Of course Energy-Efficiency and realization of mitigating all the unnecessarily consumed Megawatts, colloquially often named “Negawatts” is a must. Unfortunately focusing Energy-Efficiency only tends to lose sight of Carbon-Efficiency, which in turn would always imply Energy-Efficiency. If Carbon-Efficiency had been adopted earlier, economic energy storage would already have become a matter of attention. Particularly solid and heavy fuel power plants consume substantial amounts of chemical input energy under idling of power generation. Hydropower can bypass turbines, wind-power may turn blades out of wind, but carbonaceous solid or heavy fuels must be combusted continuously. Coal power-plant idling may vary between 20-60% generating CO2 without any use from let’s say an average of 40% fuel input. It may seem paradox but high rate renewable energy supporting grids tend to have the highest idling ratios of its back-up coal power-plants. So assumption of zero emission Renewable Energy may be problematic as long as they need back-up from fossil fuels.
Due to Renewables’ volatility a real Carbon reduction can only be assessed including idling of its back-up capacities causing extra costs on top. Only with appropriate storage solutions Renewables may ever fulfill Carbon-Efficiency expectations. Natural Gas [NG] engines or turbines back-up on demand might become a preferred design of choice for quick start-stop and output-fluctuation margins. In times of serious intends to exit from fossil fuels completely it’s hard to project Natural Gas power replace coal power-plants.
Astonishingly little is heard about Hydrogen Fuel Cell power generation which could double Carbon-Efficiency of existing Fossil power-plants. Burning carbonaceous fuels for power generation requires a 3-step transformation: Heat -> Pressure -> Motion for a Dynamo ≈ 35% electricity. Hydrogen Fuel Cell generation is a 1-step electro-chemical transformation achieving ≈ 65% electricity of Hydrogen Energy at zero Carbon emission. Therefore Carbon Efficiency of Hydrogen-Power depends on fuel and production process used for it. If produced by electrolysis from water the CO2 per MWh is 2.3 times the used electricity grid’s carbon-footprint. Hydrogen-Power off Steam Reformed Natural Gas [SMR] would emit 0.35 tonnes CO2 per MWh versus 0.5 tonnes CO2 from combustion Natural Gas-Power. Using Dry Thermo-Catalytic Dissociation [DTCD] for SMR off-gas treatment Hydrogen-Power from NG would get below 0.3 tonnes CO2 per MWh.
Over 100 years ago water-gas process splitting water over coal’s Carbon was established, releasing Hydrogen at 12.5% of transformation energy required by electrolysis. Each Carbon molecule holding 380kJchem can release two Hydrogen molecules carrying 280kJchem each adding 90kJth transformation energy. Replacing coal-power of 1.2 tonnes CO2 per MWh by water-gas Hydrogen-Power can reduce CO2 to 0.53 tonnes per MWhel close to NG-Power. To replace approximately 14PWhel Fossil-Power 550 million tonnes of Hydrogen would be required. Order of magnitude for recyclable Carbon of organic residues not useful for agricultural compost or material recycling is 2.2 Gt. Theoretically Carbon Recycling could unlock renewable water-gas Hydrogen-Power to outplace 100% of today’s Fossil-Power.
Last but not least incineration of waste or residues for energy stands at 5% the energy recovery rate of water-gas Hydrogen-Power potential from Recycled Carbon of the same feedstock. This hopefully explains our skepticism on how effective the Carbon Efficiency of today’s Waste to Energy is.