From
http://www.peercointalk.org/index.php?PHPSESSID=fgikh52l7qanv4o67q7t8lo7m4&topic=634.msg7397;boardseen#newCurrent Energy Efficiency Statistics:
As of November 12, 2013
Market Cap: (Bitinfocharts)
Bitcoin 11,984,125 BTC
Peercoin 37,439 BTC
Hash Rate:
Bitcoin 5.1Q
Peercoin 12.25T
Value secured by a Giga Hash
Bitcoin: 11,984,125 / 5,100,000 = 2.35 bitcoins secured per GH
Peercoin: 37,439 / 12,250 = 3.06 bitcoins worth of Peercoins secured per GH
Calculation:
(3.06 - 2.35) / 2.35 = .302 (or 30.2%)
Conclusion:
Peercoin is currently 30.2% more energy efficient than Bitcoin. I would think that this energy efficiency should increase over time as well.