Efficiency of a Hybrid System

if the input is 17.82 V and 0.57 A, and the output we take is 2 V and 1A, how do we calculate the efficiency?

input power = 17.82 X 0.57 = 10.16 Watts

output power = 2 X 1 = 2 Watts

efficiency just less than 20%

On your question about DC-DC converters, the source power (DC input) has to be converted to AC where it can be transformed to an appropriate level and then converted back to DC at the desired level.

The product of Volts and Amps yields Watts. Efficiency is always Output divided by Input. Note that you can never get more out than you put in. So, it is impossible for the output to exceed the input. Continuous output current requires continuous input power within the specifications. The solar panel is most likely old technology which is subject to rapid reduction of power output if shaded or under cloudy conditions.

A human in good health can generate about 40 Watts of continuous power. So, at 10 Watts you be going anywhere very fast.