Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: scientizscht on 21/06/2018 15:42:24

Title: Efficiency of light as energy source?
Post by: scientizscht on 21/06/2018 15:42:24
Hello!

What is the optimum lux to maximise conversion of light into energy? What is the efficiency of this conversion?

Thanks!
Title: Re: Efficiency of light as energy source?
Post by: Bored chemist on 21/06/2018 20:26:04
Light already is energy.
Title: Re: Efficiency of light as energy source?
Post by: evan_au on 21/06/2018 22:56:54
Quote
maximise conversion of light into energy?
What sort of energy do you want to convert it into?
- If you want to convert it into light, an ordinary mirror will do that with over 50% efficiency (and an astronomical mirror will do it with over 99% efficiency)
- If you just want heat, any black surface will do. Covering it with a sheet of glass will reduce the amount of heat lost by convection and re-radiation.
- If you want electricity, cheap solar cells will give about 10% efficiency, while space-rated ones might give you over 20%. In this case, you have to allow air to circulate to keep them cool, as they lose electrical efficiency when they get hot.
- Commercially, both thermal and electric systems are optimised for sunlight, with about 700W per square meter
- In theory, they would both continue to work (a bit) under a full Moon, at about 0.01 Watts per square meter, so it would be a challenge to measure it!
See: http://forum.solar-electric.com/discussion/22560/full-moon-wattage
Title: Re: Efficiency of light as energy source?
Post by: scientizscht on 22/06/2018 00:00:50
Light already is energy.

Not very useful as electricity.
Title: Re: Efficiency of light as energy source?
Post by: PmbPhy on 22/06/2018 10:02:07
Light already is energy.

Not very useful as electricity.

Light isn't energy. It has energy. Big difference.
Title: Re: Efficiency of light as energy source?
Post by: scientizscht on 22/06/2018 14:33:04
Light already is energy.

Not very useful as electricity.

Light isn't energy. It has energy. Big difference.

Well said.
But what about some figures for my question please?
Title: Re: Efficiency of light as energy source?
Post by: Bored chemist on 22/06/2018 18:16:40
Light already is energy.

Not very useful as electricity.
True, but very handy if you want to see where you are going.
Title: Re: Efficiency of light as energy source?
Post by: Bored chemist on 22/06/2018 18:19:40
Light already is energy.

Not very useful as electricity.

Light isn't energy.

Unless, of course, it is.
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/energy/heatrev4.shtml
What do you think it is; chicken soup?

Title: Re: Efficiency of light as energy source?
Post by: scientizscht on 22/06/2018 18:52:27
Light already is energy.

Not very useful as electricity.

Light isn't energy.

Unless, of course, it is.
http://www.bbc.co.uk/schools/gcsebitesize/science/aqa_pre_2011/energy/heatrev4.shtml
What do you think it is; chicken soup?

It's like saying electrons are energy, when in fact their movement is.
Title: Re: Efficiency of light as energy source?
Post by: jeffreyH on 22/06/2018 19:17:35
Photons are defined in terms of energy, E = hf. Here h is Planck's constant and f is the frequency of light. Since frequency is variable then any equivalent mass that can be defined for the photon also changes. This cannot be defined as rest mass and therefore must depend entirely upon kinetic energy. In terms of objects with rest mass, kinetic energy is connected to a change in velocity and not to any change in frequency. The energy changes for entirely different reasons. This is like comparing apples and pears.