Design check before buying - Storm backup

[Spark4234]

Hi All, long time lurker first time poster.

I'm building a shopping list for a simple gas generator replacement type of battery-based backup system inspired by Will's videos. In a perfect world, this system would never need to come online, but storms can be unpredictable. I prefer not to over-complicate things with automatic transfer switches, grid-tie, sub-panels and the like. The goal is to treat it like a portable gas generator, offline until absolutely necessary. If/when the power goes out, I'm happy to take my time checking things over before flipping any switches, so it can be a fully manual process as far as I'm concerned. Small household of two adults. Napkin math says costs add up to about $3800 before any tax credits.

Requirements:

• Allow 240V/2800W deep well pump to cycle (priority #1)
  • We have a massive 120gal pressurized water tank that helps with the frequency of pump cycling - the drawdown rating is about 40gal
  • May be switched off overnight to prevent unnecessary draw
  • Cycle time approx. 1 minute based on normal use
• Run fridge, minimal interior lights, comfort accessories like a fan or phone chargers on demand (priority #2)
• Allow 240V/4500W water heater (50gal) to run as-needed (controlled at the breaker panel - priority #3)
• Run internet devices, small TV for critical updates (priority #4)
• No HVAC necessary
• Runtime of 2-3 days with some personal comfort adjustments
• Runtime of 4+ days with bare necessities, minimizing draw (historically has not been necessary)
• Future support for solar (TBD)

Overview:

• 200A main panel
• 50A breaker for inverter, with interlock kit, to energize panel from backup source
• System located in utility room, will require hanging some plywood, racetrack, conduit, etc.
• Main panel, inverter, battery, accessories all share one wall - layout using best practices/code as guide
• No exterior connections at this time
• No net metering
• 120V/15A battery charger to maintain battery health - unplugged when inverter is on

A general overview of the big pieces:

 

[WorldwideDave]

Welcome to the forums. For a simple manual battery backup system to replace a gas generator, use a 240V pure sine inverter (4–5 kW) with a 48V LiFePO4 battery bank (~12 kWh), manual interlock kit for your 200A panel, essential load sub-panel for pump/fridge/lights, small 120V charger for maintenance, proper wiring, fusing, and future solar provisions, all mounted neatly on a plywood backboard. The battery bank will cost a bit. I have half that storage amount and I built myself but didn't save any money doing so :-(