Is it reasonable, in panel data, to use past values of explanatory variables as instruments to deal with simultaneous causality? I am trying to examine the determinants of economic growth, essentially regressing a number of variables upon economic growth. I face a problem that there is likely simultaneous causality between many of my explanatory variables and the dependent variable. To deal with it I am using instrumental variables. I was wondering would it be reasonable to use the past values of my explanatory variables as instruments for their current values? 

Thank you so much for the answers.
I suggest looking into System GMM. It is a panel regression method that uses past values as instruments and is exactly what you're looking for, I think. It has a few restrictions that much be met, the most important requires you to have more cross-sections than time periods. Without seeing your model and other details that is all I can provide for help. I hope this works for you.