How do I know the produced heat on the focal point of a solar parabolic trough per different radius if made from steel and also from glass?
Your question is not very well formed - here are some considerations:
- incident power from the sun is about 1.3 kW / m$^2$ for normal incidence with the sun overhead, no clouds. Depending on the orientation and dimensions of your trough, you should be able to compute the maximum power collected
- If you make the trough of steel or glass, the reflectivity will be less than 1.0 - this means that not all the incident power is reflected to the focus (some will heat up the reflector)
- The collector will not absorb all the radiation (it is not "perfectly black") - this means it will reject some of the incident power
- As the collector heats up, it will become a radiating black body
A lot of this can only be estimated by measurement. Lucky for you, somebody did the measurements, and published the result here. They suggest an efficiency of about 77% is possible.