DC boost for low voltage?
You're going to struggle with only 0.5 V. Look for a different solar cell or array that can supply at least 1.5 V. There are a few existing solutions aimed at running off a single 1.5 V cell. Have a look at the LTC3400 from Linear Technology.

Note that it's hard to even turn on a transistor with only 0.5 V, so even if you could get the converter running correctly, it would be pretty challenging to bootstrap itself into starting at such a low voltage.