I'm thinking about my house heating and calculated the cost of different technologies and the cost associated with the for my OffGrid house.

I live in a cold climate (Saskatchewan Canada) so I need a lot of heating.
At this moment I use a temporary heating solution that uses a small tankless propane water heater and small 20lb propane tanks (those used normally on barbecue).
This heating with propane is extremely expensive. Even if I get larger propane tanks it will still be extremely expensive.
My plan is to heat the house with electricity from solar PV directly no battery.
I was thinking about geothermal but that offers no savings it will be more expensive that just use the electricity directly not to mention simpler.
My house is probably a bit different that average since it requires just about 1000kWh/month in the worst winter moth for heating is small 65sqm (~700sqft) and well insulated.
It also has a good thermal storage in the large thermally isolated concrete floor 14cubic meters with a capacity of 100kWh at 10C temperature delta.
So currently I use about 4 to 4.5MWh / heating season with peak month around January with 1MWh that month but this is based on propane with an estimated efficiency of the propane heater at around 80% so real energy for the house is 20% less than this.
I use Solar PV for my electricity needs is a small system 3x 240W = 720W solar PV panels and LiFePO4 battery with monthly use between 60kWh and 90kWh.
So for heating I need about 12x more around 7 to 9kWh of solar PV that is now around 80cent/Watt so about $7k for PV some additional for ground mount supports cable and the in floor resistive heat elements I can round all around $10k and this should be able to last 25 to 30 years. I will need to design and build a Digital MPPT but this is a different story not that complex or expensive.
If I only use this electricity for heating that gets me to $10k / 25 years = 400$/ year for heating. (I have other uses for this electricity but I do not get this included)
Now say I can use a geothermal heatpump with an average COP of 3 I will need less PV panels say just 3kW instead of 9kW that is a saving of around around $5k.
Not sure I can for $5k have a heatpump and ground loops + this needs to last or 25 years or replacement parts included in this cost.
Also I will need to get a battery even if is a small battery to work with a Heat pump.
Do you think that is possible for $5k ? getting a 3kW heatpump with 9kW peak output + a ground loop to serve this in a cold climate. I think the ground loop alone will be more than that. But you may have more experience so what do you think?   

 
   
 

Well, I'll start the responses with...
I'm a homeowner and novice when it comes to geo and efficiency (although I have a 4 ton geo and love it), so you may want to disregard anything I write!
But..

I think most pros would agree that geo is not perfect in EVERY situation. There are definitely some unusual house & location situations that Geo does not make sense. Obsolete? No, but maybe in your case, not ideal.

If I understand it correctly, you want to convert the sun's energy into electricity then use that electricity to run resistive heating elements in the floor to make the slab warm enough to keep the house warm at night when the sun isn't shining?
Everything I've read about solar suggests you would better off using the sun's energy directly for heating, rather than converting to electric, then using the electric to run a heater. Sort of like having a solar panel on the roof generating electricity that goes into the house to operate a light bulb directly. It would be better to just put in a window, especially as you aren't storing the electric for overnight use for heating.
Can you get more direct sunlight shining right on the slab itself for warming?
Can you use evacuated tube heaters?

Just a homeowner here... Gotta say the choice of thread title is an attention grabber! Considering you are off grid, it seems logical that geothermal is not optimal for you. But to consider it obsolete for those of us "on grid"? I believe it is an excellent option for central heating and cooling when compared to other types. While I admire your abilities, the investment in time and technical details is just not possible for me. Kind of reminds me of the "Mountain Men" episode where Eustace ran his truck with a gasifier instead of gasoline because he didn't want to pay for fuel. He got it to work, but spent a good amount of his waking hours to get and stay there.

I don't think you make a good case to support your title.

