Solar Cooker Efficiency vs. Gas Grill Efficiency Question

[ashtonnaja]

Hi, my name is Ashton, and I am a 10th grade student at Carroll High School. I am conducting an experiment that compares the efficiency of solar cookers (I already have the data for this). I was wondering if there was any kind of formula or a place where I can find the efficiency of my Weber gas grill, and how this data could compared to the efficiency of solar cookers.

Thank you for the help!
Ashton Najarian

[deleted-71709]

I can imagine numerous ways to measure the efficiency of a cooker.

In general, to measure the efficiency of anything, you divide what comes out of the device by what goes into it. In the case of a cooker, you would divide the amount of energy that comes out of it by the amount you put into the cooker.

In the article I have cited here, the input to the solar cooker is calculated by the area of the collector and the amount of solar energy received per unit area. The output is determined by measuring the time required to boil off a known quantity of water. I don't know if this is the method you plan to use to determine the efficiency of your solar cooker or not, but I'm sure you're using something similar.

Solar Grill:

http://solarcooking.wikia.com/wiki/Efficiency

You can use a variation of this for a conventional gas grill. The output energy would be measured just the same way you measure it for the solar grill - boiling away a known amount of water. For the input energy, it would be reasonable to assume (if the grill is fairly new) that the input energy is that specified by the manufacturer. In this web site from Weber, you can see the the INPUT is specified as 38,000 Btu (British Thermal Units) per hour. All grills have similar ratings. As grills get older, the burners get corroded, or clogged with cooking remnants, and don't flow as much gas. So, in that case, the input Btu would drop some. In a laboratory, engineers putb flow meters on the gas supply lines and measure the amount of gas going into the grill. They convert that to Btu per hour to get an accurate measurement of the true input energy. I don't recommend attempting to measure the actual gas flow as a 10th grade science project. It requires special equipment - EXCEPT if you have a very accurate scale, and are using a propane fuel grill, you could measure the weight of propane used over the time you boiled away the water and convert that to input Btu's.

Weber Grill:

http://www.weber.com/explore/grills/gen ... esis-e-330

I hope these ideas help and that you HAVE FUN with your project.

[ashtonnaja]

That information helped a lot, but is there any way I could plug that information into a formula to get the percent efficiency?

[prih 123]

Hey Ashton it's Patrick H I just wanted to say hey and I think your project is awesome!!!!!!!!!!!!!!!! (-:

[deleted-71588]

Efficiency comparison between different methods has historically been done with "cost" functions. In one sense, Solar energy is "free". We don't have to pay anybody to use it, we just have to pay for the equipment to convert it to perform some task. In the case of a propane grill, we have to pay somebody to provide us with the gas and we have to pay for the equipment to convert it to perform some task.

It would be easy to compare the efficiency of two different solar cookers. Just see which one heats an identical object from the same initial temperature to some final temperature in side by side comparisons done at the same exact starting time and solar orientation and compare the times. In that kind of a cost comparison, you don't consider how much energy is theoretically possible to collect.

You can do the same thing to compare the efficiency of two gas grills and measure how much gas was used by each in the process and ignore the time taken.

I'm not sure how you can come up with a "cost" function that could be used to compare the efficency of a solar cooker with a gas grill because the cost of the solar energy is free.