Here is the source that cites the 173,000 terawatts of solar power:

https://phys.org/news/2011-10-vast-amounts-solar-energy-earth.html

Professor Yehia Khalil, Yale University, USA

Fellow of the University of Oxford, UK

Dear Ahmed

in the two wikipedia entrys a citation for the 173000 terawatt is given. 

The reference is: "Archer, D. (2012). Global Warming: Understanding the Forecast. ISBN 978-0-470-94341-0".

The third link is a pdf of that book. You will find a lot of calulations with respect to the incomming solar radiation there; but I havn't found the number '173000 terawatt'.

Please have a closer look at  the appropriate chapter. You may have more luck than me.

Dear Yehia, in your reference the '173000 terawatts' are only mentioned. I do not think that Ahmed can use this as a real citeable reference of that number.

https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget#cite_ref-4

https://en.wikipedia.org/wiki/Earth%27s_energy_budget#cite_ref-10

http://tiwrm.haii.or.th/sharewater_download/books/Global%20Warming%20-%20Understanding%20the%20Forecast%20(2nd%20ed,%202012).pdf

Dear Ahmed:

Solar irradiance is Gs = 1360.8 +- 0.5 W/m2 (Kopp G. & Lean J.L.(2011). A new lower value of total solar irradiance: Evidence and Climate significance. Gephysical Research Letters, Vol 38).

Mean radius of Earth = 6.371x10*6 m.

So Solar Power on the outer layer of Earth´s atmosphere is approx.

P = 3.1416 x (6.371)*2 x 1360.8 x 10*12 W = 173 524 TW

But Earth´s albedo = 0.30 and  0.19 of intercepted solar radiation is absorbed by atmosphere, so the Solar Power on Earth Surface is 'only'

P = (173 524 TW) ( 1 - 0.3 - 0.19) =  88 500 TW +- 3.3% , very approximately.

Thank you all for your valuable time and kind replies. I have considered them with care, and I find the calculations written by Dr. Eduardo very convincing. I see that they also emphasize that the widely-known claim concerning this number is not accurate. This amount of power does not reach the Earth surface, but rather is on the outer layer of the atmosphere. This is very interesting ! 

Indeed those 173 000 TW don't reach the Earth's solid or liquid surface. However, the 888 500 TW that really impinges on this surface corresponds to 2 790 100 EJ. The total human consumption of energy in 2015 was 550.66 EJ, according to the BP Statistical Review of World Energy 2016. This way, solar energy at soil level was more than 5000 times greater than this consumption !

All proved and probable reserves of oil, gas, coal, Uranium, Thorium,... are TINY AND INSIGNIFICANT compared to the free and clean solar energy !!