help me choose a battery?

[nakman]

So in my quest for more energy independence, I want to add a battery to the house. I want to do this in phases, starting with a battery, then transitioning some of my solar panels to the battery directly, then based on experience either transition more solar panels, or add another battery, or both.

Here's a quick illustration... currently 17 solar panels feed the grid and my 200 amp service. And from that service is a 50 amp sub panel that feeds my hot tub and EV charging, and a couple other 15amp breakers for plugs in the garage, etc.

This is what I want to do next: Cut the wire that runs between the main panel and sub panel, and add a plug and socket. So without adding anything else, add the capability to unplug the sub panel by just yanking the big scary 4-prong plug out of a socket on the wall. Or keep it plugged in and it's doing the same thing it does currently. This then gives me the ability to put a battery between the main panel and sub panel, like this:

Simple enough, right? So if I just leave that battery plugged in all the time I haven't really solved anything, other than I could still use the hot tub and probably charge the car 1 time during a power outage. Don't get too hung up on total wattage need, outage time, etc., as I don't know that it's really necessary.

Phase 2 then involves diverting some of my solar panels directly into the battery. Which then opens up the option of unplugging the battery from the main panel. Idea being, I start to figure out if I can charge a car x times per week and keep the hot tub running, only from solar charging... or do I still need to plug the battery in on occasion, etc. Here's what that setup looks like visually:

Then Phase 3 is really determined by how well phase 2 is working... if I'm always having to plug the battery in, I can divert (or just add) more solar panels. OTOH, if my solar gets the battery to 100% fairly regularly but I'm running out of juice, then I can add another battery. And once the system feels pretty sustainable, then what else can I move from the main panel to the sub panel, most obvious targets being AC and/or a heat pump, others being some of the plugs in the kitchen (fridge) or plugs in the bedrooms.

What I know I need is...
- a plug on the battery for the 50 amp sub panel
- good amount of amp hour capacity, like 4kwh minimum
- capability to charge from the solar panel inverters- I believe they put out 240v at like 1 amp (Enphase IQ)
- expandable. Want to be able to add a second, maybe even a third battery.

What I don't know I need is..
- a control panel?
- something else I haven't considered.

 

[Romer]

One of the things I looked at was output capacity to power what I wanted in an outage. Since I wanted to power the whole house (less AC, Oven and Dryer) I needed to have two batteries to carry the load I wanted. If I wanted just some circuits like you suggested, then I would only need one.

My system has a panel for those items powered by the batteries. When the grid goes down, only what is wired in that panel gets powered. If you consider that for location and size, you can expand what is there as time move on.

On my system, I have a 200 amp main and a 80 Amp sub panel which is fed off the main.

The backup panel is near the main and the power routed to the sub panel runs through it plus most of what is in the main panel.

Nice thing about having a abttery in a system is that if the grid goes down and the sun is up, the panels will provide power, but only to what is on your backup panel

The word file is from when I was first looking at solar and defining my loads vs the battery and likely changed after I did this and worked it with the contractor. The end chart was developed by the contractor to estimate my needs. I tweaked it a bit after that.

The below is the design of my system along with components used

Batteries and Inverters are in my Basement, Panels on roof (duh) and everything else outside

The panels feed to the inverters and then batteries

Main panel on left, then meter, then Breaker for batteries, then Backup panel. I forgot what the far right panel is. I think its what detects the grid is down and isolates the house from the grid, but I may be wrong


Not sure if this helps you at all