A few obvious points are:
Your first costs are optimistic unless you intend to do the work yourself
If you intend to do the work yourself, geo is much cheaper as well (if you were to do the work yourself then depending on floor plans, you may be able to get a geo system put together on the cheap)
3 COP is not an honest average
You already invested in a partial solar system
Most homes are larger than yours
Some folks wish to cool their homes as well

We could look at an area where electricity is 6 cents/kwh and while first building (before money has already been spent on one technology or another) ask whether solar or geo make more sense and we would arrive at a very different conclusion. Or we might ask ourselves if foam insulation makes sense vs an extra ton of geo since electricity is so cheap.

That said someone did call me and ask for a geo estimate (on a similarly sized home with electric heat) and I suggested they should pay for insulation improvements instead.

The average person is looking at using a geo HP powered from the grid - so no upsizing of the compressor and loop needed such that it can produce a days worth of heat while the sun shines. In other words, don't generalize from your special solar case to the general case.

Maybe someday we will have more affordable choices for air to water heat pumps. Or if you are into the DIY thing, then take a low temp air to air HP and modify it.

Posted By electrodacus on 14 Mar 2015 05:53 PM
... OffGrid house ... Saskatchewan Canada ... 1000kWh/month ... good
thermal storage ... concrete floor ... 100kWh at 10C temperature delta

Stating the thermal storage capacity as 100kWh per 10°C tends to make
it look much rosier than a more realistic/livable 10 kWh per 1°C delta-T.
That's only about 7 hours storage capacity for a 1000kWh/month load.

What's the winter sunlight profile in Saskatchewan -- and how much
temperature droop do you plan to accept before firing up the propane?

...good luck,

Looby

I see most replays have about the same points so I will try to answer all in a single replay.

The house size is not that important same with the amount of thermal insulation.
What I'm interested is cost / kWh of heating. Yes electricity rates are different all over the word with huge variations.
Someone mentioned direct heating of the thermal mass using large windows. That will be way more expensive than PV heating and resistive heat elements at least in my climate. To have any net gain with windows in my climate I need triple pane windows and the amortization cost for those is way larger than PV.
I have good solar recurses in winter here so that is an important point that is why I consider PV for heating. PV will cost about about 3 cent /kWh if I can use all the available energy but even if I use that PV array for heating only and include support cables resistive heaters all those 10k I mentioned and a bit of work not that much then 4500kWh needed for heating season x 25 years = 112.5MWh I get to about 8.8cent/kWh not that different from some locations with inexpensive grid electricity.
So let me ask the question in a different way at what rate /kWh can the geothermal make an positive return on investment?
I think the heat pump will need a few replacements over 25 years of PV life but not familiar with the new heat pumps and how much will they last. If you can know the cost and much it lasts you can calculate the amortization cost /kWh then you need to add the ground loop probably even more expensive.

Stating 100kWh thermal storage capacity per 10°C makes the number
look much rosier than a more realistic/livable 10 kWh per 1°C delta-T.
That's only about 7 hours storage capacity for a 1000kWh/month load.

Maybe is a bit rosier but I considered 27C to 17C for concrete floor as acceptable since concrete floor is not the same with air temperature.
I need very lite energy to heat the air as long as the concrete floor is at least at 16 to 17C.
Currently with my propane heater I have up to 75C hot coolant that goes in a heat exchanger and I can bring a 200 liter buffer water tank to max 45C and the concrete can get to no more than 20 to 21C and the lowest temp I had was 16C so even with just 4 to 5C delta at the moment I can skip one or two days of heating with no problems.
With PV and resistive heaters I can get the concrete much warmer. I think staying under 27C is a safe value.

3 COP is not an honest average

Is that to low or to high what will a honest average be ?
I used a air to air heat pump in the past when I was living in a warmer climate and that was able to get best case at COP2.5 but wen was below freezing outside the COP was getting really close to 1.
Not sure horizontal ground loop is possible here the ground is frozen quite deep and a vertical one will probably cost a fortune and not possible to do that myself.

I need very lite energy to heat the air as long as the concrete floor is at least at 16 to 17C.

