Stand alone system for shed

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Stand alone system for shed

Postby jonda » Tue Feb 13, 2018 7:33 pm

Hi there,

I have 5 x 250 watt 24 volt Luxor 60 cell panels, 575 Ah of AGM batteries, a 12 volt / 2500 watt PSW inverter and PWM regulator.

I was looking at designing a system to run my back room (shed/man cave) separate from my house. My shed consists of new 300 litre refrigerator, computer with a 700 watt power supply, 80cm flat screen TV (Not plasma) and lights. it is connected to the mains via over head cable at the moment so looking to reduce electricity costs.

I have a 1.5 Kw grid tie system on the house already and cannot expend or modify it lest I lose my generous feed in tariff. So don't want to touch that.

I understand I will need to get a MPPT regulator. Will I be able to charge my 12 volt battery bank with the 24 volt panels using the MPPT regulator? Anything else I need to get or look out for?

What does anyone suggest to help me get this done. Any advice will be appreciated.

Cheers
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Re: Stand alone system for shed

Postby Gordon-Loomberah » Tue Feb 13, 2018 8:24 pm

With the sort of loads you are talking about, you wont be able to run everything for very long when the sun isn't shining on the panels.
Fridge 150W
Computer 700W
TV say 50W
thats 900W, and if you want the batteries to last very long, it's best not to take them below 25% DOD too often. That is not allowing for inverter inefficiencies.

575AH @12V = 6.9kWh, 25% = 1.7kWh, so less than 2 hours battery run time... and that is not allowing for inverter inefficiencies. However, that 575AH rating may be for a 20hr discharge rate, so it could be a fair bit under that at a 7.5hr discharge rate due to the Peukert effect.


One other question. Does a MPPT regulator allow you to have nominal input from the panels of 24+ volts and still charge a 12 volt battery bank at the correct charge of ~14.7?


Yes, although you may have to set the battery voltage manually, depending on what brand MPPT charge controller you buy, and probably the charging set points as well, to suit your AGM batteries. You'll need to check the battery specs for recommended charging rates and voltage set points.
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Re: Stand alone system for shed

Postby davef » Wed Feb 14, 2018 5:09 am

Computer 700W or is that computers 700W?
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Re: Stand alone system for shed

Postby jonda » Wed Feb 14, 2018 3:05 pm

Only one computer, 700 a bit high. I was just going on the power supply rating.
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Re: Stand alone system for shed

Postby jonda » Wed Feb 14, 2018 5:32 pm

Thank-you, all useful information.

Can I use these panels to just supplement day time usage direct from an inverter into the mains. I assume some safeguards would be needed if it is at all possible that is. Keeping in mind i already have a grid tied system on the main house.


Thank-you.
Jon
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Re: Stand alone system for shed

Postby davef » Wed Feb 14, 2018 6:57 pm

Jonda,

What does it say on the power supply for the computer? I would be surprised if it was more than 70 Watts.

The medium-sized Samsung fridge I use consumes about 400Watts/day. But that is in a cooler climate in NZ.

How long you want to use the computer and/or TV each day will have a significant impact on the storage you will need.

Dave
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Re: Stand alone system for shed

Postby Gordon-Loomberah » Wed Feb 14, 2018 8:54 pm

davef wrote: fridge I use consumes about 400Watts/day.


Dave I suspect you meant 400Wh per day, it certainly wouldn't be consuming 400W continuously, which is nearly 10kWh/day :o


Jon, you can't just whack a few panels on an inverter (which one?) and hook it up to the grid yourself- safety and legality must be considered ;)

You could use it to run some smaller loads continuously, off-grid, but in cloudy weather you'll probably have to switch over to mains power to avoid flat batteries, or else have a charger to maintain SOC in cloudy weather, or overnight with larger loads.

Using the PSW inverter off-grid and using a mains powered battery charger when required (automated with a voltage dependent switched relay, or manually/timer operated) would be the least expensive and safest way to go, with the equipment you have now.
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Re: Stand alone system for shed

Postby jonda » Wed Feb 14, 2018 8:58 pm

Thanks Gentlemen for the advice. :)
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