Geothermal or Solar ??

There's more to renewable energy than just wind and solar power - hydro, wave, geothermal to name a few. Discuss these RE alternatives here!

Geothermal or Solar ??

Postby MJL » Thu Jun 26, 2014 11:06 am

Hi, I have read a bit on this topic but nothing is very recent. We are about to build a 42sq weatherboard house with colorbond roof and double glazed windows. We have no natural Gas but will have a wood combustion fire in the living area. We are trying to work out if Geothermal is worth the spend ? and who should do it in Vic ? Or should we just go a solar system ? or neither. We will most likely add a pool down the track which I would like to use for as long as possible year round.

Any help would be greatly appreciated. Thank you.
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Re: Geothermal or Solar ??

Postby Gordon-Loomberah » Thu Jun 26, 2014 11:28 am

Welcome to the Energy Matters Forums MJL :)

When you say geothermal, do you mean a ground source heat pump, which is often incorrectly referred to as geothermal these days? True geothermal relies on hot rocks very deep down, or shallower high temperature thermal zones in volcanically active areas, such as in NZ.

Ground source heat pumps are very efficient, but also very expensive to set up, as a lot of trenching needs to be done to lay pipework. I think CO2 powered heat pumps would be more economical to install, and they work well in colder climates. Solar hydronic heating is also a good way to heat your house, but if you have extended wet cloudy periods of weather, it will need supplementation with a heat pump, or other other less efficient method such as gas or resistive electric heating.
Wood fires are great if you have access to a cheap supply of wood, and if you have a wetback, you can use that as a source of hydronic heating as well.

The large black water circulating mats that you can put on your roof are quite effective for pool heating, but of course, they dont work so well in cold overcast weather. A heat pump can be used for pool heating, as well as house heating.
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Re: Geothermal or Solar ??

Postby MJL » Thu Jun 26, 2014 11:39 am

Thank you for the quick reply. To clarify, yes I am referring to ground sourced heat pumps not true Geo (sorry all very new knowledge to me). I should be in a position where I can do the majority of the excavation, so I thought that may make it more viable. We are definitely in a cloudy area. I have access to some wood, which will be fine for our indoor fire, but I don't want to have to get enough wood for a 'burner' on a full hydronic system ? (I don't know what a 'wetback' is ?). Are heatpumps expensive to Run ?
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Re: Geothermal or Solar ??

Postby Gordon-Loomberah » Thu Jun 26, 2014 1:22 pm

A wetback is a water manifold that can be used on some wood burning heaters and many stoves, it just heats and circulates water via a thermosyphon to a tank in the ceiling, but it can be done with a hot water pump to a tank in another location. Its a non-pressurised system, as in vented at the high point, as the heat soure is somewhat uncontrolled. That hot water can be circulated through radiators elsewhere in the house to better spread the heat around, and stored in an insulated tank. Wood is a great source of inexpensive energy if you have it on your own property and are growing more wood to replace it.
Heat pumps are very efficient, and operate much like a refrigerator in reverse, or a reverse cycle air conditioner set to heat. They produce a lot more heat than the energy required to run the compressor and fans etc, so have efficiencies measured in the hundreds of percent, compared with a resistive heater's efficiency of 100%.
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Re: Geothermal or Solar ??

Postby Smurf1976 » Fri Jun 27, 2014 9:57 pm

A heat pump is, in a practical sense, really just a means of using electricity far more efficiently as a heat source. Put one unit of electricity in, get 3 - 5 units of heat out of it. End result = one third to one fifth as much electricity is needed to do the heating when compared to using a conventional electric resistive (with elements) heater.

Costs vary around Australia, but in general terms the cheaper non-solar means of adding heat (to the house, the hot water or anything else eg a swimming pool) are heat pumps, wood and natural gas with off-peak electricity via a simple element coming next. Peak rate electricity used via an element, LPG and any sort of liquid fuel are in general by far the most expensive means.

Prices do vary between locations however but in general that's how it is. Notable exceptions are that wood is relatively expensive in the larger cities and that peak rate electricity for heating is relatively cheap in Tasmania.

I haven't mentioned wood pellets since the price of those varies hugely with location. In some areas they're quite cheap, comparable to gas, whereas in other locations they're expensive. Need to check the price locally if you're interested in that option.
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Re: Geothermal or Solar ??

Postby Benny » Sat Jun 28, 2014 11:46 am

I hope you've followed Rule 1 with the new house MJL - which is to design the house to need the minimal amount of energy in the first place. Sounds like you are considering tit with double glazing but also high R walls and ceiling ? Insulated slab ? N facing windows for solar passive design ?
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Re: Geothermal or Solar ??

Postby Quokka2 » Sat Jun 28, 2014 8:33 pm

Hi Benny and welcome. We looked at a dam or ground-coupled heat pump system a few years back but it didn't come close to stacking up against a few good inverter split systems, financially or practically. If you live in colder parts of Victoria you might consider coupling to your pool, to heat the pool water and extend your swimming season in Summer, and hopefully not freeze it in Winter. This isn't as silly as it sounds, because air coupled heat pumps CAN freeze up in winter (as can plastic pool heating coils on the roof).

Think carefully and PM me if you're considering DIY double glazing!

Wetbacks draw heat off a fire and ours is a bit harder to start, methinks; the heat that is going into your water is not going into the room. You can get a water heater that fits over the flue and recovers energy from that, which might otherwise be largely wasted; it also wouldn't effect the fire. Take Gordon's point about growing replacement timber; it ain't renewable energy if you're just assuming it will be renewed somewhere else, by someone else :lol:
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Re: Geothermal or Solar ??

Postby Tracker » Sun Jun 29, 2014 10:14 am

Quokka2 wrote:....... heat that is going into your water is not going into the room. You can get a water heater that fits over the flue and recovers energy from that, which might otherwise be largely wasted..... replacement timber; it ain't renewable energy if you're just assuming it will be renewed somewhere else, by someone else :lol:

I could never understand why flu heat was not the first heat to recover energy from... I have been tempted to look at a suburban wood fire, just to prove it is ultimately better..
Even to the point of using a heat pump to recover that heat, so that it can be more efficiently moved to other house parts..

The difference between using timber that someone else grows, is that it can be grown, but coal and natural gas etc.. can never be man made without a deal of extra energy being needed.. so I kinda think saying that using someone else's wood, is looking for excuses.. ;)
..
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Re: Geothermal or Solar ??

Postby Quokka2 » Sun Jun 29, 2014 10:48 am

Tracker wrote:I kinda think saying that using someone else's wood, is looking for excuses.. ;)


As far as the planet is concerned, mining a forest is no different to mining coal. Both processes can be reversed if you have a mind to, the coal just takes a little longer... :(
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Re: Geothermal or Solar ??

Postby Gordon-Loomberah » Sun Jun 29, 2014 11:10 am

Some discussion about wood fires and flue heaters, wetbacks etc can be found here: https://forums.energymatters.com.au/ren ... c1289.html
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