When fresh water rivers flow into the sea the concentration difference leads to a change in entropy. US researchers have developed a battery that generates power from that entropy difference.Yi Cui's team at Stanford University, California, extract energy with 74 per cent efficiency using manganese dioxide nanorods and silver electrodes1. 'What we have really demonstrated that this idea can work,' says Cui.Cui's team estimate that if the technology was used on all world's rivers this renewable energy technology would hypothetically generate 2 TW, or approximately 13 per cent of current global consumption.Entropy based power generation has been done before but is most reliably done today...