Now, don't get me wrong: I'm not rubbishing penal substitution. But there are other options that have been advocated by Reformed thinkers of the past.
In the chapter on the nature of the atonement [in the book saving Calvinism] I argue that it is a mistake to think that penal substitution is the only option on the doctrine of atonement.
I'm sometimes asked about my productivity, which I find a bit embarrassing to be honest. I don't really have a particularly interesting answer to this question.