Off grid connection for a shed.

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Re: Off grid connection for a shed.

Postby Grakat » Mon May 25, 2015 7:44 pm

Hi everybody.

Thank you for the feedback and information so far. From what I have read, it is better to split the inverter away from the charge controller so that you get better quality with both. I'm happy to go down this path.

What equipment would you reccomend to start off. I don't want to blow the bank at this stage as it's going to be a weekender? We will upgrade in the future when the house is built.

I know the fridge uses 4A when on 12v because I have metered it. I guess a 50% duty cycle is a good place to start.

Regards
Graham
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Re: Off grid connection for a shed.

Postby Gordon-Loomberah » Mon May 25, 2015 8:13 pm

Not only will you have better quality by having separate components for separate tasks, but your system will be more resilient. Failure of one component doesn't necessarily make your house unliveable.
If your charge controller fails you send it away for repair, but you still have 230V from your inverter, for a while at least. If your inverter fails, you still have DC available for lights- and for extra electricity supply security a second small inverter is a handy backup to cover the load of your fridge and a couple of lights etc.

Whilst you don't want to blow the bank now- you also don't want to have to buy everything again later on.
Buy items that can be used on a larger system, as well as initially for the shed.

We have a few new items on clearance ATM as part of the change to SunEdison, charge controllers, PV panels etc, so PM if looking for various components and I'll have a look to see what is available. Some it will be listed on the forum 2nd hand section in the near future.

Second hand good quality inverters and charge controllers can also often be found, and are much better value than new low quality gear. Inverters from Selectronics and Latronics- reliable Aussie made gear, are worth looking out for.
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Re: Off grid connection for a shed.

Postby jules » Tue May 26, 2015 11:09 am

Quote Grakat:

What equipment would you recommend to start off. I don't want to blow the bank at this stage as it's going to be a weekender?


This will depend to a fair extent on whether you set the shed up as a weekender but plan to connect the house to the grid later, or, if you set the shed up in such a way that the equipment you install now can be used later as part of a larger offgrid system. In financial terms it's well worth making that decision now.

Offgrid systems don't have to be huge and expensive ;)

Jules
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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Re: Off grid connection for a shed.

Postby Grakat » Tue May 26, 2015 12:42 pm

Hello Jules

I have been thinking about that as well. When it comes time to build the house it is possible that we will go off grid. However to learn I want to put a smaller system into the shed. Whilst it is only 120m to the power pole for the block, connecting the shed to the grid prior to the house being built is cost prohibitive.

I'm now looking at charge controllers and inverters to see what is out there. I don't think my electrical demands are high, if I went for the luxurious weekender I would struggle to hit 1kW load.

Regards
Graham
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Re: Off grid connection for a shed.

Postby jules » Wed May 27, 2015 6:14 pm

Graham,

there's various ways you could approach this but here's one:

* go for 24V. In your situation this will work with your lighting [without an inverter] and while 48V might be better for a bigger system, 24V will work well with what you've got.

* get yourself 4 X 200-250W, 24V solar panels. You might get away with as few as 2 but 4 will allow you to use tools and other items during the day while the batteries will be more likely to be fully charged. A weekender does have the advantage of getting a breather to re-charge during the week so you don't have the problems associated with a week or more of overcast skies but it's better value to overdo it slightly on panels rather than batteries in most situations.

* Whatever combination of batteries you choose, make sure they can be connected in series and NOT in parallel. You could elect to go for half a full scale 48V [=24V] battery bank now and increase it later [by doubling] to the full 48V but batteries might be a point in the system where you don't spend too much at the moment if you might connect to the grid eventually.

* Pick a regulator that can be ganged up with other identical regulators later to increase capacity. You'll only need 40amp max capacity to start with. I use a Plasmatronics PL40 and while they aren't MPPT, they have been around for a long time, they are very reliable and very adjustable. There's plenty of other options though. Some regulators have fans and can be quite noisy if you have to live with them.

* Inverters have some slightly annoying characteristics ... In standby mode they draw a small but constant current which tends to add up when multiplied x 24 :) . When operating, they tend to be far less efficient at low current draws than they are when running at higher capacity. For a weekender you're going to be better off using 24V for as much as you can and only turning the inverter on when you need to run a tool etc. Take Gorden's advice on using a DC to DC converter to run your fridge [rather than 240V inverter which would be very inefficient in this role]. A 1Kw inverter might be enough for you but it's quite easy to go above that. A power saw will draw 1500W +. Maybe something around the 2Kw second hand in a good brand?

If you've got the time and patience to hunt around on ebay, gumtree etc you can do well on second hand gear as Gordon said above.

Jules
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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Re: Off grid connection for a shed.

Postby MnT » Thu May 28, 2015 1:02 pm

Hi all,

For what it's worth, we designed a full off-grid PV system that would run the future house then fitted the system to our existing shed. That way the power supply for the whole site was done once, correctly, and we could move on.

