Is photosynthesis more efficient than solar panels? If so, by how much?
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asked Apr 23, 2014 at 20:45
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3$\begingroup$ It would help if you could define what you mean by "efficiency". Solar panels work by converting radiation to electricity, while photosynthesis uses radiation to synthesize sugars. It's difficult to meaningfully compare the energy output of the two since the useful work you might do with each is typically quite different. $\endgroup$– Kyle OmanCommented Apr 23, 2014 at 21:10
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$\begingroup$ I think this is a nice question, but as Kyle points out efficiency is kind of ambiguous. For instance, if you are talking about ultimate conversion into energy in the grid, then you also have to account for the burning of the plant matter to extract its chemical energy. Perhaps you mean quantum efficiency which tells you number of output electrons per number of incident photons. In either case, I expect that solar panels are better except in some narrow wavelength regimes. $\endgroup$– Chris MuellerCommented Apr 23, 2014 at 22:45
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1$\begingroup$ @kyle Actually, the 2 processes are very similar; both capture light and excite electrons. If you take just this portion, then you can compare the 2. $\endgroup$– LDC3Commented Nov 1, 2014 at 13:54
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3 Answers
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Rather than considering quantum efficiencies or such details it's instructive to step back and take a broader view. One of the main fuel crops grown in the UK is miscanthus. There are various figures around for the yield produced by miscanthus, but these people estimate it as about 14 tonnes per hectare per year. The energy content is 19GJ/tonne, so that's 266GJ per hectare per year or about 8.5kW per hectare.
Commercial PV panel installations typically produce 500kW per hectare (NB the link is a PDF) though this is peak power and would be a lot less averaged over the year. However, even if averaging over the year reduces the yield by a factor of 6 this still leaves the PV panels producing ten times as much power as miscanthus per hectare.
For comparison the intensity of sunlight at midday is around 10MW per hectare.
Incidentally, I don't mean to belittle miscanthus. PV panels are vastly more expensive to make than miscanthus is to grow, and we have yet to persuade PV panels to reproduce themselves. Both have their role to play in supplying energy.
answered Apr 24, 2014 at 9:37
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4$\begingroup$ Further to your last paragraph and maybe of interest to the OP: biofuel is portable, like oil: a property we have yet to really reproduce in solar. This property is vital for mechanised agriculture: hence the reason for keen interest in battery technology, and hydrogen fuel cells (hopefully both will allow solar to be stored and used for agriculture in the future). Also, there are many more hectares in the world that could be solar hectares toegther with other uses (rooftops for example): the ones that can be miscanthus hectares are far fewer in number. $\endgroup$ Commented Apr 24, 2014 at 9:46
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$\begingroup$ Hemp is a considerably more efficient bioenergy feedstock than the dominant annual energy crops. algae and bamboo even more so. $\endgroup$ Commented Apr 12, 2021 at 15:07
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Photosynthesis is less efficient than solar panels. According to the Wikipedia page on photosynthetic efficiency, typical plants have a radiant energy to chemical energy conversion efficiency between 0.1% and 2%.
Most commercially available solar panels have more than 10 times this efficiency.
answered Apr 23, 2014 at 22:00
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1$\begingroup$ That page doesn't mention algae (up to 98% efficient?) and bamboo (up to 87% efficient?). $\endgroup$ Commented Apr 12, 2021 at 14:45
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$\begingroup$ @CeesTimmerman These numbers cannot be total efficiency. The Wikipedia article talks about how there are different measures of efficiency, and for total efficiency, there is a theoretical maximum of around 11% $\endgroup$ Commented Sep 27, 2023 at 12:04
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$\begingroup$ @stochastic Explain why
while plants only store an average of 12 percent of the energy, algae can store up to 98 percent. “That enormous degree of efficiency makes algae ideal for energy storage and conversion”, explains Sem Tamara, PhD Candidate at Utrecht University.is incorrect. $\endgroup$ Commented Sep 28, 2023 at 12:21
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The big difference is that plants are "storing" the energy, and solar cells are not. The utility of stored energy is much greater than the output of something like a solar cell.
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$\begingroup$ A Tesla Powerwall (old car battery) is over 90% efficient. Passenger car diesel engines have energy efficiency of up to 41% but more typically 30%, and petrol engines of up to 37.3%, but more typically 20%. $\endgroup$ Commented Aug 28, 2020 at 11:52