Power
With naught but your fingers, a hardhat, and the tools gripped in your calloused hands, you are single-handedly building the future. With every solar panel you install, you will reduce carbon dioxide use (in opposition to coal power) by up to thirty times (source). That's right, you're directly reducing humankind's carbon footprint.
And lest we remind you, ridding the world of its carbon footprint means crushing global warming (source)—and that makes you the savior of penguins, polar bears, and ultimately all of humankind.
Unfortunately, no matter how much you try and convince your Nana of this obvious fact, she will probably never realize the truth.