Published at The Energy Collective, Nov. 25, 2013
Renewable energy sources and natural gas should be considered as complements and not rivals. A hybrid gas-electric clean energy provides a workable engineering solution while 100% Renewables models based heavily on wind, solar and efficiency fall short of the meeting the functional needs of a modern technology intensive society.
Natural gas and renewables are already functional partners on the grid. Because wind and solar are intermittent sources of electricity, some form of backup power is required to fill the down times. By and large this backup power has been provided by natural gas because gas is the most flexible in its deployment. Gas turbines can be turned on and off quickly to meet fluctuating power demands. Large boiler based systems such as coal and nuclear are not so flexible in their operations, they can take hours to turn up and efficiency is lost. Big boilers work best when they are operating consistently which makes it more challenging to integrate with the intermittent wind and solar power sources.
Secondly, natural gas is primarily methane and methane is itself renewable. Methane can be manufactured in vast quantities and is indistinguishable from fossil sources. Renewable methane can be made from biomass, garbage, sewage, farm waste and is given a variety of names; biomethane, renewable natural gas, substitute natural gas, biogas and others. Many of the best resources for biomethane are waste products today and are treated as liabilities but could be converted into assets. Biomethane can be produced in greater quantities than other biofuels such as ethanol or biodiesel.
Third, power-to-gas offers the potential to convert excess electricity into methane and store it in the pipeline infrastructure. Electrolysis uses electricity to separate water (H2O) molecules into hydrogen and oxygen. This hydrogen can be used directly for a variety of industrial purposes and powering fuel cells, but can also be used in the manufacture of biomethane which is CH4. In Germany experiments are being run to determine how much methane can be injected directly into the natural gas pipelines. While power-to-gas is not being implemented in commercial scales today, the technology is all completely proven. As solar and wind deployments ramp up the need for storage becomes more pronounced and gas production has advantages over batteries because gas can be stored indefinitely while batteries lose their power over time. Gas can also be easily transported in pipelines and tankers and converted into other products.
The natural gas infrastructure enables the use of fuel cells to produce emissions free electricity. Proton Exchange Membrane (PEM) fuel cells use pure hydrogen as fuel and are being developed for vehicles. Solid Oxide fuel cells can use methane as fuel but are best for stationary power production. There is great promise in hydrogen fuel cell vehicles but there is a fundamental challenge in distributing and storing pure hydrogen. Hydrogen is tiny and extremely volatile, it both leaks out of conventional steel pipes and reacts with steel making it brittle. Hydrogen distribution requires the use of stainless steel (or other specialty material) pipes with high test welds at all joints and special valves. This is a very expensive and complex engineering proposition compared to the existing natural gas infrastructure that uses common galvanized steel pipe. The practical and economic answer is to connect hydrogen fueling stations to natural gas distribution and steam reform and pressurize the hydrogen on site where it is sold. Industry generally produces hydrogen from natural gas as it is far cheaper than producing hydrogen from electrolysis. In this way natural gas enables the widespread use of hydrogen and fuel cells.
As the cleanest burning of all hydrocarbons methane is naturally a friend to the environment when used to replace coal and petroleum. Renewable electricity solutions can replace many uses of coal for power but are challenged at replacing petroleum for vehicles, big ships and high horsepower machines such as mining equipment, freight trains and airplanes. Natural gas is a direct replacement for diesel, gasoline and bunker fuel and can be converted into high quality liquid fuels such as jet fuel. Dirty fuels such as coal and diesel are loaded with particulates, heavy metals, sulfur and other contaminants that cause toxic pollution and kill hundreds of thousands of people every year globally. Methane is clean enough to burn indoors and cook food on, its widespread adoption to replace dirty fossil fuels would create significant air quality improvements and save many lives. Methane also has the lowest carbon content of any hydrocarbon so when used to replace coal and petroleum it reduces carbon pollution.
Methane is the most abundant and versatile of all hydrocarbons. It can be used to produce heat, power and transportation. Methane can be converted into ultra clean diesel and jet fuel through Fischer-Tropsch processes. Methane is also a critical raw material for the production of plastics, chemicals and fertilizers. Recycling plastics back into methane can help facilitate zero-waste goals. Natural gas resources are broad and deep and found all over the world. The shale gas revolution has already overturned global energy markets and there appears to be vast resources to be tapped. If the methane hydrate resources in the ocean can be brought to market that would further tilt the energy landscape towards natural gas as those reserves are massive and dwarf all coal and petroleum known to exist.
Natural gas has an excellent safety record, though it is often thought of as very dangerous. LNG in transport is very safe. LNG has been shipped in huge quantities by ship for decades and there has never been a disaster (knock on wood). When used for a vehicle fuel it has distinct safety advantages over gasoline, diesel and propane because methane is the only one that is lighter than air and dissipates quickly if released while the others pool on the ground awaiting ignition. Methane has a very narrow range for ignition making harder to combust accidently. Also the tanks used for CNG and LNG are very robust by nature, whereas liquid fuels are often carried in thin walled tanks.
Methane combustion does produce carbon emissions but far fewer than other fossil fuels, and methane is itself a greenhouse gas, so its use does need to optimized to mitigate any global warming effects. Capturing leaking methane is important, and has the benefit of increasing fuel supplies. Natural gas is easily deployed as fuel for power production and can be deployed nearer to where the electricity is used minimizing line losses and improving efficiency. Combined heat and power is part of this efficiency playbook that natural gas enables.
In conclusion methane, aka natural gas, is a clean, high performance and versatile fuel that complements the roll out of renewable electricity technologies. In practice, intermittent power sources such as wind and solar require stored fuel to be available at all times to keep the grid online. Electrical sources are also not proven to power high horsepower vehicles while gas can. Natural gas is the most abundant, clean and safe of all hydrocarbons and fulfills a critical role in our energy infrastructure. Renewables advocates should recognize this fundamental harmony between these energy sources.