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You couldn't use solar power and help the environment because you live in the rainy Northwest. Because of all the water on your slope, you can't build an elevated garden that will last. It's either move or find a way to respect the environment while battling the elements. Some terraced garden designs don't actually need a terraced garden.
DoItYourself.com recommends using groundcovers other than grass--you don't like to use your power mower and you can't, anyway, because your slope is too steep. DoItYourself.com suggests some attractive groundcovers that help the environment and improve the appearance of your lawn:
This technique of how to build a terraced garden is called stripcropping. These strp gardens are better than strip malls, will contribute to the health of the ecosystem, and will make you happy that you chose to live in a rainy climate.