Fractional reserve banking isn't about lending out "excess cash".
It allows a bank to lend a multiple of its cash reserves, previously circa maintaing a 10% reserve of the total lending.
Money was created out of nothing using the relevant reserve formula.
The system trades on the fact that depositors are unlikely to require all their monies at one time.
You are misunderstanding the point and the problem that banks are facing. Let's say Bank A takes deposits of €1000 and is required to hold 10% reserves. It can then lend out €900, which effectively increases the money supply from €1000 to €1900. That's the magic/fraud/fault of fractional reserve banking.
Now let's say that Bank A gets into trouble and it's reserves fall to €50 and it is recapitalised back to €100. This is effectively what has happened with Irish banks. That bank can now not lend out more money unless it takes in more deposits, i.e. cash in excess of its reserve requirements. If the bank manages to attract deposits worth €100, it can make another loan for €90. The problem is that Irish banks cannot even convince Irish people to deposit their money with them. Therefore it is not possible to expand credit without either (a) increasing deposits or (b) reducing reserve requirements.