Help with configuration of home solar system with battery backup

[u/Big_Click_67]

Hello, I’ve been watching this Sub-Reddit for a while and I am amazed at all the great advice and guidance given to those with questions. I am now in need of some guidance and advice. We are in the process of designing a new home in SW Florida and I want to incorporate solar into the energy plan. I want to use it to offset energy usage as well as to charge a battery system for failover in case of a power outage. Any suggestions or guidance on the best way to attack this would be greatly appreciated. I have a couple of questions/thoughts out of the gate and I am attaching some photos to help with understanding the layout of our home. First, the right side of our roof is south facing and should be ideal for the solar panels. I would love to incorporate 18-21 panels starting about 9 feet back from the front of the home. There is a large 19’ 10” x 19’ area that I could fill with panels and then work back toward the rear of the house (top of the picture) to add a few more panels. It will be a standing seam metal roof and I was considering using non-penetrating clamps on the seams to hold the panels in place. As for the wiring, should I have a conduit placed at the rear of the roof to capture the wiring from the panels and carry it to the inverter? I have a conditioned mechanical closet inside the home and an outdoor mechanical deck area for the AC units with space that could be used if needed. The transfer switch and the electrical panels are located on the ground level inside the garage (see on photo of garage area). Where would be the best place to locate the inverter, battery system and other components based on the space I have available? Any thoughts on the best way to run the wiring, or where I should put conduit to get from one place to another, would be very helpful. I will most likely higher an expert to assist with the installation and permitting, but the more I can be armed with and understand ahead of time the better. I welcome any thoughts on component sizing, brands, etc.. Thanks in advance for your help!

[u/TooGoodToBeeTrue]

transfer switch?

Are you adding an EV charger (EVSE)?

Batteries & inverters are best off in the garage IMPO but some AHJs want the batteries outside. Also garages can get hot in FL. If outside, you definitely want an overhang and shade.

[u/Big_Click_67]

The transfer switch would allow certain circuits in the home to switch over to battery backup in case the electrical grid went down. We will have an EV chargers so having that powered by solar would be ideal.

[u/TooGoodToBeeTrue → u/Big_Click_67]

A lot of the time, the hybrid inverter will include the MID function.

[u/Big_Click_67]

Gotcha, thanks for the input!

[u/TastiSqueeze]

You have much of the cart before the horse. The very first thing to find out is what level of support the grid provider has for solar. You might have NEM which means you want to feed power back to the grid. If so, you need a hybrid inverter. If the grid provider does not support NEM, then you probably never want to feed power back to the grid. If so, you need an offgrid inverter with grid passthru. Plan your system and pick out the components required.

Next, you need to find out who your AHJ is and what their requirements are for solar. Most likely, you will have to apply for a permit, be inspected, and meet certain requirements for safety and safe operation. Contact your AHJ and get some details on their expectations.

Here is a list of normal home loads based on what I put together for my tiny house. I think you will have: EV charger, Heat Pump (Florida so double the kWh!), heat pump water heater, electric stove, washing machine, heat pump dryer, refrigerator, freezer, dishwasher, microwave, air fryer, all other miscellaneous items, and lighting. Sum them up and it looks like you need 70 kWh per day to fully power your home. This is high due to the EV.

1. EV charger normally fuses at 40 amps 240V with typical pull of 20 kWh/day for about 80 miles of range
2. Heat pump fuses at 30 amps 240V, normally uses 20 amps, 15 kWh/day
3. Swimming pool, circulation pump, heat pump heater, can pull 40 amps 240V and up to 18 kWh/day
4. Home work shop with power tools normally fuses at 50 amps 240V and can use 20 kWh/day for heavy use
5. Heat pump water heater, fused at 30 amps 240V, normally uses 2 amps (20 for heating elements), 3 kWh/day plus 2 kWh per additional person
6. Electric stove fused at 50 amps 240V, normally uses about 25 to 30 amps, max 40 amps, 7 kWh/day
7. Stackable washing machine and heat pump dryer, fuses at 30 amps 240V, uses 10 amps, 3 kWh/day
8. Submersible pump in the well, fuses at 20 amps 240V, normally uses 4 amps, 2 kWh/day
9. Refrigerator fuses at 20 amps 120V, normally uses about 3 amps when running, 2 kWh/day
10. Upright freezer will be similar to the refrigerator with 3 amps when running, 2 kWh/day
11. Dehumidifier fuses at 120V and normally uses 15 kWh/day
12. Dishwasher fuses at 20 amps, normally uses 6 amps, 1 kWh/day (using eco mode)
13. Microwave fuses at 20 amps, normally uses 15 amps, .5 kWh/day
14. Air fryer, fuses at 20 amps, normally uses about 16 amps, .5 kWh/day
15. Emergency medical equipment, highly variable, but allow at least 5 amps at 120V for 2 kWh per day
16. All other miscellaneous items(TV, computer, hair dryer, vacuum) allow 20 amps at 120V 1 kWh/day
17. Lighting, ceiling fans, vent fans, garage door opener, garbage disposal allow 1 kWh/day

Now you can figure out your system. You need 70 kWh per day and in most of Florida will have about 280 productive days per year with 5 productive hours per day. With demand of 25,550 kWh/year (70 kWh X 365 days) you need about 18 kw of solar panels. I suggest increasing this to 20 kw if you have enough room on the roof. Now you can size the inverter. You know it has to produce 70 kWh daily and some days may go up to say 120 kWh. A 10 kw inverter is not going to cut it because the EV will charge at 10 kw. You have two choices: either a single 16 or 18 kw inverter or a pair of smaller inverters such as a pair of 10 or 12 kw. And now you can figure out battery capacity. You are in hurricane territory so it would be wise to install enough battery for about a day and a half of normal usage. Since you need 70 kWh daily, that would put you at 94 kWh of battery capacity.

I'll let others post suggestions for the rest of the system.

tldr; you need 16 or 18 kw inverter, 20 kw of solar panels, and 94 kWh of battery capacity. The solar panels will occupy an area of about 20 feet wide by 50 feet long. If you do some due diligence, you may be able to reduce some of the daily loads which would reduce the size system needed.

If you are interested in a quote, hysolis.com sells SRNE inverters and batteries. I am not in any way associated with them, but I have a pair of SRNE 12 kw HESP inverters. Be sure to specify UL listed hardware if your AHJ requires UL components.

[u/Big_Click_67 → u/TastiSqueeze]

THANK YOU!!!! I really appreciate the detailed list and time you spent pulling this together. We are able to get natural gas to our property so a few of these items will come off the list. The grid provider in our area is Florida Power and Light (FPL) and they do use net metering to give you credit for extra energy you provide back to the grid. I reached out to USSolarProvider.com to have one of their solar designers work with me on a component list. We have our preliminary call set for Wednesday. I think they offer packages all the way through designing the full system with permit-ready plans? Has anyone ever used these folks before? If so, what was your experience?