Can a solar panel generate electricity from candlelight?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

23 December 2007

Peter G would like to know how a solar panel turns solar energy into electric energy. He asks, “What does it convert, heat or light? If it is light, can it convert light from other sources like moon?”

The more accurate name for this device is “photo-voltaic converter”. Now the word photo implies something to do with light (as in photograph) and voltaic has to do with voltage, or electricity. Thus this is a device for converting light into electricity.

The source does not matter – light is light, is light! A solar panel will therefore produce electricity even under moonlight or candlelight, albeit very little. In fact, you can try to be canning and connect a bulb to the panel and shine the light back on it to generate more power!

But as explained in May this year, that would not be a sustainable process since the panel converts only five to ten percent of the light into electricity. And the bulb converts only another ten percent of electrical energy into light.

The net result is that you would lose about 99 percent of the energy thus the bulb would go dim very quickly – in a mater of seconds.

But why are solar panels still used if they are that inefficient? Well, light from the sun costs us nothing. If we don’t make use of it, it will just go to “waste”. So, even the “little” five percent converted by a photo-voltaic is worth everything.

This question brings out another fact about the sun’s radiation that is usually not widely appreciated: most of it (aver 99 percent) is visible light. Even though we feel very hot when we stand out in the sun, only a small fraction of the radiation is heat. For that reason, solar panels are designed to work with light; not heat.

To appreciate this, imagine what would happen if you exposed your body’s light detector (the eyes) to direct sunlight. That is, if you looked at the sun directly. You would go blind immediately! (DO NOT TRY TO DO THIS!!! It is dangerous)

But we are always exposing the body’s heat detector (the skin) to the sun with little damage – as you read this, I am doing so on the sandy shores at Diani Beach! Of course prolonged exposure can be harmful, but the damage does not happen as quickly as the blindness.

And another thing: Yellow is the brightest colour in sunlight. Our eyes are also most sensitive to yellow light. They were designed (or they evolved – if you subscribe to the theory of evolution) to see in the presence of sunlight, which is predominantly yellow.

It is no wonder that yellow object are sometimes described as “screaming”, meaning that they appear very bright.