Micro-scale solar thermal power
No matter WHAT you use to generate your electricity, you are still limited by your collector area, your latitude, and the fact that Earth rotates with an approximate 24-hour period.

Assuming you're in North America, your fundamental limits are:


\$1.3 kW/m^2\$ at high noon on a severe clear day in Tucson AZ.
\$6 \text{ to } 8 kWh/m^2/\text{day}\$.


Any competent solar energy text will give you these numbers.  Also note that these are DC-to-light numbers: the energy is spread out across the electromagnetic spectrum, not concentrated in nicely usable wavelengths.

Applying those numbers to your proposed collector, you have:

$$300 mm \text{ diameter} = 150 mm \text{ radius}\\
\pi \cdot 0.15m \cdot 0.15m = 0.070 m^2$$

That means your limits are \$92 W\$ at high noon on a severe clear day in Tucson, and 424 to 565 Watt-hours/day.

Multiply that by your conversion efficiency, and Bob's your uncle.

I haven't kept up with photovoltaic conversion efficiencies.  Last I heard, 16% was STILL about all you could get with inexpensive materials and processing.  I keep hearing someone is working on 30% efficient cells, and will have product Real Soon Now...

Here's an article talking about a solar-heated Stirling engine system.  They cite 31% efficiency, compared with 16% for photovoltaics.  They're putting some of their power into an az-el sun tracking system, and they're in Arizona.