So, how lite is "very lite?" Your stated 1000 kWh/month winter load works out
to about 33 kWh/day, averaged over 24 hrs (including daylight hours with higher
outdoor temps and some solar gain). What's the expected night time droop rate
in air temperature (°C per hour) when you're 100% coasting on thermal inertia?

With 7-9 kW of PV capacity, it sounds like you need the equivalent of 4 hrs/day
of maximum output from the PVs -- with no protracted heavy cloud cover -- to
just break even...

...and what about snow?

Looby

Posted By Looby on 15 Mar 2015 02:50 PM

So how light is "very light?" Your stated 1000 kWh/month winter load works out
to about 33 kWh/day, averaged over 24 hrs (including daylight hours with higher
outdoor temps and some solar gain). What's the expected night time droop rate
in air temperature (°C per hour) when you're 100% coasting on thermal inertia?

With 7-9 kW of PV capacity, it sounds like you need the equivalent of 4 hrs/day
of maximum output from the PVs -- with no protracted heavy cloud cover -- to
just break even...

...and what about snow?

Looby

Over 24h I can lose about 2C maybe even 3C if is extremely cold.
Usually when is cloudy is not that cold the coldest is when is sunny.
Air temperature in the morning is usually within 1 or 2C from floor temperature.
Worst months for solar are November and December here and with a 9kW array I can produce in average 867kWh in November and 943kWh in December from January things get much better 1222kWh
November is not that cold usually so no problem probably 600kWh needed for heating and for December I think I will be OK since the 1000kWh worst month is for propane that is just 80% efficient.
I already have two years in this house and I have a small 720W array so I know-how much energy I can get from solar PV.
Snow is not a problem in December and January since the panels are tilted for winter at about 70 degrees and is so cold that the snow will not stick to the panels + is usually windy and that helps keep the panels clean.
In extremely cloudy days the PV still produce about 8% or more of a sunny day. The lowest production I seen from those 720W was 0.3kWh/day so from 9kW array I expect about 3.5kWh worst case and this can be used to heat the air in those days (the air from the heat recovery ventilation).
Is true this is an extreme house since I designed it with the passive house standards in mind.
It is about R35 fro walls and R70 for roof also extremely well sealed.
But to have a better idea of how it is build especially the foundation take a look at my youtube video
https://www.youtube.com/watch?v=Y3g4gmRvgko 

"The house size is not that important same with the amount of thermal insulation."
How can this be? The larger the home the greater the heating requirement. Geo excels in heating so the more you need the better the geo option.

"So let me ask the question in a different way at what rate /kWh can the geothermal make an positive return on investment?"
No. Somebody here schooled me on the fact that geo is not an investment it is an expense. Can geo be a smaller expense than other methods of heating?
Yes.
Can geo save you enough over other heating methods in its lifetime to pay for itself?
Yes.
Is this true in every application?
No.

"I think the heat pump will need a few replacements over 25 years of PV life but not familiar with the new heat pumps and how much will they last."
And solar never needs repair?

"Is that to low or to high what will a honest average be ? "

3.5 on the low end 5 on the high.

You must remember again your question:
Is Geothermal Heating obsolete ?

Then I ask what the following has to do with the price of tea in China-
"I used a air to air heat pump in the past when I was living in a warmer climate and that was able to get best case at COP2.5 but wen was below freezing outside the COP was getting really close to 1."
How does your experience with an air source heat pump support your premise?

"Not sure horizontal ground loop is possible here the ground is frozen quite deep and a vertical one will probably cost a fortune and not possible to do that myself."
Difficult to dig? So. I presume you are not going to install solar in adverse weather conditions.....

and again you didn't ask if geo was a good fit for you or your house did you?

Do you suppose everyone is comfortable with a 4 or 5 C delta in the winter?

"Is true this is an extreme house since I designed it with the passive house standards in mind."

Clearly and congratulations on an efficient home.
Clearly geo is not a good fit for you.
I have no quarrel with you at all, I'm simply trying to answer your question.

