You need to set up a burning bush, use it to whisper to them they need to start storing up food for seven years, the ones that listen to you. Tell them they are the chosen ones, they will be blessed, and all the others, that didn't listen to you, didn't believe you, didn't save, they'll be cursed, impoverished, enslaved, by falling victims to seven years of famine that will follow, the non-believers. Between them, the believers and the non-believers, they'll use technology including money to perpetuate the slavery, turning into an energy scourge on your backyard that will eventually run out of energy, in a couple of thousand years, then they'll all die, annihilating one another.
Wait, scrub that, too late...
Somebody already did!
Now you just need to hope they won't discover solar energy, they'll never issue money on it, distributing the energy to all, they'll just carry on enslaving and annihilating one another, never understanding they could relieve their self imposed scarcity more or less instantly, by just monetising solar energy.