Simply put, the process of photosynthesis uses light energy to convert carbon dioxide and water into sugar and oxygen. It would be more efficient to convert the light energy from the sun directly into electricity than to try to harvest power from photosynthesis. It's possible to convert the plant sugar into a fuel (biodiesel) as well, but plain old photovoltaic cells are more practical if you need electricity.

As long as we're futzing with genetic engineering, why not re-engineer a tree to produce batteries as fruit. A battery is a rather simple object as conpared with the highly complex molecular structure of an apple or a banana.

There are researchers trying to create artificial photosynthsis. The whole idea is to store the energy from the sun. Batteries are not good storage mediums for 2 reasons - the energy density is low (in your car a pound of batteries will take you much less distance than a pound of gasoline) and the storage is only temporary, over time the energy is lost. So if you can either replicate the proces or genetic engineer plants to great high density energy reserves which are compatible with fossil fuels (i.e. oil and coal) so lets make trees which produce large quantities of high quality oil. There must be researchers out there looking at ways to increase the oil content of crops such as soybeans and corn --- but a tree with oil laden fruit is an interesting idea.

All that's really needed hypothetically if we are able to harvest the energy from such a source, is a way to take that harvest (sugar/oxygen) and convert it back into energy...

If we forget the oxygen production (it's a usefull biproduct) and focus on the sugar created by photosynthesis, you get about 16.5KJ/g (compared to about 35KJ/g of petrol), not a bad harvest.

Maybe we should concentrate on an efficient, energy creating process much like the stomach undertakes? A huge stomach to grow fruit for, producing fertilizer for new crops and new giant stomach's... scary!

Ok, excuse the slightly ridiculous, but you see the point i'm trying to imply...

I almost can't believe your saying that you wish there was a way to store the energy from photosysthesis to get it out later. It's called firewood.

Plants are the ultimate self-replicating, self-healing, most efficient aiming, indefinite energy storing creations ever made. Better than any engineer will come up with.

Whether your burning firewood or 'digesting' sawgrass for alcohol, it's still the best solar collector you could ever imagine.