A role for renewables toward sustainable energy systems

The use of fossil fuels causes not only the exhaustion of resources, but also global warming. Before we exhaust all fossil fuels or fall into catastrophic climate change, we need to develop new energy systems that are fossil fuel-free and fully renewable. In the study, the author developed a global land use and energy model that includes new technological concepts such as intermittent renewables (photovoltaic and wind) with small capacity storage and with large capacity storage. Using the model, the author conducted simulations and obtained the following results. In the sustainable scenario in 2060 (when we achieve zero fossil use) the dominant resource of primary energy supply will be photovoltaic directly connected with electrolysis, at the global level of 445 EJ/year. The second and the third largest resources are biomass and photovoltaic with large capacity storage at 332 EJ/year and 116 EJ/year respectively. At that time, the dominant energy resource for power generation connected with the electricity grid will be photovoltaic with large capacity storage at 116 EJ/year in the world. Globally, BGCC (biomass gasifier combined cycle), hydropower, and photovoltaic with small capacity storage are greater than 40 EJ/year each. However, the energy system costs in the sustainable energy scenario will be at 19 trillion US$/year, almost three times as expensive as the costs in the base case (without constraints of fossil fuels or CO2 emissions).