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Off-grid house
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Pepperman



Joined: 10 Oct 2010
Posts: 747

PostPosted: Fri Apr 07, 2017 8:42 am    Post subject: Reply with quote

Thanks! I think I follow it but will need to think about it some more. It sounds a little like a DC version of three phase AC.

Battery balancing was the first thought that popped in to my head as I was reading the first post but you've got some useful suggestions in the second. Very interesting.
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Pepperman



Joined: 10 Oct 2010
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PostPosted: Fri Apr 07, 2017 9:00 am    Post subject: Reply with quote

One additional thought for your system Chris would be to fit a simple to understand meter.

We use a Smartgauge which gives battery voltage of two banks and an SoC readout of the main bank. It's voltage sensing so doesn't need a shunt and it doesn't suffer from the problem of drift that you can get with Ah meters as batteries age.

It's not definitive (e.g. it doesn't handle batteries under charge quite right) but it's so simple to use that anyone can use it to get a reasonable idea of the SoC without having to think about resting voltage, tail currents or specific gravities. It can also trigger relays / alarms based on voltage or SoC set points which could be handy to help avoid accidental deep discharge.

But... I just checked and it looks like it can be used on 12V and 24V batteries only.

Anyway it's a useful piece of DODGY and is very popular amongst boaters. It's certainly helped to keep our T105s pretty fresh through >1,000 cycles over about 3.5 years and I hope to get the same again (or more) out of them over the next few years.

http://www.smartgauge.co.uk/
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adam2
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Joined: 02 Jul 2007
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PostPosted: Fri Apr 07, 2017 9:13 am    Post subject: Reply with quote

Yes, 3 wire DC could be considered as the DC equivalent of 3 phase AC.

Back in the old days, IEE regulations prohibited outlets on different phases of an AC system, or ON DIFFERENT OUTERS OF A DC SYSTEM from being in the same room, unless at least 6 feet, later 2 meters, apart.

The traditional colour code for 3 wire DC was red for the positive outer, black for the center wire and blue for the negative outer.

A 2 wire circuit derived from a 3 wire DC system was meant to use red for the live conductor, giving rise to the confusing situation of the blue wire from the street main being connected to the red wires in the consumers home. No worse however than a single phase AC supply derived from the yellow or blue phase of a 3 phase AC system.
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clv101
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PostPosted: Tue Apr 18, 2017 9:09 pm    Post subject: Reply with quote

For my battery store, I'm currently looking at eight 6V 468Ah VRLA. Eight of these give a 50% discharge of just over 10kWh.

Not sure where in(?) the house to locate them. They need to be close to the inverter (within a metre) to keep the cabling reasonable, don't want to be exposed to outside low temperatures but don't want to vent into the house... Maybe a well insulated lean-to on the outside, the the inverter etc on the inside wall? Or maybe they should be in a insulated cupboard in the house, with a vent to outside?
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adam2
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PostPosted: Tue Apr 18, 2017 10:44 pm    Post subject: Reply with quote

For VRLA, previously known as sealed batteries, I would consider indoor use to be acceptable.
Under normal conditions no hydrogen or other objectionable gases are emitted.
Some hydrogen is produced under fault or failure conditions but this is normally so diluted by room air as to be non hazardous.

Looking at the partially built house, might a suitable location be under the ground floor ? That should be away from extreme temperatures, and ventilated against wood rot already.
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Mr. Fox



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PostPosted: Wed Apr 19, 2017 11:38 pm    Post subject: Reply with quote

clv101 wrote:
.. currently looking at eight 6V 468Ah VRLA. Eight of these


Rolls S-605 isn't VRLA (valve regulated), is it?

Deffo vent!

http://www.off-grid-europe.com/downloads/dl/file/id/80/rolls_battery_ventilation.pdf

Rolls also used to do these funny caps as an extra which captured evaporating electrolyte and dripped it back into the cell... they weren't that cheap, but extended the period between maintenance top-up quite significantly... Smile

"Hydrocaps" : http://support.rollsbattery.com/support/solutions/articles/19469-hydrocaps
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adam2
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PostPosted: Thu Apr 20, 2017 9:10 am    Post subject: Reply with quote

If the chosen batteries are not VRLA but are the conventional vented sort, then in my view they are better either placed outside, or reliably vented to the outside,
In many cases a suitable indoor location is in an air tight box vented to the outside. A bench seat mat be built over the box.
The vent fan need not run continually, it may be controlled by a voltage sensor such that it only runs when the battery is nearly fully charged, as that is when dangerous gases are emitted.

Alternatively consider a small outdoor store.

To be strictly accurate, the hydrocaps referred to above do not capture evaporated water and return it to the battery. They capture the hydrogen and oxygen emitted during charging, and chemically combine these two gases back into liquid water which drips back into the battery.
This reaction is strongly exothermic and the hydrocaps become warm in use. They can melt or catch fire if the volumes of gas are grossly excessive due to bad overcharging.
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Pepperman



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PostPosted: Fri Apr 21, 2017 9:41 am    Post subject: Reply with quote

Yeah the S605 is a conventional flooded lead acid.

