off grid at Gloucester

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off grid at Gloucester

Postby Hastings » Sun Oct 21, 2018 11:16 am

Hi all.
1st post other than saying hi.
I'm wanting to build a stand alone system at Gloucester NSW.
Ive worked out we will use around 2.5 - 3 kws a day. That was the easy thing.
Ive read just about every article on the net relating to sizing and now are completely bamboozled.
This is what I don't/know so far.........
I'll be fitting the panels on a rack in the paddock that is turnable (by hand)
I'm thinking 10/250 watt x 24 v panels. (how do i make 12v into 24 v panels?) or is this done at the battery bank.
Will be around 12 mtrs from house. (What size cabling do I use for this run?) Are the panels connected in series/parallel.
If I went 48v how much more expensive is this? Do I need to go 48v given the amount of power consumed?
I can't work out what size MPPT for this size panels?
I think I need 1000 amp/hr 24v battery bank. Can I use 6v high amp/hr golf cart batteries?
What size inverter given losses to run higher than required?
Do i split circuits. 12v for lights/pumps/fans and 240v for fridge/computer/tv/ washing mach?
Im budgeting up to $8k for the system.
Hope for some answers, but in the meantime will keep bamboozling myself on the net.
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Re: off grid at Gloucester

Postby Gordon-Loomberah » Mon Oct 22, 2018 2:13 pm

Hi Hastings, when you say "2.5-3kws", do you mean 2.5 -3kWh/day or 2.5-3kW maximum load?

If the former, then a 24V system is fine, but you shouldn't need anywhere near a 1000AH battery.

Are you planning to use a generator for battery charging/backup?

With 2.5kW of panels on a 24V system, it might be best to split them into 2 arrays, each with a 50 or 60A MPPT charge controller. You can run short panel strings to give a string voltage of around 100V, which will significantly cut down the cable diameter required between PV arrays and charge controllers.

Inverter size depends on your max loads, allowing for new items you might run in the future, otherwise a new inverter may be required.

I'd stick with 230VAC for everything, no need to duplicate the wiring to run 12V appliances/lighting, which often are more expensive and/or less capable.
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Re: off grid at Gloucester

Postby Hastings » Tue Oct 23, 2018 12:23 pm

Thanks for the Reply Gordon.
Regarding the system size, I have found an online spreadsheet from Conergy.
Its now saying that I need total AC and DC loads of 3317 Watt hrs/day
Energy to be generated 4993 Watt hrs/day
Minimum battery bank 1387 amp/hrs
I haven't factored a generator into the budget, but it looks like I'll have to?
I was also scared to price out lithium ?
So from what you are saying, just go with 230V ac with inverter that matches daily load or peak load?
I get what you say about 2 strings.
So cable size would be slightly larger than 100v and fuse would also be 120v or greater?
Its getting complicated, perhaps I should purchase a pre wired board with inverters and MPPT systems already attached?
Thank you for taking the time for me.
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Re: off grid at Gloucester

Postby Gordon-Loomberah » Tue Oct 23, 2018 12:48 pm

Victron certainly make some partly completed/wired systems, worth having a look at.

The 1387AH battery is ridiculously oversized if you are really only consuming 3.3kWh per day! It's over 33kWh of storage, although you generally only want to use no more than about 20% depth of discharge overnight on a regular basis for a Lead-acid battery.
For say 2kWh overnight discharge, you really don't need any more than about 10kWh of storage, ie, about 400AH @ 24V.
I think you could safely use a 200AH LiFePO4 26V battery, ie 8 cells.

