Electricity needs to get from the plants generating it to the individual consumers. This is done through a network of wires which run across all the locations where electricity gets delivered. However, this network of cables, or the grid, needs to be optimized to carry all the required electricity sustainably, without interruptions, to prevent blackouts and power shortages. Higher voltage lines would ensure that more power meeting the increased demands flows uninterrupted and less of it gets lost on the way.
Moreover, when you think about energy from the sun – it does not get generated 24 hours. And some locations have less or no sun on some days or parts of the day. They need to be connected to a grid, to which electricity gets from another location, where there is more sun which supplies more power. With new energy sources, we need new networks to deliver it.