Over 70 cities have made commitments to reach 100% renewable energy. Several states, including Hawaii and California, have adopted or plan to adopt similar targets. But what’s often ignored is how inexpensive it would be to meet the goals.

Bottom line: in nearly 40 states, renewable electricity is less expensive than the existing power supply.

This map shows the cost of reaching a 100% renewable electricity supply in each state, based on the wind and solar resource, publicly available power purchase agreement data, and ILSR’s calculation of the lowest cost choice between wind and solar.

Map originally published in Reverse Power Flow (ILSR, 2018). For a map of 100% renewable cities, see ILSR’s Community Power Map. To see a 2015 version of the map below, see our original blog post on Georgetown.

Assumptions and Calculations

The 100% electricity supply cost calculated by ILSR using Level10’s PPA 2018 PPA report and Berkeley Labs 2016 Utility-Scale Solar report for solar costs, and Energy Information Administration data on average wind capacity factors to estimate wind costs. In general, two-thirds of electricity was presumed to come the cheaper of the wind or solar resource. This annual average cost does not account for daily, monthly, or seasonal resource variation and does not represent the cost to operate a 100% renewable grid.

Comparison to existing power supply costs used a proxy figure of 30% of the average residential retail revenue per customer, based on data from the Energy Information Administration.

This article originally posted at ilsr.org. For timely updates, follow John Farrell or Marie Donahue on Twitter, our energy work on Facebook, or sign up to get the Energy Democracy weekly update.