Perhaps a slightly different question is in order. The _energy efficiency_ of solar energy is very much secondary to the _monetary efficiency_ of solar energy.
The total solar energy hitting the Earth's surface is something like 10000x the total energy that humans use (electrical power, nuclear, fuel burning, etc.) It doesn't matter if your power source converts solar power to electrical power with 95% efficiency or 5% efficiency, what really matters is how much it costs to get each watt of output. Efficiency does come into play, because a low efficiency system will require more surface area, and this means greater installation costs.
Photovoltaic solar power is still way to expensive to replace most of our electrical power use, although it is currently quite viable for small loads away from the grid, where the cost of the solar cells is less than the cost of installing wires.
_Wind_ power is essentially very inefficient solar power, where the solar collector surface already exists and is free. Wind power is currently almost at break-even with new natural gas fired power plants.
-Jon
