My Sisters have built a cabin and will try to live off the grid. Well, actually they will HAVE to live off the grid because in order to get electric service from the street, they would need a building permit. There is power and cable at the edge of their property. There is no water and people have it delivered or use catchment, primarily for toilets or irrigation, however with treatment others drink that rainwater. I would not.
They purchased 3 acres in the largest housing development in the U.S. which is 10,697 acre lots above the highway and 1200 one to three acre lots below, so about 36 square miles. There are miles of roads up and down with many lots not built upon. Population total for the areas, about 5,000 people 
There is a lot of lava from fairly large to gravel. Houses range from very nice houses professionally built to shacks. Weather is fairly warm and tropical and varies as you travel from sea level to 5,000 feet elevation.
Essentially, they built the place from watching Youtube videos. I guess hey COULD get a permit if an architect created plans based upon what they currently have. Many of the places near them are non-permitted.
Our island is a microcosm of weather and you can choose what you want. They are located near the southernmost point in the U.S. where we have lots of wind. Yesterday for example, they had winds above 10mph for about 19 hours with an average of 15 mph and gusts up to 36 mph. There also is solar but they get lots of clouds too.
Because the wind blows day and night we are going to look for a primary wind generator that also has a solar ability. Even though they get wind most of every day, if the generator breaks or what have you, they would still have some generation from the sun. Since they can generate electric with at least 8 mph breeze and they exceed that, their need for battery storage is smaller. They also have a small gas generator for emergencies, however gasoline is pretty expensive and they will be quite a distance from Costco. Getting parts quickly here can be an issue. One issue I have heard is that for wind generation you need a well-built system. Cheap blades or alternator can cause squeals and other noises which might drive you crazy. Also they are only a few miles from the ocean so salt corrosion can be an issue. Luckily there has never been a hurricane hit that location but they do pass by. The wind was a real issue trying to get plywood on the roof and not have it fly away. You wait for the wind to drop to nothing and hope it stays that way for 30 seconds or so as we shoved plywood from inside through the rafters onth the roof.
I have a neighbor who designed his electric system so that he can run most of his house from solar. He created his own battery system using good cells from discarded rechargeable battery packs and laptops. To hear that it sounds cobbled together but is quite industrial looking. He has meters and data on performance, etc.
The girls have cellphone coverage, but recently Verizon’s tower seems to have taken a hit and coverage at their cottage took a nosedive. They are considering cable internet once they get the power situation addressed.
Personally, at my house many miles north of them, I have county water, electric, cable internet, a generator that uses both gas or propane and am closer to Costco. I also have 80,000 gallons of standby water (from rainfall) for irrigation. However in event of a water outage, I figure I can flush the toilet for 6 years with that storage.
For them it has been a challenge to build the place. Plywood flooring (3/4 in tongue and groove) went from $30 to $130 during COVID. Supplies dwindled and we had issues getting many things. Luckily they are living at my house so they were not stuck with no roof or side walls down there. Lowes has truck deliveries but their one lumber delivery truck broke down and their estimate was 2 months to get parts. I ended up filling my truck with wood and plywood and made multiple trips down there making deliveries. Granted, in places which are not remote islands, some of these issues are not a problem.
I am able to help some but our ages range from 50’s to 70’s.
