Btw, the sun is practically a cold fusion engine, temperatures in the core are very low when compared to human fusion installations.
While this is true, it's because the sun can be far less efficient than human fusion needs to be.
The solar core has a power density of around 276.5 Wm
-3. ITER, the most ambitious and large fusion reactor so far planned which has the (hopefully slim) potential to be too big to work, is only 840 m
3, with the plasma volume only taking up 100 m
3. If we were working with reactions on the order of solar fusion we would only seen a 27,650 W power output. ITER is designed for 500 MW. That's an 18,000 fold difference.
As far as cold fusion goes, actual cold fusion is simple impossible. You need to overcome the coulomb barrier between nuclei; the electromagnetic repulsion of the two positive ions you are trying to fuse. That requires at least the atoms that are being fused to be 'hot', or moving fast enough to break through that energy barrier.
Most of the seemingly plausible models of cold fusions are actually variations on inertially confined fusion, where the ions are locally given a high inertia by rapidly compressing a sample of material. The last claim that actually got attention from physicists was so-called
bubble fusion, based on the relatively poorly understood
sonoluminescence. We actually had an option to do an undergraduate report on the topic back in about 2007/8.