So I tried an experiment today.

I built a cheap solar collector by snaking 400' of 3/8 black funny pipe on my roof.

I split the flow into four subfields.

I tied it into my slinky field and hooked up the solar loop to my WEL.

I turned on my loop pumps and the water coming out of the solar loop was 3° warmer than the water going in.

I was kind of excited about this thinking I am going to warm my slinky loop.

This setup ran for about 3 hours before running out of daylight.

There was no appreciable gain in the slinky loop temps.

I am hoping to run it for about 8 hours tomorrow.

As near as I can tell the solar loop is giving me 10,000 - 15,000 BTUh.

It might never raise the slinky temp since it takes 25 to 30 minutes for the water to make a complete pass through the slinky loop.

'couple thoughts
Works great for pools.
That would be enough BTU's for many basements.
J

What if you switched it so that it raised the water temp from the loops 3 degrees. You'd have warmer water entering the HP and wouldn't that still result in warmer leaving temp back to your loops?

If the sun shone at night this might work :) My heat pump doesn't run on bright sunny days as the solar gain is enough to keep my house warm.

I did run this for two more days of about 6 hours each. Each day the loop warmed almost 1°. My conclusion is that this would work if you had a big enough solar unit to pump more BTU's into the ground.

What I don't know is if you would ever increase the efficiency of your heat pump enough to pay for the solar collectors needed to warm the ground.

My guess is you might get some warm fuzzy feelings from doing this, but not much in the way of savings.

You are probably right - the incremental geo savings won't ever cover the cost of the panels unless electricity goes way up and panels come way down.

Both are possible, though, given Obama's plans.

I would introduce these solar heated loops downstream of the ground loops on sunny days to raise EWT not ground temp. That would directly raise COP but not on cloudy days or night time. I guess the way to make this work would be to heat water in a storage tank that entering water has to pass through on it's way to the heat pump to lift EWT's (something like a boiler mate).

Bingo bango joe
this is not a new idea seach solar assisted geo in feild COP of 8-10 are claimed
a large indirect hot water heater will give you a good amount of night cushin , high end units like apricus will still give a good amount of heat on
cloudy days, a bunch of heat exchangers so you solar is in your domestic when you EW is absorbing its heat is key so you can bypass in summer with out wasteing the solar when it does the most, you could also automate the feild loop to act as a heat sink in the summer if your solar tank got to hot

I guess it makes more sense to store heat in an insulated tank than underground - you'd likely get more of it back.

Seems they were trying to use heat storage at University of Alabama Mall many years ago. The theory was to use groundwater as the heat transfer fluid and then reverse the flow in the winter to use the warmer water when they needed heat. I never saw a follow up on it. My guess is that it was tried because the mall only heats a few days a year and the cost of reversing the flow likely exceeded potential returns (thats my theory and I am sticking to it).

and then the "how much heat could you really store" question. Might be a better DIY project (given cost v return).
J