Off grid solar system voltage. Which one to pick?  - Page 1
Forum section: electronics / general

author: Bendba
author_rank: Regular Contributor
timestamp: June 23, 2017, 01:49:14 pm
content: 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 335VWhat 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?

author: tszaboo
author_rank: Super Contributor
timestamp: June 23, 2017, 01:58:07 pm
content: Quote from: Bendba on June 23, 2017, 01:49:14 pmYou 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 pmNo. 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.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: June 23, 2017, 02:22:56 pm
content: Quote from: NANDBlog on June 23, 2017, 01:58:07 pmYou must have slow electricity in Europe.

author: tszaboo
author_rank: Super Contributor
timestamp: June 23, 2017, 02:32:59 pm
content: Quote from: HackedFridgeMagnet on June 23, 2017, 02:22:56 pmNo, ours is so fast, it will usually be twice 0 every 20ms.. Not as fast, as the US though. Its because of the Km - mile conversion.

author: Bendba
author_rank: Regular Contributor
timestamp: June 23, 2017, 02:38:21 pm
content: Quote from: NANDBlog on June 23, 2017, 01:58:07 pmThat 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 pmNot 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 pmI'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

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 23, 2017, 05:53:10 pm
content: Quote from: Bendba on June 23, 2017, 01:49:14 pmGreat idea but some potential gotcha's, firstly i understand your in Australia and from what I read they have draconian electrical regulations that require someone with a phd and license to even install an internet cable let alone anything to do with power.......Secondly you are right an SMPS without PFC can be powered by DC BUT its protection devices are not rated for DC most notably the fuse and also any on/off switch. The problem with DC is breaking the circuit and extinguishing the resulting arc.I have heard over there you may be able to get away with readily available plug in GTI's as they dont count as a permanent installation although I understand your panels have to stay in the yard too (not on roof).As you already have some lowish voltage panels you may as well buy a cheap "plug in" GTI to match them. I think you will end up in a legal tangle if you go for higher voltage panels and a "plumbed in" gti.Of course you could always emigrate to somewhere with a more reasonable regulatory framework

author: Bendba
author_rank: Regular Contributor
timestamp: June 23, 2017, 10:53:19 pm
content: Yes, basically, when it comes to mains, all you can do yourself is change a light bulb or use plug in appliances.When it come to DC, it's very muddy. Can't seem to find any law book and unfortunately I don't have any electrician friend to give me answers. I asked a builder but he didn't have a clue (actually, he didn't even know what the difference is between a safety or earth leak breaker and an over current breaker)I'm not really interested in grid tie inverter for two reasons. First is that, as far as I know, even plug in isn't legal, even if you could get away with it.Second is, on the long term, I would like to be able to have a system capable of running off grid as we would like to buy a property in the bush.The only emigration would be from town to the bush. I'm already immigrant (from Belgium)That circuit breaking in dc seems to be the only practical deal breakerOn my experiments, I was using those big >1000V beakers. I've used HV microwave oven fuses on one occasion but they usually are low current (700 to 900 mA)Though I've seen some nasty sustained arcs in 24V high current relays. When they start, they are like an arc welder until something melts even to open the circuit. So even low voltage need special beakers and fuses when playing with high currents, just looking for where to set the limit of compromise.

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: June 23, 2017, 11:53:53 pm
content: Quote from: Bendba on June 23, 2017, 10:53:19 pmTo clear the mud.The appropriate standard is called AS/NZS 3000 Wiring rules. It should be free but for some stupid reason the government wants you to pay to read the rules???Anyway up to DC 120 volts or AC 50v rms is considered 'extra low voltage' and so an electrical licence is not required and the above rules dont apply.Bear in mind a property in the bush will not get you away from regulations, there are a lot of fire related rules for people building in bushland.I think 48v lighting or even 96 volt would be the way to go. If you chose 96v certain low power AC lights and appliancesmightwork off the shelf.On the other hand AC is much safer now with the advent of RCDs and fire is probably a bigger hazard than electrocution.Personally these days I would go with 230v mains, whereas a couple of years ago I was all for getting DC lighting in my house.Batteries are getting cheaper, these power walls are less than $Au6000http://sol-distribution.com.au/Delta/Datasheet/delta-e5-hybrid-5kw-inverter-data-sheet.pdf

author: The Soulman
author_rank: Super Contributor
timestamp: June 24, 2017, 12:12:44 am
content: In the Netherlands (and probably entire EU and maybe overseas) you don't have to follow any rule for a installation of up to 50 Volts (ac or dc) above that all rules apply.Personally I wouldn't diy a high voltage DC installation in my house without following every single rule for accountability issues alone.24 volts dc is in my opinion a good option because (thanks to the truck drivers) of all the stuff that is available for it including lights, coffee machines, TV's, and also inverters to 230V ac are fairly cheap, fusing can be cheaply done with automotive style blade fuses.

