Try hotels bell desk-my trick

Since 911, many airports no longer have airport lockers any more. Some have storage service but not sure if San Francisco is one of them.

Here is a little trick that I use from time to time and probably no one else will tell you in travel books. Depending on your situation, I don't know it will make life much easier for you.
-Find a major chain hotel near SFO (Hilton, Marriott, Hyatt) that has a free shuttle service from the airport. It must be a hotel away from the airport terminals. Some airport hotels may be next to the terminals and those won't work.
-When you get into the airport, take the free hotel shuttle to the hotel of your choice.
-Take your luggage to the bell desk and have them store it for you till your departure. They will give you claim checks for your luggage pieces.
-When you pick up your luggage, pay them a good tip.

I believe SFO uses the same shuttle service to all airport hotels. Good luck.