Vertical Geothermal Wells for Energy Storage and Removal

Discussion in 'Geothermal Loops' started by JoergK., May 5, 2019.

  1. JoergK.

    JoergK. New Member

    Hello All,

    I am new to this forum and like to introduce myself.

    My name is Joerg and my location is southern Alberta, Canada. I follow the geothermal issue, heat pumps etc. for probably +40 years. Our economy is energy, gas, oil, coal and heating cost where relatively low but that has changed. Not necessarily the cost for the actual energy, but all the ransom money one has to pay to be on the grid. What I mean is paying 1/3 for actual energy purchased and 2/3 for hook-up and line fees. This changes during the year, the more one uses, the lower the fees and vise versa. Plain-out, I don't like paying for something that I don't use, so I want to go of the NA grid.

    My facts:
    1. I have 70 acres irrigated where I live, a new house, full developed basement (~5000 sqft and workshop 60'x80', 18' eve). All heated with in-floor heating, second floor of our house has radiators and A/C.
    2. Two NA boilers, the house has 250,000 btu, the shop 125,000 btu. The house system has no problem keeping warm at -40° C/F, the shop run steady at that time last winter.
    3. I installed two grid-tied PV (solar power producing) arrays, one fixed south facing at 39° and one single axis tracking also facing south. Total production about 28,000 kWh/year. Both systems produce more then I use with purpose. Even so we don't get paid for overproduction, the higher production could be used to power a heat pump.
    4. Our climate is semi-arid cold winters with hot summers with lots of sunshine (~1400 kWh/KW/ year). Freezing down to 6-7'.
    5. NA cost per year is CAD3800-4000. Any system build should be paid within 10-15 years, meaning I got about $38-60,000 depending on the amortization I pick. Also, we assume the cost for energy is going to increase, so in general terms, the amortization should be quicker by general thinking.
    6. I received one quote when we build our house for geothermal combined with PV, but only for a portion of the energy usage, we would still need to have boilers and that quote was for $120,000 in 2010.
    7. One quote for the drilling of five wells, 100m (330') deep was received on April 28th for CAD117,000 plus room & board and meals for the crew. This excludes all loops, grout, connections, pump & switch gear/controls. So, by the time this would be installed I am looking at $160-200,000, $140,000 over budget.
    8. The five well scenario would include four wells with closed ground loops and one well in the center to determine the soil and water structure and to insert a senor wire with temperature sensors every 10m (32.8') to monitor the core temp. during operation.
    9. My plan is a geothermal well system of four wells to eliminate the purchase of NA (Natural Gas) for the future. This system would have solar collectors roof or ground installed and the energy generated and not immediately used would be moved in to the four wells to be stored, to be removed when needed and upgraded with electrical energy from our solar system through a heat pump.
    Now comes the calculation of the energy needed. If I convert peak demand of 375,000 btu to kWh, I arrive at 110 kWh or 31 tons. Does this make sense? This is what the max. output of my system in one hour has to be able to deliver, correct? This could happen only once in 10 years for 1 or 2 days, but nevertheless, it needs to be calculated to this term unless one is willing to suck it up and freeze, correct?

    If I take the potential 1400kWh from sunshine and use a 50% efficiency, I arrive at (theoretically) 700kWh that 1 m/2 (1.2 yd/2) could produce per year, 30 m/2 (36 yd/2) would produce 21,000kWh or 6,000 tons.

    I don't have my annual NA consumption available at the moment, but will submit this later.

    It would be great if I could get a general feedback for my basic thoughts. I noticed many threads start here after the project has started, I want to avoid this and get as much info, help and corrections before I start.

    I am waiting for more quotes from others, outside the oilfield to drill the holes, or, I could buy my own drill truck, drill the holes and then sell the unit, but I am not a driller, but a farmer. So lets see how this comes along.

    Joerg K.
     
  2. wing

    wing New Member

    A lot here, let me make a few comments. Your overriding concern seems to be converting to a geo system that makes sense from a financial benefit standpoint.

    Start with a rigorous manual J calculation for the projected heating load. Basing a geothermal design on the existing size of your oil burners is a bad idea and result in an oversized system. Further economic benefits could be gained if in fact the geo system is slightly undersized with backup during the coldest days supplied by either electric, one of your existing boilers or by accepting a lower house / shop temperature and wearing a sweater.

    Much of the expense of your system is associated with the five vertical boreholes. The concept of a monitor borehole with distributed temperature sensors sounds really cool, not sure what impact this has on your cost or what you can do with the information other than have interesting data points for the sake of science. Surely this is something that can be eliminated.

    With 70 acres of farm ground, is there a reason you don’t substitute a lower cost horizontal loop field for the vertical boreholes. You are in irrigation country, lots of excavators locally available for ditch clean outs and maintenance. I estimate you could install a horizontal loop field for a fraction of the cost of what you were quoted for the boreholes.
     
  3. JoergK.

    JoergK. New Member

    @wing, thank you for your thoughts. The horizontal loops would be an option if I would only look after taking energy from the ground. It would mean digging 9-10' down and installing the loops, I am clear on this. But, I want to store energy from solar collectors (possibly evacuated tubes) in to the boreholes, this does not make sense for the horizontal loops. In addition, we receive about 10" of moisture in a year and our soil, even with irrigation is dry, so conductivity is a questionable issue.