"How can this be? The larger the home the greater the heating requirement. Geo excels in heating so the more you need the better the geo option."

The important part is the amortization cost for the unit of energy.
 
"No. Somebody here schooled me on the fact that geo is not an investment it is an expense. Can geo be a smaller expense than other methods of heating?"

How long will that geo unit last ? 10 years 20 years by that time it will have output a fix amount of energy that is for the heat pump part.
For the ground loop that may last much longer you still need to have an amortization period even if is 50 or 60 years.
All pumps also have a number of hour's if those are separate from the heat-pump you need to add those also.
You can not ignore the initial investment since you can invest those money in something else.
PV also last quite a long time at least 25 to 30 years but you still use an amortization cost for them. Same thing for a house.

Look at my concrete case I have a limited capital to invest in heating say $10K
I can invest all that in 9kW of PV panels and have heating done that way for the next 25 to 30 years. After that I will need to reinvest in PV panels at whatever the cost will be by that time.
But I can also chose to install a geo heat pump and ground loop that has an average COP of 3 and only get 3kW PV panels the saving on panels about $5K will need to be sufficient else it will not make much sense in my opinion.
But say the ground loop last "forever" 100 years I will still not pay $20K just for that it will be more expensive than extra PV for 100 years.

    
"Can geo save you enough over other heating methods in its lifetime to pay for itself?"
"Yes."

Give me a concrete example of this.
Cost of installation then average COP the amount of energy used each heating season cost on input energy / kWh and then the amount of years you need to amortize the cost based on savings.

"And solar never needs repair?"
 
How so ? what will you repair on solar. It only needs replacement after 30 years or so or you can add more panels since they only degrade to about 80% of they initial capacity so you just ad a few more PV panels.

"How does your experience with an air source heat pump support your premise?"

Using an air heat pump showed me that COP is highly variable that will happen with a ground loop also so average COP may be smaller than ideal numbers.

 
"Difficult to dig? So. I presume you are not going to install solar in adverse weather conditions....."

I need at most a few days to install solar PV. Digging in my soil manually is almost impossible and renting machinery will increase the cost substantially.
But with so much gravel and large rocks here I assume horizontal ground loop is not even an option.
And vertical will probably cost a fortune the drilling part can not be cheap. But is maybe just an impression and in not so expensive.
I build my own house so I can work and I prefer to do everything my self but drilling hole is just not possible without machinery.
So if you have experience with the cost of ground loop let me know what will that be.

"Do you suppose everyone is comfortable with a 4 or 5 C delta in the winter?"

You probably have more delta than that. All you do is have heating that works all the time. What happens if that fails?
In this climate an average house without heating for 12h will have all pipes frozen and a lot of damage.
My house can survive for more than one week without any heating and the temperature inside will still be above freezing.
 
Anyway question is then for you what is the amortization time for your geo if you have one ?
a) To answer this you need to know the average amount of heat used during a typical heating season (for me is 4 to 4.5MWh)
b) Then you need to know your electric rate (for me with solar PV no battery is about 8.8 cent/kWh if I only use the PV panels for heating)
c) Then you will also need to know the average COP your heat pump is working (I think my COP of 3 was generous)
d) Initial investment cost and estimation on how often parts need to be replaced and maintenance cost.

Did you say what the depth to water is? What is the groundwater temperature?

"Did you say what the depth to water is? What is the groundwater temperature?"

Water dept is at around 100m (300ft) here not sure what the water temperature is. Drilling to that depth is not an option for me even for water.
Is about 15 to $20k for a watter well. Not going to have one since at the amount of water I use it will never recover the investment.
Rain water collection is way less expensive and the water is better lower TDS.
Even if my house needed 10x more energy for heating drilling that deep and for $20k will probably not have been a solution.

But I'm curios of your cost investments in geo and if it makes financial sense? How may years to recover the investment?
I think the most expensive part is the ground loop. Curios to hear some numbers from those that did this.
 

