renewable energy systems extracting energy from natural water flow or wind . the energy systems are configurations of long - stroke open - channel reciprocating engines employing one or two flow engaging elements such as drogue chutes for water flow or airfoils for wind applications tethered to a power drum and useful to generate electricity or to pump water as from wells . a wind energy system using two buoyant airfoils emblazoned with advertising messages is suitable for urban deployment generating electric power and also supporting an advertising revenue stream .