Keep in mind the OP said "portable generator" so we are not talking about having to install a generator, connect a gas line, and wire it into the house electrical system. We are talking about a smaller generator that can either be carried or is on a wheeled cart. Connect that with an extension cord to the refrigerator and a few backup loads and I do not think you are going to get a permanently installed BESS wired into the house with an ATS cheaper.I agree with JB. That's what got me thinking about this, I mean you're probably looking at 10K minimum for a small generator installed, maybe more for gas hookup. If you're not looking to back up a lot of load, I think battery would be competitive.
The whole concept also depends on how often and for how long someone needs backup. In the last five years there has been one time when my power was out for more than a few hours. For me the cost to install any kind of fixed backup is way more than the usage I will get out of it. For me a small portable generator that can sit untouched for years in my garage and was just enough to run the refrigerator and a few lights would be more than enough. Now for someone who has a week long blackout once a year they should be looking at a more permanent fixed generator wired into the house to get a whole house backup. A BESS would be a good consideration here.
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