Wind and solar power are highly variable, so it is it unclear how large a role they can play in future power systems. This work introduces a new open-source electricity planning modelSwitchthat identifies the least-cost strategy for using renewable and conventional generators and transmission in a large power system over a multidecade period. Switch includes an unprecedented amount of spatial and temporal detail, making it possible to address a new type of question about the optimal design and operation of power systems with large amounts of renewable power. A case study of California for 2012−2027 finds that there is no maximum possible penetration of wind and solar powerthese resources could potentially be used to reduce emissions 90% or more below 1990 levels without reducing reliability or severely raising the cost of electricity. This work also finds that policies that encourage customers to shift electricity demand to times when renewable power is most abundant (e.g., well-timed charging of electric vehicles) could make it possible to achieve radical emission reductions at moderate costs. INTRODUCTIONThere is a strong consensus that anthropogenic climate change must be limited to 2°C or less in order to avoid dangerous changes to the environment. 1 The best estimate is that this will require limiting cumulative CO 2 emissions to about 10 12 tonnes of carbon before fossil fuels are completely phased out. 2 However, it is possible that the safe emissions budget is as low as half this levelapproximately the amount we have already emitted. 3 Achieving deep emission reductions early in the century will increase the chance of achieving the 2°C target, and/or raise the emission budget available later in the century.Renewable power sources could make a major contribution to this effort. Wind and solar power are available on a much larger scale than human energy demand. 4,5 Wind power is now cost-competitive with natural gas plants in some locations 6 and the cost of solar power is falling rapidly. 6,7 Use of both wind power and solar photovoltaics have grown at over 25% per year for the last 25 years or more. 8,9 However, it remains unclear how much it will cost to use these resources on a large scale. The cost of achieving any particular emission target depends on exactly which renewable and conventional electricity projects are developed, so answering this question requires two steps: first, develop a least-cost plan for using renewable and conventional resources to reduce emissions while maintaining reliability, and then calculate the cost of following this plan.Several models use stochastic linear programming to propose optimal deployment plans for wind, solar, and conventional generators and transmission. These are chiefly distinguished by the amount of spatial and temporal detail they include.

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Abstract-Wind power production is variable, but also has diurnal and seasonal patterns. These patterns differ between sites, potentially making electric power from some wind sites more valuable for meeting customer loads or selling in wholesale power markets. This paper investigates whether the timing of wind significantly affects the value of electricity from sites in California and the Northwestern United States. We use both measured and modeled wind data and estimate the time-varying value of wind power with both financial and load-based metrics. We find that the potential difference in wholesale market value between bettercorrelated and poorly correlated wind sites is modest, on the order of 5-10 percent. A load-based metric, power production during the top 10 percent of peak load hours, varies more strongly between sites, suggesting that the capacity value of different wind projects could vary by as much as 50 percent based on the timing of wind alone.

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This research quantifies the extent to which the US has shifted the environmental impact associated with the goods it consumes to other countries through trade. To achieve this, we use a life-cycle, consumption-based approach to measure the environmental impacts embodied in US trade activities for global warming potential (GWP), energy, toxics, and the criteria air pollutants.We use these values to determine the amount of environmental impact "leaked" from current, production-based approaches to analyzing national environmental trends for the years 1998-2004.We find that with reasonable assumptions about the environmental intensity of imports and exports, this leakage exceeds 10% for all studied impacts, exceeds 25% for GWP, energy, and most criteria air pollutants, and exceeds 80% for lead emissions and toxics. By including the environmental impacts embodied in trade activities into national environmental accounts, we provide consumption-based, US per capita, environmental impacts, which we use to evaluate the relationship between income and environmental impact. We find evidence for rising per capita environmental impacts with rising income in the US, contra the Environmental Kuznets Curve.The paper concludes with a discussion of the implications for international environmental policy of increasing embodied emissions in trade.