Running Appliances off grid

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wellygary

8261 posts

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#2031470 7-Jun-2018 15:31

What ever you do, and what ever fridge you buy, upgrade the insulation,

go down to bunnings/wherever and buy slabs of poly insulation and then glue this to the sides./top/back... is will look a bit crappy (you can seal and paint it if you like)- or you can put it inside, but you lose storage space...

But it will lower the overall energy required - and the condenser will run less (but it still wont help with your peak load)

http://www.thebackshed.com/forum/forum_posts.asp?TID=1280&PN=13&TPN=1

Rikkitic

Awrrr
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#2031493 7-Jun-2018 15:54

If you are going to do that, just build a box with open sides, cover it with canvas kept wet by wicks feeding from a bowel of water on top, and put it somewhere nice and sunny outdoors. The hotter the sun, the cooler the fridge. And it doesn't use any energy (other than the sun) at all!

Plesse igmore amd axxept applogies in adbance fir anu typos

tripper1000

1609 posts

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#2031536 7-Jun-2018 15:59

890 W/Hr without someone going into it for a beer/bubbly every 5 minutes, and without kids holding the door open as they gaze into it looking for a snack. Figure could be double that if the fridge is getting hammered.

Then you need battery capacity to keep it running for a couple of consecutive cloudy days when solar production is cut by 90%, then you need enough solar production to replace all of that on the 3rd day when the sun finally shines again.

A common mistake is to go 890 W/Hr divided by 8 hours of sunshine = 111 watts of solar panel, failing to account for anything but ideal conditions, then the batteries are continually flat and the system simply doesn't work after the 2nd or 3rd day.

890w/hr x2 cloudy days, plus the 890w/hr consumed on the 3rd sunny day, plus 20% losses in the battery, plus 10% losses in the inverter, plus 10% losses in the solar regulator, plus 20% losses due to the average angel of the sun, divided by 8 hours of glorious sunshine = 581 watts of solar required if you don't open the fridge door. Closer to 1000 watts if you are opening the fridge.

Wind can be good to compliment solar because the bad weather that stops solar production is often conducive to wind generation, and it works in the dark.

Hydro, if you can make some decent power from it and it is dependable 24/7, could dramatically cut the size of the batteries eliminate solar. That 24/7 thing is the clincher.

tripper1000

1609 posts

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#2031543 7-Jun-2018 16:15

wellygary: What ever you do, and what ever fridge you buy, upgrade the insulation,

go down to bunnings/wherever and buy slabs of poly insulation and then glue this to the sides./top/back...

Check your fridge before doing this, a lot of modern fridges use the external casing as the radiator on the hot side, so if you insulate the case in the wrong place you prevent them from working. Have a look at your fridge at home, the old ones have a radiator externally mounted on the back, so no issue if you upgrade the insulation, but on the new ones the radiator/condenser is integrated into the casing. You'll probably be able to feel that one or more of the sides or back is warm to the touch when the motor is running and it needs to lose this heat to the environment to work properly.

Also, as alluded to in my other post, if you are going into it frequently, the open door becomes more of an issue than the poor insulation.

MichaelNZ

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#2031659 7-Jun-2018 19:54

I live off the grid normally.

Good idea to use LPG for heating food, water and air.

Don't waste your money on an LPG or energy saver fridge. Just get a normal unit from Harvey Norman, Noel Leeming, etc, and put the money you saved towards more panels and a better power system.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

MichaelNZ

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#2031661 7-Jun-2018 19:59

trig42:

I am looking at getting a couple of High Capacity 12V batteries (say 100Ah each), an inverter (500W would be plenty, but maybe 1000W for safety) and a couple of 55W solar panels.

You will need at bare minimum 200 Watts of solar to just charge that battery bank. 400 Watts or more would be better.

You should rate your PV with a capability to deliver a minimum charge current of 10% though 20-30% is better.

Also keep in mind your normal load needs to be added to the charge current else you are going to struggle to get your batteries to float when you are there and using power for stuff.

So "back of the envelope calculations" are in this ballpark-

tripper1000:

890w/hr x2 cloudy days, plus the 890w/hr consumed on the 3rd sunny day, plus 20% losses in the battery, plus 10% losses in the inverter, plus 10% losses in the solar regulator, plus 20% losses due to the average angel of the sun, divided by 8 hours of glorious sunshine = 581 watts of solar required if you don't open the fridge door. Closer to 1000 watts if you are opening the fridge.

I would strongly advise you go for a 24 Volt configuration with your 2x batteries. 48V (which I use) is best but 12V is hellish.

What is wrong with 12V? Pretty much everything, including-

1. Voltage drop issues

2. Expensive cabling and DC breakers/fuses.

3. You will hit a ceiling at around 1,500W, after which (ie: when you decide you want to extend) you will end up ripping your system apart and loosing lots of money on the bits you have to dump/sell.

By comparison, my 48V system has a 3kW Outback inverter and I can double or triple this if I wanted and keep all the main system components - inverter, charge controller etc (several thousands of dollars worth)

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

Scott3

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#2031796 8-Jun-2018 01:28

Regarding fridge power consumption, best bet is to get one of the below (you can get them from hardware stores and similar), and put it on your fridge in your house for a few days. Should give a ballpark number. (I imagine your batch fridge will be smaller, but more frequently used.)

https://www.jaycar.co.nz/mains-power-meter/p/MS6115

Regarding off grid solar setup, if you are going to get one, might as well get one that can handle lighting, device charging etc.