Posted By electrodacus on 16 Mar 2015 02:10 PM
"Did you say what the depth to water is? What is the groundwater temperature?"

Water dept is at around 100m (300ft) here not sure what the water temperature is. Drilling to that depth is not an option for me even for water.
Is about 15 to $20k for a watter well. Not going to have one since at the amount of water I use it will never recover the investment.
Rain water collection is way less expensive and the water is better lower TDS.
Even if my house needed 10x more energy for heating drilling that deep and for $20k will probably not have been a solution.

But I'm curios of your cost investments in geo and if it makes financial sense? How may years to recover the investment?
I think the most expensive part is the ground loop. Curios to hear some numbers from those that did this.
 

$40/ft us is the rate I see here for a water well...

Ground temps are, imo, important for a GSHP to work...The water out of a neighbors tap could be measured, which would give you the climatalogical temperature average there. Also, I just am curious what you get there...we are at about 4c.
Anyway, I can see that this reply could be longer and still not provide a lot of info.
I will keep it short and say that you are screwed (pardon the vernacular) for geo as you are OFF THE GRID. Why screwed? At the time of solar deficit, right at winter solstice, December 21 or December 22, and bracketed on either side of those dates by several weeks, your location is going to have the greatest average heating degree days, yet you want solar as the energy source.
As we say around here: "Not gunna doit."

As written earlier, 'geo' is possible as a DIY and you have the potential to save a lot of money, but ymmv.

"I will keep it short and say that you are screwed (pardon the vernacular) for geo as you are OFF THE GRID. Why screwed? At the time of solar deficit, right at winter solstice, December 21 or December 22, and bracketed on either side of those dates by several weeks, your location is going to have the greatest average heating degree days, yet you want solar as the energy source."

I have good solar recurses here. November and December are the worst but with 9kW PV enough to directly heat my house in those months.
If I will have been in a different location with less amount of sun in those cold months then I will have needed more PV to cover those months.


"As written earlier, 'geo' is possible as a DIY and you have the potential to save a lot of money, but ymmv."

As I mentioned before I want a real example. I'm sure many of you have geo installations so what is the amortization cost?


For my direct solar PV heating setup calculation is quite simple as I mentioned before.

My house uses about 1000kWh in the worst month and around 4.5MWh for the entire heating season (there are about 5 months of heating here)
Yes is not typical house is abut 10x less than what a typical house needs but that is irrelevant. (My house is about 3x smaller than average 65sqm (700sqft) and about 3x better thermal insulation so 3x3 about 9x)
If I had a house that required 10x more energy I will have needed 10x more PV panels 90kW but the cost per unit of energy will have been the same about 8.8 cent/kWh of heat.

This 8.8 cent /kWh is the same or better than what you get from the grid probably.
The question is: Will I have any saving if I reduce the size of the PV array and use a geothermal installation?

I do not see how for my particular location with soil hard to dig or drill. But maybe with 20cent/kWh or higher rate and better soil condition geo is a good investment (I do not know). That is what I want to find out here (but I need concrete numbers).

I think geothermal is not a good investment but I'm here for you to prove that I'm wrong.
The only way you can do that is with real numbers.

1. The way I would handle it is use a machine to dig...have you ever physically pushed your car up a driveway? Compare that to using the engine and drive up the driveway...


2. YMMV: my case is different that yours...do we value our time or not? The equipment is Not expensive.


3. The relevant term is ( I think) locked rotor amps. To turn the motors, one would need some amperage, and in the land of ice and snow in December, using PV, with batteries, and maybe even a properly sized (oversized to start the pumps) generator, I think the issue is moot. You need to run the pumps. Did I miss your point? What I focus on is you say "reduce the size of the PV" when it sems you would need a bigger PV array to run a GSHP, not a reduced size.


