Buy the Travel Adapter before you go to Spain
all countries in the EU, including Spain, use 220V...
get the travel adapter kit before you go to Spain...the online apple store has it...
make sure your MBP power supply can handle the 220V...
read the reviews - this one in particular:
Explanation: Adapter vs Converter
Written by DA
January 22, 2006
Some Apple power adapters are rated 110-240V which means that they will work around the world. The only limitation is the physical connection on the adapter. This is why Apple offers the World Travel Adapter Kit. With this kit it is possible to physically plug into virtually any wall socket in the world.
There are several people reporting here that they have fried their Apple device when "using" the WTA kit. This probably means that they had a power adapter rated for 110v ONLY and plugged it into a 240v source/socket. I bet they also fried the power adapter.
So, be careful. Read the spec on the side of your power adapter. If it says 110-240v, and you have been successfully using the adapter in the U.S., then you shoud be able to use the adapter elsewhere around the world. Use the Apple World Travel Adapter Kit to make the plug physically compatible with the country you are visiting.
Have fun in Spain!

I spent three weeks in Spain and Portugal this past summer - where will you be studying?