A study from the Journal of Power Sources indicated that by 2030 the grid could be powered almost entirely using a mix of wind (both on- and off-shore), solar and grid-scale energy storage, and that this grid would be both affordable and reliable. It would require building solar and wind capacity up to three times the grid’s actual load across a large geographical area. The concept challenges the notion that renewables need back-up power from fossil fuels for base load power generation.(i)