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Berkeley study finds renewable portfolio standards insufficient to meet 2030 GHG emission targets; new policy required

One possible scenario for the electricity system in the Western US in 2026-29. Pie charts show the proportion of different types of energy sources generating power and flowing between load areas if there were a carbon tax of $70 per ton. Click to enlarge.

The least expensive way for the Western US to reduce greenhouse gas emissions enough to help prevent the worst consequences of global warming is to replace coal with renewable and other sources of energy that may include nuclear power, according to a new study by University of California, Berkeley, researchers. Their paper is in press in the journal Energy Policy.

The researchers used a mixed-integer linear programming model—SWITCH (a loose acronym for Solar, Wind, Hydro and Conventional generators and Transmission)—to analyze least-cost generation, storage, and transmission capacity expansion for western North America under various policy and cost scenarios. Their analysis also found that current renewable portfolio standards (RPS) are insufficient to meet emission reduction targets by 2030 without new policy.

With a stronger carbon policy consistent with a 450 ppm climate stabilization scenario, power sector emissions can be reduced to 54% of 1990 levels by 2030 using different portfolios of existing generation technologies, they found. Under a range of resource cost scenarios, most coal power plants would be replaced by solar, wind, gas, and/or nuclear generation, with intermittent renewable sources providing at least 17% and as much as 29% of total power by 2030.

Although the carbon price to induce these deep carbon emission reductions is high, if the carbon price revenues are reinvested in the power sector, the cost of power is found to increase by at most 20% relative to business-as-usual projections.

Decarbonization of the electric power sector is critical to achieving greenhouse gas reductions that are needed for a sustainable future. To meet these carbon goals, coal has to go away from the region.

—Daniel Kammen, Distinguished Professor of Energy in UC Berkeley’s Energy and Resources Group

To achieve this level of decarbonization, policy changes are needed to cap or tax carbon emissions to provide an incentive to move toward low-carbon electricity sources, Kammen and the other study authors said.

While some previous studies have emphasized the high cost of carbon taxes or caps, the new study shows that replacing coal with more gas generation, as well as renewable sources like wind, solar and geothermal energy, would result in only a moderate increase to consumers in the cost of electric power—at most, 20%. They estimate a lower ratepayer cost, Kammen said, because the evolution of the electrical grid over the next 20 years—with coordinated construction of new power plants and transmission lines—would substantially reduce the actual consumer cost of meeting carbon emission targets.

While the carbon price required to induce these deep carbon emission reductions is high—between $59 and $87 per ton of CO2 emitted—the cost of power is predicted to increase by at most 20%, because the electricity system will redesign itself around a price or cap on carbon emissions. That is a modest cost considering that the future of the planet is at stake.

—Daniel Kammen

Burning coal, a non-renewable resource, produces about 20% of the world’s greenhouse gases, but also releases harmful chemicals into the environment such as mercury, sulfur dioxide, nitrogen oxides and sulfuric acid, responsible in some areas for acid rain and respiratory illness.

California has few coal-fired power plants, but gets about 20% of its electricity from coal-burning plants in neighboring states. About 46% of the state’s power comes from gas-burning plants, 11% from hydroelectric, 14% from nuclear and 11% from other renewables: geothermal energy, wind and solar.

While California has a relatively high RPS target of 33% renewable sources by 2020, other Western states have less ambitious targets. Additional policy action throughout Western North America will be required to meet climate targets, Kammen said.

Coauthors of the study are Josiah Johnston, Ana Mileva, Ian Hoffman, Autumn Petros-Good and Christian Blanco of UC Berkeley’s RAEL lab and the Energy and Resources Group; and Matthias Fripp of the Environmental Change Group at Oxford University in the United Kingdom.

Funding for the Energy Policy study was provided by the National Science Foundation, the Environmental Protection Agency, NextEra Energy Resources, the Karsten Family Foundation, Vestas Wind LLC, the UC Berkeley Class of 1935, the CPV Consortium, the Berkeley Nerds Fellowship and the Link Energy Fellowship.


  • James Nelson, Josiah Johnston, Ana Mileva, Matthias Fripp, Ian Hoffman, Autumn Petros-Good, Christian Blanco, Daniel M. Kammen (2012) High-resolution modeling of the western North American power system demonstrates low-cost and low-carbon futures, Energy Policy doi: 10.1016/j.enpol.2012.01.031


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Beside above all the green house gas produced from automobiles, also share major part in global warming. If the fossil fuel diesel is not replaced with alternative fuel technology process which produce fuels like dimethyl ether and bio diesels. GHG emission will cross the studied values also


All the farm biomass waste can be gasified and made into bio methane, methanol, synthetic gasoline and synthetic diesel. No reason to convert trucks to DME, CNG nor LNG. We have what we need right now, we just need to make the fuels for combined cycle power plants, trucks and car ourselves from renewable resources and not from fossil fuels.


Farm wastes are plowed under as fertilizer. If they are made into bio-fuel then you have increase fertilizer usage - paying Peter to rob Paul.


My view is less optimistic.

Natural gas is probably not less carbon intensive compared to coal because of well site leaks. All that fracking has created underground fractures that the methane find a way to leak to the surface.

Bio-fuel encourages destruction of forests, and is unlikely to see carbon reductions. Cellulosic biofuel can use marginal lands, which also include forests.

Wind and Solar are too diffuse and too intermittent to carry the base load. They can do 10% to 20% in the overall mix, and no more.

Modern nuclear technology such as Thorium, and the Molten Salt Reactor will have to be called upon to carry the majority of the load to have a chance to meet the greenhouse target. That is my emphasis right now.

The Coal and the Oil & Gas industry is not going to simply lie down and let themselves be replaced. They have been fighting all this time, and they seem to be winning currently.

Nick Lyons


I agree with the need to develop MSRs. We need cheap, as well as green, electricity. In the meantime, I hope small modular reactors in the pipeline,such as NuScale, can come online. Commercial MSRs are ten years away, best case. In the meantime, rooftop solar and conservation make a lot of sense in most of the West.


The Department of Agriculture did a study and half of the waste in the field can be harvested with no adverse effects. I do not usually post this because I have before several times and I assume that people who post on here know this.

We have 100 million acres planted in corn and 2 tons per acre can be harvested with no adverse effects on the land. At 100 gallons of fuel per ton that is 20 billion gallons per year just from corn stalks and cobs (stover). That is more than enough to make E10 just from stover and use the corn grain for feed and food.


Along with biomass we can convert coal plants to IGCC and make fuels. Using coal, natural gas and biomass, we can make enough synthetic fuel to run 20% of the cars on the roads in the U.S. That is 20% less imported oil, 20% less money going out of the country for imported oil with less sulfur and mercury being released into the air.


One of the likely sites for a FOAK SMR (small modular reactor) is Iowa. Iowa, lousy with corn, has ample supplies of excess stover and corncobs. The temperatures of even PWRs are sufficient to break down the cellulose in these to sugars and lignin, allowing the entire feedstock to become a product feedstock with none lost for process energy.

Converting Iowa's ethanol plants from grain-fed and gas-fired to cellulose-fed and nuclear-fired would be an immense improvement on all fronts.


Broin has converted an ethanol plant to use corn cob cellulose as feed stock. They plan to do more of that in the future. Right now investment money is hard to come by, when an administration breaks the country with debt and war, it takes a while to come back.

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