I've never met anybody who went with solar for their main power supply who was happy with it and would do it again if they could get power to their place. For $25,000 it's a no brainer having the power company supply it over solar. When you hit the $100,000 mark, that's when you might consider solar, and even then, I know two people who went with solar instead of paying for the power lines to be run and they both regretted it.
SIPS are very expensive and highly rated, but the only real advantage you get is in saving a little time in building. Heat goes up and down, so the main place that affects heating and cooling is the ceiling. You can go with SIPS on your roof, but it's a lot cheaper to get the same results just blowing in two feet or insulation to get an R60 rating then paying for foam. If you want big vaulted ceilings, then foam becomes relevant.
For walls, you have to remember that wind is where you lose most of your energy. It is much more important to have a solid barrier to keep out the wind then going crazy maximizing your R value on your walls. With 2x6 walls, you get R19 with fiberglass at a quarter the cost of SIPS. While the SIPS will have a much higher R value, it's overkill because you lose so much with your windows. Most double pane windows are only R2 to R4. Tripple pain will raise this a fair amount and I even know of one guy who bought four pane windows for a extreme amount of money. But back to reality, the windows and doors limit what you can get out of a wall more then anything else. The only thing worse then a window in a room is a skylight. Those are total energy wasters and probably the dumbest thing you can do for energy savings in a house. But back to the walls, sealing them up is what really matters. Taping the windows, using a high quality house wrap with good tape is where you get your money's worth. Be sure to tape the top and the bottom. I personally like to fold my house wrap over the tops of my walls and then have my rafters or trusses go over the top of the wrap to make the seal 100 percent tight.
Something of interest that I recently discovered is that when I added a huge doggy door, I have not noticed any change in my electric bill. I figured it would cost me more because of how poor the seal is, but we where losing just as much energy opening and closing the door for them all day long, so it's proven to be the same either way.
Another thing to avoid is french doors. Massive waste of energy since it is impossible to get them to seal. I've installed and replaced dozens of them. While brand new, you can barely get them to close, after a few years, leaves are blowing into the house through the gaps in them. When I add on to my house and built my great room, I am going to built my own 4 ft wide door so I can get everything in and out of the room that wouldn't fit through a standard 3 ft door because there is no way I would ever install french doors in my house.
Porches are a huge energy saver. Keeping the sun off the windows will save you money, and also extend the life of the seals around them. Most people just assume that the doors are what needs protecting from the elements, but covering the windows also has a huge benefit.
Be very careful of the latest craze green house energy building techniques. Most are very expensive building techniques or materials that will not show any return compared to proven methods. I never want to be the guinea pig when I build something to last.
