Help on solar powered car's power source

[Lonely Stark]

< Mentor Note -- thread moved to HH from the technical engineering forums, so no HH Template is shown >

I have taken part in a competition about solar car racing recently. The car I am going to make is just as big as a toy car. I have some problems about it's power source.
I am going to use converging lens to concentrate sunlight to my power cell and I have think of two ways to do it:
First, I will use one converging lens place on top of my power cell
Two, instead of using one, i will use about five of them to place around the power cell to get as many sunlight as possible.
I want to know which one is better and their output current (DC) so I can buy a proper engine.

 

[Danger]

Your approach is a bit confusing to me. I would think that lenses would seriously decrease the effectiveness of the solar cells. After all, they don't in any way increase the amount of light impinging upon them—merely the intensity. Using the cm³ of area that the lenses would occupy by filling it with more cells would be weight-saving and collect more light.
Am I missing something?

 

[Lonely Stark]

Your approach is a bit confusing to me. I would think that lenses would seriously decrease the effectiveness of the solar cells. After all, they don't in any way increase the amount of light impinging upon them—merely the intensity. Using the cm³ of area that the lenses would occupy by filling it with more cells would be weight-saving and collect more light.
Am I missing something?

You are not missing anything but in the competition, we can use only one power cell which is given by the organizer so I have to make the most out of it. That's why I decided to use lenses. Because lenses are use to concentrate light in an area, I think it would be better to use them to focus light into my power cell so it can generate more electricity. In my opinion, I don't think lenses would decrease the effectiveness of the solar power cell

 

[Vagn]

You are not missing anything but in the competition, we can use only one power cell which is given by the organizer so I have to make the most out of it. That's why I decided to use lenses. Because lenses are use to concentrate light in an area, I think it would be better to use them to focus light into my power cell so it can generate more electricity. In my opinion, I don't think lenses would decrease the effectiveness of the solar power cell

Have you considered using a large, plastic Fresnel lens?

 

[Danger]

Given the circumstances, I agree with Vagn's suggestion. Be very careful, though, to measure the intensity at the focal point before operation to make sure that it doesn't exceed the thermal limitations of the cell. You'll go nowhere fast if you melt the thing.

 

[edward]

Also bear in mind that solar cells lose efficiency as their temperature rises.

The output of a solar cell, and therefore a solar panel, is affected by its temperature. As a result the power output will be reduced by between 0.25%(amorphous cells) and 0.5%(most crystalline cells) for each degree C of temperature rise.
Panel temperatures in the summer in warm climates can easily reach 50oC resulting in a 12% reduction in output compared to the rated output at 25oC.

http://www.solar-facts.com/panels/panel-efficiency.php

 

[Danger]

Also bear in mind that solar cells lose efficiency as their temperature rises.

I was unaware of that, Edward. Thanks for putting it out there.

 

[Lonely Stark]

Thank you guys for giving me a lot of useful informations. I didn't know that solar cells lose efficiency due to temperature. I thought they just overheated and melted.

 

[dragoneyes001]

curiosity question: if you mount the cell on a super-cooled (Dipped in liquid nitrogen) light-weight metal backer would that actually increase the cells output for the time it takes the metal to reach ambient temp?

 

[DaveC426913]

Weight.

A plastic fresnel lens might be light enough to have minimal impact on the weight and therefore speed and distance of the car, but you will reach a point of diminishing returns. You must factor in the weight cost of any complexity you add.

 

[DaveC426913]

Just posted:
https://www.physicsforums.com/threa...sed-to-improve-solar-cell-performance.784339/

 

[CWatters]

Solar cells have an optimum operating point. If you plot power out against load resistance you will probably find the graph has a maximum power output at a particular value of load. The position of that peak will vary depending on the brightness. Ideally you need to insert a circuit between the motor and cell that keeps the cell at it's optimum operating point. However such a circuit is quite complex and might be beyond the skill level expected of competitors.