The usefully convertable fraction of solar on Earth may be far closer to present or anticipated energy demands than is commonly thought. Panel efficiency, spacing factor, lifetime, capacity factor, storage requirements, essential fuel-based needs (marine shipping, powered flight, mobile power, remote reserve generation & thermal), process energy (steel coking, Haber-Bosch, etc.) leave some large holes and very uncomfortable margins remaining.
The alternatives to solar are either secondary or tertiary options (biofuels, wind, wave) and hence, more limited, or comparatively finite (geothermal, possibly our best non-solar option, tidal).
I do largely suspect that humanity's future will be principally solar powered. The question is largely of how much energy and in what forms it will be available. And aagain, demographic trends and expectations shade strongly against pleasant transition.
I find Vaclav Smil's and the late David MacKay's works quite illuminating.
(This is really a reflection of the difference between primary energy, which today is largely thermal, and delivered energy, which is largely work or chemical. The conversion to renewable energy will greatly reduce the importance of thermal energy conversion, and will not require a 1-1 replacement of today's primary energy use.)
It's not at all clear energy use will grow that much more. Lesser developed countries will use more, but in advanced countries energy use has plateaued. We are currently very far away from limits on solar energy imposed by shortage of sunlight. The Earth is hit by 100,00 TW of sunlight; global primary energy use is 20 TW.
If we're talking about limits OFF the Earth, solar is vastly more abundant than uranium (or, for that matter, artificial fusion, since the Sun fuses starting with ordinary hydrogen, not comparatively rare isotopes/elements like deuterium, lithium, or boron.)