4. As also said on this forum (Engineer?) you might need to continue to light something on fire...Maybe run your own numbers with a COP of .8 or whatever you make heat with your propane tanks (Huh? What Are you making heat with??) vs. a COP of 3 or 4


5. Real numbers, me no me non; no amortization schedule here, just unsubstantiated empiricism where my DIY GSHP is working at a COP of over 3, maybe 4+


6. Oh, and not being too snarky here, the only location that would have less sun at the winter solstice is farther north of you and logically, if you are far enough north at that date, there is no sun above the horizon at all...more PV doesn't help...

The problem is you asked if geo is obselete on a geo forum and asked me to support my numbers. When I have time I might. However, you are making an assertion, so I suggest you support your premise not the other way around. Start with the can put it in for 80 cents a watt.
Please also support your assertion that solar has little maintenance i.e. inveters et al.

The reason I ask if geothermal is obsolete has to do with the drop in price of PV panels.
Geothermal is usually used for heating. Solar PV panels can be used for heating directly no inverters or batteries just a resistive element.
My plan is to heat my small 65sqm (700sqft) house directly with solar PV and a simple device that I call Digital MPPT (that will cost almost nothing just a few power FET's and a micro controller mostly) the heat from PV panels will be stored in to the large concrete floor that will act as a thermal battery.
My budget for this is about $10k sufficient for all this parts and I can demonstrate in details that this is sufficient to heat my house.

Question is will a geothermal installation (DIY as much as possible) make sense in this situation where I can save about 5000$ by installing only 3kW array instead of the 9kW needed for direct electric heating.
A different more general question is what is the amortization cost of a typical geothermal installation. Anyone that installed a geothermal installation should know the answer to this question.
I recently made a video about obsolete technologies related to low cost solar PV panels. I was concentrating mostly on MPPT one of the most asked question (MPPT is obsolete) and included other things like solar trackers and solar thermal (vacuum tubes) all this obsolete.
Geothermal is in a bit different category but as is the case at my location with plenty of sun in the winter months it seems that geothermal can not compete with PV direct heating. And yes there is no maintenance for this type of heating PV panels may need occasional cleaning or snow removal but not mandatory the Digital MPPT is solid state not fans or electrolytic caps to fail and resistive heating elements embedded in concrete also do not need any maintenance and can last indefinitely.
For amortization cost calculation I used all parts PV + ground mount, Digital MPPT and resistive heat elements not included the installation that will be done by me (not that much work).
All this cost around $10k and amortization time used is 25 years as PV panels will be at 80% of original capacity by that time (adding 20% more PV panels should make this last for another 25 years).
If energy from this is only used for heating cost / heating season is 400$ and more relevant cost / unit of energy is 8.8cent/kWh since annual heating load for the house is 4.5MWh
          
   

large concrete floor that will act as a thermal battery.

Unless you have insulation between this floor and the house, it is also an "uncontrollable heater/radiator" that limits how much heat you can store there without large fluctuations in interior temp. So tell us more about this aspect. I suggest that water is much better at storing heat on a per cubic foot basis and is easily controlled. But it is a more complex system and air ducts and insulation could address the control issue with concrete.

I recommend not using the term "obsolete" every time something doesn't work for your situation.

Posted By electrodacus on 18 Mar 2015 01:10 AM
Geothermal is usually used for heating.

1) I believe geothermal is USUALLY used for heating AND cooling.
If that doesn't apply in Saskatchewan, Waterfurnace will somehow
find a way to muddle through.

2) How much did that 14 cubic meters of concrete cost ... and
would it have been needed with an on-grid heating alternative?
It's always easy to cherry-pick the numbers to justify [whatever].

3) Although lifetime cost-of-ownership is certainly a consideration,
for many homeowners (me) it's secondary to other things -- such as
time, comfort, and convenience. If you enjoy DIY cost-minimization,
and can tolerate the compromises (e.g., temperature droop) have a
blast! I'd rather write a check to the HVAC pros and spend my time
doing stuff that I care about (and/or get paid for).

...is DIY homebuilding obsolete?

Looby