Solar-hydrogen electricity generation and global CO 2 emission reduction

Abstract

The relative costs and CO 2 emission reduction benefits of advanced centralized fossil fuel electricity generation, hybrid photovoltaic-fossil fuel electricity generation, and total solar electricity generation with hydrogen storage are compared. Component costs appropriate to the year 2000–2010 time frame are assumed throughout. For low insolation conditions (160 W m mean annual solar radiation), photovoltaic electricity could cost 5–13 cents kWh −1 by year 2000–2010, while for high insolation conditions (260 W m −2) the cost could be 4–9 cents kWh −2. Advanced fossil fuel-based power generation should achieve efficiencies of 50% using coal and 55% using natural gas. Carbon dioxide emissions would be reduced by a factor of two to three compared to conventional coal-based electricity production in industralized countries. In a solar-fossil fuel hybrid, some electricity would be supplied from solar energy whenever the sun is shining and remaining demand satisfied by fossil fuels. This increases total capital costs but saves on fuel costs. For low insolation conditions, the cost of electricity increases by 0–2 cents kWh −1, while the cost of electricity decreases in many cases for high insolation conditions. Solar energy would provide 20% or 30% of electricity demand for the low and high insolation cases, respectively. In the solar-hydrogen energy system, some photovoltaic arrays would provide current electricity demand while others would be used to produce hydrogen electrolytically for storage and later use in fuel cells to generate electricity. Electricity costs from the solar-hydrogen system are 0.2–5.4 cents kWh −1 greater than from a natural gas power plant, and 1.0–4.5 cents kWh −1 greater than from coal plant for the cost and performance assumptions adopted here. The carbon tax required to make the solar-hydrogen system competitive with fossil fuels ranges from $70–660 tonne −1, depending on the cost and performance of system components and the future price of fossil fuels. Leakage of hydrogen from storage into the atmosphere, and the eventual transport of a portion of the leaked hydrogen to the stratosphere, would result in the formation of stratospheric water vapor. This could perturb stratospheric ozone amounts and contribute to global warming. Order-of-magnitude calculations indicate that, for a leakage rate of 0.5% y −1 of total hydrogen production — which might be characteristic of underground hydrogen storage — the global warming effect of solar-hydrogen electricity generation is on the order of 1% the impact of the hybrid system. Impacts on stratospheric ozone are likely to be minuscule.