This would be straightforward in a hydrogen economy by diverting some hydrogen production from fuel to feedstock use. For example, in 2002, Iceland produced 2,000 tons of hydrogen gas by electrolysis, using excess electricity production from its hydroelectric plants, primarily for the production of ammonia for fertilizer. The Vemork hydroelectric plant in Norway used its surplus electricity output to generate renewable nitric acid from 1911 to 1971, requiring 15 MWh/Ton of nitric acid. The same reaction is carried out by lightning, providing a natural source for converting atmospheric nitrogen to soluble nitrates. In practice, natural gas will remain the major source of hydrogen for ammonia production as long as it is the cheapest.