While you may not think that this is the best time of year to complete photosynthesis science fair projects, the fall is actually a great time to conduct plant experiments. As you are most likely aware of, photosynthesis requires light in order to occur. As the source of light that a plant is exposed to is changed, so does their internal chemical reactions.
Most students that are going to produce photosynthesis projects are going to rely on spring or summer time data. You can distinguish your project from your peers’ projects by conducting fall or winter time projects. For example, you can examine how the reduction in light affects the chemical and biological processes inside a plant. You can also look at how plants in regions of the world that go long periods of time with limited access to light differ from plants who still receive ten hours of light of day during the winter.
Finally, developing a unique photosynthesis science fair project is going to depend on your ability to apply what is known about this process to answering a question. For most students this means conducting in depth background research and completing basic experiments, such as those presented by photosynthesis project boards. After you have an understanding of the process of photosynthesis you will be in a much better position to figure out ways to manipulate the factors that impact photosynthesis to test your hypothesis.