This needs the additional information that photosynthesis is incredibly inefficient. It's <5% IIRC, so we already have solar panels almost a magnitude better than what nature did.
(RuBisCO as the protein at the center of the process is also quite strange: it's huge and slow. As in 'this ain't funny any more, start working' slow with about a reaction per second.)
The comparison of photosynthesis vs energy generated by solar panels isn't very good, because it neglects the whole biology of the organism, which is optimized for things other than maximum photosynthetic output. For example, leaves are often targets of herbivory, so a plant might want to make a tradeoff [1] of less efficient photosynthesis for better herbivory defense. Or, it might be too costly to do photosynthesis, which requires the input of carbon dioxide, water, and light. In a very dry & hot environment, to get enough carbon dioxide into the leaf, the leaf will lose water by having its stomata open. Google "leaf economics spectrum" for a quick tutorial (the concept isn't 100% correct but it's a good starting point). Compare the leaves of tropical plants (say a banana palm) to arid plants (mesquite tree).
[1] I use this a teleological shorthand for "the selective environment has weeded out species that happen to fall on the wrong side of the tradeoff."
Exactly. I suppose the energy density of sugar is pretty high. The non-nuclear fuel with the highest volumetric energy density is jet fuel[1] at 37.4 MJ/L. I wonder how the most efficient natural compound (adenosine triphosphate / sugar / etc) compares...
ATP + H20 -> ADP + P produces only 30kJ/mol. A mole of ATP weighs ~500g. You likely get a lot more energy from burning it (the Wikipedia doesn't say), as you do with jet fuel, but that reaction is too hard to reverse to be useful for organisms.
A mole of glucose produces 2800kJ/mol when you burn it. A mole weighs ~180g.
Using http://lmgtfy.com/?q=jet+fuel+density to get a range of 775.0-840.0 g/L for jet fuel, that gives us 37.4MJ/807.5g (taking the average of the jet fuel's mass) against 2.8MJ/180g for glucose.
Scaling the denominator of each to 1kg, that's ~46.3MJ/kg for jet fuel and ~15.6MJ/kg for glucose.
Given how biochemically cheap glucose is to produce compared to jet fuel, I'm surprised it's only off the state-of-the-art by a factor of three.
I believe the trick is that they harvest "95 percent of it from the light they absorb", emphasis added. It's sort of like saying an efficient solar system only loses 5% of the energy absorbed by the solar panels.
Photosynthesis may be quite efficient internally, but it's not very good at capturing all of the available power. It really is 3-6%, where even cheap solar panels can achieve 15-20% or higher these days.
Efficiencies are ~1-3% in most plants, with 5% a possible high. Algae can reach 10% without various artificial stimulation. Given gro-lites and other factors (which tend to defeat the purpose), much higher per-hectare yields have been achieved.
As others note, plants offer many, er, plantly services. They're (usually) self-supporting, have disease, insect, and pest deterrance capabilities, self-transport water and minerals, and arrange for their own replication.
In many cases, a seed in a hole, or even on bare ground, is all the infrastructure you need to start manufacturing a new plant. Constructed infrastructure tends to have higher investment requirements.
I suspect there might well be an evolutionarily balanced tradeoff between "construction cost" and "lifetime energy output" of a plant's photosynthesis machinery - as well as a likely overabundance of available solar energy in terms of what a plant actually can use. (Why build a potentially more complex and fragile photosynthesis pathway that's 50% more efficient, if you can instead just grow twice as much leaf surface area?)
But there are places where plants compete fiercely for small amounts of sunlight, such as in forests (especially tropical rainforests). Doesn't your theory suggest they'd use more efficient systems there?
Don't forget plants get the energy back from making a leaf in a few weeks. Solar panels take considerably longer. Generally plants are optimized to compete with others in their niche and as such it's exponential growth that's most important not total energy capture.
Is it actually tropical rainforests, or temperate, that limit sunlight most? Old-growth PNW forests often have large patches of western hemlocks that produce so much shade that no other tree can grow under it, not even conifers - and unless there's a fire to clear some space out, it can stay that way for centuries.
Selection pressure may well have shifted towards C4 in the future if we hadn't come along and been kind enough to dig up some fossilized carbon and put it back into circulation.
I don't know but my guess is to have more efficient collection/processing may require bigger leaves which may be too heavy or catch more wind damaging branches.
> The device uses solar electricity from a photovoltaic panel to power the chemistry that splits water into oxygen and hydrogen. Microbes within the system then feed on the hydrogen and convert carbon dioxide in the air into alcohol that can be burned as fuel
Only the hydrogen + co2 -> alcohol part uses biological components.
I remember my biology teacher's description of photosynthesis: "If you have a river of gold running through your backyard, you don't care how much of it you splash all over the place when you carry the buckets full back to your house."
(RuBisCO as the protein at the center of the process is also quite strange: it's huge and slow. As in 'this ain't funny any more, start working' slow with about a reaction per second.)