Solar and wind have some great qualities as energy sources: they're low carbon, non-fossil, and they're renewable.
But they also have one huge drawback: they are intermittent, which means they're not nearly as reliable as the coal-fired power plant down the street. At night, or on a calm day, you still need backup power. Which means you can't just turn off that coal-fired plant when you put up a wind turbine. Which sort of defeats the purpose.
In other words, the big problem with renewables is energy storage. If we could capture and store the wind for windless days, or capture and store the sun for use during the night, we could turn off the coal fired power plant and everything would be peachy. So what we need is an efficient way to store intermittent renewable energy, and an equally efficient way to get that energy back out of storage again.
During the past few months, two big breakthroughs may be pointing the way to a new, efficient renewable energy cycle based on methane (CH4). We may now have both halves of an efficient methane storage/extract cycle on the horizon. It may now be possible to build an efficient and totally renewable energy system that supplies nearly all our energy needs: for electricity, for transportation, and for direct heating.
The first breakthrough was diaried here a couple of months ago. It turns out that if you take a certain species of methanogenic archaea -- the same microbes in your gut that cause you to pass gas -- and you coat them on an electrode and supply them with water, CO2, and one volt of electricity, they produce methane like gangbusters. In fact, initial lab reports show that the process, called electromethanogenesis, is 80% efficient -- and that's before we've even tested all of the dozen or two methanogens out there, and before we've done any selective breeding with them. It's not unlikely that when more experimentation is done, even higher efficiencies might be achieved.
In an earlier reclisted diary, a new fuel reformation and fuel cell generation process was reported that generates electricity from natural gas (methane) with zero carbon emissions. The process does produce CO2, but in a pure stream that is easy to sequester. But why sequester that CO2 when you can use it directly?
Put these two processes together, and a totally renewable cycle is apparent. Renewable but intermittent electricity from solar and wind is used (either on-site or remotely) to run electromethanogenic biocells. These cells use water, carbon dioxide, and renewable electricity to produce methane. Because the electricity is intermittent, methane production is also intermittent. But that's okay, because methane is easy to capture and store.
Once a methane storage system is in place, the reformation and fuel cell process can draw a continuous supply of methane from storage to create a continuous supply of electricity. Since the electricity is produced continuously from this half of the cycle, we can actually turn off that coal fired power plant! It's no longer needed.
The reformation and fuel cell process produces as output pure water and pure CO2, which are piped directly back to the methanogenic biocells for recycling back into methane.
If the methane production is large enough, some of the methane can be drawn off for direct heating of homes, or for transportation fuel. Since that methane will not be recycled into electricity, methane production for those purposes will require removing CO2 from the air, which is just what we want to do.
What needs to be done?
The fuel cell half of this cycle has already been demonstrated at industrial scales, up to 250 kilowatts (your house probably draws between 1 and 2 kilowatts), and scaling up is not inherently difficult. In fact, it is scaling down that would be more difficult, since part of this process requires economies of scale that a single-family sized production plant could not achieve. So no, this doesn't mean everybody can create their own power: we're still going to need power plants (though they may not be as big).
Given that renewable energy is intermittent, and that this process isn't 100% efficient, it would probably take something like 1 MW of installed (rated) renewable source to feed a 250 KW fuel cell plant. That's roughly one large wind turbine.
The bottleneck at this point is the methanogenic biocell, which has only been demonstrated in the lab. However, methanogens need no light or oxygen to grow, and we already have some industrial processes that use similar microbes on large scales -- think beer brewing, for example, which uses yeast.
What about hydrogen?
The methane cycle proposed here would replace the much talked-about, never implemented hydrogen cycle that has been (up to now) the touchstone for a renewable energy economy. Methane has a number of significant advantages over hydrogen:
- Hydrogen is highly reactive and makes many metals brittle, which means you need special materials for storage and transportation. Methane is the principal component of natural gas, so existing transportation and storage infrastructure can be used without modification.
- Methane is a lot denser than hydrogen, which means you can store more energy in a smaller tank. That makes it easier to use as a transportation fuel. There are thousands of methane vehicles already on the roads; the handful of hydrogen vehicles are still experimental.
- Even after decades of research, hydrogen electrolysis still isn't as efficient (50%-70%) as electromethanogenesis has demonstrated in its first lab experiment (80%).
Links
Fuel Cell & natural gas reformation:
http://www.sciencedirect.com/...
http://www.sciencedaily.com/...
Electromethanogenesis:
http://pubs.acs.org/...
http://www.sciencedaily.com/...