I just started researching geothermal.  I want to power the wholes system via solar panels and get off the "grid".  Has anyone heard of this being done?  Is this feasible?

I heard on a home improvement show about a geo thermal system that uses gas, which can be compressed and thereby giving more than enough heat on the coldest days.  Anyone familir with this?  Where can I learn more?

Thanks

The first thread on this forum is a good place to start.

Basically a 4 ton geo system would pull about 5000w while running and require about 10,000 watts of inverter to start. Assuming you would only run it when the sun was out, you would need about 5000 *1.2 (solar panels typically put out 80% of their rated capacity) or 6000 watts of panels at $8/w installed or $48,000. Then add in two stacked XW5548 to start the unit $6000 and 3 charge controllers for another $2000 or a grand total of $56,000. And that will let your run your geo setup for 4-6 hours on a sunny day. If you want to run it 12 hours a day double the solar panel costs.

...and add another $10-20k for batteries?

Now if you get something like $1 / watt for panels like some of the various CIGS and CIGSe panels are shooting for, then you're in business.
Similar situation for the batteries with hydrogen capture methods found at MIT. So check back in 2 to 5 years and ask the same question.

Wow! thats very discouraging.  There has got to be a better way.  It would take 15 + years to reach the break even point.

I obviously have to do more research.

It seems to me that the system should not require that much electricity.
   1. pump the fluid or gas through system
   2. power the blower moter to to cool/heat the house

I'm running 2 tons variable speed at 1600 watts, 3.3 tons variable speed at 3200 watts, and both together at about 5000 watts, all GSHP.

Best regards,

Bill

You're throwing out what is probably the biggest cost - push or pull heat out of the system. That's the big thing. It's also the magic of a heat pump. Moving heat is a lot more effective than making it, but even when you talk about 300 to 500% efficiency, it's still a lot of watts to move.

Consider, I have a heat calc from the furnace system designer I saw on the foreclosure I'm buying (I got a lot of documents from the county before I purchased it). The calc calls for ~72000 BTU's / Hr during the coldest time of year (-10 temperatures) for heating 3125 sq. ft. of the house (other parts are on baseboard). That runs out to 21,000 watts or 21 Kilowatts moving prefixes. Now even if you had a super duper DX system that gets a 5.0 COP (and it actually performs at that level), you're still looking at using 4.25 KW to move nature's free lunch of heat into your house, out of the fluid.

Like I said, wait a few years. There are a lot of people pumping money into solar research, trying to get it to the magic rate of $1/watt for a panel. If that happens, and they can produce enough, almost everyone with room to will be installing panels.

There is a better way. Build much smaller with much better insulation. If you only need a half ton instead of 4 it follows that your upfront investment costs for electricity will be about 1/8th as much. A smaller house will also cost less to build.

DOH yes engineer, if you want to run when the sun isn't out, add another $15K for batteries.

Your best bet is to go with a grid tie solar setup, it has the fastest payback (still longer then solar hot water) since it uses no batteries and pumps power back out the grid. Then get time of use rates, they typically are the highest rates when you are making power with solar panels so you get the credit then. For example if your "normal" rate is $.10 / kwh, on peak or high demand time is typically $.20 / kwh, then if you make power at that time your credited for it at $.20 / kwh. Then at night when you use power your buying it back at $.05 / kwh. So you essentially cut your payback time in half. Then just get enough solar panels to cover your base load.

As far as solar panels being produced for a dollar a watt, they already are just barely over that, just add in shipping and the middle man and resale markups and you’re in the $4 per watt range. If you have the know how to install them yourself then you can save a bundle, but it is much like a geothermal setup, if your not really sure about what your doing, get someone who has done it before. Often installers will let you help to offset some of their costs, lowering your cost in the end.

Kunta,

I thought about doing the very same thing for our new house and ran into the same obstacles.  I have a great deal of hope for some of the solar technologies on the horizon, but today it just doesn't make - economic - sense.  Great idea.  Awesome intention.  No financial sense - even if you install the PV panels yourself.

As one of the posters indicated, a small, super insulated structure is easier to heat (requires less watts) and cool.  In my opinion, this is a great idea, but selling the philosophy to the majority of the home buyers/builders in the US is not going well.  Home values are still hugely dependant on usable square footage.  A small house at net zero does not have the same market value as a larger - energy sucking beast of a home.  Right or wrong, this is the (current) fact.

You never stated if you are building a new house or considering an existing home for a GSHP retrofit.  In either case, insulation is the first thing you should look at.  It has a, larger than you might expect, effect on both up-front and life-cycle costs.  First off, the insulation in our new house allowed us to cut our GSHP system by nearly 1/2 - say 4 tons vs. 8 tons.  This immediately cuts the cost of the GSHP installation by almost 1/2.  In your case, this would also ripple into the system requiring 1/2 the number of PV generated watts.  With 1/2 the heat and cooling load, operating costs are approximately 1/2 for the life of the equipment / house. 

We are going with closed cell spray foam in areas of our house that are not SIPs.  It is more expensive than alternatives, but I am pretty certain the payback will be worth the extra cost.  Not sure is doing your load calculations, but ask how much heating and cooling is required due to air changes per hour (ACH).  You might be surprised at how much additional BTUs are required.   If I may also suggest - do some research into homes with low ACH values.  I haven't found one that uses fiberglass or cellulose.  Build tight, ventilate right, and you can further reduce the size of your HVAC.

Check out the status of our project... perhaps the most energy efficient modular home ever built - www.GouinGreen.com.

Good luck,

Ed

Thanks for the feed back.  This is an older brick home.  2 story's and a basement.  A total of about 2400 sqr ft.  I think I can get 5,000 watt for about $6,000.  But the problem is finding a geothermal unit that runs on 110 vs 220.  does such a thing exist?

I'd like to know where you can get that kind of deal.

Not that I am aware of.