Connecting Dots and Change for the Better
by: Paul Kando
If you and I produce more solar electricity on our roofs than we can use, our electric utility credits us for that excess, but only up to the amount we purchased from them. At the end of the year they simply take the power we generated over that limit without credit or compensation. So, what if, instead of feeding power into the electric power grid we collectively used our excess power to make methane out of carbon dioxide and water, releasing oxygen into the atmosphere - kind of like green plants are doing? We could store the methane for later use to generate electricity, heat houses, or fuel vehicles. We could make other fuels from it, for distribution through the existing gas station network. We could use our excess electric power to turn CO2 emitted by such notoriously carbon-polluting processes as concrete manufacturing into a clean energy source.
A pipedream? - Well, a few days ago North America's first floating offshore deepwater wind turbine was launched off Castine, the first of many to tap a vast, multi-gigawatt renewable energy resource along the Atlantic seaboard, enough to cover over a third of US energy needs. This, too, has been a dream until the persistence of a collaborative effort lead by the University of Maine turned it into reality.
But wind power is intermittent and, unlike solar, not well matched to the load pattern of the power grid into which it will be integrated. Most wind power is produced at night when demand is low. Powerful storms can generate huge amounts for days and days, followed by periods of calm. To store excess wind power for later use would require huge banks of advanced and affordable batteries we don't currently have - at least not at anywhere near the scale required. Pumped storage - pumping water back over a hydro-dam when excess power is available - works great as long as there is enough water available to pump and sufficient capacity above the dam exists to hold it. In many places these conditions simply don't exist.
Enter "Volt Gas Volt" (VGV), a project recently presented to the European Parliament as an alternative to both petroleum and first generation biofuels. The idea is to use free "excess" energy - nighttime wind, off-peak nuclear electricity - to power two simple processes heretofore considered too energy intensive to be commercially viable: 1. Electrolyze water to produce hydrogen and oxygen, and 2. Using the Sabatier reaction, discovered by French chemist Paul Sabatier a century ago, to combine hydrogen with carbon dioxide (at elevated temperatures and pressures, in the presence of a catalyst), to produce methane and water. The water is recycled. The oxygen can be captured or released. The methane (a natural gas we explored in some detail last week) is stored indefinitely, and retrieved as needed - to produce electricity, heat, or motive power. The process can displace fracking for natural gas, and even support the orderly phase-out of nuclear power plants, the assembly was told.
Methane (CH4), and two derivatives — methanol and dimethyl ether — used as distributed "storage" of renewable energy, can minimize the problem of wind and solar intermittency and enable the transmission of energy through gas pipelines and liquid fuel distribution systems instead of only wires. They can alleviate our dependency on fossil fuels without the need to electrify vehicles or converting to fuels, like hydrogen, which require a new distribution infrastructure.
With an oxygen atom inserted between methane's carbon and one of its hydrogens, methanol (methyl or wood alcohol) is essentially oxidized methane. Burned in a combustion engine, methanol releases carbon dioxide and water. It can be used in gasoline engines without major modification and distributed, like ethanol is, through the existing gas station network. It has a high octane rating but, gallon for gallon, packs less energy than gasoline. It is also hygroscopic - attracts water from the air - so methanol containers must be kept tightly covered.
Dimethyl ether (DME), already in use for heating and power generation, is another promising fuel. It is produced from hydrocarbons (such as methane) in a two-step process: methanol synthesis and methanol dehydration. The same process will work using organic waste or biomass as raw material. DME, like diesel fuel, self-ignites under high pressure and temperature and has a high cetane number. With only minor modifications any diesel engine can burn DME. (A 30% DME / 70% LPG blend will also work in gasoline engines.) DME's carbon chain is short and simple, so its combustion emissions - particulate, NOx, and carbon monoxide - are low. Unlike diesel oil, DME is sulfur-free and meets even the most stringent fuel-emission standards.
This summer, after a successful three year pilot-scale evaluation, a commercial size, 6 MW carbon dioxide to methane plant goes into production in Stuttgart, Germany. Built by automaker Audi, it will run on excess wind and solar power. Since the CO2 comes from captured exhaust gases, the methane produced is carbon-neutral. In line with Germany's national commitment to become a 100% renewable energy based economy by 2050, Audi considers itself responsible for not only the vehicles it produces but also for how they are fueled.
How refreshingly grownup! Can we, with our floating wind towers, become producers of non-fossil based fuels? Turn carbon-pollution from concrete manufacturing into an environment-friendly energy source? Or is that too much to ask?