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Wind energy has experienced accelerated cost reduction over the past five years-far greater than predicted in a 2015 expert elicitation. Here we report results from a new survey on wind costs, compare those with previous results and discuss the accuracy of the earlier predictions. We show that experts in 2020 expect future onshore and offshore wind costs to decline 37-49% by 2050, resulting in costs 50% lower than predicted in 2015. This is due to cost reductions witnessed over the past five years and expected continued advancements. If realized, these costs might allow wind to play a larger role in energy supply than previously anticipated. Considering both surveys, we also conclude that there is considerable uncertainty about future costs. Our results illustrate the importance of considering cost uncertainty, highlight the value and limits of using experts to reveal those uncertainties, and yield possible lessons for energy modellers and expert elicitation.

The underlying simulations were conducted with their suite of models tools including their long-term least-cost planning program, Gen-X, their market model, UPLAN-NPM, and their regional PLATO data models.

and Patrick Brown (MIT). Of course, any omissions or errors that remain are solely the responsibility of the authors. penetrations increase, but sometimes come at a cost to the consumer that is not always accounted for in generation portfolio decision-making. (see Chapters 2 and 5) All generation types are unique in some respect-bringing benefits and challenges to the power system-and wholesale markets, industry investments, and operational procedures have evolved over time to manage the characteristics of a changing generation fleet. With increased VRE penetrations, power system planners, operators, regulators, and policymakers will continue to be challenged to develop methods to smoothly and cost-effectively manage the reliable integration of these new and growing sources of electricity supply. Less-liquid bilateral markets exist outside of ISO/RTO regions. Note also that substantial amounts of generation even in ISO/RTO regions are locked-into longer-term physical or financial contracts, in which case available wholesale market prices signal opportunity costs but may not affect immediate revenue generation for those existing generators; wholesale pricing will, of course, still affect market entry decisions for new generation. 2 Where active wholesale markets do not exist, the same basic dynamics hold: the declining cost of natural gas, for example, puts economic pressure on inflexible units even in markets that do not feature an ISO/RTO.

addition we are indebted to the helpful comments of our anonymous reviewers. Of course, any remaining errors or omissions are our own. iv EXECUTIVE SUMMARYResidential photovoltaic (PV) systems were twice as expensive in the United States as in Germany (median of $5.29/W vs. $2.59/W) in 2012. This price discrepancy stems primarily from differences in non-hardware or "soft" costs between the two countries, which can only in part be explained by differences in cumulative market size and associated learning. A survey of German PV installers was deployed to collect granular data on PV soft costs in Germany, and the results are compared to those of a similar survey of U.S. PV installers. Non-module hardware costs and all analyzed soft costs are lower in Germany, especially for customer acquisition, installation labor, and profit/overhead costs, but also for expenses related to permitting, interconnection, and inspection procedures. Additional costs occur in the United States due to state and local sales taxes, smaller average system sizes, and longer project-development times.To reduce the identified additional costs of residential PV systems, the United States could introduce policies that enable a robust and lasting market while minimizing market fragmentation. Regularly declining incentives offering a transparent and certain value proposition-combined with simple interconnection, permitting, and inspection requirements-might help accelerate PV cost reductions in the United States. HIGHLIGHTS• Residential PV system prices are twice as high in the USA than in Germany in 2012.• Different cumulative national PV market sizes explain only 35% of price gap.• Installer surveys show that price differences stem from non-module and soft costs.• Largest cost differences stem from customer acquisition and installation labor.• Incentives in the US are less effective in driving and following cost reductions.v