It might be a lot of work to put photosynthetic machinery into an animal cell. You would need all the infrastructure of the chloroplast. This is a cell organelle that, like mitochondria, probably has a bacterial origin in the distant past. One might have to move all of the nucleus encoded genes that are needed for the organelle (maybe a thousand or more), a big job, but not necessarily impossible. There are likely some other issues, but I would be surprised if we could not deal with them.
Linda Quarmby, professor of Biology at SFU, adds, "The evolutionary breakthrough that lead to photosynthesis happened after the lineage that lead to plants and animals diverged. In other words, it is not a matter of animals losing the machinery - they never had it in the first place."
making a small donation to science.ca.