Electronics > Power/Renewable Energy/EV's

Off grid solar system voltage. Which one to pick?

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Bendba:
Hi,

I've always been interested in solar power and it seems that the photovoltaic panels finally got to decent prices.
I've got 4 x 250W 24V panels, connected in series in the backyard, just using them to charge batteries and do some experiments.

I came to wonder if I was to set up a proper array, which system voltage should I go for?

You can find converters for 12V, 24V, 48V, 96V dc to 240V ac, most UPS's I find at the scrap have 144V battery banks.

Low voltage means high transmission losses.
High voltage just mean be careful.

Most modern appliances have SMPS and don't have any issues being supplied with DC supply.

But most fuses, switches, plus are rated for 240V ac, there is the greater risk of arcing. But no conversion losses.

So, where is the limit? I mean, I'm comfortable with voltages up to 400V dc but hate ac. But where is the practical limit?
Could one run a whole house on 300V dc?

But then what are the tolerances? Assume 25 12V lead acid batteries, that gives you a voltage fluctuating from around 295V to 335V

What is legal as permanent setup? What is legal as temporary setup (as in flexible wires not attached to the building)? Is there a clear limit or anything as long as you don't start a fire or kill someone?
I know anything above 24V is potentially deadly (I actually believe that under the right circonstances, 6V would be enough but that's another debate)

So, is efficient solar (eventually homemade) possible at all or is there still to much red tape and lack of standard?

tszaboo:

--- Quote from: Bendba on June 23, 2017, 01:49:14 pm ---So, where is the limit? I mean, I'm comfortable with voltages up to 400V dc but hate ac.

--- End quote ---
You shouldnt be. Making a fuse for AC is simple, since the voltage will be 0 in every 20ms. DC fuses are bigger, more expensive.

--- Quote from: Bendba on June 23, 2017, 01:49:14 pm ---Could one run a whole house on 300V dc?

--- End quote ---
No. Maybe you can run the lighting of the house from DC, but that's it.

I would suggest a 48V battery system. Since telecom systems work at this voltage, you should be able to find equipment for this voltage.

HackedFridgeMagnet:

--- Quote from: NANDBlog on June 23, 2017, 01:58:07 pm --- Making a fuse for AC is simple, since the voltage will be 0 in every 20ms.

--- End quote ---
You must have slow electricity in Europe.   ;)

tszaboo:

--- Quote from: HackedFridgeMagnet on June 23, 2017, 02:22:56 pm ---
--- Quote from: NANDBlog on June 23, 2017, 01:58:07 pm --- Making a fuse for AC is simple, since the voltage will be 0 in every 20ms.

--- End quote ---
You must have slow electricity in Europe.   ;)

--- End quote ---
No, ours is so fast, it will usually be twice 0 every 20ms.  8). Not as fast, as the US though. Its because of the Km - mile conversion.

Bendba:

--- Quote from: NANDBlog on June 23, 2017, 01:58:07 pm ---You shouldnt be. Making a fuse for AC is simple, since the voltage will be 0 in every 20ms. DC fuses are bigger, more expensive.

--- End quote ---
That might only be because of personal experience. I've been bitten a few times when younger, 400V dc have me a couple of bad burns bad I still preferred that than the feeling of the 380V ac going through my arm.
I know, been a dumb kid.

I'm actually lucky for the moment, I have several high voltage (>1000V) high current switches and breakers.
But I totally agree, when it comes to mechanical contacts, DC got a big drawback.

--- Quote from: NANDBlog on June 23, 2017, 01:58:07 pm ---No. Maybe you can run the lighting of the house from DC, but that's it.

I would suggest a 48V battery system. Since telecom systems work at this voltage, you should be able to find equipment for this voltage.

--- End quote ---

Not to contradict you but I actually found that a great amount of appliances are happy with DC. I successfully ran PC's, TV's, VHS and DVD players, phone chargers, and printers from a 16 x 12V lead acid battery bank. Even found some CFL bulbs that worked. Other resistive loads would work fine with little modifications (use of semiconductor instead of mechanical switches).

I'm obviously not saying that it is a good idea. Otherwise, I wouldn't be asking the question.

Are there any other industry standards then 48V? I know that where my father work, they have installations that run on pure DC, the mains is turned into 100V dc (50 x 2V lead acid batteries banks) and the plant runs from that because they cannot afford to even brown out. But that might only be a one off, not a standard.

Also, when it comes to the house wiring, is it legal to have a 48V (or other, eventually higher) DC circuit? I can't seem to find any clear text or law about that.

It would be easy to modify many appliances to run from 48V dc but again, what is legal? Most tv's, pc's, ... only use 3.3, 5, 12, 24, 32v internally.

--- Quote from: HackedFridgeMagnet on June 23, 2017, 02:22:56 pm ---
--- Quote from: NANDBlog on June 23, 2017, 01:58:07 pm --- Making a fuse for AC is simple, since the voltage will be 0 in every 20ms.

--- End quote ---
You must have slow electricity in Europe.   ;)

--- End quote ---

I'm actually in Australia but same story, we run on 50Hz.

But there is actually a zero cross every 10ms, not 20ms. One going up, one going down