The competition is open to manufacturers, research/academic groups and inventors to design and fly a 100+ seater passenger aircraft powered by 100% renewable energy. The plane must complete a return trip from London to New York; each leg of the trip in under 10 hours and must finish the return leg within 24 hours of starting out on the round trip.
The way it reads, 100% renewable energy, you could take a current Airbus/Boeing product and fill it with fuel made from biomass, under the rules in place at the moment CO2 produced from biomass is considered renewable energy, the reason some power stations have converted from coal to biomass, the CO2 produced doesn't count towards the country contribution.