Biofuels, Electric Cars & Solar
by
eas
07/12/2008, 1:28 PM #
There are many arguments against leaning too strongly on biofuels, including the fact that large scale agriculture is dependent on fossil fuel derived fertilizers, but there are even bigger issues.
Foremost is the question of efficiency. Photosynthesis & plant growth isn't that efficient. Sugarcane is one of the best options for converting sunlight into biomass, but even in that case, just 2% of energy from sunlight is captured in biomass. Commercial photovoltaics already capture 10%, and there is good reason to believe they'll continue to improve. Then you have to consider the inefficiency of converting that biomass to liquid fuel, which is also considerable, and then the overall inefficiency of internal combustion engines. If you look end-to-end, existing commercial solar panels, high voltage transmission lines, battery technology and electric motors are much more efficient than any biofuel scenario.
The inefficiency of biofuels has other implications as well. It will require a lot of land, which is at odds with both food production and habitat preservation. Cultivation depletes and erodes topsoil, which is already a declining resource. It can be rejuvinated by returning biomass to the soil, but then that biomass is not available for fuel, which means even more land is needed.
Even more worrying is the demand on supplies of fresh water. Much of the great plains are drawing water from wells that was deposited over a million years ago. That is not sustainable by any means.
Algae growing in salt water would mitigate this last issue, but it's totally unproven how that would work at any significant scale.
Brendan raised the concern that solar panels take a lot of energy to produce. The truth is that modern commercial solar panels will return the energy it took to manufacture them in less than a year in a sunny climate, and in less than two years in some place not typically considered sunny, like Seattle. Those numbers will only get better as panel energy capture efficiency increaces, and as manufacturing efficiency improves (particularly thin film cells that use much fewer raw materials).
Similarly, Brendan raised concerns about electrical vehicles being charged using power from dirty sources. That's worth worrying about, but the fact is that renewable forms of electricity are becoming increacingly economical. Wind is already competing on price, and solar is increacingly competitive.
The big hurdle for electric vehicles is less efficincy and more energy density. Even the best rechargable batteries deliver significantly less range than diesel, gasoline, or even ethanol. They do deliver enough range now that it is imaginable that an overnight charge would be enough for most of the commuter miles people drive (especially now that gas prices are already provoking people to find shorter commutes).
For longer trips, we may still need liquid fuels and those fuels may come from biological sources. We'll also need liquid fuels for aircraft, and trucks, though I hope we'll find a way to put more freight back on trains.
People also raise the added complexity of the powertrain of hybrid vehicles. I think that may be exagerated. Yes, there is another system to coordinate, but toyota's CV transmission for hybrids is in many ways mechanically simpler than other gear boxes. Also, if plugin hybrids become common, where batteries provide the power to get around town, and a gas engine helps keep them topped up on longer trips, I think the gas engines will get simpler, because they won't need things like variable valve trains to maintain power, efficiency, and lowered emissions over a wide range of RPMs, they can be designed to run at a single speed, and they can be smaller too.
