Opinion on Off Grid 220 System

[Darrin2k]

I purchased a house in Florida that I am renovating, currently using over 100 kWh per day, I have an old very inefficient AC unit that I will be replacing with a whole home central air mini split system, converting an old water heater to instant/on demand and I have a power hungry pool pump. The pool cannot use a variable pump because of extreme head lift and oneway valve, currently set to run 4-5 hours a day.

My goal is to reduce my energy consumption/costs and have an off-grid storm-safe system. Dipping my toes into solar, I have a plan to set up a 4kWh solar array using 400W panels on the roof and have 3-4 server rack batteries that would feed a (separate) panel and do new 220/40 runs to each appliance. I also would like to have a power transfer switch at each appliance that would be able to either run from the batter or grid.

Eventually, I would like to run a septic pump, a fridge, some emergency lighting, internet/fiber router - off this system as I scale up.

Would this type of system be feasible? Any input would be great.

 

[Brett V]

I don't have any first hand experience with the tankless water heaters except that they generally take a 40-50 amp breaker. Although only on for a moment, that's a huge amount of power you'd have to account for. I have a heat pump water heater that's very efficient. 100 kWh per day is going to be extremely expensive to produce, you need to make a list of items you can live without when the grid id down and do a power audit based on that. It's almost always cheaper to become more efficient than produce a ton of power, then go from there.

 

[Darrin2k]

Yeah for sure, that's my plan, I am currently at 100 kWh but that may be based on my pool pump running 24 hours a day for 12 days before I had a timer wired in. According to my calculations, I will need 2.2 kWh for the pool pump, the hot water is currently a large 30-year-old electric unit that I will be switching over to an on-demand/instant water heater (I still need to run calculations for that) and then the old 2002 14 ton AC will be switched over to a Mr. Cool 14/15 ton central air mini split 20 SEER2. I hope with some added insulation in a few walls and a few newer windows I'll be able to cool the house using 50 percent less power.

The solar system will supplement and eventually run critical systems in blackout or grid-down situations.

* Looks like the water heater may not be a good option for the time being, I will upgrade it for energy efficiency but it looks like it'll use 9-12 kWh per day and two 50 amp breakers, so that won't be feasible for the time being. Thanks for bringing that to my attention. I'll have to research water heaters more.

 

[MichaelK]

You really need a reality check here. The numbers you are posting right here, are way and above what 4k of panels could possibly produce. Let's assume you get a solid 5 sunhours per day in the summer, maybe 6? At 100kWh, that's 100,000W/ 5sunhours = 25kW worth of panels. I've got a 4500W array, and my max production so far has been 25.1kWh of power, last summer. So, just half of half of what you would like.

At the scale you are talking about, I'd say it could easily support a frig, TV, lights, and maybe one/two air-conditioned room(s). But whole-home air conditioning, and hot water; just forget that completely.

 

[Dnele928]

Do you have the option of running a tankless water heater on natural gas or propane? I can’t imagine an electric tankless water heater would work very well. I have a propane fueled tankless water heater and we get hot water in about 30 seconds. Plus, it uses very little propane.

 

[OffGridForGood]

Re-reading the original post, although the OP has (currently) very high consumption, the question was not about running the entire house on solar:

My goal is to reduce my energy consumption/costs and have an off-grid storm-safe system. Dipping my toes into solar, I have a plan to set up a 4kWh solar array using 400W panels on the roof and have 3-4 server rack batteries that would feed a (separate) panel and do new 220/40 runs to each appliance.

Not the whole house - dipping his toes into solar - this is a first step into solar.

I also would like to have a power transfer switch at each appliance that would be able to either run from the batter or grid.

This is very common, usually done with a Critical Loads Panel set right beside your existing load centre panel.
{I use the Reliance 306 unit, there are some larger ones too - do a search} these let you select Grid or Solar for your power supply to each circuit one by one as you see fit when ever you want. The Reliance is manual - you flip a switch to select power source - there are more expensive ones that you can control remotely also.

Eventually, I would like to run a septic pump, a fridge, some emergency lighting, internet/fiber router - off this system as I scale up.

Totally do-able with what you have planned for initial set up.
Main question will be: all 120 vAC loads, or some 120 some 240vAC - so you can narrow the search for a suitable inverter.
Pump motors can be 120 or 240 (many models can be switched internally as well) and motors are the most challenging load for an inverter to start due to in-rush-current, ie the extra amperage it takes to get a motor turning can be 3-5x the current of running steady. Look up the FLA on the motor if you have access to it, or check what size breaker supplies the motor now for an idea of the Hp of the motor.
A "kil-o-watt" P3 divice is low cost way to find out what energy the fridge and other 120-volt items consume in a day. It will total the energy consumption for you even though a fridge cycles on and off. Handy for figuring out the daily consumption you should expect.

The solar system will supplement and eventually run critical systems in blackout or grid-down situations.

Use the Resources section on this forum to get a copy of Filterguys' spreadsheet for tabulating the loads you will eventurally want to power. It is best to design a full system, even if you only build a smaller part of it at first, so that every component is sized for the eventual finished product rather than having to up-size parts as you expand (ask me how I know!).
Good luck with your project,
If you post more information we will be able to help you along with this.

One last word on PV: before you consider roof mounted PV do the research on Rapid Shut Down, and consider how you plan to hold the panels to the roof in your weather conditions.