There was much furore recently surrounding the story ‘Joule Biotech comes out of stealth with sun-powered biofuel’.
The premise is that the technology can take solar energy and use it to convert carbon dioxide directly into fuel. A one stop-shop to soak up carbon dioxide and produce a biofuel.
Having dug into it a little, the conclusion I came to is that its not as radical as it sounds. Its basically directed photosynthesis : same principle as oil from algae, or biofuels. The overall efficiencies are likely to be 10 times lower than solar PV processes, but, it in terms of where biofuels are heading, its on the right track…..
The press release included the following:“The SolarConverter captures the sun and is fed carbon dioxide and combine inside where a solution of brackish water and nutrients exist with photosynthetic organisms—secreting the SolarFuel,” Joule’s CEO Bill Sims said, describing the end-product as a hydrocarbon-based fuel, not a biofuel.
The input energy into this system is incident solar radiation. This varies from place to place but in North America, a reasonable average year round figure would be 200 Watts per m2. That’s what you have to work with. That is what is referred to as Primary energy. Solar panels are about 15% efficient, so you get 15% of that 200 Watts of incident power as useful energy, converted into electrons, which is the energy carrier. Electricity is a verstaile energy carrier, but difficult to store. Hence why high energy density liquid fuels are so good in transportation. They are an energy carrier, or ‘Secondary energy’. What is described here is the production of a secondary energy carrier via photosynthesis.This is exactly what Oil from Algae is. Algae are fast growing unicellular organisms, certain species of which produce large quantities (50%) of oil as a percentage of the total cell weight. The algae oil is very like diesel, so you can get biodiesel. The Joule Biotech system is using a photosynthetic organism also. They don’t say whether its an algae, plant cell cultures, or some new genetic hybrid, but either way, I dont think they will have improved on millenia of evolution in terms of the net efficiency of the photosynthesis process, i.e. how much of the solar energy the living organism is capable of capturing.
Compared to other plants, the photosynthetic efficiency of algae is very high – almost 3 times that of sugar cane for instance. Compared to solar energy, however, the energy efficiency of algae is very low – around 1 percent, while solar panels have an efficiency of at least 10 percent, and solar thermal gets 20 percent and more.
So the absolute efficiency of the Joule Biotech system at converting solar energy into chemical energy is likely to be similar to algae or other high yield plants.
2. There is a demand for alternative liquid fuels
Overall in terms of where the biofuels market is heading, Joule Biotech appear to be on the right track. The ability to be able to produce multiple different products, different fuels and different chemicals is key. This allows you flexibility. As the demand or price of one product increases, you can alter your output to match market demand. The future of biofuels appears to be the interlinking of technology platforms to allow the use of multiple feedstrocks, to produce multiple products. Vinod Khosla has invested in a large number of Biofuel companies which all synergise and interlink. In terms of feedstock, Joule Biotech are using carbon dioxide and sunlight. It’s a biofuel with an accelerated path, less steps, from biology to fuel and the option to tailor it to produce different fuels.
This means that they have some of the same issues and challenges as other bio-based processes.
1. Cells need phosphorus
Check out Leave the Algae Alone for an excellent piece on this.
The idea of converting solar energy into chemical energy is an excellent one. Biofuel based processes are one way of doing this. If one could avoid the biology altogether that would be even better. Check out Blue Fuel Energy for some interesting ideas on how to chemically synthesise a chemical energy carrier, or ‘liquid electricity’ using renewable energy. Its still at a very nascent stage, but it stacks up very well as an overall concept.