  Graphics Processing Units (GPUs) are now powerful and flexible systems
adapted and used for other purposes than graphics calculations (General Purpose
computation on GPU -- GPGPU). We present here a prototype to be integrated into
simulation codes that estimate temperature, velocity and pressure to design
next generations of solar receptors. Such codes will delegate to our
contribution on GPUs the computation of heat transfers due to radiations. We
use Monte-Carlo line-by-line ray-tracing through finite volumes. This means
data-parallel arithmetic transformations on large data structures. Our
prototype is inspired on the source code of GPUBench. Our performances on two
recent graphics cards (Nvidia 7800GTX and ATI RX1800XL) show some speed-up
higher than 400 compared to CPU implementations leaving most of CPU computing
resources available. As there were some questions pending about the accuracy of
the operators implemented in GPUs, we start this report with a survey and some
contributed tests on the various floating point units available on GPUs.
