1 - Efficiency, insulation, reduce use.
2 - solar hot water heaters
3 - solar air heaters
4 - solar electricity
This house will is 750 sq ft, and we will certainly use energy star appliances, a front loader washing machine. It has double-paned windows. We will install low-flow faucets, and a shower head. And we'll check out LED vs CFLs when the time comes.
Any other suggestions on efficiency? We will need to replace the roof in a couple years, so we will probably wait until that is necessary to actually buy any solar panels, so they don't have to be moved once they are placed.
This house is currently a rental we will be moving into in a few years. Does anyone know if it would make better financial sense to do this when it is still a rental? Of course, that might make us replace the roof before it is necessary... Hmm, I wonder if the tax benefit on replacing a roof is worth doing it 4 or so years before necessary...
If you have a gas water heater then you'd need to do more research on the payback. It might be a lot longer than the typical 3-8 years for going from electric to solar water heater.
Efficiency:
1. A newer, smaller, energy-efficient fridge. After the water heater, the fridge is the #2 energy hog. You may want to consider getting rid of the garage fridge and the chest freezer unless you're a volume buyer... people frequently buy those to "save money on bulk purchases" but rarely follow through. If you can find a Craigslist fridge that's just a couple years old then it's a bonus.
2. Look for a convection microwave oven (Craigslist again). It cooks food more efficiently than a convection oven because it's heating a much smaller volume. The new models have a longer payback because you're paying for caché and décor as well as the engineering. The used ones have a great payback because hardly anyone appreciates them.
3. Power strips or switched receptacles for all your vampire appliances & electronics.
4. Consider insulating your roof with two inches (or more) of polyisocyanurate foam panels, or spraying icynene foam in the attic. We did the former on our south roof (with 2"x2" furring strips supporting sheathing over the 2"-thick 4'x8' panels) and it's wonderful. Put reflective foil insulation on top of the ISO panels. (We used plywood sheathing with integrated reflective foil insulation.) It's totally changed our indoor climate. We rarely open the windows in summer and now it's actually a bit chilly around here on winter mornings. While you're replacing the roof, spend a little extra for reflective Solarex shingles.
5. Solar exhaust fans for attic spaces will drop the attic temperature 30-40 degrees. We also have one at the top of a stairwell to cool our cathedral ceilings via chimney effect. However I'm not sure if this is appropriate for attics in freezing climates.
If you buy a solar water heater, buy a real solar water heater (not a water heater used for gas/electric installations). The solar models have several different pre-plumbed penetrations for your design, and the thermocouple wiring may be installed inside the shell instead of running up the outside. It makes a huge difference having the hot return from the roof collector going into the tank on the side instead of on top-- the former has much less reverse circulation when the pump is off. The more expensive ("12-year warranty") tanks also have higher-quality components and thicker insulation. Your tank will be storing water at 150 degrees (or a little hotter) so it may even be worth your while to wrap a water-heater blanket around it, or have cross-flow ventilation in your garage to keep from heating it up in August. You may also want to keep your piping clean by installing a whole-house water conditioner (ion-exchange resin) to avoid mineral buildup inside the solar water system. You'll clean toilets & sinks much less often, too.
Good question on the rental. I'm not sure about the federal tax credits, but many state/utility credits & rebates are only for owner-occupied properties. From a tax perspective, deducting it on Schedule E just reduces your rental income at your marginal tax bracket (15%-25%). Taxing a tax credit, though, reduces your taxes at a 100% bracket...
If you already have double-paned windows then I'm not sure how much more you'll gain from UV tinting. We can really tell the difference between one pane and two, but so far the only detectable tinting benefit is minimizing UV damage to shades/drapes, carpets, & upholstery.