Here I have 21kWh of LiFePO4 battery, now almost 6 years old, and regularly use 10kWh overnight, and up to 50kwh per day in summer. I have a backup petrol generator, rated at 3.2kW (runs a 25A + 6A 48V chargers) for cloudy weather.
However, before my consumption became so high due to running 2 large aquaponics systems, I ran for 2 years with zero generator usage, mostly with about 4kW of PV panels and using about 12kWh/day over winter and higher in summer. Usage was reduced in cloudy periods of weather- loads of washing, dishwasher, water puping, welding etc.
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Re: off grid at Gloucester

Postby Hastings » Tue Oct 23, 2018 3:02 pm

Thanks again Gordan, but I need to start small so as to understand which bit affects what bit and so on, then work up from there. Its just the way my brain works.
At this stage can you give me your thoughts on 6 v golf battery for storage.I read that they are no good????
I can buy 250ah for $300 each. I would need 4 to run 24v correct? But I would only have 500ah is that correct?
I will run 10/250 w panels can 2 strings
60amp mppt for each string
3000 w inverter
In regards to the genset. I read today that they make gens to work through the inverter and this extends your cycle times which extends your battery life. I can find the article if interested.
Anyway like everyone I appreciate your interest and your kindness in helping me out with your views.
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Re: off grid at Gloucester

Postby Gordon-Loomberah » Tue Oct 23, 2018 3:34 pm

6V golf cart batteries will certainly work, how long you get out of them depends on their quality and how hard you work them. With batteries, and most other gear required for powering your house with PV panels, you do tend to get what you paid for. $300 for a 6V 250AH battery does sound rather cheap. What brand and model are they?
Yes, you'd need 4 of them in series, which will give you 250AH @ 24V. For 500AH, you would need another 4 connected in series, all in parallel with the first 4.
Re inverters, make sure you get a true sine wave unit, modified sine wave inverters are bad news for some equipment. Good brands are Latronics, Selectronic (both Oz made) and Victron.

If you want to run a generator through the inverter, I'd suggest looking into the Victron range of inverter-chargers. Reducing the depth of discharge by any means possible will extend the life of Lead-acid batteries.

Beware of cheap charge controllers as often found on ebay, many claim to be MPPT, but in reality they are not.
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Re: off grid at Gloucester

Postby Hastings » Wed Oct 24, 2018 2:44 pm

Thank you Gordan, your help is appreciated.
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Re: off grid at Gloucester

Postby Hastings » Fri Oct 26, 2018 9:03 am

Gordon, I hope you don't mind if I address you like this here?
I have a question:
I read in one of your reply posts, that solar energy can be used before it goes to the batteries and that way you won't lose 20% inefficiency.
Does this mean i can use solar power directly from the panels to run an appliance.
If so, how is this done without over or under powering the appliance.
Thank you
Hastings
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Re: off grid at Gloucester

Postby Gordon-Loomberah » Fri Oct 26, 2018 11:39 am

Whenever your panels are producing more power than what is going into the batteries, ie the difference between gross output from the charge controller and net battery charging current, then your inverter and appliances are using power directly from the panels. You still need a battery though as output from the panels wont always be enough to power the loads.
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Re: off grid at Gloucester

Postby jules » Fri Oct 26, 2018 2:38 pm

Hastings, I notice you're working on an $8K budget, which means you're going to have to hunt around and possibly buy second hand for some items.

The heart of your system will be the regulator and inverter. Both of these should be top quality because cheap stuff can and does fail, which is a total pain. You also need to decide what capacity inverter you need to cope with peaks when you're running various items together and using power tools or maybe a vacuum cleaner which could test the limits of your inverter.

My own system uses 24V for lighting and my fridge, with 240V for everything else. One advantage is that an inverter failure doesn't black out the house, or cause the [24V] fridge to die . Another advantage of this arrangement is that it takes some load off the inverter or allows the use of a smaller inverter. The system I'm using is structured this way largely because it's evolved over 30+ years from a very basic 2 solar panel set up in the days when solar panels cost the earth. I have to admit going this way is now rather outdated but it still has advantages in some situations. Since LEDs have taken over from halogen or other light sources, the wiring you need for household lighting has considerably reduced in size [50W halogen replaced by equiv. 7W LED is an easy load]

Hastings wrote:Does this mean i can use solar power directly from the panels to run an appliance.
If so, how is this done without over or under powering the appliance.
Thank you


You have to have a regulator somewhere in your system, so no, you can't run power directly from panels into an appliance.
Primary system: .8KW Trina panels; Plasmatronics PL40; 1,000Ah VRLA 12X2V battery bank; 1.7KW Selectronic inverter. Off grid for 30 years.

Spares; 5 x 12V, 1,000 Ah batteries plus a couple of regulators
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