Note that these can be kinda expensive. The below website recons that you would want to budget $15k plus for that kinda system.

2kWh Off-Grid Solar Power System

The 2kW name means you’d be able to use up to 2kW’s of stored solar power every day.
Solar Panels: 4x 260W
Inverter: 3kW inverter size
Batteries: 860ah, 24 volt batteries
Price: roughly $15,500 installed, inc GST.
Example power usage: A fridge, 4 LED lights, a cell phone and laptop charger.

https://www.mysolarquotes.co.nz/about-solar-power/off-grid/off-grid-system-sizes/

Regarding micro hydro, this would be a very fun project. (assuming accessible head, and flow in dry conditions are enough to make it stack up.)

Powerspout seem to have one of the most compelling product ranges in this space. See page 2 of the below to see if your stream matches their product line:

https://drive.google.com/file/d/0BzVDBix3S_qbWS00MXlOa25kT00/view

You will still be spending thousands of dollars. Main advantage is that you get lots of power (and only need a smaller battery bank), rather than being a low cost option. I think the cheapest powerspout is around NZD2k, then you still need batteries, inverter, pluming, intake weir, tailrace etc...

Would be happy to do a bit of analysis for free if you went this route, hydro is an interest of mine (I am a mechanical engineer, and work in the energy space). Otherwise, these guys are the NZ agents for power-spout, and would quote you for a complete setup to suit your needs: https://www.currentgeneration.co.nz/offgridpower.html

As a final note, sadly it seems that for holiday use, the most cost effective option is going to be a little honda / yamaha generator, with an extended run kit. These normally run under 60dB (conversation level / air conditioning noise level), and with strategic placement, and perhaps an acoustic surround of some sort, noise could be kept pretty low.

Tradepub

Free professional, reference and technical white papers (affiliate link).

trig42

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#2031858 8-Jun-2018 08:25

Thanks all for the input.

It does look like we have a bit more research and work to do.

Looks like either more batteries and more panels than I originally thought would be needed, or getting the hydro going.

I am confident we have the water head/flow needed for hydro, and I'd love to do the project (actually have all the bits available to build one without using a Powerspout - though if a DIY one worked as proof-of-concept then we could get the budget to but a powerspout). The issue there is user-friendliness. If I'm not there to get it going, how easy is it for someone else? Some people who use the place have issues lighting the Califont for the hot water and getting the LPG fridge going (mainly because when they get there, they haven't been running for sometimes months and it takes a while for the LPG to get through the pipes).

MichaelNZ

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#2032102 8-Jun-2018 13:03

Scott3:

Note that these can be kinda expensive. The below website recons that you would want to budget $15k plus for that kinda system.

That's the ballpark of what I had budgeted until I actually started doing it. Ended up well over $20k.

Also keep in mind - off grid electrical systems are subject to the same regs as any other electrical instalation plus a whole bunch of extra ones.

If you can make it to the Manawatu, drop me a PM and you would be welcome to come and see my setup.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

MichaelNZ

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#2032179 8-Jun-2018 14:40

Here is a couple of photos I have taken just prior to placing this post. This is the reality. This is why you need more panels than the theories and will spend more than you had budgeted. My array is 3.1kW.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

Aredwood

3885 posts

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#2032337 8-Jun-2018 20:22

Have you considered getting a 12V fridge? As a big issue that you haven't considered is inverter standby load. As inverters use power just to make 240V available, even if you don't actually need it.

To avoid this problem, you need an autosensing inverter, that can tell when the thermostat in the fridge is on, and scan start itself automatically. But then you have to find a fridge with a mechanical thermostat. So you can't get a fridge with an electronic thermostat or an inverter compressor.

Or you modify the fridge, so it's thermostat controlls the inverter - some hacking required.

MichaelNZ

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#2032339 8-Jun-2018 20:25

I run everything on 230VAC. Everything with DC is a pain in the arse.

1. Need DC rated switches and protection (fuses, breakers) AC stuff won't cut it and you could end up with a electrical fire. Don't forget this will also need to have a max fault current rating which exceeds your short circuit rating of your battery bank by 25+%. So think HRC fuses.

2. Generally DC rated stuff is made to run off a stable power supply and will not tolerate the Voltage swings present in off grid systems. This is typically 10.5-15.5V per 12V so do your sums.

At this time of the year my system will swing from 47 to 62 Volts over the day. The Outback inverter I have is made for this application by engineers who understand off grid. It can easily cope with this and provide a stable hassle free 230V AC for me to run my gear off.

3. 12V is a horrible Voltage to work with.

If you choose to ignore my advice and do it anyway - keep in mind your DC cabling needs to be rated at the higher of these two-

a. The short circuit current rating of the batteries - typically over 1,000 Amps until the protection activates.

b. Your maximum current draw + 25%.

Obviously, it will be point A is the highest.

In my system I run 50mm2 cable from the battery bank to the inverter. For a 12V or 24V system you will typically need 70mm2.

DC is not like AC. Working with battery banks is not like working with the mains. There is a bunch of stuff which is not intuitive to the average DIYer, and while the theorists (ie: pretty much 90+% of what is written on the subject) will tout all sorts of great ideas, if you actually go and do it, the pain points will likely become abundantly clear.

WFH Linux Systems and Networks Engineer in the Internet industry | Specialising in Mikrotik | APNIC member | Open to job offers

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