What are Advantages and disadvantages of using photocells to generate electricity?

The good reasons of having a photocell in a park are that it can be left alone once set up, can get energy for free (form the sun), it can store energy for long periods of time, but were there are advantages there are also disadvantages, which are it doesn't gain as much power at night or in low light conditions, its expensive to buy/ get set up.

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