#Build Solar Panels ... in SPACE
Build Solar Panels ... in SPACE
Well, when you think about it, no matter what resources we use here on Earth, $\Large\textit{there is this giant}$ $\Large\textit{supersized storage place and}$ $\Large\textit{power station}$ (a large cloud of hydrogen which seems to have caught fire we call the Sun) a few minutes away at the center of our system.
Think about it. The average whole-humanity consumption is about 16TW (in 2010), while the Sun shines about 174,000 TW on Earth alone, and about 3,846,000,000,000,000 TW more into empty space each second. That's an unimaginable amount of power, and virtually every Joule of it is wasted every second.
So the best thing you could do for future generations is to start creating a large and ever expanding cloud of solar panels around the sun, and use that surplus to power a space industry to build more and more and more solar capture technology!
The technology for creating solar panels is already with us. Technologies for mining the asteroid belt (for raw materials, to save us the pain of space launches) are being developed currently by private companies in the Western world. There is nothing technically stopping us from deploying a massive solar array in space, aside from the initial launch costs and the political will to do so.
Space based solar power has numerous advantages over regular solar. It does not take up any valuable ecosystem from the natural wild areas. It does not suffer from intermittent supply due to night or weather. It does not get dusty, for the most part. The power can be transmitted wirelessly (and has been for decades) so with some modifications it could be transmitted from space as well
Once the 'Dyson' cloud of solar panels is built, store antimatter
There are now considerable technological difficulties with antimatter production & storage, but if the technologies for production and storage can be miniaturized and made significantly more efficient (right now we're producing antimatter by smashing atom beams together -- bit like trying to produce gasoline by shooting cannon into a methane chamber) it could be the most volume- and conversion-ratio-wise efficient form of energy storage we know of in terms of space-ship reaction mass. Furthermore, the construction process for the solar encasement will realistically take a few million years, so that gives ample time for science to advance and better magnetic confinement devices to be devised.
Once the Dyson sphere is built, you can store your excess power as antimatter in containment fields, collossal flywheels, whatever. But our descendants will have zillions of times more power than we did before them. In fact, it's irresponsible not to do it. It's the only way we could have enough power to move out of the Solar system if we decide we don't like it here anymore, or the sun (billions of years from now) goes dark.
Storing this energy in space will save you from having to carry this TO space with you. The saying goes that once you're out of the Earth's gravity well, you're energetically speaking halfway to anyplace in the solar system.
Moreover, the exercise of building this massive space project will give mankind the much needed practice with building space-habitats and robust space vehicle, something that again you can only learn by being in space, not by saving every little watt on Earth.