Fact is, big and local governments might subsidize installations, but they've been running low on cash for these initiatives. The idea was better than reality.
Generating power from a free source is a nice idea, would even work if the polysilicates weren' t so expensive. In the end, its agreed by the people that know what they are talking about and have experience with solar panels, the current price for them never offsets the total cost.
As for voltage, that would depend on how large the panel is. Most solar panels are actually made up of mini panels that are linked together in series to make a higher voltage unit.
You would have to check the specifications for the panel itself. That and with newer technologies coming out. Currently most of us use the thin film type, but there are new inventions not on the market yet that are suppose to be able to give more voltage out for the same amount of sun light. But these are still being experiemented with by small developmental companies.