7. Measure the voltage output of the fuel cell right at the fuel cell output.
8. Measure the voltage drop across the resistor.
9. Compute the current output.
10. Compute the power output.
11. Divide the power output by the power input, this gives an efficiency rating.
12. Remove or block some of the solar panels and increase the load until the most efficient operation is achieved. The efficiency of the electrolyser is around 80%, and the efficiency of the fuel cell is around 50%, so an overall system efficiency of 40% can be achieved by optimizing the input and output power.
Let us know what power levels and effeciency you can obtain, we'd like to see what the best effeciency is.