I'm pretty familiar with solar - I don't (yet) have a system on my house, but I do make my living in a solar powered office (or, as more common in the winter, generator powered).
Off grid power, or semi-off-grid power, is
painfully expensive. Comically, absurdly, insanely expensive. It's useful if you're unable to get grid power for under about $50k, it's useful if you're a goof who plays with this stuff for fun to get hands on experience, and it's useful if you value standby capability for your house/projects (a friend of mine has a pretty hefty inverter and an awfully large battery bank to run his lab equipment, because if his vacuum pumps shut down, he loses quite a bit of work).
That said, let's dive in!
We live in an old farmhouse, built before electricity considerations. The electrical system has been upgraded over time, everything works well, but there's a conspicuous lack of outlets and ceiling fixtures. I'd like to rectify this, but I'd also like to go solar, at least partially. Cutting the electric bill and environmental impact of our usage down would be great.
Split your projects. Upgrading wiring and outlet count should have very little to with solar in a practical setup.
The only way you'll have an actual benefit for your power bill is a grid tied solar setup. The same is true for environmental - off grid power is really quite dirty if you trace back to the batteries, and you have a generator... small generators are not very efficient.
I'd also like to not tie into the grid, ideally, although here in NJ there seem to be a lot of incentives for doing that. I want power when the grid is down, and just plain independence from the electric company.
How important are the various aspects of the project to you?
"Independence from the electric company" is a pipe dream unless you're willing to pay 3-4x the price per kWh you pay now, perpetually. You'll need a hefty generator in the winter, and I joke with people that "off grid" is an ancient Indian term for "likes generator maintenance."
If you put any sort of inverter on your home's power wiring, you're going to need to have grid tie agreements in place with your utility, and have to meet code, etc. The wire cost alone to run a separate system is cost prohibitive.
You can design a solar power system that gives you limited grid independence (closer to a whole house UPS) that's still grid tied, but if you start thinking about this, you can forget cost savings. There's no way to do a setup that runs grid-down cheaply enough to "pay off" in most areas - around the time you catch up, the battery bank is toast and needs replacement. Yes, I've read the claims about lithium, and no, I don't think most of them will be met in home power systems.
2. Put a second circuit panel in the basement, supplied entirely by the off-grid solar panels.
3. Initially, do not use battery storage. This would be a supplemental system that would expect sudden power outages.
4. Add several outlets to the house, tied into the new solar circuit panel. Mark outlets as being supplied by solar.
You can't make this work for any useful value of work. Solar panels are a rather weird power source, and the only way you can run with no batteries is to run far, far below the rated power of the array. Say, pulling 1kW off a 6-10kW solar array. Some of the string inverters have this feature, but even then, power is unreliable. Cloud? Whoops. It drops. I've got a long blog post on this exact issue coming up, because it's complicated to explain why it doesn't work, but it doesn't.
So you're not utilizing your panels at all, practically. They're pretty black plates sitting in the sun running, sometimes, at a tiny fraction of rated output.
There are very few inverters that will tolerate this, and I assume you're not planning to build your own power conversion equipment for this project.
5. Add battery storage and more panels, if desired. Add the other necessary components as well.
6. Transition a couple of the electricity hogs (washer/dryer/dishwasher/water heater) and the light fixtures to the solar system, as the available power would allow.
Going from a direct panel powered inverter to a battery system typically involves totally different components. You'll generally have a 48V battery bank (lead acid or lithium iron phosphate) for a home sized system, and will need the charge controllers and inverters for that, instead of the previous inverter.
How are you planning to tie light fixtures and such into this obscenely expensive system? Remember, you can't touch your home's existing wiring without net metering agreements.
I'd really never see the need to abandon the grid entirely, but a supplemental system that eventually transitions to supply 50+% of our power, maybe even powering a couple A/C units during the day, would be really nice.
You... seem to operate under the belief that this system will be cheaper or greener. :) It won't be. Not by a long shot.
Just buy community solar, or install a grid tie system.
For backup power, you want a generator and transfer switch. Propane is a good option for a long term storage generator.
Is it technically feasible? Links to resources are welcomed.
See above. It's on the edge of technically feasible, in that I could put together systems that would do what you request, but... well, see below.
Is it likely to be cost effective?
No. Emphatically, no. If you can get off grid power down to about 4x grid power, you've got an efficient system.
My current cost per kWh on my system is... oh, $1.50/kWh? That'll go down, and I think I ballparked around $0.40/kWh by the time the battery pack needs replacing on my office.
Is there likely to be insurmountable red tape and restrictions?
Yes, though you could avoid that if you had totally separate power wiring for the parts you run with the solar setup. You can't do something like shut a breaker down, though - it would need to be totally separate. Have you priced copper wire lately?
Is the initial plan sound, for leading to the later improvements?
This is a bad way to achieve... whatever it is you want to do, unless the goal is to spend tens of thousands of dollars for hundreds of dollars of power.
And any other naysaying or encouragements you have would be appreciated. I've not done any specific research yet, just brainstorming. I have yet to find an example of someone who installed a system like this (off-grid, supplemental, battery-free system). There may be reasons for that.
Quite. That's because it's not technically feasible in a useful manner. You can go battery free with grid tied, you can go off grid with batteries, but what you can do off grid and without batteries is so limited as to be nearly useless.
=============
Alright, that idea shot down, I'll give you an idea as to the feasible options out there.
In general, as someone else notes, the second you say "Battery," you've lost cost effectiveness on the system, at least at home scale.
If you want to save money with solar panels, and squint a little bit at being "green," go with a grid tied system with microinverters or string inverters. That's about the only way you're going to actually save money.
If you want backup power, while you're doing that project, install a good transfer switch and a backup generator. If you have natural gas, running it off that is a good idea (there's usually pressure in the lines for a while during a power outage), otherwise I'd suggest propane. That's more expensive than gasoline, but it stores better and doesn't crud up the oil like gas does in a generator. Five year old propane works fine. Five year old gasoline is sort of a thick gel... it doesn't burn or flow and makes a mess of anything it's in.
Now, if you've abandoned the idea of saving money but really want reliable power, you can do a battery backed system. There are a few ways to do this (AC coupled or DC coupled), but if you want high reliability power, you'll probably need to go with a DC coupled system. This involves the panels running through charge controllers into the batteries, and an inverter that runs from the batteries. You can set things up so you can sell to the grid this way if you have excess, but things can also run with the grid down indefinitely (or, at least, as long as you can charge things - solar panels in dark clouds are worthless). The Outback Radian series inverters are a solid option for this, though there aren't many options because not many people want to do this. You'll still want a backup generator with this setup. But you can run most of the house post-inverter. This is what I plan on doing. I'll do most of the work myself, but it's still not going to beat grid power for operating costs. It will, however, give me extended grid down capabilities and a nice batch of hardware to work with.
Hopefully that clarifies some of the issues. I've got a few thousand words in progress talking about this exact issue, but that post isn't quite done. However,
https://arstechnica.com/civis/viewtopic.php?p=34054407#p34054407 has my first draft of that, which might be useful.