Emissions: If domestic electricity is generated from natural gas in a large unit, the associated emissions of carbon dioxide are just over 400 g/kWh. When hydrogen is produced by reforming natural gas, the emissions are around 285 g/kWh. If that hydrogen is passed through a fuel cell to produce electricity, the emissions per unit of electricity generated roughly double, as the efficiency of a fuel cell is at best about 50%. In other words, domestic electricity directly from a combined cycle gas turbine is more effective in keeping emissions down than a fuel cell running on hydrogen derived from gas. Oil generates more carbon dioxide emissions than gas: around 750g/kWh, which explains the focus on lowering transport emissions. If hydrogen fuel cells replace oil in vehicles, and the hydrogen is produced from renewable energy via electrolysis, around 226 g/kWh is saved. Yet if that renewable energy had been allowed to displace gas in an electricity network, 366 g/kWh of carbon dioxide is saved. Similar accounts can be produced for other pollutants associated with burning fossil fuel for electricity or transport
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