We have been doing our Geo research and are not comfortable making a decision b/t a DX closed loop system or an open water based system.. We were going to use PV panels to power teh gEo but now we almost want to wait 5 years before more projects are done and the kinks are worked out.

INSTEAD...we are considering loading up on PV Sanyo panels  (15KW),  using an electric boiler with radient and a high effeciency central air system to heat and cool the house instead.

This would take us "off the grid" BUT is the cost up front not worth it? Is the payback too long? Are electric boilers w/radient worth the investment? What is the best way to go here? We would like to get the soalr BEFORE the incentive rebates are taken away.

I would appreciate any help or advice that ya'll may have. Thanks,

Mike
845-239-1551

You will have to determine the payback based on where you are located (hours of sunlight per year, cost of electricity, cost of installation etc). If you are totally off grid you'll need to add the cost of batteries. Someone gave a ballpark of 1 kilowatt produced per year per 1 watt of panel rating for their location. If your location is similar you would get around 15,000 kwh per year on your 15 kw array. Around here at 4.6 cents per kwh that would be worth $690 dollars per year. If your local rate is 20 cents per kwh your 15 kw array might produce $3,000 in electricity per year. But don't use my numbers you need to check out local numbers.

Would 15,000 kwh per year run your electric boiler and A/C for the year? Keep in mind the electric output will be a lot less in the winter than summer due to the shorter days - and that's when you'll be running the boiler the most. I understand that it's pretty challenging to run an A/C on PV. Do you know what the electric requirements for your A/C will be?

If you’re going to go off grid I would recommend going geothermal. An electric boiler might be 100% efficient, but a geothermal system would be 300-500% efficient, reducing your PV needs 3 to 5 % and that’s a LOT of $ in panels. Honestly 15kw in panels might not be enough for an all electric home. 15kw should net you between 30kw and 75kw a day depending where you are and weather conditions, check you last utility bill and see if that would cover what you actually use.

Honestly you best bet would be to do a grid tied solar setup, then if it is cloudy for three days you can just use grid power and if its sunny for a week in the spring or fall and you have little loads you can just sell back to the grid. Think of the grid as a never ending battery that you can store power on for months at a time.

Mike,

I am building an off-grid house with solar power and geothermal. I installed the solar system myself 2 years ago and it has been working great. (Sharp panels, Outback inverters & mppt, Rolls Surette batteries) Only 5Kw of panels are on the roof, but I will be increasing to 7.5Kw within the next few months (there's enough room on the roof for 10Kw). I recently ordered two 2 ton geothermal units (ground source heat pumps if you will). They are two speed units manufactured by Water Furnace. I hope the installer will have them done within a month or so. I will write about that on my blog.  We are not yet living in the house, but we have a large fridge, a large upright deep freezer, and an 8,000 btu window unit (and this computer I'm typing on!) at the house site running on the solar system now.

Off the bat, I know it will not be feasible to run both heat pumps flat out during the night (their combined consumption is about 3.2Kw - my batteries would be nearly dead the next morning). In fact, it is probably only feasible to run one of the units (for the bedrooms) at half speed during the night (0.9Kw) if I've had a sunny day and anticipate a sunny tomorrow. I plan on rigging some sort of automated system to turn the heat pumps on only full blast when there is available solar power. Timed heating and cooling is not a big issue for us, since our house only gains or loses 2 degrees F within 24hrs, regardless of what the weather is doing outside. (R24 SIP walls, R50 ceilings, lots of thermal mass) With 7.5Kw of panels, and an automated system to turn on the heat pumps (4 ton peak capacity) when the sun is shining, I have calculated that I can produce the equivalent heat of $100 worth of propane in January (Jan is not a good month for sun in KY). This will not heat our house entirely - the balance of the heat will come from an outside wood furnace, circulating hot water through radiant tubes already installed in the floor. With the heat pumps, I hope to keep the house cool in the summer and not have to light a fire in the fall or spring (here in KY).

So to answer your question... by all means use a heat pump of some sort... whether it be ground source (geothermal) or air source. It will multiply the electricity from your solar panels by a factor of 2.5 to 4 (above and beyond a simple electric furnace), depending on which type of system you install. The $ payback of a ground source vs. a air source heat pump is not very compelling, even if connected to solar power and thus paying more for electricity. The equation looks better for ground source though if you start trying to run Air Conditioning from batteries. I think that your biggest issue, with 15Kw of panels on your roof, will be how to use all of that power when the sun is shining... or how to store it for later. When your batteries are full, the battery chargers will shut down and your 15Kw solar array will be a giant paper weight. This happens to me more often than not

(forgot to mention, the heat pumps will be closed loop, with the loops installed in vertical wells)
a link to my blog if you're interested

Hello. I have something you might be interested in. I am importing a radiant heating and cooling panel from switzerland. It is suspended from the ceiling and is white and you can cool with ground source water temperature of 50- 60 degrees very effectively. The panels cost will close to $15/ft2 of surface area and can handle very large cooling loads without any heat pump, but rather little 50 watt circulator pump. In Switzerland, they heat a glass office building in the ALPS in the winter with 80 deg F water and cool with the same panel in the Sunny and warm part of Switzerland in the Summer with 50 deg water. This is accomplished with 2 simple wells that are shallow, one for water rejection. It is very efficient and is ideal for your application. Ventilation is taken care of with simple ventilator with heat recovery. If you have soil termperatures of 50 deg-65 deg, I can help you and will guarantee that this will work without any heat pump. Eric Friedland Swiss Solar

The first thing to do is increase the amount of insulation so you use less heat.  We're buildihng a 3400 SF house in New England which will use two minisplilt air conditioning units - electric heat pumps - for heating and cooling.   Total cost of system about $12K.
Bob Irving

I don't see your plan as working. Geothermals reach high efficiencies because they heat and cool slowly, running continuously. Chances are, once one of your systems go off in the night, you'll never be able to reclaim the heat during the day.

Skepticism is good. As I said, I don't intend to heat the house in the middle of winter with only geothermal. But based on my experience of running a small A/C window unit in the house this summer (only during the day), I think the geothermal systems will do a pretty good job of cooling the house in the summer. Whatever heat they produce in the winter will just be that much less wood I'll have to burn.

http://massiehouse.blogspot.com

Ah, didn't know that. Then you'll probably want to make sure your contractor disables the auxiliary heating element in your system (if one will even be installed - standard practice in the cold north of MI). If your focus is on cooling, you might want to look into how it's installed. I believe I heard of certain open water column styles that basically achieve an EER of over 100.