# What would happen if you connect a solar panel to a buck-boost converter?

What would happen if you connect a solar panel with the following characteristics:

Max Power:3.5W

Voltage: 6V

Open Voltage: 7.2V

To a buck-boost converter that convert an input voltage in the range 1V-6V to a voltage of 5V? Who would "win" the fight to set the voltage? The buck-boost converter can work with any input voltage and the solar panel can work at different output voltage. I can't figure a way to calculate the input impedance of the buck-boost converter.

Bellow is the representative circuit diagram for a solar panel on the left and the buck-boost converter on the right with the converter switch represented with the letter S.

• I think I am not fully understanding this. Do you connect the solar panel to the input of the buck/boost? – jwsc Dec 8 '15 at 7:28
• yes, the solar panel is connected directly to the converter – Pat Dec 8 '15 at 9:17
• It's a good question but incomplete. A BB converter is usually controlled and NOT operated open-loop. Usually you set Vout and Vin looks after itself. In this case the nature of the load is crucial. If the 5v is a battery or includes a large capacitor this will affect the ability of the BB to alter Vout substantially in one cycle so will affect how it behaves. In this scenario if the output is a battery a common solution is to maximise energy transfer and the BB is run in MPPT (maximum power point tracking) mode. A simple pseudo MPPT method that works quite well is to choose Vpanel at some ... – Russell McMahon Dec 8 '15 at 10:47
• @RussellMcMahon My goal is effectively to put a battery as the load (R on the diagram). I know a MPPT would be the best solution but I'm wondering what would happen if I made it cheap and simple. – Pat Dec 8 '15 at 11:35
• ... semi optimum value and control the BB so Vin is maintained at this voltage. Typically Voptimum ~= 80% x Voc so here = 7.2 x 80% = 5.76V = 5.8V. So BB is set to monitor Vin so that it remains at about 5.8V . This is close enough to optimum load for the panel in such cases. – Russell McMahon Dec 8 '15 at 11:37