution panel (switch gear).
  • The labor cost is also higher due to the need to install batteries and other additional components & wiring.
  • From our experience we’ve sometimes found people accustomed to living on the grid have a tough time conserving the power necessary to function with batteries alone for extended periods of time. Larger more expensive batteries would help of course, but cost is always a major issue.


Generator Backup

generator for solarAdvantages:

  • Usually a more affordable power supply for short term outages.

– You don’t need any sun to make your power, just an ample supply of fresh fuel.


  • There’s a short power interruption in between the time the power goes off and the generator powers up.
  • They’re great for short-term outages, but most people (and neighbors) would rather not have the noise from a generator droning on for days on end.
  • They consume a disproportionately high amount of fuel when power needs are small. For example if you’re only using 50% of the generator’s power it could be consuming between 60% to 85% of the fuel it would be using if fully loaded. This problem is largely eliminated when charging batteries, however, because full generator power can be used.
  • Some generators use gasoline which may be hard to supply during a widespread outage, and also goes bad after a few months. This is why many people choose a propane or natural gas fueled generator.

– They require periodic “exercising”, which means the generator needs to run every so often, and requires maintenance on things like air filters, oil filters, and oil changes.



Of course the best of both worlds for longer term outages would be a combination system, a solar battery backup system with a generator tied into it.  Combining the two means your generator will use less fuel and only run periodically for shorter periods of time. You could take the generous 30% solar tax credit on everything but the generator and have a system that will eventually pay for itself.

A large combination system like this with no-maintenance batteries could cost $65,000 installed, not including the cost of the generator, or $45,500 after the tax credit. It could supply 14.4 kW of electric load, enough to run an entire energy-efficient home. It would include a very large 60 kWh battery storage, one that could keep everything running for 3 days without power and no sun before you’d need to run the generator in the winter months. In summer months you likely wouldn’t need the generator at all. For comparisons sake, a common grid-tied system with the same solar panels would cost $26,000 installed, or about $18,200 after the tax credit. In this case the added cost of the battery backup is $27,300.

For another example, a solar system with a smaller 10 kWh Lithium-Ion battery storage and enough solar panels to wipe out an electric bill averaging over $200/mo (about the average home’s 28 kWh/day usage) without a generator could be installed for about $41,500, or $29,050 after the tax credit. The batteries could supply 5 kW of electrical load, capable of running pretty much everything in the house during an outage other than big loads like a well pump or air conditioner.

For comparisons sake, a common grid-tied system with the same solar panels would cost $29,000, or $20,300 after the tax credit. In this case the added cost of the battery backup is $8,750.

Of course these are just two examples, the cost to add battery backup to a new solar installation depends on so many things: how much power will you be using, how many things might you be running at the same time, how many days do you want to go without the grid or a generator available (winter vs summer), the size and type of the generator, and other factors. There are almost limitless examples! Adding battery backup to an existing grid-tie system is a different topic, we’ll cover this in Part 4 of this series. In every case it’s a matter of being sure to address the practical considerations we covered in Part 2 of this series – “Power Outages – Part 2 – Practical Considerations” before giving us a call.

In the meantime, please check out these links for important information about how to be prepared in the event of a utility outage in California and Nationwide:


Public Safety Power Shutoff tips – https://prepareforpowerdown.com/

The Safety Action Center contains helpful information about wildfire risks and what you can do before, during and after an emergency to keep your family safe.


Continue to PART 4 – POWER OUTAGES  – Adding Battery Storage to an existing solar system


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Power backups using batteries and generators in Northern California are a major issue and topic of conversation our community. PG&E is proposing power outages for Nevada County, Grass Valley, Nevada City, Penn Valley, North San Juan, Auburn and surrounding Placer and El Dorado Counties. Not only will PG&E by shutting down power for maintenance in Northern California, they may also shut down full power lines due to fires and other public safety issues. Stay tuned for more information on power outages in California, Nevada County and Surrounding areas.

What is the best option for a power outage in Northern California, batteries, generators or a combination of the two? I hope this article helped in that important decision. Thank you for reading part 3 of our series and stay posted for great local CA news.

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