    Now to my sensor hole. I have to drill a first hole to evaluated my subsoil structure. This will be done in advance by a geological drilling company that does this all the time and it is not the most expensive part, but needed to know what we have and how we need to adjust to it. Lets say we have moving water at 80' or lower, I will adjust my hole depth to stay above. So, inserting the sensor cable just costs me the cable and one could build that himself if one wants to.

    Have a look at this: https://dlsc.ca/how.htm it is a working system, but without heat pump(s).

    Joerg K.
     
  4. wing

    wing New Member

    Irrigation has a big impact on water table level. If you dig a 6 foot hole - does the bottom fill with water ?
     
  5. JoergK.

    JoergK. New Member

    Dear wing,

    We would not know much of irrigation if the bottom of a 6' hole would fill with water. It is not 'some is good, lots is better'. Also, you have missed my point made earlier about the energy storage, so lets not address horizontal loops anymore..
     
  6. ChrisJ

    ChrisJ Active Member Forum Leader

    Are you planning to be off the electric grid as well as the natural gas grid?

    As you know Drakes Landing has 144 wells and 800 solar thermal collectors. I think it works because of sheer size.

    I look forward to following your project.
     
  7. JoergK.

    JoergK. New Member

    Hi ChrisJ,

    No, I will not go of the electrical grid since I need a minimum of 100 amp/480 VAC for my pumping when irrigating and some other uses included in that 100 amp. This would be expensive to store in batteries, but that is a different subject.

    Drake Landing has also long distribution lines, both ways, no heat pump upgrade and 52 homes = 2.8 holes per house and 2,300 m/2 ( 24,800 sqft) of flat-plate glazed collectors, not evacuated tubes. This equates to 44.23 m/2 (477 sqft) per house and correlates to my calculations.

    One issue with any energy extraction I have read here and in other forums is the problem with a system planned to small and the ground not being able to deliver sufficient energy to the loop. This is like 'freezing the ground around the loops' in my opinion, but correct me if I am wrong.

    I am a long way away from building this and it may never happen, but I keep digging for the right solution. 40 years ago this may have been the new frontier, but today it has (and is) being practiced. Problem is the info transfer to avoid mistakes others have made.

    JoergK.
     
  8. wing

    wing New Member

    I don’t get it. You have an inexhaustible supply of cheap geo energy with a 70 acre farm property. The loops can be sized to whatever you want them to be, limited only by your closed loop pump capacity.

    Instead you want to use an expensive storage design that is 1. Unproven and 2. Targeted for high density residential projects, not a single family home on 70 acres.

    Good luck with your project.
     
  9. JoergK.

    JoergK. New Member

    Hello wing, I am missing flexibility from your view, too, anyway, one is allowed to discuss, or not?

    Cheers, JoergK.
     
  10. geoxne

    geoxne Active Member Forum Leader

    I believe the point being missed here is the design requirements of a geothermal verticle bore field and bore hole energy storage are contradictory. They should not be considered the same.

    A geothermal vertical bore field requires conductivity and diffusivity, while bore hole energy storage underground requires the opposite. Evidenced by the careful design at Drake Landing with 7 foot bore separation, sand back fill, clay cap with polyethylene and foam insulation and the use of temperature gradient to insulate the core of the field from the surrounding earth.

    A good borehole energy storage system will not make a good geothermal verticle bore field.
     
  11. JoergK.

    JoergK. New Member

    Hello geoxne,

    Now this is something constructive, even so I would want to debate your two points of conductivity and diffusivity (had to look this up: a measure of the capability of a substance or energy to be diffused or to allow something to pass by diffusion) being contradictory. Energy (heat) has to move in both cases, not to fast, but regardless, they have to move in both cases. This is the reason why I want to drill a test hole first to create a formation log, forming the bases for any further development.

    It is sad that non of the contacts in the Drake Landing site reply. This could have many reasons, like: the whole thing does not work, the involved people have no interest to share their knowledge, ignorance, who knows. I will make a Saturday trip to the site in the near future since it is only 2 hours away and talk to residence about it.

    Your point about the careful insulation (shielding) is correct, but that can (cost effective) only be done to the top, bottom and the surroundings can not be isolated or insulated, I hope we agree on this. I will address the borehole and loop configuration much later or in a different thread since I have some basic misunderstandings or lack to see loop layouts correctly.

    The test hole results will be the bases of the final plan of attack. No wells (domestic water or other usable info) have been drilled close by, so no real formation info is available, one more reason for the test hole.

    The main point is this, made in my introduction: NA (natural gas) cost per year is CAD3800-4000. Any system build should be paid within 10-15 years, meaning I got about $38-60,000 depending on the amortization I pick. Also, we assume the cost for energy is going to increase, so in general terms, the amortization should be quicker by general thinking. No sense spending $100,000 to prove a point, I am not the government, but have to think about profitability or reduce my cost over the next 30 years and beyond.

    One report i found goes down to 75', all brownische clay to dark green shaly clay, no report of water.

    My point: if static or moving water exists anywhere it would be usable for energy extraction. If no water exists (in extractable amounts) it would be great for storage, correct?

    This is only planning, nothing else for some time!

    JoergK.
     

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