Solar has a 20-30 year payoff.
Not sure if that's even a rational investment to be honest.
You're absolutely right. Its not really rational where electrical service is readilly available.
Solar panels are great, they have no moving parts, no electronics, and usually come with a 25 year warranty.
The problems
1. Converting the solar panel DC power to AC
2. Powering your shop when the sun isn't shining.
Solar panels don't really have the amperage to run a whole lot on their own, generally you run everything off batteries and the solar panels charge the batteries when you're not using power.
So you need a big bank of batteries and a power inverter. You need enough batteries to power whatever you want to run, along with the equivalent size inverter, so you're going to spend a thousand bucks on batteries, a couple thousand more on a huge inverter, a few hundred in battery cables and related wiring accesories, and whatever the cost of the solar panels and controllers.
After the initial investment, Whoohoo, free power! For a maximum of five years when you need to replace the batteries. Inverters **** out fairly often too, they only come with a one year warranty. Don't forget the maintenance, you have to get up on the roof and clean the solar panels regularly, and keep the batteries filled with water.
I work on RV's for a living, I instal a lot of solar systems, so I figured I was going to run my workshop on Solar and battery, but the math says that over twenty years I can buy power cheaper.
It works well in an RV setup, where the lights and furnace already run on 12 volts, your 110 volts AC use is pretty minimal, a little TV, fifteen minutes of coffee maker, a few minutes of the wife using a hair dryer, microwave some soup, cellphone and laptop chargers. You use a bunch of power in the morning, but generally go out during the day and do recreational stuff which gives the solar a chance to recharge the batteries.
A shop setup is a lot more power hungry. Air compressor, drill press, grinders. Don't even think about a welder. Of course I want to use all the power during the day, leaving only a minimal amount of daylight time for the batteries to recover, and thats only if its not raining, which it generally does every day here.
Back to the OP, if the neighbor is already having voltage problems, you'll want to get them an upgrade before adding yourself to their line, although its likely the power company will already know they need to increase the line size if they're talking about a second meter for you.