Hi Tyler,
main thing is to put an inline fuse in the positive wire, that will stop any potential problem. 18 watt will give you light, just depends on if you are wanting to work at night using the light and for how long you want the light on. Next problem is the solar won't keep the battery up if you want the light on for any time. I have a lot of 12 volt stuff going on in my house, 5 smoke detectors, 3 CO2 detectors, a house number light out the front, a clock in the kitchen, high water alarm downstairs and a 12 volt submersible pump which only activate if we loose power and it is raining. I think the solar panel is 150 watt which could keep the battery charged during summer but as soon as winter hits I have a trickle charger on for 4 hours a day. I also have volt meters in the family room so I can see exactly what is going on with the batteries at a glance. I also have 2 newish batteries with combined 110 ah capacity
So in answer to your question it all depends on your usage and you are most likely going to need a 240v trickle charger to keep the battery up so it might end up being not worth it
