Please answer a question about the following article about Solar energy:

In addition, land availability has a large effect on the available solar energy because solar panels can only be set up on land that is unowned and suitable for solar panels. Roofs have been found to be a suitable place for solar cells, as many people have discovered that they can collect energy directly from their homes this way. Other areas that are suitable for solar cells are lands that are unowned by businesses where solar plants can be established.

Why does land availability have an effect on solar energy?
solar panels can only be set up on land that is unowned and suitable for solar panels