On 6th May'20 I blogged about the characteristics of a solar cell on a sunny day (Solar Cell On A Sunny Day ). Inspired by the Evaluation Kit for Epishine Light Energy Harvesting Blog by Jan Crumps (Solar Energy Harvesting with Epishine Flexible Solar Cell - Pt 1: intro ) and the fact that it is 34 C outside at the moment so I'm not going to be doing any path laying or gardening today, I thought I would repeat my measurements of a solar cell to see if there was any difference on a really sunny day. (It is important to know that any temperature over 25 C in the UK is considered to be hotter than the inside of a sun and that roads will be melting and trees dying due to the heat. so I'm mostly staying inside without any air-conditioning.)
The peak power output is 369 mW at 70 Ohms, which strangely is less than the 426 mW at 60 Ohms from my previous measurements on 6th May'20, that is 13% less. Which is a bit surprising. So either I have not repeated the setup so that it gathers maximum power or, despite the heat, the sun's intensity is actually lower at this time. My investigations seem to indicate that the peak of solar intensity in the UK is in July on average (https://www.sciencedirect.com/science/article/pii/S0960148114002857 ) so maybe my setup wasn't ideal. I will just go and check.
Back from checking. I only checked the measurements at 70, 60 and 50 Ohms and recorded slightly increased power values of 411, 413 and 386 mW respectively. This is better at only 3% less and this is now within the accuracy limits I think I can achieve.
I have also now considered the effect of the increased temperature on the solar cell efficiency and my investigations show that the efficiency can vary between 10-25% depending on temperature. (https://www.cedgreentech.com/article/how-does-heat-affect-solar-panel-efficiencies#:~:text=Photovoltaic%20modules%20are%… ) and for the solar panel listed in the reference, reduces by 0.26% per degree Centigrade for every degree above 25 C, and also increases for every degree Centigrade below 25 C. I have no idea what the temperature was on 6th May'20 due to my poor experimental technique of not recording the temperature but it was probably somewhere around 20 - 22 C. This might explain the difference in power output achieved. I did notice that the current being produced today was fluctuating rapidly at times and as it is quite windy so there may have been some cooling effect from that as well.
It is always interesting to play with solar cell as I never seem to quite achieve the result I am expecting. Still, it does seem to show that the power available stays approximately constant (when the sun is shining!) throughout most of the early summer to later summer period. Perhaps I'll remember to repeat this experiment in August and or September, assuming there are some clear sunny days then.