Berkeley Kavli Retreat on Solar Energy Fuel Generation
Eli Yablonovitch, Electrical Engineering & Computer Sciences Dept., firstname.lastname@example.org
Alexis T. Bell, College of Chemistry, email@example.com
On Tuesday February 9th 2016, over 15 faculty at the Lawerence Berkeley Lab and UC Berkeley attended the Kavli ENSI Retreat on Solar Energy Fuel Generation. The retreat was organized by Profs. Eli Yablonovitch, Professor, Electrical Engineering & Computer Sciences Dept and Alexis Bell, Dow Professor of Sustainable Chemistry. The motivation of the retreat was as follows:
Since 1980, the real price of solar panels has dropped by a factor 50. This has resulted not simply from inevitable economies of scale, but rather was produced by discrete scientific and technical breakthroughs and insights over time. As a result, there is now significant penetration of solar panels for large-scale generation of electrical power. In fact, it is predicted that in the near future electrical power will be available at very low cost during the midday period. This excess capacity could be used to produce liquid fuels by electrochemical reduction of CO2 either directly or indirectly. In the latter case, CO2 can be reduced electrochemically to synthesis gas (a mixture of CO and H2), which can be converted to a variety liquid fuels using known technology.
We are motivated, therefore, to assess how solar energy can be converted economically to liquid fuels that can be stored for long periods and used when needed. If this were possible, the solar fuel industry could become much larger than the comparatively modest solar electric utility industry currently in existence. To achieve this goal, there are a number of requirements:
1. Electrocatalysts must be discovered and developed that produce high energy density, preferably liquid, fuels or gaseous products that can readily be converted to liquid fuels, e.g., ethene or synthesis gas
2. The price of solar panels must drop by an additional factor of 3 from their already low price.
3. Owing to the solar duty factor, 25%, the capital cost of electrolyzers must drop by a factor 4 at least and must be made more reliable than automotive fuel cells.
4. Low energy demand techniques need to be developed for the separation of water miscible products, e.g., alcohols, from aqueous electrolytes.
Berkeley has the capacity to become the world leader in research on the conversion of solar energy to liquid fuels. We, therefore, propose that a Berkeley Kavli Retreat is needed to set research priorities and to discuss funding opportunities for a major scientific and engineering effort devoted to the chemical storage of solar energy.
The main conclusion of the Retreat was as follows:
We need to find new large markets for solar panels, since the over-building to panel factories in China has saturated the electric utility market. Solar panels are better matched to fuel production which can be stored, rather than the electric utility industry, where the peak demand is a poor match to the solar peak. This results in maximum solar penetration into electric utilities <10% on a yearly average basis. Thus we are led to electrolytic fuel production using the electricity from solar panels.
There are new discoveries in the electrolysis of aqueous solutions of carbon dioxide that directly produce higher hydrocarbons, including ethane and ethylene, which are especially valuable. Nonetheless the yield of these products remains well below 30%. Therefore the immediate emphasis should be placed on conventional electrolysis producing Hydrogen. This has several advantages. Hydrogen, as a product has multiple large markets:
1. The refinery and chemical process industries, including ammonia production.
2. To be blended in the natural gas pipeline network, at a partial pressure below hydrogen embrittlement of steel. This could represent a 10% partial pressure in natural gas, and a huge market. Natural gas is successfully stored, in annual seasonal cycles, in underground reservoirs.
3. For the fuel cell vehicle market which is growing rapidly.
In addition there is the prospect of employing the hydrogen in the Fischer-Tropsch process to create diesel fuel from carbon dioxide, if the work on direct hydrocarbon electrolysis falls short.
Each of these addressable markets for electrolytic hydrogen is larger than the electric utility market. Nonetheless, a Joule of fuel commands a lower price than a Joule of electricity. Therefore a further price reduction, about 3x below today’s depressed solar panel price will be needed demanding further research.
There is also a need to reduce the capital cost of Electrolyzers, owing to the 25% duty factor of solar electricity.
If these actions are taken, then solar panels will become the main source of primary energy, both electricity and fuels, by the middle of this century.