From Gizmodo.com: “Any renewable energy the government generates would be publicly owned, and a Sanders administration would prioritize selling it to publicly owned utilities and cooperatives at current rates to keep costs down. The campaign estimates that alone would raise $6.4 trillion of the $16.3 trillion needed to fund the transition.”
My own thought is hydrogen generators or hydrogen plants can be used to not require as much overbuild. When there is excess power water can be split into hydrogen then burned on demand. Burning hydrogen fuel only releases water and is green energy as long as the power used to split the water molecule was produced greenly.