Running Appliances off grid

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trig42

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#237548 7-Jun-2018 09:24

We have a bach in an area with no electricity.

It is mainly used in the warmer months (hardly ever is anyone there outside of the Daylight Savings months). It is a wider-family bach, and is used by many different parts of the family. Most people would stay for a maximum of two weeks.

We have always run hot water, cooking and refrigeration using LPG. It works really well for cooking and hot water obviously, refrigeration works OK, but the fridges are small and expensive to buy.

The current fridge we have is showing its age (it would easily be 20 years old, maybe 30), and getting it back to somewhere it could be serviced would be difficult and expensive, and it may not make it any better, and certainly not any bigger.

My idea now is to replace the fridge with a standard 240V unit, and use the savings between that and a new LPG unit (can pick up a 350L 240V fridge for ~$1000, a new 300L LPG unit is north of $2500) to go with batteries, an inverter and solar.

From what I can work out from manufacturers websites, fridges use, on average, about 40W (this Panasonic uses 328kWh/y - divided by 365, divided by 24 gives 37.45W).

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.

What I am struggling to work out is how long these batteries will last without a charge going into them (say cloudy days) and even if we get nice sunny days, is 2 x 55W panels enough to have a net gain in stored energy over a day. As mentioned, the fridge will need to be powered for up to two weeks at a time (potentially a little more if one group follows another into the bach on the same day - but we need to know the 'limits'). If it works out we will have a heap of power, we would look at running the lighting off them as well (currently we use a normal car battery and it runs the LED lights and charged USB devices for about a week before the battery needs charging - there would be about 7-8 LED bulbs, between 1 and 5W, used only when dark.

While no-one is using the bach, it would be possible to take the batteries home and plug them into a decent maintenance charger. It would be better to leave them there and have the solar (and a controller) keep them topped up. There may be security concerns around this (being it is remote, and the batteries are worth a good chunk of cash).

Has anyone done this/similar, or can provide advice on what I am missing/will need?

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#2031253 7-Jun-2018 09:35

A 100AH battery is 35kg, so moving it may be problematic. A 55W solar panel might make 40W in practice, less most of the day. You're right to consider peak current, a motor starting can use a fair bit of power for a short time.

Have you considered a generator instead of solar? $1000 or so and you're done, just take in some fuel.

wellygary

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#2031263 7-Jun-2018 09:48

timmmay:

Have you considered a generator instead of solar? $1000 or so and you're done, just take in some fuel.

This will be the most cost effective solution given you are only looking for short term summer usage,

Get a reputable brand ( Honda etc), and a good quality extension cord, build a shelter far enough away from the bach so that noise is not an issue and job done,

Sure it doesn't have the "geek cred" of a solar/battery/inverter setup, but with multiple users its probably the most user friendly and will require the least upkeep and maintenance...

trig42

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#2031266 7-Jun-2018 09:52

A generator is not really an option - noisy, and fuel usage. It could be an option to recharge the batteries though (then again, so could a car, which is already there, and jumper leads).

I'm aware that the 'surge' of the compressor coming on needs to be considered, as does the overhead on the inverter. Pretty sure with a fridge there may be times it is drawing 100W, and times it draws nothing. We also have to be aware this will be being used in Summer, in a building that is uninsulated (but has good airflow through and is reasonably cool indoors).

What I want to know is if a couple of 55W panels will give us a net gain during the day, and say if we had 5 out of 10 sunny days, how much 'reserve' would we have.

I have a contact to get the batteries and panels at a good wholesale price, and am happy with that. It would leave a couple of hundred in the budget for a charge controller and some cabling.

trig42

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#2031267 7-Jun-2018 09:54

Also - we do have the option of Micro-Hydro - the property has a stream with good height/fall and plenty of water. That is getting quite complicated though (and the Geek in me really wants to do this).

Delphinus

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#2031303 7-Jun-2018 10:42

The advantages of micro-hydro is constant power source, eg overcast days and cloudy days. http://www.powerspout.com/ might work well for you? Purchase here: http://shop.powerspout.com/

trig42

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#2031304 7-Jun-2018 10:46

Yep, the powerspout products are pretty awesome.

