the more I read up on it the more I agree the most optimal power distribution system is AC for long-range/grid power, but I also think that for studios/tinyhouses (basically <1000 sqft or so) it'd be more efficient to use a DIY powerwall and just run as much as possible off of direct current 'cause the wire losses in such a compact build are negligible.
@LexYeen in telecoms -24V to -60V DC (most common is -48V) is widely used for powering equipment (originally for resilience against grid power going off supply, and that it can power telephones at the end of a few km of cable. The battery + pole is usually connected to PE (earth ground), as historically it stopped corrosion of more expensive metal in relay contacts
- telephone exchanges have *big* accus in them.
a small building could probably just use 24V DC and a bigger one 48V DC
@vfrmedia I'm not comfortable with 48V battery banks, simply due to the arc and injury potential - it's entirely possible for the bank to go over 50V during charging, and that's the point where at least in the US you need a license to work on it safely - and 24V is a bit on the low side for my liking.
Maybe 36V for storage, and convert down to 24V for the socket wiring?
@LexYeen wow, thats a bit on the low side, in UK and EU power supplies can be up to 120V DC before they are classed as "strong voltage" and then have extra regulations.
Circuit breakers for DC are fairly widely available here and you can never have *too many* smaller ones/fuses for local wiring.
36V is a convenient voltage for lithium-ion accus, widely used for #e-bikes (although I think was also used on early local generated power in rural USA where you had a genset charging accus)
@vfrmedia I think the concern on this side of the pond isn't *just* the shock hazard - a 50V arc is a hell of a firestarter, after all - but I haven't looked into it any further than "okay that's bad 'cause safety, got it."
@LexYeen a few years ago an engineer at a UK telco *did* drop a metal tool straight across main L- busbar and earth; there *were* fireworks and large city without phones for a while but he was unharmed (there is personal protection gear against arc flashes you can get if needed
Charging accus give off hydrogen so battery room must be ventilated/fire proofed anyway.
An old training manual I have from German DBP-Telekom says "do not bring a lit Cigar into the battery room" 🚭 🔥 🚒
@LexYeen Since late 1960s Europe used 230V AC mains so 120V DC isn't viewed as that strong and can even be sent down telephone wire for ISDN or analogue circuits in very rural areas (it still bites!). -48V or even -60V is relatively harmless in comparison.
I'm slowly working a backup power system but will likely use -24V as the highest DC voltage - its possible what we consider a "small" building varies greatly across continents (my whole house is 50m^2 per floor!).