l literally did this a few hours ago

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Battery backup likely last 2 hours on AC. Good luck with that.
- Mine lasts about 8 hours with AC on constantly if there was no sun. This was during the day, so the battery was charging faster than it was discharging. If the power goes out at night, I just turn up the thermostat so the AC is only on some of the time, and it will last long enough for the sun to come back up.
  
  What is the size of your battery pack and model of you know. Also what is the size of your AC unit? What you pay for the battery pack alone?
  I have a 5kwh grid feed system on one of my houses and install solar for remote locations that power low watt towers.
  
  I have two batteries that were 13.5kWh each. The cost was exorbitant, but I live in an area that loses power extremely often (rural), so it was worth the investment, imo. Plus, it increases the value of the house, so I'll make it back eventually.
  My solar panels provide 6kW.
  My whole house with the AC running uses about 4kW. Without the AC running, my house uses about 0.5kW
  So doing the math right there, I could actually run 6 hours, 45 minutes with no sun and AC full blast, so I guess I was off by a little bit. But I never run the AC full blast anyway, it always turns on and off to maintain temperature, and it runs way less at night when there's no sun.
  
  As I said, 99 percent are grid tied no battery. You are the one percent and I think that is an important omission on your part. Your battery pack would cost around 40,000 U$ I estimate alone. Now if you are not grid tied, your solar installation will be very inefficient and often not matching your usage/charging requirements. Thus you won't be getting the most out of the 6kwh solar panels. Often getting very little return. If it is grid tied which provides access to store excess energy, that is the most efficient system. But if you include that battery pack and try to match best efficiency, then you need a much more complex charger/controller. Add 50 percent to that cost. I suspect your installation on nearing 100k if it is installed in such a way to take maximum advantage of the sun.
  Now with the battery pack, you can utilize it to provide power at night allowing for maximum savings. But if you do this, there is no guarantee you will have any battery left for those frequent power outages you have. Thus to be reliable on battery, you must keep it at full charge at all times thus not getting any real financial returns on it. It is simply a 40,000 dollar 'generator' which doesn't really make any sense both from an economical or environmental sense. The good thing is that it should last a long time if it is not discharged often. But if you operate it in daily usage, you will need to replace likely every 10 to 15 years. That is pretty expensive as well.
  While simple solar panel with grid tie can be both economical and environmentally friendly, battery packs make near zero sense from a return on investment or from an environmental sense. It sounds like you are using it to protect from power failures but that means it must be at 100 percent at all times ready for power failures. And if you are doing that, just install a far cheaper generator. Not only is it far cheaper, you can have days of power failure and the environmental impact is far less then the manufacturing environmental costs of batteries.
  
  Uh, no. My battery was nowhere near $40k. Solar + battery + installation costs wasnt even that high, and thats before the 30% rebate from the federal government. Your numbers are way, way, way off.
  I am not going to lie, most of what you said makes absolutely no sense to me. Basically what happens is my solar powers my house. Any additional power that is generated goes to my batteries. If my batteries are full, excess power goes to the grid, and I get a credit that I can use later. When the sun goes down, I start drawing from my batteries. If/when my batteries hit a threshold that I set from an app on my phone (I currently have it set to 50%), my house stops using power from the batteries and pulls from the grid. In the case of a power failure, I still have 50% of my battery left to protect me from power outages, which is enough to power my house at night at regular usage for hours.
  Yes, I mostly have the batteries for power failures, but 90% of our power failures are less than 20 minutes, so I don't need it to last hours. When we do have extended outages, I just turn up my thermostat, and it will last hours.
- WOW you can tell wich model and what type of solar panels he's using. You can even predict the amount of sun his' house is receiving and at what angle.
  You must be a genius!!!(or the opposite)
  
  I installed 5kwh grid feed on my house and professionally have installed enough systems for communications towers to know the requirements. So ya I take it with a grain of salt when people suggest they can get any significant time from a battery backup system.
  Also 99 percent of the home systems are grid tie and do not have a 'whole house' battery backup. Thus I am suspicious to begin when they say they get these long battery backup times and hands their AC tired in. And to make me more suspicious, nearly all grid tie systems shut completely down if the grid fails even if your in full sunlight. This is for safety reasons. A few people might have power wall type of systems but for ten thousand your only getting a few hours out of that and only on specific circuits in your house. Something that requires a bit of complexity in your electrical panel wiring.
  And before you all find the 1 percent of systems that are fully backed up with battery, and they do exist, these systems to be viable have to be so overbuilt that they can cost hundred thousand dollars.

149 comments