Longtime lurker going offgrid

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Re: Longtime lurker going offgrid

Postby offgridQLD » Mon May 23, 2016 6:48 pm

For water heating we have a vacuum tube water heater which only cost $1,500 about six years ago from Run On Sun. This unit has no form of booster and gives us enough hot water even in winter although there are a few days now and again where the water is not hot enough for a shower. It might be worth looking at something like this with an electric booster and big storage tank and a few extra solar panels and a smart load sharing system that would share the solar power between charging the battery and the heating the water in the tank.


I just had a look on there webpage looks like your looking at double that price now for a 270lt system is $4265... Even after the rebate it's over $3000. I'm still up in the air about what to do with our currently instantaneous gas hot water on LPG bottles.

If I have to spend $3000+ for a SHWS then probably more as I think to get the credited STC rebates (about $1200) for that size system in QLD you need it installed by some one? So they aren't going to do it for free. So well over $3500 I would say for a good size system.

It makes a very well insulated tank with a electric element a attractive option. Lets say $1000 for a good SS Electric hot water storage tank and then 2000w more PV to feed the thing. The down side is more headroom lost on your AC inverter. A 3000w element chugging away for several hrs a day cuts the headroom of a 6000w inverter in 1/2. I have seen a few 48v dc elements (only 1000w or so ) with built in adjustable thermostat (from about 50C to 80c or something like that) big dial on the front. Perhaps two of them in a dual element tank with direct PV connection ...then switching DC via the built in thermostat just hope it was a good one.

I have to do something about it soon and make a commitment.
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Re: Longtime lurker going offgrid

Postby Gordon-Loomberah » Mon May 23, 2016 7:04 pm

There is also the option of a bolt-on heat pump, which will cut the energy use by ~50-75% vs a resistive element.
Last I looked, I think they were a $couple of grand.
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Re: Longtime lurker going offgrid

Postby offgridQLD » Mon May 23, 2016 7:44 pm

Yes that is a option Gordon it would cut the load down on the AC inverter a lot over restive elements.

Though there is a little noise pollution with heat pumps. Depending on how close you need to get it to your living areas.

There is something attractive about passive systems that just do there thing with little attention or effect on the batterys/inverter or charging potential of the PV. All advantages of the vac tube hot water system and perhaps worth the extra initial investment.

I'm not to keen on the vented to atmosphere low pressure systems that bubble away and spill water over peoples roofs after running across copper and corrode the tin. I'm also not keen on any system that has the water that could be consumed in contact with sacrificial elements (YUCK!) aluminum cordial cocktail anyone :mrgreen: ?

I think A SS tank with a heat coil through the middle so the flowed to be heated water doesn't touch the heat bank water would be best. Also a system that designed to be mains pressure or presser pump connected so not open to air.

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Re: Longtime lurker going offgrid

Postby australsolarier » Tue May 24, 2016 3:38 pm

Kurt,
i have an open vented hot water system. it is open vented because it is hooked up to the wood burning cooking stove. it also has two flat panels. i have no bubbling und no water running down and corrding anything. this has been up there for 23 years.
the sacrificial anode to my knowledge is made out of magnesium and not aluminium. you cannot taste it. besides i do not drink hot water from the tap. it is used for showering, laundry, dish washing etc.
my hot water system is a solahart and needs changing the sacrificial anode every five years or so. it is a pain in the neck as i have to drain the water out and open the big hole at the side. the black plasticy sides have been pushed outside over time. but otherwise it is still going strong.
in your case you can probably hook up your hot water electric element with a device measuring your usage. say you use less than 1kw or so for the household it turns on the element. i suppose you could go for a 2400w element.

the solahart with the tank on the roof has the advantage you have always hot water (when the sun shines) and no fiddling around. no circulation pump, no power needed at all. so combined with your electric backup should be an ideal situation.
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Re: Longtime lurker going offgrid

Postby offgridCBR » Fri May 26, 2017 4:40 pm

Hi guys,

Huge change in circumstances mean we will now be connected to the grid. Yay for dropping $30k and getting nothing in return... :x

Finding the whole situation quite frustrating after all the offgrid design work. Looking to throw 10kW of solar grid tied and maybe adding storage way down the track.

We are looking at installing either 2x ultra efficient 2.5kW (c) 3.2(h) R/Cs or one 7.1kW (c) 8(h) air conditioners. I completed the fairair calculator recommending 5.3kW for the open living area of the house.

What are your thoughts re: multiple ultra efficient (if you can call them ultra) vs a single large reverse cycle aircon? It looks like the 7.1kW units draw double the power to supply ~30% more cooling?
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Re: Longtime lurker going offgrid

Postby Gordon-Loomberah » Fri May 26, 2017 6:46 pm

I'd go for multiple smaller units, that will save significant energy use due to the higher EER/COPs.
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Re: Longtime lurker going offgrid

Postby offgridQLD » Fri May 26, 2017 7:03 pm

Yes I agree with Gordon and it's what we have done in our home. The split system units are not physically proportionally scaled in there dimensions as you go up to the higher output models.

Or to put another way a 10kw split system is not even close to being 4x larger in the condenser and evaporator surface area than the 2.5kw system. Perhaps double the dimensions at best. that surface area is all that matters (or at least the biggest contributor) for efficiency.

Why they do It? It all boils down to esthetics, packaging, handling when installing. It would just look silly and be impractical to install a 8 or 10kw split system that's 3m wide 500mm deep on your living room wall domestically.

Commercial refrigeration units are scaled similar to the small efficient 2.5kw domestic systems and have massive surface area condensers and evaporators but are installed into commercial sized buildings that can accommodate them.

That said it's becoming more common to small commercial buildings retail shops with a wall of 4 or 5 small split systems.
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Re: Longtime lurker going offgrid

Postby offgridCBR » Sun May 28, 2017 4:36 pm

Sounds good, it adds about $2k in installation costs but draws half the power from their stats.
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Re: Longtime lurker going offgrid

Postby offgridQLD » Sun May 28, 2017 5:18 pm

Yes if you need to pay someone to install it then that's something to consider.More so on the grid. Though I find off grid most appliances that are very efficient and usually more expensive give back there extra cost by placing less demand on your system.
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Re: Longtime lurker going offgrid

Postby Helipos » Wed May 31, 2017 7:49 pm

offgridCBR wrote:Hi guys,
Huge change in circumstances mean we will now be connected to the grid. Yay for dropping $30k and getting nothing in return... :x


If you don't mind us asking, what happened?
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