author: IconicPCB
author_rank: Super Contributor
timestamp: June 24, 2017, 04:36:47 am
content: Automotive electricals are moving towards 48V DCsoon enough 48V will be readily accessible

author: David Hess
author_rank: Super Contributor
timestamp: June 24, 2017, 08:02:29 pm
content: For maximum economic benefit, I would use them in series/parallel to produce 48 volts and connect them to a plug-in grid-tie inverter.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: June 28, 2017, 11:49:09 am
content: Think one of the issues with using relatively high DC voltages is that conventional RCDs won't work on DC since they rely on current-balance transformers. Many electrical standards now require them, especially in wet areas like kitchens. Keeping to lower DC voltages might be an option provided the cable runs aren't too long, but copper costs and volts drop soon become an issue.

author: Monittosan
author_rank: Regular Contributor
timestamp: June 28, 2017, 01:57:03 pm
content: 24volt if its a small system and 48volt ultimately is ideal for an off Grid system.Grid tied requires you to be an A Grade Electrician and to complete a Certificate of Electrical safety as you have to certify your wiring to the Grid and ensure you inverter is approved for use in Aus.I'm looking to do the same and even though I'm a qualified electrician i'd like to avoid having to re do everything in the house for what is essentially a proof of concept trial.Sticking to lead acid for your battery's ? Lithium would get you many more cycles.

author: DenzilPenberthy
author_rank: Frequent Contributor
timestamp: June 28, 2017, 02:25:05 pm
content: Based on my experience of designing and building these kind of systems, I'd say don't worry about it. I've been through this decision process with several people, specifying fat 12v cabling runs and choosing sockets and connectors to use for 12v appliances and speccing lights that can work with 12V or 24V dc in case they want to change system voltage. As soon as the inverter is installed and working, they just use 230Vac stuff exclusively.Choose a system voltage based on what sort of load you will want. i.e. 12V = small, 24v = medium, 48v = heavy. Then pick a charge controller and a decent inverter. Then just wire the place to use 230V and save the hassle of finding DC fuses and switches, installing massive cables to deal with volt-drop etc...

author: djQUAN
author_rank: Frequent Contributor
timestamp: June 28, 2017, 03:07:29 pm
content: Played with running solar at home for many years. Started with a 12V system with a 40W panel and gradually went up in power up to 1kW.Above 1kW (PV and loads) you easily reach limits of sensible wiring and equipment capacity. So we eventually built a second system running 48V with 3.2kW of PV and 3kW inverter for the heavy loads (water pump, refrigerator, A/C).House lighting was already wired with 12V LED so I just kept a small 320W PV and separate battery just for the house lighting and 12V derived from the main 48V if the small system could not keep up with the usage.

author: fourtytwo42
author_rank: Super Contributor
timestamp: June 28, 2017, 03:10:47 pm
content: Quote from: djQUAN on June 28, 2017, 03:07:29 pmSounds a really good system, did you mean inverter or grid tie please ?

author: mtdoc
author_rank: Super Contributor
timestamp: June 28, 2017, 03:30:16 pm
content: Unless it's a very small system, 48V battery bank is the way to go. Everyone i know who started with 12 or 24V systems later regrets it when they want to expand. You'll need less copper, run more efficient and have room to grow your system (rule #1- Loads always grow over time!). String Vmp's will need to beat least70V or so. 90-100 is typical. Higher and effiency losses become an issue -even with MPPT CCs. Too high and charge controller options become more limited.On the load side, again, unless the system is very small, you'll want an inverter/AC system. What you lose in inverter efficiency (small losses with a high quality inverter), you'll make up for in less wire losses and have more choices and less headaches with your loads.And with PV prices now so low, buy more panels!

author: Bendba
author_rank: Regular Contributor
timestamp: June 28, 2017, 09:55:40 pm
content: Hi!Thanks a lot for all that information. Sound like with the solar array not on the roof, the best way to go would be 96V solar arrays charging 48V battery banks.I know lead acid doesn't last as long but they are still cheaper to run for an experimental setup than lithium.

author: djQUAN
author_rank: Frequent Contributor
timestamp: June 29, 2017, 03:17:26 pm
content: Quote from: fourtytwo42 on June 28, 2017, 03:10:47 pmI'm running both. Sort of like a hybridYou can check the system out here:http://www.quan-diy.com/projects/apower/alternativep.htm