Solar power

Solar power uses the sun as an energy source.

Types

Photovoltaics (PV) (solar panels) - generate electricity
Solar thermal panels - use sunlight to directly heat air or water, without involving electricity
Concentrated solar - produce high heat by focusing enough sunlight into one area. The heat can be then used for generating electricity or for industrial processes.

Viability

It's possible for solar power to provide most of the world's energy and replace fossil fuels. The land usage would be moderate, and rooftop solar could be the main source. However, this comes with some major challenges:

Challenge #1: Low-environmental-impact solar panels

Currently, the most popular types of solar panels involve too many rare minerals. We couldn't scale them up enough even if we tried - there simply aren't enough of certain minerals in the Earth that can be mined. Mining also comes with environmental destruction and in some cases, child labor.

What we need instead:
Requirements:

We need to be able to create approximately 375,000 km^2 of solar panels globally, without exceeding the reserves of any minerals.
If the solar panels still contain some scarce minerals, they need to be fully recoverable upon recycling.
The energy payback time(...)( defined as: {energy needed to produce the panels, including all their primary materials} divided by {power output of the panels, averaged over the full day-night cycle}. But also, if recyclability is needed as per requirement #2 above, then the energy of recycling also has to be factored in. ) should be significantly shorter than the lifespan of the panels. (...)( i.e. for panels with a 30-year lifespan, they should pay back the energy in 4 years or less. Preferable a 1-year payback - which could very well be achieveable. The first solar panels would still have to be manufactured using fossil fuel energy. Eventually after getting the ball rolling, solar powered factories would be viable. )
The solar panels don't have to be particularly efficient. 8% efficiency would probably be good enough. (...)( Today's most popular rooftop solar panels are about 17% efficient but too mineral intensive. Half that efficiency might still be enough to meet energy demand including charging electric vehicles. If not, then more solar panels would have to be manufactured, which is likely still viable as long as requirements 1,2,3 are met. )

Challenge #2: Energy storage

This comes with its own similar challenges: minerals, recycling, and energy-needed-to-manufacture.

The need for power-grid energy storage can be drastically reduced by

running factories only during the day
charging electric vehicles mostly during the day

Some energy storage would still be needed in either case.^{[QUANTIFICATION needed]}

Only a small fraction of energy demands must be truly baseload power.