I would always suggest going for this over sealed. Being able to maintain your batteries is a good thing. It allows you to do periodic EQ charges and generally keep an eye on things better.

If your batteries are readily accessible then topping up the water takes a few minutes, especially if you get one of these which stops dispensing water when it gets to the right level.
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adam2
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PostPosted: Fri Apr 21, 2017 12:36 pm    Post subject: Reply with quote

Agree, flooded batteries are IMO superior to sealed/VRLA batteries. They are also often cheaper allowing a larger battery bank for the budget.

A large flooded battery bank is better in an outbuilding or reliably ventilated to the outside.
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Catweazle



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PostPosted: Sun Apr 23, 2017 12:08 pm    Post subject: Re: Off-grid house Reply with quote

clv101 wrote:
What would you do with ~5kW on tap for several hours a day in the summer?


Mine bitcoins ?
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clv101
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PostPosted: Sun Apr 23, 2017 8:10 pm    Post subject: Re: Off-grid house Reply with quote

Catweazle wrote:
clv101 wrote:
What would you do with ~5kW on tap for several hours a day in the summer?


Mine bitcoins ?


I did briefly look at it, but it's basically a non-starter these days. Even with free electricity, to be at all competitive you need expensive custom ASICs, which will be obsolete within months: https://bitcoinworldwide.com/mining/hardware/

I think we'll end up with water heating, oven, washing machine and power tools when the sun shines.
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adam2
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PostPosted: Sun Apr 23, 2017 8:46 pm    Post subject: Reply with quote

Cut firewood for winter with electric saw bench or electric chainsaw.
Shred garden waste with electric shredder to facilitate composting.
Mill grain into flour and keep for winter.
Dehydrate surplus fruits and vegetables in a slow electric oven.
Make jam and other preserves on electric cooker.
Cook pies and freeze them for the winter.
Make fruit wine and concentrate into brandy by freezing*

* the freezing of the water uses significant energy and may result in the freezer running continually for hours rather than for say 10 minutes in each hour. Legality is doubtful
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Pepperman



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PostPosted: Mon Apr 24, 2017 10:04 am    Post subject: Reply with quote

Oh good call on the fruit dehydration front (although you can build passive solar dehydrators as well). Most fruits will be ready in plenty of time but if you want to dehydrate apples you'll need to plant some early ripening cultivars.
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clv101
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PostPosted: Mon Apr 24, 2017 8:10 pm    Post subject: Reply with quote

I already have a 1.6kW system in a barn with 165Ah/48V battery store and 3kW inverter. This system is great for running a small fridge 24/7, power tools and charging cordless tools.

adam2 wrote:
Cut firewood for winter with electric saw bench or electric chainsaw.
Shred garden waste with electric shredder to facilitate composting.

We'll certainly have electric tools, including shredder.
adam2 wrote:
Mill grain into flour and keep for winter.

This is an interesting idea. Sacks of grain last indefinitely and presumably are cheaper to buy than flour. Wonder where one can buy 25kg sacks of organic grain? I guess flour recently milled is better than stuff that's been sitting around for months - especially wholemeal.
adam2 wrote:
Dehydrate surplus fruits and vegetables in a slow electric oven.

Yes, I got a home made electric dehydrator (doubles up as a honey warming cabinet). I could do with making another, 4 times for size though.
adam2 wrote:
Make jam and other preserves on electric cooker.

For sure, we'll have a induction hob.
adam2 wrote:
Cook pies and freeze them for the winter.

Certainly lots of produce and pre-cooked food can be frozen. There's a nagging risk of putting all ones eggs in one basket with a large freezer in case of technical failure (of either the freezer or the power system).

When thinking about how to use our 'spare' power a few things come to mine. We can't afford a large capital expense (like a big fancy machine that does something clever when the sun shines), nor do we necessary want to be physically involved in using the power (cutting wood etc) when the sun shines. Might want to be relaxing, enjoying the sunshine!

Other ideas we've had include an electric kiln, to be loaded with pre-fired pottery over several days, then fired when the weather is good. Freeze drying food. Charging electric bikes, and possibly visiting electric cars. Making ice on a large scale for an ice-house, or just ice-cream....
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Pepperman



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PostPosted: Tue Apr 25, 2017 10:25 am    Post subject: Reply with quote

An ice house would be brilliant. That definitely gets my vote.

I'm not sure to what extent this might be an issue but induction hobs tend to have a pretty low power factor which leads to additional reactive power draw that needs to come from somewhere. Exactly how this would impact an off grid set up I don't exactly know but hopefully Adam can advise. My suspicion is that it will mean the induction hob won't be quite as efficient as you expect.

It's worth noting that in the case of a grid connected induction hob with low power factor, reactive power is also induced but due to homes being charged in kWh rather than kVAh it means that we don't get charged for it, but the electricity generators still need to burn a bit more fuel to deal with it.
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