Garage (partial house) System

[alfsauve]

Hi, new to the board. I'm a tinker'r. Fairly savvy in electrical and electriconics; Avionic is USAF, 1st Class FCC Commercial when they use to issue those, Extra Class Amateur Radio. Finished my career as a house electrician and lighting director for a large performance venue (5 venues actually, small to large). So here's my project.

Please, with each post I'll have one main question or concern. I know there's lots of things you'll just can't wait to share with me, but if we can make this a simple step-by-step thread to follow much better for my feeble wit.

OVERALL PROJECT IDEA

Priorities:

Save money: While N. GA has some of the cheapest electricity (~$0.15/kWh, fully burdened), it's going to go up. I've configured systems on paper in the past and they don't usually save money, unless someone else is paying, think rebates. So I'm aware this. Don't need to labor on it, what money I don't save can be thought of as applying to next priority.

Emergency Backup: It doesn't happen often, maybe once a year and usually only for 15 minutes or less, but it has been down for 6 hours once recently. Who knows however what the future will bring. Don't need to run the whole house, just enough to make it comfortable. The freezer, a few lights, some fans, maybe the TV for OTA, and oh, the garage door opener. I can justify a 15yr payback by claiming that part of that was paying for emergency backup.

Experiment: It's my nature. Spent the Wuhan flu season learning and playing with Arduino. Built a clock (doesn't everybody?) a reloading monitor and counter for my reloading bench, and a Halloween light and sound controller.

What I've considered:

Not willing to try whole house at this point. There is a challenge with my roof as it all faces East and West, however I believe I can get a small number, 4 cells, mounted on a frame work on the 1st floor roof over the garage. That way they'll be facing south. Plus they'll be right over the garage where the system will be located.

Considered and discarded a number of appliances and finally think the most cost effective will be those things right around the garage. Clothes dryer and washer, the freezer, the outside security lights, the garage lights and the garage door opener.

What I've configured so far is a 48V hybrid inverter, 240 split phase. 200Ah of LiFe batteries and four 300W+ cells. Currently it prices out about $6,000 and a 12yr payback (straight line no interest) with the new 30% rebate.

Today's question:

It's about mating the Inverter to the PV cells. Four cells in series will give me ~130v,. The first inverter I zeroed in on was the Sun Gold 6kW split phase inverter (TP 6048). I like everything about it EXCEPT the lower end of the MPPT operating voltage. Most other inverters list 60V-450V, or there abouts, but this Sun Gold is spec'd at 120V-450V. It's the low end I'm worried about. The example in their manual show 6 panels as a low end system, though they don't mention or caution about going with fewer. Not sure I have room, nor spend the money for 6 panels at this time.

Will 4 panels be enough to drive it? Why is this one inverter of this class have a higher minimum PV voltage than any of the others?
(And before you you ask, yes, I've spec'd out the appliances and four 350W cells, 5 hours a day, will provide the weekly needs.)

TIA

 

[ncsolarelectric]

You're correct, the string voltage is too low for that inverter with only 4 panels. It should have 7.
How about this. A Quad microinverter, grid-tied for under $600, and a small portable battery generator that you can connect to your fridge, or garage door, or whatever, on the occasions you need it. Your payback will be about 6 years or less.

 

[alfsauve]

Thank you, Todd. This of course adds a layer of complication making sure the panels and inverter will play nicely together, especially in a small 4 panel configuration. Sun-Gold did point me to their lower MPPT inverter model. So I have that choice though I'm still looking at other inverters. (so many options, so many choices)

Quad micro-inverter is certainly the way to go if producing solar power and getting a quick payback is the objective. Of course there's no backup for power failures. If I had the south facing roof space, I'd do micro-inverter and and probably put in a separate battery backup system.

Todd did get me thinking and reading about the the NEC rapid shutoff requirement.

Today's question is about "rapid shutoff":

I understand in a fire first responders may be crashing into a house for rescue or firefighting and they don't want to encounter live wires when cutting open the roof. I assume that in such cases they pull the house's electrical service (yank the meter out). It seem the better micro-inverters sense the loss of grid and do an automatic shutdown. For string inverters, as I've read it, the shutoff doesn't need to automagic. It can be manual but has to be, obvious, outside and clearly labeled. (and non-roof mounted panels do not need a cutoff) A cutoff on the side of the panel array (within 1' actually, 2020 code) would suffice. Of course more complex remote cutoff could be employed allowing cutoff to be affected from the service meter. Am I reading that correctly?

 

[ncsolarelectric]

The question remains about the inverter. If the inverter discharges the PV input within 10 seconds, then all you need are the Tigo RSDs on the panels. But if the inverter doesn't discharge or disconnect the PV wires, then something external to the inverter, like a DC contactor or relay must be used to de-energize the wires to < 30V in 10 seconds, from inverter to panels.

 

[alfsauve]

After doing a heck of a lot of reading and getting up to speed, I've determined that to get a decent payback, if payback is your MAIN motive, then micro-inverters tied to the grid are the way to go. OKAY. OKAY. The rest of you knew this already.

So if you want backup, what's it worth to you. Is knowing you can be comfortable, save your freezer stock for a week, worth pushing the payback from under seven years to 15yr or more? I thought I could beat the system by DIY and be being very selective as to the appliances I chose to power. Hasn't worked out. (Oh and the wife on her own, saw a great deal on a SxS fridge to replace the 15+ yo separates we now have so we'll be saving money by having a single more efficient appliance anyway.)

UNDERSTAND: I have limited southern facing space for PV panels, unless I'm willing to put up a flower pole or use part of the yard. Neither of those are going to happen for now.

So I'm down sizing this project to an emergency battery backup system with 1 panel that will keep it continually charged, a 3000W inverter and a 200AH battery. It'll be primarily to run the freezer during prolonged power outages. I think I can bring it in DIY substantially cheaper than buying the pre-packaged units. And with a solar panel, I'm going to claim the 30% fed rebate. Since it'll be conveniently in the garage I'll occasionally plug my power tools in a "exercise" the system.

Thanks to Todd for alerting me to installation pitfalls and to others who responded privately.

 

[FoxenTEC]

Thinking of doing the same Alfsauve. We don't know how long we will be in our home and don't want to invest to many dollars. I think a couple 200ah batteries, solar controller, inverter and maybe 400 watts of solar (plenty of sun) will get us through the summer potential blackouts. Just running our fridge, a few LED lights, a good fan and our small network will do.