Light to electricity efficiency

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Light to electricity efficiency

Postby Dabel » Tue Aug 03, 2010 5:40 pm

How efficient is solar power in converting light to electricity? I am wondering so I have this hypothetical experiment.

Suppose I rigged up a 1.5kW system (9 panels) in a dark room and then rigged up a search light over the panels drawing (say) 1.5kW of power to run. Now if I ran the search light for 10 hours (using 15kWh) what power would the panels generate?

Just curious about the physics involved.
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Re: Light to electricity efficiency

Postby Gordon-Loomberah » Tue Aug 03, 2010 6:05 pm

It all depends on the panel type and age, the PV cell temperature, and the intensity and uniformity of distribution over the panels of the incident light.
In sunlight, anywhere between 6 and 15%, depending on the above. Also, 1.5kW of floodlighting does not produce 1.5kW of incident light. The efficiency of the lights might be only 10-20%, depending on the type, most of it will be heat, which will reduce the PV output.

I reckon you would be lucky to get 0.3kWh from your 15kWh of expended energy.
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Re: Light to electricity efficiency

Postby Tracker » Tue Aug 03, 2010 6:06 pm

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Somewhere between 13 and 17% and that is assuming your search light is of the right wavelength for the highest conversion efficiency of the panels... Also - that the search-light is shining equally brightly on all 9 panels..

It is an almost impossible situation to set up ! .. . . :idea:

Hope this helps..
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Re: Light to electricity efficiency

Postby Dabel » Tue Aug 03, 2010 7:44 pm

Thanks for that.

Its a good thing there's plenty of sunlight about with that level of conversion efficiency.

Had a mate who put two search lights on the front of his Mini once. They sat about 6" over the top of the bonnet and he had to strengthen the suspension to maange them.

When he was bush it looked as if he could light up the night all the way to the horizon! But it would kill the battery in less than a minute if the car wasn't turning over. Even then he couldn't leave them on!

The silly things we do.
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Re: Light to electricity efficiency

Postby 470rigby » Thu Aug 05, 2010 10:16 am

Tracker wrote:.
Somewhere between 13 and 17% ................the right wavelength for the highest conversion efficiency of the panels...


Tracker,

This is something that I have wondered about and maybe I should just Google it....but I'm having a lazy day!

Do different PV technolgies vary in this respect?

Thanks,

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Re: Light to electricity efficiency

Postby ghind » Tue Aug 10, 2010 9:58 pm

Tracker wrote:.
Somewhere between 13 and 17% and that is assuming your search light is of the right wavelength for the highest conversion efficiency of the panels... Also - that the search-light is shining equally brightly on all 9 panels..

It is an almost impossible situation to set up ! .. . . :idea:

Hope this helps..
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Tracker, don't forget that a typical light may only be 10-20% efficient. Like Gordon says, the heat from the light will heat the panels further reducing efficiency.

You can expect something like 10% of 10% which is 1%!!! Even if it was 20% of 20% (which it will never be this good) it would be 4% efficiency. Or 600w. I would agree with Gordon's calculations, you'd be lucky to achieve 0.3kw from 15kw of electrical input.

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Re: Light to electricity efficiency

Postby Sojin_Muneshi » Sun Aug 15, 2010 2:41 am

Dabel wrote:How efficient is solar power in converting light to electricity? I am wondering so I have this hypothetical experiment.

Suppose I rigged up a 1.5kW system (9 panels) in a dark room and then rigged up a search light over the panels drawing (say) 1.5kW of power to run. Now if I ran the search light for 10 hours (using 15kWh) what power would the panels generate?

Just curious about the physics involved.


Well if you used high efficiency compact flourescent globes you might get somewhere?

As advised earlier you might loose 20% in the transfer efficiency of the panels so 1.5kW might need 1.8kW in.

If we use 18w compact flourescents that give off the same light as a 60W globe we would produce the same amount of light as as 1.8kW of globes by lighting the panel with 30x 18w compact flourescent globes ie 30x60W = 1.8kW, and of course this would only consume 30x18W= 540W.

If 1.8kW of solar power into the solar panel resulted in 1.5kW of power out, then 540W of these compact flourescent lamps is equal to the light output of 1.8kW of the globes, and clearly again, with 1.8kW solar power in and 20% in-efficiency, we have already shown you will get 1.5kW electrical power out.

Of course this difference only becomes greater as energy measurement with each hour of power (kW) becomes energy (kWh) and more glaring a difference with multiple hours, despite putting out the same amount of light as 1.8kW of incandescents, we would only be using just of half as much energy per hour!

So based on the above calculations you have either now proven energy is not a constant in physics and just invented the perpetual motion device, or more likely that my mathematics are very misleading but simply offered in jest and fun and tongue in cheek -following more serious and correct answers above.

There will always be losses in the conversion from electricity to light/heat, and losses in the conversion of light/heat back to electricity.

regards

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Re: Light to electricity efficiency

Postby Dabel » Sun Aug 15, 2010 8:59 pm

Ha - I like it Sojin.

My guess is that the reason you can output the same light with an energy efficient 18w bulb as a 60w bulb is not that you get 60w of light energy with a 60w bulb but that the 60w bulb is very inefficient.

Very interesting though. I like you idea of a perpetual setup that creates energy!!
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Re: Light to electricity efficiency

Postby Tracker » Mon Aug 16, 2010 7:09 am

Dabel wrote:I like you idea of a perpetual setup that creates energy!!

Gee Whiz - I think that we have created the world's very first Perpetual-energy machine,
. . . . . and we did it here . . . . . :!: . . . NOT. . . ;)

Dabel - I would strongly suggest that you don't consider such a venture.. Despite what you think you have been told, do consider that the brightest minds in the world and throughout history have slaved to produce a perpetual-motion or energy machine and no one has ever succeeded !

ghind wrote: don't forget that a typical light may only be 10-20% efficient.

And who would chose a light source that was not THE most efficient in the worlds-best-practice ?
Sojin_Muneshi wrote:If we use 18w compact fluorescents that give off the same light as a 60W globe

The presumption here is that the light from the 18Wcfl will be the equivalent of 60W of sunlight - which I seriously doubt. ( Gordon might know the spectral density/spread of each - I won't be wasting time finding out )

Sorry - but the topic should not have been encouraged and seems to have gone from bad to worse :!:
It's a nonsense !
Gordon gave the best advice from the top --- "I reckon you would be lucky to get 0.3kWh from your 15kWh of expended energy."
The full explanation/answer would likely be best answered in the form of a Master's Thesis, which I don't propose to write .. . . :cry:
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Re: Light to electricity efficiency

Postby greg c » Mon Aug 16, 2010 10:02 pm

I would say you would be lucky to get 300w from your 15kW setup. You have to get all the light from the lamp to hit the panel, this will be doubly difficult with a CFL. I would rate the efficiency of a normal incandescent at 5%. Also the rays have to hit the panel at right angles for max power transfer, impossible to do if the lamp is too close. In fact the lamp would have to be a long way from the panel and then your problems with beam control and dispersion by the atmosphere will increase markedly.

The sun is the right distance away and the energy is free.

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