Electronics 2000

Hi there, I'm a 3rd year Aeronautical Engineering student at Brighton University currently working on my dissertation, which is a solar powered model aircraft.

I am not the best with electronics so I apologise if I'm a little dense not the topic.

My aircraft will have an array of solar cells producing around 2.5A at 12V

I will be using a 3s Lipo battery 1100mah 11.1V

The motor will be drawing more power than the solar array provides, so how can I draw all the current from the solar array and the rest that is needed from the battery?
I was going to use a maximum power point tracker but as I will be using more power than I am producing I feel it is an unnecessary weight.

Any help would be greatly appreciated, as it is holding my project up but it is not an important aspect I am being assessed on due to being an Aero engineer.

Thanks, Sacha.

I'd try just wiring them in parallel with the solar array buffered with a diode so the battery can't back feed to it.

Personally I'd use MPPT anyway - you might as well extract maximum power from your solar cells even if the load exceeds it. There's at least one chip you can get that does this (I forget who makes it though, sorry).

If you wire it so the solar cells feed the battery via MPPT and the battery feeds the motor, the whole thing should balance out such that the power from the solar cells is used first and any excess comes from the battery. The MPPT will raise the output voltage until all available power is being delivered, and as long as that voltage is greater than vBat, the battery will charge or at least not discharge. As the motor load exceeds the solar cell output capacity, the voltage will drop to the point where the battery starts to support the output.

The output of the panels depends on the intensity of light falling on them, cloud cover, angle to the sun etc. The voltage of the battery will be slightly higher when charging, all you need is the diode, you don't need that if the sun is bright enough... Is not dawn, dusk, night or pissing down...dark cloud, snow etc. The power will be used from the panel first assuming the open circuit panel voltage is higher than the batt and it will be.