Golf caddies could soon be at the vanguard of the clean-energy movement. Engineering firm Soluções Racionais de Energia (SRE) of Torres Vedra, Portugal, has built a fuel-cell-powered golf bag carrier, which is being tested at tournaments in Europe. The 100-watt stack of fuel cells measures just 10 by 8 by 6.5 centimeters and has powered the carrier during rounds of golf lasting up to eight hours. An onboard canister supplies hydrogen fuel, which is stripped of its electrons inside the fuel cell to make electricity for the motor. The only significant emissions are droplets of water. When trials finish by the end of this year, SRE intends to ask an independent auditing firm to certify that the golf bag carrier meets international safety and quality standards so that it can go into production.