I am working on an Arduino project that will need to be solar powered. The project consists of a sonar sensor, mp3 player shield, and a speaker. When a person is detected in front of the sonar sensor, the speaker should play an mp3 file. While the project is in idle (nothing detected), I think that it will draw around 135 mA. When the speaker is triggered, the project could draw up to 500 mA.
I need some guidance on how to solar power the project. What electronics should I use? What size battery and solar panel would be necessary to allow the project to run most of the time?
Your questions can 't be answered without quite a bit more information.
What do you mean by “run most of the time” (h/day)?
What are the minimum and maximum current draws? Measure them.
How often and for how long will the circuit draw the maximum current?
How often do you expect full sun on the solar panel, and for how many hours/day?
How long should the circuit run in the absence of sunlight?
I suggest to learn about sleep modes. It is possible to reduce power requirements to nearly zero for a substantial fraction of the time. See for example this project: http://www.gammon.com.au/forum/?id=12821