To improve efficiency. The technology is varied. New agricultural technology, including bioengineered plants, is improving that efficiency, getting more food from less sun. Of course, the population on earth is also increasing, and the poor people of earth are getting richer as well. This means that despite the rapidly increasing efficiences of agricultural and industrial machines and devices, there will still need to be substantial new energy sources developed.
More people means more mouths to feed and more desires to satisfy.
Fortunately it also means more hands and more minds to take up the twin challenges of improving efficiency and of developing new energy sources. Solar energy, stored as fossil fuels or renewed daily as wind, sun and water power, is not the only source of energy in the universe, or on earth. One important source that is just in its infancy on earth is the same source that earth's sun and all of the other stars in our universe use. The energy inherited from the Big Bang. On earth it is called nuclear energy.