Is the sun enough to power all of our needs?
On average, there is plenty of sunlight power hitting the ground on this planet to power all of our fixed installations.  This isn't currently being done because:

It's too expensive.  The cost per Joule of capturing sunlight and turning it into readily usable form, like electric power, is still significantly more than burning fossil fuels or fissioning uranium.

Even if it were economical, it would take a while since the total investment would be huge.

Sunlight only hits the ground intermittantly, so significant energy storage would be required for the times when the sun isn't shining.  This is still inefficient in energy out/in terms, and quite costly.  We also don't know how to store any meaningful amounts of AC electrical power, so the storage has to be in other forms.  That adds inefficiency and cost in coverting to and from the stored power.

Even if all the above were solved, sunlight doesn't work well for highly concentrated but mobile uses of power, like is required in transportation.  A airplane, for example, doesn't intercept anywhere near enough sunlight for the power it uses.



Added:

From the downvotes and some of the comments, I can see this hit a few nerves, which isn't all that surprising.  However, those people fail to recognize this answers the question as asked.  The OP simply wanted to know why more solar energy isn't the source of most of our power today.  This says nothing about what we should do, how things could work, what if different economic insentive were in place, if we had run out of fossil fuels, etc.

You can argue for a long time about true costs of fossil fuels, nuclear, etc.  However, none of that matters in why we are doing what we are doing today.  The current situation is based almost exclusively on the immediate economic cost, which is what I answered.

There are legitimate discussions on what our energy future should look like and how we should get there, but not here, and that's not what this question was about.