I actually have an old smart drive tucked away that has already got an inlet into the old bowl and a pelton wheel attached to the motor. I just need to re-wire the stator and find somewhere to install it (and get a couple of hundred metres of PVC piping to get the water to where I need it).

Agreed that micro hydro is way better. Could run a lot more off it too.

lxsw20

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#2031322 7-Jun-2018 11:06

As I understand it, motors have a large current draw on start up, so you may find a 1kw inverter is not enough to get the motor spinning. Hopefully someone who knows more about it will comment.

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timmmay

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#2031323 7-Jun-2018 11:08

PowerSpout could do with putting an example system up on their website, to give people an idea of total cost. Just listing the parts is useful for experts, not so much for beginners.

trig42

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#2031343 7-Jun-2018 11:24

lxsw20:

As I understand it, motors have a large current draw on start up, so you may find a 1kw inverter is not enough to get the motor spinning. Hopefully someone who knows more about it will comment.

From what I have read, startup can be up to 10x running current.

I have read a few forum posts elsewhere and all say running a fridge on a 1000W inverter is not an issue. a lot seem to be able to run on 5-600W.

EDIT: Just checked - the Inverter I'm getting is 1000W, surge 2000W. True Sinewave.

SATTV

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#2031351 7-Jun-2018 11:36

During the recent power cuts my boss kindly lent me a 800W inverter generator.

When connecting the generator to our F&P fridge ( 15 years old ) the generator just about had a hernia but once started it worked.

Our 18 Year old westinghouse fridge in the garage which does not have the smarts that the F&P does would not work on the generator, it had a hernia and I thought it was working but after 30 minutes there was no change.

There are 3 way fridges for about $2000 from RV and Marine shops, no idea what the quality is like.

Putting in batteries is nice but expensive, you will need at least 500w to top up the batteries but once you have electricity for the fridge, you will suddenly have someone plug in a light or a TV and there wont be enough charge.

I do like the Micro hydro and I do know someone getting 2kw out of a F&P smart drive motor but I dont know have much flow is needed to gain that power.

Also if you do go down the battery front, hide them, solar and batteries are hot property and I know of someone that lost a couple of batteries.

John

I know enough to be dangerous

trig42

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#2031358 7-Jun-2018 11:46

Thanks John,

No issues with a TV up there. I suppose it could be done, but it has never been a consideration.

Completely agree on hiding them. We've had all sorts of thing nicked from up there in the past. Gas bottles were pretty popular for a while.

We've got pretty good at hiding stuff/locking it up.

I think the hardest thing to do will be hiding the wiring etc. that will let the scumbags know there is something worth nicking in there.

Rikkitic

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#2031362 7-Jun-2018 11:51

Haven't done any of this so no expert, but I have always wanted to. The PowerSpout is fairly irresistible and would definitely have a lot of cool factor, but I would also add a backup generator. Why not? You don't have to use it all the time, unless you are really unlucky with the sun. We have a small petrol Yamaha inverter generator for power cuts on the farm. It could also be used to charge batteries, though it isn't really suited for that. It certainly isn't noisy. You hardly hear it running.

Plesse igmore amd axxept applogies in adbance fir anu typos

tripper1000

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#2031393 7-Jun-2018 12:47

I think if you do the maths carefully, you will find it is worth spending the money on a decent LPG fridge.

Your system will need to be a bit bigger than you propose.

1) Batteries: Traditional deep cycles are good for approx. 100 cycles when taken to completely flat and 400 cycles when taken to 50% flat all assuming you immediately recharge to 100% which is unlikely in a solar system - so you don't want to regularly go under 50% charge. It takes 8 to 12 hours of charging to charge them from 80% to 100%, meaning they will only be above 80% on the first day. You batteries need to be big enough to run the system for several days, because this is N.Z. and the sun doesn't shine all day, every day. What his means to your battery budget is that because you are/should be working in the 50% to 80% zone, you batteries should be 3 times larger than the maximum capacity you think you will consume over 2 or 3 days. That is quite a lot of battery.

