The fundamental factor of solar panel's inefficiency is the solar radiation itself.Physicists William Shockley and Hans Queisser at Shockley Semiconductor were the first to calculate the detailed balance limit: the maximum theoretical efficiency of a solar cell using a p-n junction to collect power from the cell. Their finding of this limit is widely considered the one of key contributions to understanding solar energy potential.

In effect, it says, that in ideal sunlit conditions about 1,000 watts of sunlight fall to earth per square meter, and of this, only up to about 33.7% can be utilized in photovoltaic solar. And silicon has a maximum efficiency of 32%. In effect the solar panels do their job 100%. the concentration should be on how to convert the sun's radiation more effectively using different methods or other materials to trap the solar energy fully. that's why we go for solar thermal systems.

In solar thermal systems, the optical and thermal losses are minimum 25-30% so the maximum is close to 70-75%

The Thermal and optical losses play a decisive role in energy efficiency:

- For thermal solar collectors, the sensor geometry and the type of fluid are also decisive.

- For PV panels, the technology and manufacturing material are also important factors.

Solar-thermal application, the solar insolation available is periodic i.e, 6-7hours a day, but surplus energy is available in distributed form. We need to concentrate(store) the solar power based on our need. So solar concentrators are quite costlier also solar energy is available during daytime only for night time we have to do some energy storage arrangements. Thus these all factors increase the initial investment cost

As Poornima D said, the theoretical limitation is 33.7% . The theoretical and the design of solar panel wafers will have to be changed to improve the gain close to (62-69)% which is double the limitation. How is another thing.