If it cannot be used in the sun for a long time, it means it has a built-in battery (usually there are button batteries in solar calculators. Sunlight is converted into electricity from the solar panel and then stored in the button cell, so that the calculator can have continuous power supply) has taken effect and needs to be replaced.
Normally, power can be restored after being exposed to sunlight for a while. .
In your case, you need to replace the built-in battery (you can take the calculator to a watch store to replace it, or you can replace it yourself)
It's was originally called a dual power calculator, but I discovered that if my calculator is backlit by a solar panel, the numbers will not display clearly, if at all, I just need to remove a solar panel and install it on udo another calculator without exposing it. under the sun.
Even if it is a brand new 5# dry cell, if the solar cell does not work, you will not see the numbers on the screen if you connect the positive and negative poles solar energy. the new cell dries in parallel, nothing will happen. But if there is no dry cell, there will also be a solar cell.