how to measure solar output over a period of time

[Garyw]

My daughter is trying to do a science fair project that would measure the output of a small solar panel over a certain period of time and then compare it to another panel placed at a different location, angle, time of day, etc... My question is how to measure the output over that period of time.
Thanks

 

[Sceadwian]

Operate a small pump to transfer water from one tank to another; something a little less wet might be to spin a small motor that is turning a worm screw or other high reduction rate gear set (kind of like a gas meter uses) , the both have a nice visual appeal to them. Basically ANY method that uses electricity to do something else that you can measure would be useful, those are the first two that popped into my head.

 

[RCinFLA]

The simplest reliable method to measure PV output versus sun illumination is to measure short circuit current of the panel. It has the least temperature variance.

For direct comparison the panels should be of same type.

**broken link removed**

 

[Sceadwian]

RCinFLA that has the visual appeal of watching grass grow for a science project. If you want people intersted, and accurate results, doing WORK is a good method. I don't think Garyw's daughter is going for six sigma accuracy.

Your short circuit current would only measure an 'ideal' power output not a real one. The work done by a motor will show real world loss, like what occurs in the real world. In theory good power conversion circuitry can get within 80-95% of full power utilization out of a solar cell, but again this is a school science project, gotta keep it real.

 

[leftfield95]

I would suggest that the solar panels are used to drive small electric motors. The motors via a worm wheel and other gearing are used to raise a heavy weight over a fixed amount of time. The height that each weight achieves can be used to calculate the amount of work done (useful energy produced), and the difference easily calculated.
The difference in the two amounts of work done (difference in height) will be very visual, if I recall schools like that sort of thing.

 

[MrAl]

Hi,

It's not going to be easy to measure the total power output for comparison because the two different arrays need to be loaded to their max power point and that requires knowing the current and voltage. If both arrays are loaded with the same motor for example that will only tell you what array can drive THAT motor the best. If you want to know the real difference you have to measure the max power of each array and sum that over time.
For example if one array happens to be loaded close to its max power point and the second array is loaded far from its max power point but has more cells, both arrays might end up looking the same when really they arent at all. Same goes for the angle relative to the solar arc or the angle twisted away from the arc...the max power point has to be measured.

Measuring the max power point is not easy, but it is very interesting. To load in this way the load is changed automatically with some sort of feedback system in order to keep the product of voltage times current at its maximum:
maximum(Power)=maximize(Voltage*Current)
and note that this changes throughout the day with the relative solar movement and cloud cover.
The act of keeping the array automatically loaded to its maximum power point is usually referred to as "Max Power Tracking".