It has to be done at some point anyway if you are serious about being off-grid, so just jump in and do it properly the first time.

We did and we haven't looked back.

Cheers,

M.
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Re: Off grid connection for a shed.

Postby Grakat » Fri May 29, 2015 8:04 pm

Hello again everybody.

Thank you all for the valuable input. A special thanks to Jules for breaking it all down for me. The system you have outlined is pretty much what I want to do.

I have one question with regards to batteries. For the system that Jules has outlined what total AH should I be targeting. Would 200AH be a good place to start? At this stage I am looking for 2 days autonomy, which is the usual weekend duration. During the week there will be minimal energy draw.

Then as things develop I can add batteries, and PV panels to increase my autonomy......right?

Regards
Graham
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Re: Off grid connection for a shed.

Postby jules » Sun May 31, 2015 8:40 am

Would 200AH be a good place to start?


That should be ok for your needs. Ah capacity can be slightly confusing. If you have 12V batteries rated at 200Ah and you connect them in series the voltage increases but the Ah rating of the battery bank is the same. So, 4 X 12V batteries rated at 200Ah gives you 48V at 200Ah.

Then as things develop I can add batteries ... ?


If you're talking about expanding that to a full size house system, probably not because you'd be looking at maybe a minimum battery bank size of 1000Ah at 24V [or more!] and the 200Ah batteries wouldn't fit into such a system.

Then as things develop I can add ..... PV panels ... ?


Most probably yes, though they would have to be close in specs to those you already have.

I don't want to start going round in circles here but it would be best if you could figure out if you want to go off-grid in the future before you start. Borrowing from Mnt's suggestion, you could limit your initial expenditure by buying a full 48V battery bank, 4 solar panels, a charge controller and a smallish inverter [and later on expand to 20+ panels, add an extra charge controller and a larger inverter suited to efficient standby operation]. A set-up like this in a shed would probably cost you half of a full system for a house with all the extra complexity involved but it could be expanded without having replace parts of the system. If you want to do something like this you should chat to davidg or Gordon or one of the people on this forum who specialize in installation.

Jules
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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Re: Off grid connection for a shed.

Postby Grakat » Sun Jun 07, 2015 6:06 pm

Hello everybody.

I have been reading through what has been written. I have a few thoughts and questions.

Following on from what has been written above about quality I was thinking of starting off with a decent charge controller. The Outback Kid looks like a good starting point as they can be incorporated into a bigger system in the future.

For the PV panels, based upon the 4 x 200w recommendation, I am looking at doing a virtual tracking setup, with 2 x 200W on the East roof and 2 x 200w on the west roof. I just need to check the kid can handle the input. Panels would be 24v

I have been looking at batteries, this is where it gets confusing. I don't want to run a lot of 2V batteries to get the result, so have been thinking about 4 x 6V 225AH golf cart batteries in series to get 24V. What do you think about this battery setup? If this was insufficient would it be appropriate to put in another 4 x 6V string to increase the capacity to 450AH? These two strings would need to be paralleled to increase the capacity.

Court is still out on the inverter. I can run my camping fridge on 12v using a 24v to 12v step down unit. School is still out on the inverter. Still working out the difference between an inverter charger and a straight inverter.

I know it's putting the first bit last, but the loads I am looking at are as follows.
12v camping fridge running 24hrs/day approx 4A/hr.
24V LED lighting.
In the future I woul look at upgrading the 12v fridge to a 230v fridge, probably a 250l unit with inverter control on the compressor.
I would also be looking to charge cordless tools, the only 230v tool I would be looking to run would be my SCMS.
Depending on what happens with the plumbing I would also need to factor in a small 300w water pump.

Again thank you all for your input. I am keen to learn while building this system.

Regards
Graham.
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Re: Off grid connection for a shed.

Postby Gordon-Loomberah » Sun Jun 07, 2015 7:41 pm

Grakat wrote: The Outback Kid looks like a good starting point


Outback? I suspect you mean Midnite Solar. That will do 30A, so 4 X 200W as a virtual tracker should be fine at 24V.

If you are thinking of adding additional parallel strings of batteries, you don't want to leave it too long, batteries should be properly matched in capacity if you want them all to last a long time. 225AH at 24V isn't very much usable capacity- you should aim to be cycling them no more than about 25% per day, which is about 1.3kWh. You'll need a generator if it is cloudy. If you have a 230V generator, an inverter-charger may be useful, alternatively a motor driven 24V truck alternator to directly charge the battery can be set up reasonably inexpensively. That's what I used for many years.

12v camping fridge running 24hrs/day approx 4A/hr.


Your terminology is a bit confusing - "A/hr" is meaningless, Amps are multiplied by Hours to get AH, not divided. Do you mean it draws 4A continuously, or 4AH/day? Big difference!
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