2 ms·
I don't have a definitive answer for you, but you can kind of back into a rough approximation (someone please correct my math if I went astray). High-efficienc
by mdorazio 10y ago
I don't have a definitive answer for you, but you can kind of back into a rough approximation (someone please correct my math if I went astray).
High-efficiency solar cells are about 20% efficient across the daylight spectrum.
For some reason, no one gives hard stats on how much energy LEDs waste as heat, but the claims are that incandescents waste about 90% of energy input as heat, and LEDs are about 80% more efficient than that. So let's say LEDs convert about 80% of input power into light at their operating wavelengths as a guess.
So if we put these together, we'll get about 16% of the input daylight back out as light at the wavelengths we want.
According to wikipedia [1], about 47% of light that falls on chlorophyll is wasted because it falls outside the ideal range for plants (400-700nm). Another 3% or so is lost due to wavelength conversion. The rest we can't really do anything about because it has to do with biological limitations. Put another way, our total system has to be about 50% efficient to be better than just putting the plants in the sun. As you can see, we're not even close. In fact, it's not even possible since the theoretical maximum efficiency of solar panels is only about 34% [2].
[1] https://en.wikipedia.org/wiki/Photosynthetic_efficiency https://en.wikipedia.org/wiki/Photosynthetic_efficiency
[2] https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...
- deleted 10y ago[deleted]
- TTPrograms 10y agoThe Shockley-Queisser limit only applies to single-layer cells under unconcentrated light. Different cell designs have surpassed it by significant amounts in practice already.
- mdorazio 10y agoDo you have a link where I can read more? I'm aware of light concentrators being more efficient, but that defeats the whole point since the surface area required is far more than size of the panel itself.
- jsight 10y agohttps://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit#Tandem_cells https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...
- legulere 10y ago> In fact, it's not even possible since the theoretical maximum efficiency of solar panels is only about 34% Theoretical maximum electrical efficiency of LEDs is over 100% though, as light is a form of heat. (Yes it has been already done: http://www.wired.co.uk/article/230-percent-efficient-leds http://www.wired.co.uk/article/230-percent-efficient-leds)
- mdorazio 10y agoFair point, but that's not really helpful in this particular situation since plants can't use heat as an energy source. We're only concerned with the % of input power that is converted into the specific wavelengths we actually want (400-700nm).
- mdorazio 10y agoUpdate on this for future reference: using multi-junction solar cells, the theoretical ceiling for efficiency is about 68% [1], and we can probably assume LEDs will get up to about 90% efficiency in producing desired wavelengths. Thus in an ideal future scenario it might be possible to do better with solar collection + LEDs than plants themselves do, but we're pretty far off in actuality. https://en.wikipedia.org/wiki/Multi-junction_solar_cell https://en.wikipedia.org/wiki/Multi-junction_solar_cell