2) Fridges consume a fair amount of power. Those advertised ratings can be best case scenario which isn't realistic. You should spend $25 on a watt meter, plug it into your fridge at home and measure the consumption in real world, N.Z. conditions. Consumer grade mains fridges tend to be inefficient because they have relatively poor insulation - most people look at the ticket price, not the total cost of ownership, so they are made cheaply and with savings made in the insulation department. There are fridges made with good insulation specificlly for off-grid use, but they cost over $2K which is no better/more expensive overall than an LPG fridge.

3) Inverter: a fridge generally uses 3 to 4 times its rated running current on startup, so your inverter needs to be able to cope with that. Make sure you get a pure sine inverter - people cheap out and buy modified-sine inverters but these produce a noisy waveform and an electric motor will run hotter on this, wasting power.

4) Solar Panel size. Your solar panels need to be big enough to run the fridge and completely (or 80%) charge the batteries in a day. 110 watts simply isn't going to do this. If your batteries are left flat or in a low charge state they deteriorate extremely quickly. Systems like have a habit of running the batteries down and consuming power as quick is the solar makes it, so you end up replacing the batteries all the time which isn't cheap.

5) Management and Communal use: Solar systems like this usually require management and are not fool-proof so can be troublesome in a communal situation. Many regulators will not recharge a battery that is less than 4 volts so after an "accident" you need to shut everything off and leave it off for a while to get the system up and going again - to most people this is counter intuitive because they want that fridge cold as fast as possible. A lot of people will plug in additional appliances with no knowledge or thought as to how much they consume - one of my mates wives takes her 2000 watt hair drier everywhere with her and as soon as you turn your back, plugs it in and 10 minutes later your batteries are completely flat and she's protesting that it wasn't her because she only used "10 minutes" of power. The non-technical types typically think that because solar is "free" there is unlimited power and can end up using even more power than at home where they are conscious of the $$ cost.

6) Project Creep: Don't think this system will only ever run a fridge. As soon a people hear these is solar power and 12/230v, they will start bringing other things to plug into it - it will be a futile as herding cats to try and stop them - they'll be pulling the fridge out from the wall to get at the socket. You yourself will probably think that it would great to hook up some lights after a while and the loads will soon exceed the original design.

7) On going Costs: People typically think that because sunshine is free, the system is cheap or free to run and there are no on going costs. Given the above battery info, you may need $1000 or more of batteries. If/when someone does something to leave the batteries flat for a month (eg leaves the place with the fridge running and door ajar, or leave it running before winter or a long spell of overcast weather), the batteries will be ruined and you will need to replace them. Given that batteries will last 100 to 400 cycles best case scenario you will be replacing them every 2 or 3 years anyway. it only takes one or two accidents or 5 years of text book use, and the LPG fridge will have been the cheaper option.

8) Sum-bags: Solar panels are like a light to moths for Sum-bags, and your solar panels won't be insignificant.

Don't get me wrong, I'm a big fan of solar and alternate energy, but I've seen a number of people waste money and go completely off the idea from not doing their solar/battery/money budgets and properly designing the system first.

Edit: Spelling and Grammar. Yes there will still be some errors in there.

trig42

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#2031437 7-Jun-2018 14:12

@tripper1000

Great post, thanks for all of that. It is interesting reading.

I see the biggest issues being - keeping the batteries well conditioned and the communal use issues you mentioned.

Luckily at the bach, it has been in the family for many years (longer than I have been alive) and all the users are aware of the issues surrounding power and the need to conserve (no-one has ever brought a hair dryer for example). The only devices which draw power that are taken there now that weren't 10 years ago are smartphones/tablets. As it is also in a cellular black hole (if the weather is right, you can get a 3G signal, but it is pretty unreliable), most people aren't sitting on their phones all day anyway.

We need to do some more thinking around this obviously.

My 'back of the envelope' calculations have suggested the batteries could get us a maximum of 30 days running. This is not practical because a) there will be inefficiencies and b) it would kill the batteries. More work is needed, and contingencies need working through. You may be right that LPG will work out better (or, maybe, dual/triple powered if we are forking out for an LPG unit anyway).

djtOtago

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#2031462 7-Jun-2018 15:17

The fridge uses 328kWh / year
Thats ~ 890Wh / day
To run this off a 12v battery for 1 day 890Wh / 12v = 74.16 Ah.
So a 12v battery rated at 74Ah will run you fridge for a day. And that will completely flatten the battery.

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