However to run something larger, such as a factory, hospital or office building "carefully conserved small amounts of electricity" just do not cut it. You need large amounts of totally reliable electricity. And sometimes your demand will suddenly jump meaning that an excess supply has to be there.
Lived off grid for ten years, still off grid capable and it does work fine on the small personal scale. But even with very good regular maintenance the batteries need to be replaced about every 5-6 years. Central heating and A/C was out of the question.