Some good advice from stevehull, but there is one thing I would question. He says:
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With panels, even on a cloudy day, you will boost this cold water inlet temp to about 70-80 F.
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Maybe the cloud cover here is different from Steve's, but I don't find that. I have 100 evacuated tubes and for three months at the end of the year, when there is typically heavy cloud cover here, they produce basically nothing. I don't know what the cloud cover is like in Seattle but don't count on a solar contribution year-round.
Another comment I would make is you might consider linking your solar and geothermal efforts. I have a GSHP and when that was installed the installer talked me out of linking it to my solar panels. I now think that was a mistake. The relatively cool water coming from the ground loop would be a good way of harvesting heat from the solar panels on days when they are too cool to contribute to heating or hot water. This may not be a huge gain but since you are installing both I suggest you allow for this in your design.