Update:  We built the cabin, did not do GSHP.  Now building house, considering PV powered GSHP for 2000sq/ft ICF building. Pls add any thoughts/resources/info that have become available since 2008 original post.  Thx!!!   CB.


Hello,

I'm building a small, tight, off-the-grid log cabin - 750sq/ft, 1 story and would like to keep the building above freezing year round.
It's located in Colorado, at 10,500', and we see everywhere from 75degF in the summer to -35degF in the winter.
We have two fireplaces for primary heat during visits.
The property is totally off the grid.

Is it possible to find a small GSHP unit that can be powered by a bank of PV panels and a decent sized battery bank?
We have great sun, southern exposure and only every now and then do we go a few days without sun in the winter.

One installer indicated that the starting current for the compressors would be difficult(impossible) to provide using PV, although the operating current may not be too much of a problem for PV. 

I just hate to consider relying on propane, or another commodity fuel where we can't control availability, price or access to the property during the winter.
Any input would be appreciated!

Corey..

Eek!

39 Views, no responses.....

I'm thinking I may be chasing my tail on this one...

Sorry about not responding, but I don't no the power outputs you can expect from solar. I do know that heat pumps run on 220volts. Have you tried asking this question on the solar power board?

Maybe it is possible to have a geothermal system with variable speed pump/blower so that the system runs continuously (which I would think is better anyway than on/off), then you only need to start it up once or after a system failure or shutdown. If your components are 12VDC, you could possibly use your car or a portable generator for startup of the system. But I have no idea how feasible this is.

The idea of using solar to run heat pumps has been discussed in these forums not too long ago. It was part of another thread, you might have to search some to find it.

Let us know what you find out, we would all like to know.

  You can't do this with logs. They don't insulate well enough. ie R1 per inch. I know it's probably too late but if I were doing it I would use SIP's for the floor, walls and roof. Poor a lightcrete floor lined with pex. Collect sun with non evacuated tube CPC collectors (almost vertical) and appropriate antifreeze with a solar pv powered pump and storage tank with battery backup for the pump. All of that, building included, would still be cheaper than what it would take to pv a gshp with the excavation or drilling required.

That's probably right. Sounds like a good idea.

Like you guys correctly point out, you can't plan anything until you know what you need, you need a heat load number. Solar hot water is very limited in it's ability in Maine during the winter.

Even if it's possible to run a geothermal system off of solar, the first big snow storm that sweeps thru is going to cover the solar panels for days, robbing you of your power source. Without someone around to brush snow off the panels I would guess it would take some time before the snow melts off them, unless they were on a very steep angle, which would cost you on sun efficency all year round. 

My second thought is all this equipments is going to take up some room. I'm assuming this place has a basement. With A geothermal system, Pump, invertor and batteries this suff is going to take up some room in the basement. Also I beleive the batteries are going to require some ventulation to ensure toxic fumes from them do not build up inside the house. And if it doesnt have a basement, your going to lose one of the rooms to this stuff.
 
My third concern would be outright theft. The cost of installing enough solar panels to generate enough power to run an entire house is somewhere around 40k. With the high cost of solar panels, an unoccopied house in the middle of nowhere is going to make a tempting target to thieves. Far-fetched? Thieves are stealing aluminum siding and copper piping from foreclosed houses in many populated parts of the country. Imagine what they could do to a house with no one around for a few weeks?
 

Wow, folks!  Thanks for all of the responses on this.

My studies have pretty much confirmed most of what is in this thread.
The solar system would simply be too large and expensive to be economically an asthetically feasable to run compressors/pumps.
The primary issue is starting load on the motors, and most seem to want 208/240 volt servcie.

I am doing a load calc on the house, and plan to use solar for lighting, well pump, etc...

We have no real hope of electricity over the next 15 yrs, as density is too low.

Our lift station for engineered septic will require a small generator to run it's pump periodically - so that puts the camel's nose under the tent...however...   I'm not planning to run anything else on gen power.

The most likely scenerio is that we'll end up with the dreaded small propane boiler to keep the cabin above freezing, but hoping that the gazing on the south side will keep the thermostat on the good side most of the time.  Firewood will stil be the primary heat source during occupancy (EPA rated enclosed wood burner).

I'm not too worried about theft - although it is a possibility.  (#1 reason we don't live in the city)
Our townsite entrance shack reads   "Welcome to Irwin.  Residence are armed, unstable and friendly."

As far as the log construction - we will build and seal the lots and joinery as tight as possible, and have some good plans for insulation between logs.  Even knowing logs, I'm hoping we can seal this building up pretty well.  I'm investing in tripple pane windows, and an excellent roof system, and ICF to help.  All utilities will be located in a portion of the ICF basement - there is ample room for the eqpt.

Also - I've discussed the idea of storing solar heat in large, insulated water tanks beneath the building.  While it's a possibiliby, it's a bit experimental and if it fails, could be quite a disaster to clean up/remove.  But, it's not out of the question.  Then just use a flash heater to raise the temp to domestic levels.

Thanks again for all of the input!

Corey..

TTT.

Ok, we built the cabin.  Did not do GSHP for it.  Now looking into building a house and considering GSHP. 2000sq/ft ICF building.   Would like to run this off solar as well. 

Up for any new ideas!

Thx in Advance,

Corey..

Maybe a new thread would be appropriate for a new place, (unless you are trying for the solar/GSHP thing again). You might include the location when you start out.

I think the offering of truly variable compressors may start to make the" heat pump powered by solar" a possibility.

WaterFurnace only makes a 3 ton unit in their variable speed but they are a soft starting compressor.
If you were to purchase a smaller 1-2 ton WaterFurnace unit you can add the intellistart feature that also allows for a very small LRA. I show 17 LRA on a 2 ton unit, there is no data on a 1 or 1.5 ton unit or maybe the feature is not available.

Most importantly, size the heat pump so that it can heat up a water tank during the day and not need to run off batteries at night. Batteries are expensive, inefficient and don't last very long.