We purchased some 12 Volt DC compact fluorescent bulbs from Backwoods Solar Electric for use in our PV solar power system. One nice thing about using 12 Volt loads is that you don't need to use an inverter. This means that there is less power wasted in the conversion from 12 Volts DC to 120 Volts AC. 12 Volts is also a bit safer to work with, since it isn't high enough of a voltage to shock you. Do be aware, though, that solar power systems usually have high amperage available, which means it is easy to burn yourself or start fires when wires go up in flames. The low voltage can be misleading. That reminds me, please read this site's terms of use. We purchased the 23w model:

The lights screw in to a standard bulb base. We found some plastic bases for $1.40 US at our local big box home improvement store:

The tip is positive on our bulbs. Use heavy gauge wire to connect the bulbs in parallel:

We insulated the connections and bolted them up without a base. The bulbs take up to 20 Amps combined to turn on, but this doesn't seem to be a problem with this system. More bulbs might be a problem, though. We now have an excellent source of backup light in our basement as part of our solar power system:

These lights also work well if I'm in and out of the basement during the day and it is sunny out. The PV solar system power controller from this article has an on/off switch for the load. The bulbs are kind of expensive, though, so turning them off and on repeatedly during the day isn't something I'd advise. When the sun is out, leaving the bulbs on all day shouldn't drain the battery at all.