I have just come across the 2011 edition of the Pew Charitable Trusts report, "Who's Winning the Clean Energy Race?", ranking the total investment on clean energy. In absolute terms, the US have re-taken the lead , surpassing China (although it might prove a temporary victory, as many US initiatives expired in 2011).

According to Tom Konrad's analysis, Italy is the clear winner in that race, as long as the investment is measured relatively to a country's economy:

For skeptics who worry that Italy is wasting money on clean energy at a time it can least afford to, it's important to note that solar, which accounts for virtually all Italian investments in Clean Energy, has reached grid parity in Italy.  In other words, Italian solar investments are profitable investments. 

Konrad points out how the investments in clean energy are helping the Italian economy in the long term:

Italian solar power also reduces future imports of natural gas to produce electricity, improving the long term balance of trade in a country with too much debt.