Sustainable Energy Solutions for Climate Change Mitigation

1. The first priority has to be cutting back on fossil fuel burning • As we discussed last time, more efficient energy use can quickly reduce CO2 emissions. It has positive results for individuals or corporations because it reduces energy costs. Worldwide energy supply in TW • But efficiency is not enough, we need to reduce CO2 emissions by 80% or more by 2050.

2. The first priority has to be cutting back on fossil fuel burning Worldwide energy supply in TW • What are the tools or technologies that can reduce the impact of the evil triplets - oil, gas and coal - and expand the role of renewables?

3. I’m going to organize the discussion around a remarkable paper: Stabilization wedges: solving the climate problem for the next 50 years with current technologies Pacala S, Socolow R. (2004) Science 305:968-72. Their major points are: Humanity already possesses the fundamental scientific, technical, and industrial know-how to solve the carbon and climate problem for the next half-century. A portfolio of technologies now exists to meet the world's energy needs over the next 50 years and limit atmospheric CO2 to less than a doubling of the preindustrial concentration. Every element in this portfolio has passed beyond the laboratory bench and demonstration project; many are already implemented somewhere at full industrial scale. Although no technology can do the entire job (or even half the job) by itself, the portfolio as a whole is large enough that not every element has to be used.

4. There is a big contrast between CO2 emissions under a Business As Usual (BAU) projection and emission reductions that would stabilize CO2 concentrations at 500 ppm. (preindustrial was 280 ppm; we are currently at 380 ppm) The graph can be simplified so the difference between BAU and stabilization is a triangle that represents the reductions in CO2 emissions needed for stabilization at 500 ppm. To look at the possible contribution of multiple technologies, Pacala and Socolow divided the green triangle into 7 wedges, each representing 1 GtC of avoided CO2 emissions.

5. Then the question is, can we find enough “wedges” to reduce CO2 to stabilization levels? They identify 15 technologies, any 7 of which would be sufficient.

6. Potential wedges: Strategies to reduce carbon emissions in 2054 by 1 GtC/year 1. Efficient vehicles 2. Reduced use of vehicles 3. Efficient buildings 4. Efficient coal power plants 5. Replace coal with gas power plants 6. Capture CO2 at coal or gas power plant 7. Capture CO2 at H2 plant 8. Capture CO2 at coal-to-synfuels plant 9. Double nuclear power 10. Wind electricity 11. Solar electricity 12. Renewable hydrogen 13. Biofuels 14. Reduced deforestation plus replanting. 15. Conservation tillage

7. Despite its high CO2 production, nearly twice that for natural gas, coal will be very difficult to quickly eliminate from our energy production. • Coal is cheap and abundant • It supplies more than half our electricity • It is a big part of industrialization in other countries, notably China Thus, it seems necessary to learn how to burn coal cleanly - so most of the CO2 is captured and sequestered.

8. Carbon capture and storage (CCS) Technology for large scale capture of CO2 is already commercially available and fairly well developed. The relatively untried part is the long term storage of CO2 in geological formations underground. There are a few demonstration projects, but as yet no large scale power plant operates with a full carbon capture and storage system. The storage capacity geological formations is estimated to be at least 2000 Gt CO2. Currently, 30 Gt per year of CO2 is emitted due to human activities. For well-selected and managed geological storage sites, IPCC estimates that CO2 could be trapped for millions of years, and the sites are likely to retain over 99% of the injected CO2 over 1,000 years.

9. CCS applied to a modern conventional power plant could reduce CO2 emissions by 80-90%. Capturing and compressing CO2 requires much energy and would increase the fuel needs of a coal-fired plant by about 25%. As a result energy from a new power plant with CCS would cost more, maybe as much as 90% more. Retrofitting old plants or transporting the CO2 long distances before injection underground would increase the cost more. Currently, electricity from coal-fired plants is cheap, about 3-5 ¢ per Kwh. Adding in the cost of CCS begins to acknowledge the carbon cost and will make renewable energy more competitive with coal.

10. Electricity from solar power Usually when we hear solar power, we think of panels on people’s roofs. These photovoltaic (PV) panels convert sunlight directly to electricity and work only when the sun is shining. PV panels are wonderful for local, individual power generation but the power is quite expensive - about 25¢ per Kwh. A number of government subsidies and financing plans reduce the upfront cost of PV panels.

11. Electricity from solar power Another kind of solar power is more suited to rapid expansion that can substantially replace fossil fuels. Concentrating solar power uses mirrors to focus sunlight on a fluid filled tube. The high temperature fluid (200-500° C) is then used to produce steam that drives a turbine to produce electricity. An important advantage of CSP is that the heated fluid can be stored for long periods of time (4-16 hours) and then used later to produce steam. Thus CSP plants can produce electricity when it’s needed, even at night. This is important for a technology that might replace a substantial fraction of fossil fuel plants.

12. The direct solar resource needed for CSP is concentrated in the southwestern US and in other arid areas like North Africa, the Middle East, western China.

14. Although there is currently less than one GW of operational CSP, a rapid expansion is underway. More than 5 GW are currently in permitting stages or under construction in the western US. A similar amount is being developed in Spain.

15. Biofuels • The idea is that producing CO2 from plants that just incorporated it is “carbon neutral”. It doesn’t quite work out that way because you have to figure in the CO2 released • By farm equipment during planting, cultivating, harvesting • During fertilizer manufacture and irrigation • In transport of the crop to ethanol refineries • In the refining process

16. Unintended consequences - corn ethanol • High CO2 production - as bad as gasoline? • Diverting food to fuel - raises food prices and encourages new planting in rain forest or savanna areas.

17. Test plot of Miscanthus • Ethanol from sugar cane or cellulosic sources is better, about 4-5 fold • There will still be effects on food prices and deforestation.

18. Overall, I think that biofuels will be an important but transient solution to help wean us away from oil. Over the long term, I think solar electricity and electric cars will gradually replace liquid fuels and the internal combustion engine. Not everyone agrees that biofuels will have a limited impact. Vinod Khosla, a Silicon Valley venture capitalist who has invested heavily in green technologies, including biofuels, said in a SF Chronicle interview last week: “I have no question that in 10 years, there's no way oil will be able to compete with biofuels. Even in five years. Now it will take a long time to scale biofuels, but I'm the only one in the world forecasting oil dropping in price to $35 a barrel by 2030. I'll put it on the record: Oil will not be able to compete with cellulosic biofuels.” He’s also not concerned that growing cellulosic feedstock will compete for land with food crops.

19. Using economics to drive changes • Carbon tax • Cap and trade • Tax credits - investment and production • Mandates - AB32, RPS, CAFÉ standards (corporate average fuel economy) These are really important topics because they represent the methods that can actually shift in our economy away from fossil fuels. However, don’t worry about them for the final. I didn’t have time to discuss them in any detail.