It takes quite a bit of doing, all this off-grid home stuff!
Worst of all, the only thing I could remember from high school electronics was that V=IR (voltage = current x resistance) and P = IV (power = current x voltage). And I assure you that I have zero ability to visualize any of the tangentially related metrics. But the whole thing is fascinating no end.
Anyhow… Look at all this equipment that’s needed!
Hunt down some solar panels!
Of course. If you’re in sunny climes, this is the most obvious alternative source of energy versus drawing entirely from the local electricity grid. In fact, you can still be grid-connected and sell your excess power to the grid! But that’s another topic. The example setups I’ve seen are usually around 8 x Solar panels at maybe 135 Watts each… yielding about 1KW (though per what… I didn’t catch it)…
Find a charge controller
Energy from the solar array comes into the house via the charge controller. It basically does a DC to DC conversion to ensure that it’s output matches the voltage needed by the battery bank (you’ll meet the battery bank below). There’s usually also a small computer panel / interface for managing the charge controller (and inverter, if you have a combo device… and truth be told, isn’t it just easier to have one thing to deal with instead of two? Of course it is. Inverters described further down).
Get you some batteries
OK. These, I get. But I had no idea how many were needed! I’ve come across setups with 8 to 12 batteries at least. I can’t even remember how you measure battery charge, but it seems like 400 Amp-hours is a viable metric (Ah). The voltage metric is a bit more familiar. I saw a setup with 4 x 6V batteries wired in series… and then just when I thought that was a lot, they had another 24V in series and then they wired both sets together in parallel. High school physics tip: you do this for twice the capacity (current), but the voltage stays the same (24V in this example).
Scrounge an inverter from somewhere
So, there’s the issue of transforming the low-voltage DC power you’ve got so far, to a high-voltage AC current that things generally run off of, inside the home. The North American domestic supply is basically 120 V AC at 60Hz (the alternating frequency). In terms of the actual current feeding stuff around the home, circuit breakers will funnel about 15 to 20 Amps to outlets.
Note: a modern inverter can also do double-duty as a charge controller and funnel juice direct from the solar array to the battery bank.
a quick note on Sine waves
Turns out, inverters fake the sine wave that household devices expect: they basically shunt the power from the batteries one way through a circuit and then the other way, basically creating a crude square wave (hence the label “modified sine-wave inverter”). If you fork out more and more $$dosh though, you basically buy a better and better approximation to a smooth sine and items with seriously unpredictable current needs (microwaves, drills, dimmer switches, etc) will thank you for it. The example setups I saw online seemed to quote their inverters at 3600 to 4000 Watts… which seems to be the ballpark for a basic home? In short, you need to tot up all the different types of equipment in your home – you can check online or on manufacturers’ websites to get a sense of basic and peak power usage… and sort of come up with a power budget for your home. This will help you buy the right size of inverter (update: you can use energy monitors for this and actually measure it).
Backup Generator (or, as I like to call it, “plan B”)
Obviously, this is for when there’s not enough solar (or wind or whatever) and the batteries are low. It’s essential to have a backup energy source for your generator (e.g. fuel of some sort). The generator will top up the batteries (ideally via the inverter) as described above. I saw a 6500 Watts example so I’m not sure if this was for just a bigger / more power-hungry home or if the generators should generally have a higher power output than everything else.
Odds ‘n ends
DC Disconnects: each of these components go to this box on a separate circuit. Any issues, the circuit will break. Also saw something about a ventilation system for your batteries… basically every once in a while you send an overvoltage to the battery bank, and any harmful gases are vented to the outside of the home.
What about heat sources?
I hadn’t even thought about this. One cool thing I saw was a thermosiphon water heater:
Basically it’s a giant water drum with a top hose and a bottom hose which feeds out to a solar panel or two. The solar panel heats the water and it feeds back via the top inlet of the tank… where it’ll stay, since hot water rises. Pretty clever! Otherwise you could get a bank of propane cylinders or something.
More info from experts
To learn more about net metering; how to prevent wastage, micro-inverters (**brilliant** idea!!!) etc, this is a really great video for an overview (good for noobs):
update: love the diagram up top; wish I knew it’s original source so I could attibute it properly! Turns up in a couple of places…