Is 55°C best status for solar cells?
Where did you get this from? Increasing temperature generally decreases performance of solar cells as far as i understand.
how much is the best ?
It's complicated because the cell temperature and irradiance (energy density of the sun's rays) are linked assuming no artificial heating or cooling of the cell. In general if you heat a cell when the irradiance is fixed the efficiency will decrease. It also depends on the materials used in cell construction though.
Your question is too general to really give an answer, could you be more specific or give any more background to your question?
This is all true. But to try to answer your question, the colder the better. So what would be good is to make the incident light as intense as possible, but while keeping the cell as cold as possible. Now depending on how you aim to do this, you just might be spending too much power compared to what you are generating. Clearly there are trade-offs.
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