Bathroom/water

The goals here are to reduce water consumption and to lower the amount of energy needed to heat water, which can be up to 25 percent of a home's energy use.

Low effort: Put an aerator on your bathroom sink--for 50 cents, you'll make your money back quickly on lower water consumption. Then, get a low-flow shower head, which save between 20 percent and 60 percent water. Fix those leaks.

Medium: Consider getting an on-demand (also called tankless) hot water heating. In some cases, you can have an electric on-demand water heater placed directly in the bathroom and other places in the home that need hot water.

High: Get a solar hot water system, either flat panel (left on this photo) or evacuated tubes. While solar electric (photovoltaics) cost about $25,000, you can get a solar hot water system for $10,000 or less. These systems have been around for decades (remember Jimmy Carter) but are more reliable and efficient than the 1970s variety