In fact, the symbiotic partners were often found bordering mitochondria, organelles responsible for generating a cell's energy. Thus, it's likely that the mitochondria were taking direct advantage of the oxygen and carbohydrate, byproducts of photosynthesis that were generated by the algae.
I had heard about Jellyfish that could do this (photosynthesize),
Because vertebrate cells have what is known as an adaptive immune system — which destroys biological material not considered 'self' — it was thought to be impossible for a symbiont to live stably inside them. But, in this case, the salamander cells have either turned their internal immune system off, or the algae have somehow bypassed it.
"On a lark, I decided to take a long-exposure fluorescent image of a pre-hatchling salamander embryo," says Kerney. When this revealed widely scattered dots of unstained cells fluorescing in the background — an indicator that those cells might contain chlorophyll — Kerney switched to transmission electron microscopy (TEM) to take a closer look.
[*] So if all light hitting on our bodies was converted into useable energy, that would be 500 Watts times 60 seconds per minute times 60 minutes per hour times 24 hours per day, for a total of 43,200 kilojoule. or about 10,000 kilocalories.
What if we assume the efficiency is similar to that of a leaf? How much would that get us?
To add to my last post: even if we were able to get 100% energy from photosynthesis, we'd still have to eat to get other nutrients. What if we got too much sun and had too many calories?
A German dieting book I own uses the rule of thumb that you need to eat 30 kilocalories(*) per day for every kilogram of bodyweight you wish to keep. For a body of average weight, 70 kg or 155 lb say, that would be 2100 kilocalories.
(*) Colloquial English drops the "kilo" and just calls a kilocalorie a calorie. This usage, however common, is off by a factor of thousand.